Speculations in Science and Technology 19, 3-31 (1996)
Optimization of human performance for all ages
Ariel Dynamics Inc., 6 Alicante, Trabuco Canyon, CA 92679, USA
Normal human evolution spans a lifetime from infancy to old age. Modem civilization is confronted with the lengthening of that time and its effect on the individual and society. Housing improvements, employment alterations, labour saving devices, and modern medicine are but a few of the factors protecting humanity from those instances which previously shortened life. While many of the difficult, threatening experiences have been eliminated or reduced in severity, problems remain to be solved. Concerns for the quality of life as people become older includes maintaining self sufficiency. Many solutions conflict with beliefs generally termed `current wisdom' in areas such as training, dieting, exercising, and aging. While society ages, the challenge for each individual is to strive to retain the lowest 'biological' age while their 'chronological' birthdays increase. The dilemma concerns the best way to accomplish this task.
The main purpose of this article is to focus on the biomechanical principles of movement, the scientific bases of training and fitness, and the optimization of human performance at any age. These are not just nonsense concepts added to the quantities of known theories, but are objectively quantifiable procedures which encompass man's understandings and can produce precise conclusions. Mathematical principles and gravitational formulations provide the cornerstones for optimizing human performance. Biological, anatomical, physiological, and medical discoveries are always under investigation, challenge, and improvement and these findings will be incorporated into many of the current theories. The struggle will continue among scientists to establish new principles for revolutionizing the world of gerontology, diet, physical fitness and training, and amplifying those factors necessary for extending life not only in length but in its quality. Scientists with expertise in many different areas will be addressing the problems associated with aging from their specialized perspective.
In order to address the optimization of human movement and performance, the underlying philosophical premise metaphorically compares life with sport. The goal is that everyone should be a gold medalist in his or her own body regardless of age. Most people, however, do not achieve their `Gold Medal' because their goals, potential, and/or timing are uncoordinated or nonexistent. For example, an individual may envision him/herself as a tennis champion yet lack the requisite physical and physiological traits of the greatest players. Given this situation, can his or her potential be maximized? Achieving one's maximum potential necessitates tools applicable to everyone for improving their performance, whether in tennis, fitness, overcoming physical handicaps and/or disease. Useful tools must be based, however, on correct, substantive scientific principles.
0155-7785 Q 1996 Chapman & Hall
With each passing year, the composition of the population in America and probably many other `modem' societies is becoming older. This population increase of older citizens appears to be due, in part, to the large number of individuals of all ages who are experiencing modifications of lifestyle in a variety of ways, including better working conditions, improved health/medical opportunities, and changing activity levels. Pollock et al.  noted that the activity levels of elderly people has increased during the previous 20 years. However, it was estimated that only 10% of elderly individuals participate in regular vigorous physical activity and that 50% of the population who are 60 or more years of age described their lifestyles as `sedentary'. Scientific studies and personal experiences continue to link many of the health problems and physical limitations found in the aged to lifestyle. Sedentary living appears to be a major contributor to the significantly adverse effect on health and physical well-being. Certainly there is increasing evidence indicating the vital need for improved national and international policies for better fitness, health, and sports for older individuals. In order to address some of these indicators, new attitudes and policies must emphasize activities and resources to meet the minimal requirements for keeping older people in good health, preventing their deterioration with age, and meeting the special interests of individuals with various disorders. In addition to the difficulties that hospitals, insurance companies, children of the elderly, and legislators face, the medical and scientific communities require time to determine the most appropriate solutions for improving the quality of these lengthening lives.
Many of the myths about aging are being disproved while the true nature of age-related changes appears to be less bleak than previously thought. Disuse and disease, not age alone, are increasingly, revealed as culprits. There is an increasing awareness of the need for more emphasis on fitness to maintain wellness and prevent degenerative illness, for more research to understand the aging body of the healthy older person, and to determine the exercise needs of the ill and/or the handicapped. Pollock et al.  noted that physical capacity decrements are normally associated with the aging process. This loss has been attributed to the influence of disease, medication, age, and/or sedentary lifestyle. Additionally, it was noted that the majority of the elderly do not exercise and that it is unclear whether the reduced state of physical conditioning associated with aging results from the deconditioning due to sedentary living, age, or both.
It is a fact of life that muscle tissue suffers some diminution from age. Age-associated changes in organ and tissue function, such as a decline in fat-free mass, total body and intracellular water, and an increase in fat mass  may alter the physiological responses to exercise or influence the effect(s) of medication. However, any discussion about `age' realistically utilizes arbitrary time periods apportioned aeons ago by men who evaluated time relative to the number of revolutions of the earth around the sun and the rotation of the earth on its own axis. These predetermined periods may or may not have any relationship with the aging of the cells in the body. The linkage between the chronological age and the biological age of people is imprecise. Perhaps a more accurate consideration of the relationship between chronological and biological age would be one that is non-linear, may differ with gender, or be dependent on other factors. It is an inevitable evolutionary consequence that individuals within a species differ in many ways. The characterization of an individual on the basis of a chronological age scale may be practical but biologically inappropriate. Function may have a greater influence on determining biological age rather than the number of times the earth has revolved around the sun. It appears that biological age can be affected by genetic code, nutrition and, most importantly,
Optimization of human performance 5
physical activity. Astrand  suggested that as an individual ages, the genetic code may have more of an effect on the function of systems with key importance in physical performance. He also noted that a change in lifestyle, at almost any chronological age, can definitely modify the 'biological age', either upward or downward. It has been suggested that the disparity of older persons is a hallmark of aging itself . It is important to determine how much age variance is due to the passage of time and how much is caused by the accumulation of other, non-time dependent, alterations. Previous attitudes towards physical adversities observed in the elderly were that they were attributable to disease. More recently, a third dimension associated with poor health in older persons has been described by Bortz  as 'The Disuse Syndrome'. For example, one of the most common markers of aging was thought to be a decreased lean body mass. However, analysis of 70-year-old weight lifters revealed no such decline. The components of the Disuse Syndrome has been similarly grouped by Kraus and Raab  in their book, Hypokinetic Disease, and are:
(1) Cardiovascular vulnerability (2) Musculoskeletal fragility (3) Obesity
(5) Premature aging
Use is a universal characteristic of life. When any part of the body has little or no use, it declines structurally and functionally. The effects of disuse can be observed on any body part such as atrophied intestinal mucosa when a loop is excluded from digestive functions or the lung becomes atelectatic when not aerated. A lack of adequate conditioning and physical activity causes alterations in the heart and circulatory system, as well as the lungs, blood volume, and skeletal muscle [6,7,8,9]. During prolonged bed rest, blood volume is reduced, heart size decreases, myocardial mass falls, blood pressure response to exercise increases, and physical performance capability is markedly reduced. On the other hand, although acute changes within the cardiovascular system result in response to increased skeletal muscle demands during exercise, there is evidence that chronic endurance exercise produces changes in the heart and circulation which are organic adaptations to the demands of chronic exercise [10,11,12,13,14,15].
Cardiac performance undergoes direct and indirect age-associated changes. There is a reduction in contractility of the myocardium  and this increased stiffness impairs ventricular diastolic relaxation and increases end diastolic pressure . This suggests that exerciseinduced increases in heart rate would be less well tolerated in older individuals than in younger populations. The decline in maximal heart rate is known and the cause is multifactorial, but is mostly related to a decrement in sympathetic nervous system response. Fifty % of Americans who are more than 65 years of age have a diagnostically abnormal resting electrocardiogram . Another factor associated with aging is a progressive increase in rigidity of the aorta and peripheral arteries due to a loss of elastic fibres, increase in collagenous materials, and calcium deposits . When aortic rigidity increases, the pulse generated during systole is transmitted to the arterial tree relatively unchanged. Therefore, systolic hypertension predominates in elderly hypertensive patients. Other bodily systems demonstrate age-related alterations. Baroreceptor sensitivity decreases with age and hypertension [20,21] such that rapid adjustment of the cerebral circulation to changes in posture may be impaired. Kidney function reveals a defect in renal concentrating ability and sluggish renal conservation of sodium intake causes elderly patients to be more susceptible to dehydration . Hyaline cartilage on the articulator surface
of various joints shows degenerative changes and clinically represents the fundamental alteration in degenerative osteoarthritis . A decrease in bone mass (osteoporosis) can reduce body stature as well as predispose the individual to spontaneous fractures. Older women are more prone to osteoporosis than older men and this may reflect hormonal differences . Older persons are less tolerant of high ambient temperatures than younger people  due to a decrease in cardiovascular and hypothalamic function which compromises the heat dissipating mechanisms. Heat dissipation is further compromised by the decrease in fat-free mass, intracellular and total body water, and an increase in body fat. Unfortunately, the effects of disuse on the body manifest themselves slowly since humans normally have redundant organs which can compensate for ineffectiveness or disease. In addition, humans are opaque so that disease or deterioration are externally unobservable and, thus, go unheeded. (e.g. the early changes in bones due to osteoporosis are subclinical and are normally detected only after becoming so pronounced that fractures ensue). Cummings et al.  mentioned the difficulty of distinguishing manifestations in musculoskeletal changes due to disease related to aging. Muscle mass relative to total body mass begins decreasing in the fifth decade and becomes markedly reduced during the seventh decade of life. This change results in reduced muscular strength, endurance, size, as well as a reduction in the number of muscle fibres. Basmajian and De Luca  reported numerous alterations in the electrical signals associated with voluntary muscular contractions with advancing age. As yet, there are no findings published that have definitively located age-related musculoskeletal changes in either the nervous or the muscular system. The diaphragm and cardiac muscle do not seem to incur age changes. Perhaps this is due to constant use, from exercise, or possibly a genetic survival mechanism.
There is growing consensus that many illnesses are preventable by good health practices including physical exercise. Milliman and Robertson  reported that, of the 15,000 employees of a major computer company, the non-exercisers accounted for 30% more hospital stays than the exercisers. Lane et aL  reported that regular runners had only two-thirds as many physician visits as community matched controls. The beneficial effect of exercise on diabetes has long been recognized and is generally recommended as an important component in the treatment of diabetes . Regular endurance exercise favorably alters coronary artery disease risk factors, including hypertension, triglyceride and high density lipoprotein cholesterol concentrations, glucose tolerance and obesity. In addition, regular exercise raises the angina threshold .
Jokl  has suggested three axioms of gerontology:
Sustained training inhibits:
(1) the decline of physique with age
(2) the decline of physical fitness with age (3) the decline of mental functions with age
Health in older people is best measured in terms of function, mental status, mobility, continence, and a range of activities of daily living. Preventive strategies appear to be able to forestall the onset of disease. Whether exercise can prevent the development of atherosclerosis, delay the occurrence of coronary artery disease, or prevent the evolution of hypertension is at present debatable. But moderate endurance exercise significantly decreases cardiovascular mortality . Endurance exercise can alter the contributions of stress, sedentary lifestyle, obesity, and diabetes to the development of coronary artery disease . For example, the four-time Olympic discus champion, Al Oerter, at the age of 43, focused his training to qualify for the 1980 Olympic Games which would have been his 5th consecutive Olympiad.
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Oerter threw his longest throw - 220 feet - but, since the US boycotted the 1980 Moscow Olympic Games, his chance was denied. By the time of the 1984 Los Angeles Games, Oerter was 47 years old. Even at an age well beyond most Olympic competitors, he again threw his best, exceeding 240 feet in practice sessions. Oerter's physique and strength suggested that his biological age was less than his chronological age. Biologically, he was probably between 25 and 30, although chronologically he was 15 to 20 years older. Unfortunately in the competition that determined which athletes would represent the United States, Oerter suffered an injury which precluded him from trying to achieve an unprecedented fifth consecutive Olympic Gold medal.
The optimum performance concept
When they talk about their physical goals in work or in sports, people usually say they would like to do their best, meaning, reach their maximum output. It is a matter of achieving their absolute limit in speed, strength, endurance or skill and combining the elements with accuracy. This is no different than an athlete training for maximum performance in the Olympic Games. The difficulty with focusing everything on maximum performance is that only a single goal, getting the highest results - fastest, biggest, quickest, longest, or most graceful - is considered a superlative or acceptable achievement. Maximums do not take into consideration other aspects of body performance which often prove to be just as important to the individual. Emphasis upon the demands for maximum performance is frequently portrayed with the thought that 'Winning isn't everything, it's the only thing.' Imagine for a moment a 'maximum' performance in the car industry - the perfect automobile. It is incredibly graceful and the aerodynamic, functional lines make it a thing of beauty. It accelerates from zero to 60 miles per hour within a few seconds. It brakes, corners and steers with a fineness that would permit a shortsighted 75-year old to compete at Le Mans. The suspension is so smooth that a passenger can pour liquids without spilling a drop. The car requires only minimal maintenance while averaging 50 miles per gallon in city driving. Best of all, it is the vehicle of the common man at a price of $5000. If all that sounds impossible - it is. Incorporating all of these 'maximums' into a single automobile exceeds the ability of any designer or manufacturer. Instead, the individual shopping for a car must choose the attributes he or she feels are most important.
Therein lies the problem, some goals are partly, if not wholly, incompatible with others. An automatic transmission uses more gas than a standard shift, but it does make driving easier. Sleek aerodynamic lines add grace and reduce drag, but they can also lessen head room. High performance engines provide power, but require constant care. The solution is a compromise, a willingness to make tradeoffs. This same spirit of compromise, of accepting something less than a single maximum, should govern the operation of the most important machine in our lives - our body. Reality must be applied when comparing ourselves to Olympic athletes or, with the progression of age, mimicking various youthful physical activities. For example, there is no need to have an endurance capacity equal to the current gold medalist or the strength level equivalent to the World heavyweight record holder. Likewise, senior citizens may resist relinquishing their drivers' licenses despite their slower reaction times, poorer eyesight, and/ or hearing, as well as frequently suffering from some type of chronic disease which may further reduce their strength, joint mobility, or even cognitive processes, such as memory or decision making. Instead of a maximum, what most people really want from their bodies is to 'optimize' their performances and lives. They seek the most efficient use of energy, of bodily action consonant with productive output, health, and enjoyment. Many people are beginning to
appreciate that certain types of exercise add to the vitality of the cardiovascular system, lessen the risk of heart attack, and make it possible to live longer and more active lives. In other words, the willingness to sacrifice 20 yards on a drive off the golf tee may mean that the golfer's feet will be able to walk the entire course without being tortured during every step. The desire is to play a couple of hours of winning tennis, stroking the ball with pace and purpose, but not if the extra zing means a tennis elbow that will be sore for several weeks. Sensible joggers prefer to run six rather than ten miles a day in 40 minutes, if the latter leads to tender knees and shin splints. In other words, human beings must compromise between anatomy (the structural components) and physiology (the bodily processes). A correct balance between the two, at all ages, will assist in optimizing bodily efficiency. In addition to the desire for our `internal environment' to be physical fit, pertinent questions should be posed about our `external environment'. For example, is it really necessary for that designer chair to cause a bone ache deep in the buttocks after sitting for five minutes? Can a person not spend a day labouring over a desk or piece of machinery without feeling as if a rope had been tightly tied around the shoulders at the end of the project? Why must a weekend with shovel or rake inevitably produce lower back pain on Monday? Why is it that some individuals who are 50 years old seem able to work and play as if 10 to 20 years younger, while some 30-year-olds act as if infected with a malignant decrepitude? The answer is that, as with the anatomy and physiology achieving optimal coordination, so should the whole human organism coordinate better with its environment. Perhaps these examples could be dismissed as the minor aches of a hypochondriac society overly concerned with its comfort. But the overall health facts for the United States and many other modern civilizations appal even those jaded by constant warnings of disaster. Some 25 million American adults suffer from heart disease; a total of 75 million Americans are afflicted with chronic disease. On any given day, more than one million workers do not show up for their jobs because of illness, and sickness prevents a million of these from returning in less than a week. Twenty-eight million Americans have some degree of disability. Perhaps not coincidentally, a quarter of the population is classified as overweight. At least three million citizens have diabetes, and half are unaware of the problem, and the US accounts for most of the deaths due to cardiovascular disease. The health profile of the future, the condition of the youth of today, offers no comfort. About one in five youngsters still cannot pass even a simple test of physical performance. More than nine million American children under the age of 15 have a chronic ailment. From one third to one half of US children are overweight and one third of America's young men fail to meet military physical fitness requirements (which are not terribly high).
In pursuit of technological achievement, Americans have almost eliminated the one major element besides food and rest needed to sustain the human body - physical activity. This has lent impetus to a subtle yet deadly disease which has reached epidemic proportions in this country and others. Cardiovascular disease is often referred to as hypokinetic disease or lackof-motion disease. Unfortunately, degeneration with Americans begins earlier rather than later. One study indicates that middle age characteristics start to show at approximately age 26. The peak age for heart disease among American men is 42 years. In Europe, it is 10 years later. A corporate wide employee health survey conducted by a large computer manufacturer indicated that smokers have 25% higher health care costs and 114% longer hospital stays than nonsmokers. People who did not exercise have 36% higher health care costs and 54% longer hospital stays than people who did exercise. Overweight people have 7% higher health care costs and 85% longer hospital stays than people who are not. In general, people with poor
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health habits have higher health care costs, longer hospital stays, lower productivity, more absenteeism, and more chronic health problems than those who do not. Some questions both workers and their companies should ask are:
(1) How many heart attacks, strokes, cancers, or coronary by-pass operations did your company pay for last year?
(2) How much better would profits have been if heart diseases had been reduced 10, 20, or 30%?
(3) How much would corporate profits increase if employee health care costs were reduced by 10%?
One large US corporation developed a comprehensive wellness programme at numerous sites. During the first year, grievances decreased by 50%, on-the-job accidents by 50%, lost time by 40%, and sickness and accident payments by 60%. The corporation estimated at least a three to one return per dollar invested.
The requirement for such an optimum way of life is a scientific analysis of the way people live and use their bodies. Only after such a quantitative examination can a concept of cost be determined or a better way of doing something which is more efficient and less damaging to the body, discovered. For instance, rapid weight loss may result from running long distances, such as 15 miles a day, fasting drastically, or performing aerobics for five hours a day. However, such excessive training regimens may be as detrimental to the body as sitting all day in an easy chair and simply ignoring one's obesity.
Evolution, culture, and the changing demands of existence have tended to develop forces and stresses upon the body which are not necessarily in harmony with the basic design and structure of the human equipment. Standing upright, humans employ one pair of extremities for support and the other pair capable of tremendous versatility. It would seem that of all animals, man, fortuitously assisted by the evolution of his brain and other organs, optimized the use of his body. Unfortunately, the human body has had to pay a stiff price for its upright posture. Human vertical posture is inherently unstable, therefore, humans must devote more neuromuscular effort and control to maintain balance, than four-legged animals. There is a tendency to lean forward, which adds to the ability to move in that direction, but increases the risk of falling. A complex neuromuscular process is constantly at work to prevent man from toppling. Many things may interfere with this balancing act, such as consuming too much whiskey or walking on an icy sidewalk. These interruptions of the flow of information to and from the brain centre which coordinates the balancing process can result in staggering or falling. This postural condition creates a constant strain on all the muscles employed to retain balance and upon the set of bones forming the spine. The spine is basically a tower of I-beams which supports the skeletal frame and, in order to remain in good health, proper mechanical alignment is essential. Any deviation from this mechanical alignment will result in pain relating to non-alignment, such as low back or neck pain. The vulnerability of the back is threatened frequently by work, recreation situations, and furnishings, since their uses subject an already tenuous upright position to undergo increased stresses. As the body compensates for alignment problems by creating excess bone tissue and neural pain, certain arthritic conditions may be the result.
Correction or prevention in tools or activities may assist in the optimization of performance and in more closely aligning the biological with the chronological age. Clearly, optimization and compensation may conflict within the human mechanism since a logical idea may violate physical principles. Based on this introduction of merely a few of the internal and external
challenges to the human organism, the need for adequate and accurate assessments, improved tools, and human behavioural modifications becomes more apparent.
Scientific principles for quantifying motion
Human movement has fascinated men for centuries including some of the world's greatest thinkers such as Leonardo da Vinci, Giovanni Borelli, Wilhelm Braune, and others. Many questions posed by these stellar geniuses have been or can be addressed by the relatively new area of Biomechanics. Biomechanics is the study of the motion of living things, primarily, and it has evolved from a fusion of the classic disciplines of anatomy, physiology, physics, and engineering. 'Bio' refers to the biological portion, incorporating muscles, tendons, nerves, etc., while `mechanics' is associated with the engineering concepts based upon the laws described by Sir Isaac Newton. Human bodies consist of a set of levers which are powered by muscles. Quantification of movements, whether human, animal, or inanimate objects, can be treated within biomechanics according to Newtonian equations. It may seem obvious, with the perfect vision of hind sight, that humans and their activities, such as the wielding of tools (eg., hammer, axe) or implements (eg., baseball bat, golf club, discus), must obey the constraints of gravitational bodies, just as bridges, buildings, and cars, do. For some inexplicable reason, humans and their activities had not been subjected to the appropriate engineering concepts which architects would use when determining the weight of books to be housed in a new library or engineers would apply to designing a bridge to span a wide, yawning abyss. It was not until Newton's apple fell again during the 20th Century that Biomechanics was born.
Biomechanics, then, is built on a foundation of knowledge and the application of the basic physical laws of gravitational effects as well as those of anatomy, chemistry, physiology, and other human sciences. Early quantification efforts of human movement organized the body as a system of mechanical links. Activities were recorded on movie film which normally consisted of hundreds of frames for each of the desired movement segment. Since each frame of the activity had to be processed individually, the task was excessively lengthy, tedious, and time intensive. The hand calculations of a typical 16 segment biomechanical `human' required many hours for each frame, necessitating either numerous assistants or an individual investigator's labour-of-love and, frequently, both. Unfortunately, these calculations were susceptible to numerical errors. The introduction of large, main-frame computers improved reliability and reasonableness of the results, replacing much of the skepticism or distrust associated with the manually computed findings. Computerization accelerated the calculations of a total movement much more rapidly than had been previously possible, but presented new difficulties to overcome. Many of the early biomechanical programmes were cumbersome, time intensive main-frame endeavours with little appeal except to the obsessed, devotee of computers and movement assessment. However, even these obstacles were conquered in the ever expanding computerization era. The computerized hardware/software system provides a means to objectively quantify the dynamic components of movement in humans regardless of the nature of the event. Athletic events, gait analyses, job-related actions as well as motion by inanimate objects, including machine parts, air bags, and auto crash dummies are all reasonable analytic candidates. Objectivity replaces mere observation and supposition. One of the most important aspects included in the 'Bio' portion of Biomechanics is the musculoskeletal system. Voluntary human movement is caused by muscular contractions which move bones connected at joints. The neuromuscular system functions as a hierarchical system with autonomic and basic, life sustaining operations, such as heart rate and digestion, controlled at the lowest, non-cognitive
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levels and with increasing complexities and regulatory operations, such as combing the hair or kicking a ball, controlled by centres which are further up the nervous system. Interaction of the various control centres is regulated through two fundamental techniques each governed like a servosystem. The first technique equips each level of decision making with subprocessors which accept the commands from higher levels as well as accounting for the inputs from local feedback and environmental information sensors. Thus, a descending 'pyramid' of processors is defined which can accept general directives and execute them in the presence of varying loads, stresses, and other perturbations. This type of input-output control is used for multimodal processes, such as maintaining balance while walking on an uneven terrain, but would be inappropriate for executing deliberate, volitional, complex tasks like the conductor using the baton to coordinate the music of the performing musicians.
The second technique which the brain utilizes to control muscular contractions applies to the operation of higher level systems which generate output strategies in relation to behavioural goals. These tasks use information from certain sensory inputs, including joint angle, muscle loading, and muscular extension or flexion which are assessed, transmitted to higher centres for computation, which then executes the set of modified neural transmissions received. Cognitive tasks requiring the type of informational input which influences actions are the ones with which humans are most familiar since job execution requires more thought than breathing or standing upright. One of the most important concepts which is frequently misunderstood is that limb movement is possible only through contractions of individual muscle fibres. For most cases of voluntary activity, muscles work in opposing pairs with one set of muscles opening or extending the joint (extensors) while the opposite muscle group closes or flexes the joint. The degree of contraction is proportional to the frequency of signals from the nerve as signaled from the higher centers. Movement control is provided by a programmable mechanism so that when flexors contract, the extensors relax, and vice versa. The motor integration 'programme' generated in the higher, cognitive levels regulates not only the control of the muscle groups around a joint, but also those necessary actions by other muscles and limbs to redistribute weight, to counteract shifts in the centre of gravity. The importance of the nervous system in the control and regulation of coordinated movement cannot be underemphasized. When a decision is made to move a body segment, the prime muscles or 'agonists' receive a signal to contract. The electrical burst stimulates the agonist muscular activity causing an acceleration of the segment in the desired direction. At the same time, a smaller signal is transmitted to the opposite muscle group, or antagonist, which causes it to function as a joint stabilizer. With extremely rapid movements, the antagonist is frequently stimulated to slow the limb in time to protect the joint from injury. It is the strength and duration of the electrical signal to both the agonist and antagonist which govern the desired action. The movement of agonists and antagonists, whether a cognitive process such as throwing a ball or an acquired activity such as postural control, is controlled by the nervous system. Many ordinary voluntary human activities resulting from agonist-antagonist muscular contraction are classified by different terms, 'isotonic', 'variable resistance', and 'ballistic'. Slower, tracking movements demonstrate smaller, more frequent, electrical signal alterations and controls for both agonist and antagonist. These types of motion are 'tracking' movements. One control mechanism available involves the process of information channeled between the environment and the musculature. Closedloop control involves the use of feedback whereby differences between actual and desired posture are detected and subsequently corrected, whereas open-loop control utilizes feedforward strategies that involve the generation of a command based on prior experience rather than on feedback. Braitenberg and Onesto proposed a network for converting space into time by
providing that the position of an input would determine the time of the output. This `open loop' system would trigger a preset signal from the nervous system to the muscle generating a `known' activity. Kicking a ball, walking, throwing a baseball, swinging a golf club, and hand writing are considered ballistic movements. When a limb moves, a sophisticated chain of events occurs before, during, and after the movement is completed. The fineness of control depends upon the number of motor nerve units per muscle fibre. The more neurons, the finer the ability to manoeuver, as with eye movements or delicate hand manipulations. In contrast to the high innervation ratio of the eye, the biceps of the arm has a very low rate of nerve-to-muscle fibre resulting in correspondingly more coarse movements. While the amount of nervous innervation is important when anticipating the precision of control, the manner of interaction and timing between muscles, nerves, and desired outcome is probably more important when evaluating performance. Recognizable actions elicit execution of patterned, synchronous nervous activity. Frequently repeated movements are usually performed crudely in the beginning stages of learning but become increasingly more skilled with use and/or practice. Consider the common activity of handwriting and the execution of one's own signature. The evolution from a child's irregular, crude printing to an adult's recognizable, consistently repeatable signature is normal. Eventually, the individual's signature begins to appear essentially the same every time and is uniquely different from any other person. Not only can the person execute handwritten signatures consistency, but can use chalk to sign the name in large letters on a blackboard producing a recognizably similar appearance. The individuality of the signature remains whether using the fine control of the hand or recruiting the large shoulder and arm muscles not normally required for the task. Reproduction of recognizable movements occurs from preprogrammed control patterns stored in the brain and recruited as necessary. Practising a golf swing until it results in a 300 yard drive down the middle of the fairway, getting the food-laden fork from the plate into the mouth, and remembering how to ride a bike after a 30 year hiatus illustrate learned behaviour that has become `automatic' with practice and can be recalled from the brain's storage for execution.
Volitional tasks require an integration of neurological, physiological, biochemical, and mechanical components. There are many options available when performing a task, such as walking, but eventually, each person will develop a pattern that will be recognizable as that skill, repeatable, and with a certain uniqueness associated with that particular individual. Although any person's movement could be quantified with biomechanical applications and compared to other performers in a similar group, e.g. the gold, silver, and bronze medalists in an Olympic event, perhaps it will be the ability to compare one person to him/herself that will provide the most meaningful assistance in the assault on aging. There are many areas of daily living in which biomechanical analyses could be useful. Biomechanics could be utilized to design a house or chair to suit the body or to lift bigger, heavier objects with less strain. This science could be useful in selecting the most appropriate athletic event for children or for improving an adult's performance. With increasing international interest in competitive athletics, it was inevitable that computers would be used for the analysis of sports techniques. Computer calculations can provide information which surpass the limits of what the human eye can see and intuition can deduce. Human judgment, however, is still critically important. As in business and industry, where decisions are based ultimately upon an executive's experience and interpretive ability, the coach or trainer is, and will remain, the ultimate decision maker in athletic training. Rehabilitation and orthopaedic specialists can assess impaired movement relative to normal performance and/or apply computerized biomechanical techniques to the possibilities of achieving the restoration of normal activities. With the increase in the popula-
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tion of older citizens, gerontological applications will increase. The computer should be regarded as one more tool, however complex, which can be skillfully used by humans in order to achieve a desired end.
One factor which man has lived with is change. The environment in which we live is changing during every one of the approximately 35 million minutes of our lives. The human body itself changes from birth to maturity and from maturity to death. The moment man first picked up a stone to use as a tool, the balance between humans and the environment was altered. After that adaptation, the ways in which the surrounding world changed resulted in different effects and these were no longer regular or predictable. New objects were created from things which otherwise would have been discounted. These changes were made possible by humans due to the invention of tools. The more tools man created, the faster was the rate of environmental change. Today, the rate of change due to tools has reached such a magnitude that there is a great danger to the whole environment and frequently to the people who use the tools such as were discovered during the Industrial Revolution, or even today with such problems as carpal tunnel syndrome. Human beings seem to have become so infatuated with their ability to invent things that they have concentrated almost exclusively upon improving the efficiency, safety, durability, cost, or aesthetic appeal of the device. It is ironic that with all of the innovative development, little consideration has been given to the most complex system with the most sophisticated computer in the world - the human body.
Principles for exercise and training
Physical fitness and exercise have become, as previously discussed, an increasing concern at nearly all levels of American society. The goal of attaining peak fitness has existed for centuries, yet two problems continue to obfuscate understanding. The ability to assess strength and/or to exercise has occupied centuries of thought and effort. For instance, Milo the Greek lifted a calf each day until the baby grew into a bull. Since this particular procedure is not commonly available, humans have attempted to provide more suitable means to determine strength levels and ways to develop and maintain conditioning. Technology for assessing human performance in exercise and fitness evaluations, in both theory and practice, exhibits two problems. First, a lack of clearly defined and commonly accepted standards which results in conflicting claims and approaches to both attaining and maintaining fitness. Second, a lack of accurate tools and techniques for measuring and evaluating the effectiveness of a given device designed to diagnose present capabilities for exercising or even to determine which exercises are appropriate to provide `fitness', regardless of age or gender. Vendors and consumers of fitness technology have lacked sound scientific answers to simple questions regarding the appropriateness of exercise protocols.
Reviewing studies conducted to determine the effects of strength training on human skeletal muscle suggests many benefits with appropriate exercise. In general, strength training that uses large muscle groups in high-resistance, low-repetition efforts increases the maximum work output of the muscle group stressed . Since resistance training does not change the capacity of the specific types of skeletal muscle fibres to develop different tensions, strength is generally seen to increase with the cross-sectional area of the fibre . The human body can exercise by utilizing its own mass (e.g. running, climbing, sit ups). These and other forms of non-equipment based exercises can be quite useful. In addition, there are various types of exercise equipment which allow selection of a weight or resistance and then the exercise against that machine resistance is performed.
The relationship between resistance exercises and muscle strength has been known for centuries. Milo the Greek's method of lifting a calf each day until it reached its full growth probably provides the first example of progressive resistance exercises. It has been welldocumented in the scientific literature that the size of skeletal muscle is affected by the amount of muscular activity performed. Increased work by a muscle can cause that muscle to undergo compensatory growth (hypertrophy), whereas disuse leads to wasting of the muscle (atrophy). This information has stimulated the medical and sports professions, especially coaches and athletes, to try many combinations and techniques of muscle overload. Attempts to produce a better means of rehabilitation, an edge in sporting activities, as a countermeasure for the adverse effects of space flight, or as a means to improve or enhance bodily performances throughout a life time have only scratched the surface of the cellular mechanisms and physiological consequences of muscular overload. Muscular strength can be defined as the force that a muscle group can exert against a resistance in a maximal effort. In 1948, Delorme  adopted the name `progressive resistance exercise' for his method of developing muscular strength through the utilization of counter balances and weight of the extremity with a cable and pulley arrangement. This technique gave load-assisting exercises to muscle groups that did not perform antigravity motions. McQueen  distinguished between exercise regimes for producing muscle hypertrophy and those for producing muscle power. He concluded that the number of repetitions for each set of exercise determines the different characteristics of the various training procedures. When muscles contract, the limbs may appear to move in different ways. One type of motion is a static contraction, known as an isometric type of contraction. Another type of contraction is a shortening or dynamic contraction which is called an isotonic contraction. Dynamic contractions are accompanied by muscle shortening and by limb movement. Dynamic contractions can exhibit two types of motion. One activity is a concentric contraction in which the joint angle between the two bones become smaller as the muscular tension is developed. The other action is an eccentric contraction in which, as the muscles contract, the joint angle between the bones increases. Owing to ambiguity in the literature concerning certain physiologic terms and differences in laboratory procedures, the following terms are defined:
(1) Muscular strength: the contractile power of muscles as a result of a single maximum effort. (2) Muscular endurance: ability of the muscles to perform work by holding a maximum
contraction for a given length of time or by continuing to move submaximal load to a
certain level of fatigue.
(3) Isometric: a muscular contraction of total effort but with no visible limb movement (sometimes referred to as `static' or `anaerobic').
(4) Isotonic: raising and lowering a submaximal load, such as a weight, a given number of times (sometimes called `dynamic' or `aerobic').
(5) Isokinetic training (accommodating resistance): muscular contraction at a constant velocity. As the muscle length changes, the resistance alters in a manner that is directly proportional to the force exerted by the muscle.
(6) Concentric contraction: an isotonic contraction in which the muscle length decreases (that
is, the muscle primarily responsible for movement becomes shorter).
(7) Eccentric contraction: an isotonic contraction in which the muscle length of the primary
mover is believed to increase. That is, the muscle primarily responsible for movement
Optimization of human performance 15
(8) Muscle overload: the workload for a muscle or muscle group that is greater than that to which the muscle is accustomed.
(9) Variable resistance exercise: as the muscle contracts, the resistance changes in a predetermined manner (linear, exponentially, or as defined by the user).
(10) Variable velocity exercise: as the muscle contracts with maximal or submaximal tension, the speed of movement changes in a predetermined manner (linear, exponentially, or as defined by the user).
(11) Repetitions: the number of consecutive times a particular movement or exercise is performed.
(12) Repetition maximum (1 RM): the maximum resistance a muscle or muscle group can overcome in a maximal effort.
(13) Sets: the number of groups of repetitions of a particular movement or exercise.
Based on evidence presented in these early studies, hundreds of investigations have been published relative to techniques for muscular development, including isotonic exercises, isometric exercises, eccentric contractions, and many others. The effectiveness of each exercise type has been supported and refuted by numerous investigations but no definitive, irrefutable conclusions have been established.
Hellebrandt and Houtz  shed some light on the mechanism of muscle training in an experimental demonstration of the overload principle. They found that the repetition of contractions which place minimal stress on the neuromuscular system had little effect on the functional capacity of the skeletal muscles. They also found that the amount of work done per unit of time is the critical variable upon which extension of the limits of performance depends. The speed with which functional capacity increases suggests that the central nervous system, as well as the contractile tissue, is an important contributing component of training.
Results from the work of Hellebrandt and Houtz  suggest that an important consideration in both the design of equipment for resistive exercise and the performance of an athlete or a busy executive is that the human body relies on pre-programmed activity by the central nervous system. Since most human movements are ballistic and since the neural control of these patterns differs from slow controlled movements, it is essential that training routines employ programmable motions to suit specific movements. This control necessitates exact precision in the timing and coordination of both the system of muscle contraction and the segmental sequence of muscular activity. Research has shown that a characteristic pattern of motion is present during any intentional movement of body segments against resistance. This pattern consists of reciprocally organized activity between the agonist and antagonist. These reciprocal activities occur in consistent temporal relationships with the variables of motion, such as velocity, acceleration, and forces.
In addition to the control by the nervous system, the human body is composed of linked segments, and rotation of these segments about their anatomic axes is caused by force. Both muscle and gravitational forces are important in producing these turning effects, which are fundamental in body movements in all sports and daily living. Pushing, pulling, lifting, kicking, running, walking, and all human activities result from the rotational motion of the links which, in humans, are the bones. Since force has been considered the most important component of athletic performance, many exercise equipment manufacturers have developed various types of devices employing isometrics and isokinetics. When considered as a separate entity, force is only one factor influencing successful athletic performance. Unfortunately, these isometric and isokinetic devices inhibit the natural movement patterns of acceleration and deceleration.
The three factors underlying all athletic performances and the majority of routine human motions are force, displacement, and the duration of movement. In all motor skills, muscular forces interact to move the body parts through the activity. The displacement of the body parts and their speed of motion are important in the coordination of the activity and are also directly related to the forces produced. However, it is only because of the control provided by the brain that the muscular forces follow any particular displacement pattern and, without these brain centre controls, there would be no skilled athletic performances. In every planned human motion, the intricate timing of the varying forces is a critical factor in successful performances. In any human movement, the accurate coordination of the body parts and their velocities is essential for maximizing performances. This means that the generated muscular forces must occur at the right time for optimum results. For this reason, the strongest weightlifter cannot put the shot as far as the experienced shotputter, although the weightlifter possesses greater muscular force, he has not trained his brain centres to produce the correct forces at the appropriate time. Older individuals may be unable to walk up and down stairs or perform many of the daily, routine functions which had been virtually automatic before the deterioration produced by weakness, disease, or merely age.
Resistive exercising methods
There are significant differences in the manner of execution of the various resistive training methods. In isotonic exercises, the inertia, which is the initial resistance, must be overcome before the execution of the movement progresses. The weight of the resistance cannot be heavier than the maximum strength of the weakest muscle acting in a particular movement or the movement cannot be completed. Consequently, the amount of force generated by the muscles during an isotonic contraction does not maintain maximum tension throughout the entire range of motion. In an isokinetically loaded muscle, the desired speed of movement occurs almost immediately and the muscle is able to generate a maximal force under a controlled and specifically selected speed of contraction. The use of the isokinetic principle for overloading muscles to attain their maximal power output has direct applications in the fields of sport medicine and athletic training. Many rehabilitation programmes utilize isokinetic training to recondition injured limbs of athletes to their full range of motion. The unfortunate drawback to this type of training is that the speed is constant and there are no athletic activities that are performed at a constant velocity. The same disadvantage applies to normal human activities. In isotonic resistive training, if more than one repetition is to be used, a submaximal load must be selected for the initial contractions in order to complete the required repetitions. Otherwise, the entire regimen would not be completed, owing to fatigue or, the inability to perform. A modality that can adjust the resistance so that it parallels fatigue to allow a maximum effort for each repetition would be a superior type of equipment. This function could be accomplished by manually removing weight from the bar while the subject trained. This is neither convenient nor practical. With the aid of the modern computer, the function can be performed automatically. Another drawback with many isotonic types of resistive exercises is that the inertia resulting from the motion changes the resistance depending on the acceleration of the weight and of the body segments. In addition, since overload on the muscle changes due to both biomechanical levers and the length-tension curve, the muscle is able to achieve maximal overload only in a small portion of the range of motion. To overcome this shortcoming in resistive training, some strength training devices have been introduced that have `variable resistance' mechanisms in them. However, these `variable resistance' systems increase the
Optimization of human performance 17
resistance in a linear fashion and this linearity may not truly accommodate the individual. When including inertial forces to the variable resistance mechanism, the accommodating resistance can be canceled by the velocity of the movement.
There seem to be unlimited training methods and each is supported and refuted by as many 'experts'. In the past, the problem of accurately evaluating the different modes of exercise was rendered impossible because of the lack of adequate diagnostic tools. For example, with isotonic exercises, the investigator does not know exactly the muscular effort nor the speed of movement but knows only the weight that has been lifted. When a static weight is lifted, the force of inertia provides a significant contribution to the load and cannot be quantified by feel or observation alone. In the isokinetic mode, the calibration of the velocity is assumed and has been poorly verified. The rotation of a dial to a specific speed setting does not guarantee the accuracy of subsequently generated velocity. In fact, discrepancies as great as 40% have been observed when verifying the bar velocity. Most exercise equipment currently available lack intelligence. In other words, the equipment is not 'aware' that a subject is performing an exercise or how it is being conducted. Verification of the speed is impossible since a closedloop feedback and sensors are absent. However, with the advent of miniaturized electronics in computers, it became possible to unite exercise equipment with the computer's artificial intelligence. In other words, it became possible for exercise equipment to adapt to the user rather than forcing the user to adapt to the equipment.
'High technology' refers to the use of advanced, sophisticated, 'space age' mathematical and electronic methods and devices for creating tools which can enhance human activities as well as expanding the horizons for future inventions. NASA put a man on the moon, sent exploratory spacecraft to Mars and beyond, and shuttle missions have become nearly routine. Polymer science invented plastics, mechanical science produced the automobile, and aeronautical engineering developed the airplane. Despite all of the knowledge and explosive developments since the rock became a tool, few advances have considered first the most important component in a complicated system, the human body. The usual developmental cycle creates something and humans must adapt to it rather than the reverse. Computers can provide precise computations rapidly for complex problems that would otherwise require enormous quantities of time, talent, and energy to complete. The strength of these electronic wizards to follow instructions exactly, remember everything, and perform calculations within thousandths of a second has made them indispensable in finance, industry, and government. Application of the computer was a perfect enhancement for the human mind in order to quantify and evaluate movement performances. Used in conjunction with the human mind's ability to deduce, interpret, and judge, the computer provides the necessary enhancement to surpass the limits of what the eye can see or what intuition can surmise. Technological advances, such as these, can assist humans irrespective of their age. For good health, it is necessary to follow a training method which incorporates all of the various bodily systems. In other words, the body should be treated as a complex, but whole, entity rather than as isolated parts. While it is not wrong to evaluate one's diet, an assessment of health would be incomplete without consideration of physical training, stress reduction, and other components which constitute the integrated organism of the human body. For a person to be able to jog five miles it is not important only to run, but to develop the cardiovascular system in a systematic way to achieve a healthy status. Strength exercise, flexibility routines, proper nutrition and skill are necessary to achieve this goal.
Two sophisticated systems have been developed to analyze human performance and both are appropriate for the assault on aging. These systems include tools to (1) assess movements of the human body and (2) assist in exercising human beings. The first one is the biomechanical system which was developed to analyze movement performance. Currently, biomechanical analyses are routinely performed on a wide range of human motions in homes, work settings, recreation, hospitals, and rehabilitation centres. The second system, which incorporates space age technology, allows diagnoses and training of the musculoskeletal system. Each of these systems will be discussed subsequently in detail. Both of these technologies and the scientific principles and techniques discussed may help achieve physical and mental goals. The technological advances provide tools for quantification of the results and to analyze the potential of a person. With this information and these tools, it should be possible to train the various body system for optimal results at any age.
Tools to assess movement of the human body
Biomechanics is the study of the motion of living things and it has evolved from a fusion of the classic disciplines of anatomy, physiology, physics, and engineering. Biomechanics, then, is built on a foundation of knowledge and the application of basic physical laws. Quantification of human, animal, or even inanimate objects are treated within biomechanics according to Newtonian equations. The theoretical basis of biomechanics models the human body as a mechanical system of moving segments upon which muscular, gravitational, inertial, and reaction forces are applied. Although the physical and mathematical model for such a system is complex, it is well defined . Early efforts to quantify human movement characteristics as a system of mechanical links were lengthy, tedious, and time intensive. Hand calculations for a typical 16 segment biomechanical `human' required many hours for each frame necessitating numerous assistants or a labour-of-love for an individual investigator. Unfortunately, these calculations were fraught with numerical errors. The introduction of large, main-frame computers enabled movement quantification to achieve an elevated status concerning the reliability and reasonableness of the results replacing much of the skepticism or distrust associated with manually computed findings. The initial impact of computerization eliminated many of the errors caused by human computations as well as completing the calculations for a complete performance much more rapidly than previously possible. Unfortunately, many of the biomechanical programmes were cumbersome, time intensive main-frame endeavours which necessitate greater computer technical skills than many biomechanists possessed at that time.
The first person to develop a computerized biomechanical system is the author of this article  and that system can serve to illustrate the general concepts and procedures associated with biomechanical quantification of movement. The computerized hardware/software system provides a means to objectively quantify the dynamic components of movement in humans, such as athletic events, gait analyses, work actions, as well as motion by inanimate objects, including such items as machinery actions, air bag activation, auto crash dummies. This objective technique replaces mere observation and supposition. It was only after the commercial availability of modern technological advances that it was possible to develop a computer-based system to measure, analyze, and present movement characteristics. This system provides a means to quantity motion utilizing input information from any or all of the following mediums: visual (video), electromyography (EMG), force platforms, or other signal processing diagnostic equipment.
The Ariel Performance Analysis System provides a means of measuring human motion based
Optimization of human performance 19
on a proprietary technique for the processing of multiple high-speed video recordings of a subject's performance [40,41,42]. This technique demonstrates significant advantages over other common approaches to the measurement of human performance. Firstly, except in those specific applications requiring EMG or kinetic (force platform) data, it is non-invasive. No wires, sensors, or markers need be attached to the subject. In fact, the subject need not be aware that data is being collected. Secondly, it is portable and does not require modification of the performing environment. Cameras can be taken to the location of the activity and positioned in any convenient manner so as not to interfere with the subject. Activities in the workplace, home, hospital, therapist's office, health club, or athletic field can be studied with equal ease. Third, the scale and accuracy of measurement can be set to whatever levels are required for the activity being performed. Camera placement, lens selection, shutter and film speed may be varied within wide limits to collect data on motion of only a few centimetres or of many metres, with a duration from a few milliseconds to a number of seconds. Video equipment technology currently available is sufficiently adequate for most applications requiring accurate motion analysis. Determination of the problem, error level, degree of quantification, and price affect the input device selection.
A typical kinematic analysis consists of four distinct phases - data collection (filming), digitizing, computation, and presentation of the results. Data collection is the only phase that is not computerized. In this phase, video recordings of an activity are made using two or more cameras with only a few restrictions: (1) all cameras must record the action simultaneously; (2) if a fixed camera is used, it must not move between the recording of the activity and the recording of the calibration points; (3) these limiting factors are not necessary when a panning camera and associated mechanism is used. A specialized device accompanied by specialized software was developed to accommodate camera movement particularly for use with gait analysis and some longer distance sporting events, such as skiing or long jumping; (4) the activity must be clearly seen throughout its duration from at least two camera views; (5) the location of at least six fixed noncoplanar points visible from each camera view (calibration points) must be known. These points need not be present during the activity as long as they can be seen before or after the activity. Usually they are provided by some object or 'apparatus' of known dimensions that is placed in the general area of the activity, filmed and then removed; (6) the speed of each of the cameras (frames/second) must be accurately known, although the speeds do not have to be identical; (7) some event or time signal must be recorded simultaneously by all cameras during the activity in order to provide synchronization.
These rules for data collection allow great flexibility in the recording of an activity. Information about the camera location and orientation, the distance from camera to subject, and the focal length of the lens is not needed. The image space is 'self-calibrating' through the use of calibration points that do not need to be present during the actual performance of the activity. Different types of cameras and different film speeds can be used and the cameras do not need to be mechanically or electronically synchronized. The best results are obtained when camera viewing axes are orthogonal (90 degrees apart), but variations of 20-30 degrees can be accommodated with negligible error. Initially, the video image is captured by the computer and stored in memory. This phase constitutes the 'Grabbing' mode. Brightness, contrast, saturation, and colour can be adjusted so that the grabbed picture may, in fact, be better than the original. Specialized software corrects for inherent inconsistencies of the VCR as well as eliminating any preprocessing to time code the video. Grabbing the image and storing it on computer memory eliminates any further need for the video apparatus. It is possible to digitize directly from the VCR which is typically referred to as 'on the fly'. This procedure, unfortunately, permits
inconsistencies in the timing of the video fields and synchronization since the field advance depends on the mechanically moving heads of the VCR. In other words, the final results could be distorted due to small, undetected fluctuations in the VCR so the better option is to store the image prior to digitizing.
`Digitizing' is the third step in biomechanical quantification. The image sequence is retrieved from computer memory and displayed, one frame at a time, on the digitizing monitor. Using a video cursor, the location of each of the subject's body joints (e.g. ankle, knee, hip, shoulder, elbow) is selected and stored in computer memory. In addition, a fixed point, which is a point in the field of view that does not move, is digitized for each frame as an absolute reference. The fixed point allows for the simple correction of any registration or vibration errors introduced during recording or playback. At some point during the digitizing of each view, a synchronizing event must be identified and, additionally, the location of the calibration points as seen from that camera must be digitized. This sequence of events is repeated for each camera view. Digitizing is primarily a manual process. An alternative option permits the digitizing procedure to proceed automatically although this choice requires acceptance of basic assumptions which may not be palatable to every investigator. A third type of digitizing combines manual and automatic, so that the activity progresses under manual control with computer-assisted selection of the joint segments, or points. User participation in the digitizing process, provides an opportunity for error checking and visual feedback which rarely slows the digitizing process adversely. A trained operator with a reasonable knowledge of a consistent pattern of digitizing and with a knowledge of anatomy, can rapidly produce high-quality digitized images. It is essential that the points are selected precisely because all subsequent information is based on the data provided in this phase. The computation phase of analysis is performed after all camera views have been digitized. At this point in the procedures, the three-dimensional coordinates of the joints centres of a body are calculated. The transformation methods for transforming the data to 2D or 3D coordinates are Direct Linear Transformation, Multiplier, and Physical Parameters Transformation. This phase computes the true 3D image space coordinates of the subject's body joints from the 2D digitized coordinates obtained from each camera's view. The Direct Linear Transformation Computation is determined by first relating the known image space locations of the calibration points to the digitized coordinate locations of those points. The transformation is then applied to the digitized body joint locations to yield true image space locations. This process is performed under computer control with a some timing information provided by the user. The information needed includes, for example, starting and ending points if all the data are not to be used, as well as a frame rate for any image sequence that differs from the frame rate of the cameras used to record the sequence. The Multiplier technique for transformation is less rigorous mathematically and is utilized for those situations when no calibration device was used and only a few objects in the background are available to calibrate the area. This situation usually occurs when a non-scientific, third-party recorded the pictures such as a home video or even a televised sporting event. The third type of transformation, the Physical Parameters Transformation, is primarily applied with panning camera views or when greater accuracy is required on known image sources.
Following data transformation, a smoothing or filtering operation is performed on the image coordinates to remove small random digitizing errors and to compute body joint velocities and accelerations. Smoothing options include polynomial, cubic and quintic splines, a Butterworth 2nd order digital and fast Fourier filters [43,44,45]. Smoothing may be performed automatically by the computer or interactively with the user controlling the amount of smoothing applied to each joint. Error measurements from the digitizing phase may be used to optimize the amount
Optimization of human performance 21
of smoothing selected. Another unique feature is the ability to display the Power Spectrum for each of the x, y, and z coordinates. This enhancement permits the investigator to evaluate the effect of the smoothing technique and the chosen value selected for that curve by examining the Power Spectrum. Thus, the investigator can determine the method and level of smoothing which best meets the requirements of the specific research. After smoothing, the true 3D body joint displacements, velocities and accelerations will have been computed on a continuous basis throughout the duration of the sequence.
Analog data can be obtained from as many as 64 channels for input into the A/D system. Processing of the analog signals, such as those obtained from transducers, thermistors, accelerometers, force platforms, EMG, EKG, EEG, or others, can be recorded for analysis and, if needed, synchronized with the video system. The displayed video picture and the vectors from the force plate can be synchronized so that the force vectors appear to be `inside the body'. At this point, optional kinetic calculations can be performed to provide for measurement and analysis of the external forces that are applied to the body during movement. Inverse Dynamics are used to compute joint forces and torques as well as energy and momentum parameters of single or combined segments. External forces include anything external to the body that is applying force or resistance such as a golf club held in the hand. The calculations that are performed are made against the force distribution of the body. The presentation phase of analysis allows computed results to be viewed and recorded in a number of different formats. Body position and motion can be presented in both still frame and animated `stick figure' format in 3D. Multiple stick figures may be displayed simultaneously for comparison purposes. Joint velocity and acceleration vectors may be added to the stick figures to show the magnitude and direction of body motion parameters. Copies of these displays can be printed for reporting and publication. Results can also be reported graphically. Plots of body joints and segments, linear and angular displacements, velocities, accelerations, forces and moments can be produced in a number of format options. An interactive graphically oriented user interface allows the selection and plotting of such results to be simple and straightforward. In addition, body motion parameter results may also be reported in numerical form and printed as tables. Utilizing this computerized system for biomechanical quantification of various movements performed by the elderly may assist in developing strategies of exercise, alterations in lifestyle, modifications in environmental conditions, and inventions to ease and/or extend independence. For example, rising from a chair is a challenging task for many elderly persons and getting up quickly is associated with a particularly high risk for falling. Hoy and Marcus  observed that older women moved more slowly and altered their posture to a greater extent than younger women. The strength levels were greater for the younger subjects, but it could not be concluded that strength was the causal mechanism for the slower speed. Following an exercise programme affecting a number of muscle groups, younger and older women significantly increased in strength. Results of this study suggest that age-associated changes in muscle strength have an important effect on movement strategies used during chair rising. Following participation in a strength-training programme, biomechanical assessment revealed changes in movement strategies that increased both static and dynamic stability. Other areas appropriate for biomechanical assessment would be on the well known phenomenon of increased postural sway  and problems with balance [48,49,50] in the aged.
It is also important to study the motor patterns used by older persons while performing locomotor tasks associated with daily life such as walking on level ground and climbing or descending stairs. Craik  demonstrated that older subjects walking at the same speed as younger ones exhibited similar movement characteristics. Perhaps the older subjects selected
slower movement speeds which produced apparent rather than real reductions in performance. These types of locomotor studies are easily assessed by biomechanical procedures. A biomechanical inquiry by Williams  examined the age-related differences of intralimb coordination by young and old individuals. Williams observed a similarity of general intralimb coordination for both old and young participants for level ground motions. One age-related change was suggested with regard to the additional balance constraints required for going up stairs because of adjustments not required on level ground. More profound differences were observed by Light et al.  with complex, multilimb coordinated movements performed in a standing position which necessitated dynamic balance control. These types of tasks showed significant age-dependent changes. Compared with younger subjects, the older participants were slower in all timing components, had less predominance in their movement patterns, less coupling of their limbs for movement end-points, and were more susceptible to environmental uncertainties. The alterations in movement performance reflected age-related loss in the ability to coordinate fast, multilimb movements performed from an upright stance suggesting that older individuals may have uncoordinated and unpredictable movement patterns when required to move quickly. Additionally, it was suggested that the more uncertain the environment, the greater the disturbance on the movement, thus, increasing the risk of falling. These studies provide realistic examples of one role biomechanics can perform by not only specifically identifying the locus of change but also providing objective quantification.
Another interesting application of the biomechanical system involves a multidimensional study of Alzheimer's disease currently in progress at a leading medical school. The study's strength is similar to the blind men who must integrate all of the information each has gathered in order to accurately describe the elephant. Examination of the brain's response to specific drugs and at varying dosages, magnetic resonance imaging (MRI), thermographic, endocrine, and hormonal changes, vascular chemistry, as well as other aspects are being evaluated for each patient and their specific motor performances are being quantified biomechanically with the Ariel Performance Analysis system. Preliminary evidence indicates that performance on a simple bean-bag tossing skill improves daily although there is no cognitive recognition of the task. The activity of tossing a bean bag into a target circle from a standing position employs postural adjustments as well as coordinated arm and hand directed skills. Skill acquisition, or motor learning, involves both muscular capability and neural control mechanisms. Both activities involve closed-loop and open-loop mechanisms. The goal-directed movements needed to perform the bean-bag toss require the anticipatory postural adjustments that are inherent in an open-loop control. Because these findings suggest that muscular control and skill acquisition remain viable, this enables investigators to narrow the direction of the research and continue the study while continuously honing the focus. With each scientific finding, the research can be directed toward identification of the underlying cause.
The preceding discussion has described a computerized biomechanical system which can be utilized for the quantification of activities and performance levels particularly where appropriate for gerontological issues. Following the identification and definition of an activity, a second and equally necessary component follows. This is the ability to evaluate, test, and/or train the musculoskeletal components of the body in a manner appropriate to the specifically identified task(s) and according to the capabilities of the age and health of the individual. The integration of both technological assessment tools should assist the individual and others involved in their daily life to identify and measure those portions of an exercise program which can enhance performance, fitness status, or exercise capabilities for each gender and at
Optimization of human performance 23
different ages. In other words, one of the principles should should be remembered is the goal of optimizing performance at every age.
Tools to assist measurement and training of human fitness and exercise levels
For centuries, many devices have been created specifically for strength development. These devices include treadmills, bicycle ergometers, rowing machines, skiing simulators, as well as many of the more traditional resistive exercises with dumb bells, bar bells, and commercially available weight equipment. Each type of exercise has some advantages but none are designed to cope with the difficulties inherent with the gravitational effects which affect the multi-linked human body performing on various exercise equipment.
All systems that employ weights as the mechanism for resistance have major drawbacks in four or more areas, as follows:
(1) biomechanical considerations, (2) inertia,
(3) risk of injury, and
(4) uni-directional resistance.
The biomechanical parameters are extremely important for human performance and should be incorporated into exercise equipment. The biomechanical factors were discussed previously. Inertia is the resistance to changes in motion. In other words, a greater force is required to begin moving weights than is necessary to keep them moving. Similarly, when the exercising person slows at the end of a movement, the weights tend to keep moving until slowed by gravity. This phenomenon reduces the force needed at the end of a motion sequence. Inertia becomes especially pronounced as acceleration and deceleration increase, effectively reducing the useful range of motion of weight-based exercise equipment. The risk of injury is obvious in most weight-based exercise equipment. When weights are raised during the performance of an exercise, they must be lowered to their original resting position before the person using the equipment can release the equipment and stop exercising. If the person exercising loses his/her grip, or is unable to hold the weights owing to exhaustion or imbalance, the weights fall back to their resting position; serious injuries can, and have, occurred. Finally, while being raised or lowered, weights, whether on exercise equipment or free standing, offer resistance only in the direction opposite to that of gravity. This resistance can be redirected by pulleys and gears but still remains unidirectional. In almost every exercise performed, the muscle or muscles being trained by resistance in one direction are balanced by a corresponding muscle or muscles that could be trained by resistance in the opposite direction. With weight-based systems, a different exercise, and often a different mechanism, is necessary to train these opposing muscles. Exercise mechanisms which employ springs, torsion bars, and the like are able to overcome the inertia problem of weight-based mechanisms and, partially, to compensate the unidirectional force restriction by both expanding and compressing the springs. However, the serious problem of safety remains. An additional problem is the fixed, nonlinear resistance that is characteristic of springs and is usually unacceptable to most exercise equipment users. The third resistive mechanism commonly employed in existing exercise equipment is a hydraulic mechanism. Hydraulic devices are able to overcome the inertial problem of weights, the safety problem of both weights and springs, and, with the appropriate selection or configuration, the unidirectional problem. However, previous applications of the hydraulic principle have demonstrated a serious deficiency that has limited their popularity in resistive training. This deficiency
is that of a fixed or a preselected flow rate through the hydraulic system. With a fixed flow rate, it is a well established fact that resistance is a function of the velocity of the piston and, in fact, varies quite rapidly with changes in velocity. It becomes difficult for a person exercising to select a given resistance for training due to the constraint of moving either slower or faster than desired in order to maintain the resistance. Additionally, at any given moment, the user is unsure of just what the performing force or velocity actually is.
In the field of rehabilitation  especially, isokinetic or constant velocity training equipment is a relatively new fitness technology that has enjoyed wide acceptance. These mechanisms typically utilize active or passive hydraulics or electric motors and velocity-controlling circuitry. The user or practitioner selects a constant level of velocity for exercise and the mechanism maintains this velocity while measuring the force exerted by the subject. Although demonstrating significant advantages over weight-based systems, isokinetic systems possess a serious limitation. There are virtually no human activities that are performed at a constant velocity. Normal human movement consists of patterns of acceleration and deceleration. When a person learns to run, ride a bike, or write, an acceleration/deceleration sequence is established that may be repeated at different rates and with different levels of force, but always with the pattern unique to that activity. To train, rehabilitate, or diagnose at a constant velocity is to change the very nature of the activity being performed and to violate most biomechanical performance principles.
Feedback control of exercise
A newer form of exercise equipment can determine the level of effort by the person, compare it to the desired effort, and then adjust accordingly. The primary advantage of this resistive mechanism is that the pattern of resistance or the pattern of motion is fully programmable. The concept of applying a pattern of resistance or motion to training and rehabilitation was virtually impossible until the invention of computerized feedback control. Prior to the introduction of computerized feedback control, fitness technology could provide only limited modes of resistance and motion. Bar bells or weights of any type provide an isotonic or constant resistance type of training only when moved at a constant velocity. Typically, users are instructed to move the weights slowly to avoid the problem of inertia resulting from the acceleration or deceleration of mass. Weights used with cams or linkages which alter the mechanical advantage can provide a form of variable resistance. However, the pattern is always fixed and the varying mechanical advantage causes a variation in velocity that increases inertial effects. Users must move the weights slowly to preserve the resistance pattern. Another deficiency with these types of equipment is that they do not approximate the body or limb movement pattern of a normal human activity.
An exercise machine controlled by a computer possesses several unique advantages over other resistive exercise mechanisms, both fixed and feedback controlled. The most significant of these advances is the introduction of software to the human/computer feedback loop. The computer and its associated collection of unique programmes can regulate the resistance to vary with the measured variables of force and displacement as well as modify the resistance according to data obtained from the feedback loop while the exercise progresses. This modification can, therefore, reflect changes in the pattern of exercise over time. The unique programme selection can effect such changes in order to achieve a sequential or patterned progression of resistance for optimal training effect. The advantage of this capability over previous systems is that the user can select the overall pattern of exercise and the machine
Optimization of human performance 25
assumes responsibility for changing the precise force level, the speed of movement, and the temporal sequence to achieve that pattern.
The first resistive training and rehabilitation device to employ computerized feedback control of both resistance and motion during exercise was the Ariel Computerized Exercise System . For the first time, a machine dynamically adapted to the activity being performed rather than the traditional approach of modifying the activity to conform to the limitations of the machine. Biomechanical results previously calculated could be used to program the actual patterns of motion for training or rehabilitation. The equipment utilizes a passive hydraulic resistance mechanism operating in a feedback-controlled mode under control of the system's computer. A simplified functional description of this mechanism and its operation is described: A hydraulic cylinder is attached to an exercise bar through a mechanical linkage. As the bar is moved, the piston in the hydraulic cylinder moves which pushes oil from one side of the cylinder, through a valve, and into the other side of the cylinder. When the valve is fully open there is no resistance to the movement of oil and, thus, no resistance in the movement of the bar. As the valve is closed, it becomes harder to push the oil from one side of the cylinder to the other and, thus, harder to move the bar. When the valve is fully closed, oil cannot flow and the bar will not move. In addition to the cylinder, the resistance mechanism contains sensors to measure the applied force on the bar and the motion of the bar. To describe the operation of the computerized feedback loop, assume the valve is at some intermediate position and the bar is being moved at some velocity with some level of resistance. If the computer senses that the bar velocity is too high or that bar resistance is too low, it will close the valve by a small amount and then check the velocity and resistance values again. If the values are incorrect, it will continue to regulate the opening of the valve and continually check the results until the desired velocity or resistance is achieved. Similar computer assessments and valve adjustments are made for every exercise. Thus, an interactive feedback loop between the computer and the valve enable the user to exercise at the desired velocity or resistance. The feedback cycle occurs hundreds of times a second so that the user experiences no perceptible variations from the desired parameters of exercise.
There are a number of advantages in a computerized feedback controlled resistance mechanism over devices that employ weights, springs, motors, or pumps. One significant advantage is safety. The passive hydraulic mechanism provides resistance only when the user pushes or pulls against it. The user may stop exercising at any time and the exercise bar will remain motionless. Another advantage is that of bi-directional exercise. The hydraulic mechanism can provide resistance with the bar moving in each direction, whereas weights and springs provide resistance in only one direction. Opposing muscle groups can be trained in a single exercise. Two additional problems associated with weight training, noise and inertia, are also eliminated because the hydraulic mechanism is virtually silent and full resistance can be maintained at all speeds.
The Ariel Computerized Exercise System allows the user to set a pattern of continuously varying velocity or resistance. The pattern can be based on direct measurements of that individual's motion derived from the biomechanical analysis or can be 'designed' or created by the user with a goal of training or rehabilitation. During exercise, the computer uses the pattern to adjust bar velocity or bar resistance as the subject moves through the full range of motion. In this manner, the motion parameters of almost any activity can be closely duplicated by the exercise system allowing training or rehabilitation using the same pattern as the activity itself. The software consists. of two levels. One level of software is invisible to the individual using the equipment since it controls the hardware components. The second level of software
allows interaction between the user and the computer. The computer programs necessary to provide the real-time feedback control, the data program and storage, and the additional performance manipulations are extensive. The software provides computer interaction with the individual operator by automatically presenting a menu of options when the system is activated. Selection of the diagnostics option allows several parameters about that person to be evaluated and stored if desired. The diagnostic parameters include the range of motion, the maximum force, and the maximum speed that the individual can move the bar for the specific activity selected. The maximum force and maximum speed data can be determined at each discrete point in the range of movement as well as the average across the entire range. The diagnostic data can be used solely as isolated pre- and post-test measurements. However, the data can also be stored within the person's profile so that subsequent actions and tests performed on the equipment can be customized to adjust to that specific individual's characteristics.
The controlled velocity option permits the individual to control the speed of bar movement. The pattern of the velocity can be determined by the person using the equipment and these choices of velocity patterns include: (1) isokinetic, which provides a constant speed throughout the range of motion; (2) variable speed, in which the speed at the beginning of the motion and the speed at the end of the stroke are different with the computer regulating a smooth transition between the two values; and (3) programmed speed, which allows the user to specify a unique velocity pattern throughout the range of movement. For each of the choices, determination of the initial and final velocities are at the discretion of the individual through an interactive menu. The number of repetitions to be performed can be indicated by the person. It is possible to designate different patterns of velocity for each direction of bar movement.
The controlled resistance option enables the person to control the resistance or amount of force required to move the bar. The alternatives include: (1) isotonic, which provides a constant amount of force for the individual to overcome in order to move the bar; (2) variable resistance, in which the force at the beginning of the motion and the force at the end of the movement are different with the computer regulating a smooth transition between the two values; (3) programmed resistance, which permits the individual to specify a unique force pattern throughout the range of movement. An interactive menu enables the person to indicate the precise initial and final values, the number of repetitions to be used, and each direction of bar motion for the three choices. The controlled work option allows the individual to determine the amount of work, in Newton/metres or joules, to be performed rather than the number of repetitions. In addition, the person can choose either velocity or resistance as the method for controlling the bar movement. As with the previous options, bi-directional control is possible. The data storage capability is useful in the design of research protocols. The software allows an investigator to `program' a specific series of exercises and the precise manner in which they are to be performed, e.g. number of repetitions, amount of work, etc., so that the user need only select his or her name from the graphic menu and the computer will then guide the procedures. Data gathered can be stored for subsequent analysis. The equipment has the capacity to `program' a sequence of events, such as a series of different exercises; determination of that sequence is solely at the discretion of the research investigator or other user. Data storage is presented as an option; it is not a required mode of operation. The equipment is fully operational for all options irrespective of whether the data storage option is activated.
Numerous features further enhance the application of this advanced fitness technology. Individual exercise programmes can be created and saved on the computer or a diskette. Users can perform their individual programme at any time merely by loading it from computer
Optimization of human performance 27
memory or the diskette. Measurements of exercise results can be automatically saved and progress monitored by comparing current performance levels to previous ones. Performance can be measured in terms of strength, speed, power, repetitions, quantity of work, endurance and fatigue. Comparison of these quantities can be made for flexors versus extensors, right limb versus left limb, as well as between different dates and different individuals. Visual and audio feedback are provided during exercise to ensure that the subject is training in the proper manner and to provide motivation for optimal performance. Accuracy of measurement is essential and it is deemed as one of the most important considerations in the software. Calibration of the equipment is performed dynamically and is a unique feature that the computerization and the feedback system allow. Calibration is performed using weights with known values and the procedure can be performed for both up and down directions. This type of calibration is unique since the accuracy of the device can be ascertained throughout the range of motion.
As discussed previously, a large diagnostic and/or exercise system exists but sheer bulk precludes it's convenient use at home or in small spaces. One future goal is to develop a computerized, feedback-controlled, portable, battery-powered, hydraulic musculoskeletal exercise assessment and training equipment based on the currently available full-sized system. The device will be portable, compact, and operate at low-voltage. Although physical fitness and good health have become increasingly more important to the American public, no compact, affordable, accurate device either for measurement or conditioning human strength or performance exists. This deficit hinders both America's ability to provide convenient, affordable, and accurate diagnostic and exercise capabilities for hospital or home-bound patients, children or elderly, to adequately perform within small-spaced military areas, as would be found in submarines, or in NASA shuttle projects to explore the frontiers of space.
The frame will be compact and light-weight with a target weight of less than 10 kg. This is an ambitious design goal which will require frame materials to have maximum strength-to-weight ratios and the structure must be engineered with attention directed towards compactness, storage size, and both ease and versatility of operation. The design of a smaller and lighter hydraulic valve, pack, and cylinder assembly is envisioned. Software can be tailored to specific applications such as for the very young or the aged, specific orthopaedic and/or disease training, or other applications.
Another future development will be the ability to download programs through the Internet. For example, each patient could have one of the small exercise device at home. His/her doctor can prescribe certain diagnostic activities and exercise regiments and transmit them via the Internet. The individual can perform the exercises at home and then submit the results to the doctor electronically. Biomechanical quantification of performances will become available electronically by downloading the software and executing the procedures on the individual's personal computer. Parents will be able to assist their child's athletic and growth performances, doctors or physical therapists can compare normal gait with their patient's, and many other uses which may not be apparent at this time. The Internet can also function as a conduit between a research site and a remote location. Consider a hypothetical example of the National Institute of Health conducting a study on the effects of exercise on various medical, chemical, neural, and biomechanical factors for a large number of subjects around the world. The exercise equipment could be linked directly with Internet sources, the other data could be collected, and sent to the
appropriate participating institutes. Findings from each location could then be transmitted to the main data collection site for integration.
National and international attitudes and policies focused on improving the health of older people must be directed towards good nutrition and improving lifestyles. Exercise is nc substitute for poor lifestyle practices, such as excessive alcohol consumption, smoking, overeating, and poor dietary practices. Attention must be directed to the importance of creative movements, posture, perceptual motor stimulation, body awareness, body image, and coordination. However, the importance of physical activity is too valuable to be limited to the young and healthy. Exercise, sports, and other physical activities must include all ages without regard tc their frailty or disabilities.
The laws of nature rule the human body. Chemical and biological laws affect food metabolism, neurological transmissions within the nervous system and the target organs, hormonal influences, and all other growth, maintenance, and performance activities. Mechanical influences occur at the joints according to the same laws that return the pole vaulter to earth. Food. water, air, and environmental factors interact with work and societal demands. Human life is an interplay of external and internal processes and energy and, according to the Second Law of Thermodynamics, the system will move towards increased disorder over time . In terms of the universe, the First Law of Thermodynamics states that the total energy of the universe is constant. The Second Law states that the total entropy of the universe is increasing. The measure of a system's disorder is referred to as entropy and Eddington said, `Whenever you conceive of a new theory of unusually attractiveness, but it does not in some way conform tc the Second Law, then that theory is most certainly wrong' . Everyone inevitably grow: older. Delaying the process of disorder by keeping the subsystems of the organism at a low level of entropy does not flaunt the Second Law, but rather exploits it. Logically, consumptior of proper food, sleeping or resting sufficiently, and engaging in an appropriately amount of intense physical activity should keep the tissues and organs functioning maximally. To extend and improve the length and the quality of life depends on an increased awareness of humar anatomy, biology, and physiology with continuous research efforts in these and other areas which impact human life. The aging process cannot be overcome, but it should be possible tc negate many of the debilitating aspects of it. The Declaration of the United States of America is the only document of any country in history which includes the statement of 'pursuit of happiness' and this concept should apply to the health and quality of life for all peoples. regardless of location, and at every age - even during the twilight years.
1 Pollock, M.L., Lowenthal, D.T., Graves, J.E. and Carroll, J.F. (1992) The elderly and endurance training. In: Shephard, R.J. and Astrand, P.-O. (eds), Endurance in Sport, pp. 390-406. London: Blackwell Scientific Publications.
2 Sidney, K., Shephard, R. and Harrison, J. (1977) Endurance training and body composition in the elderly. Am. J. Clin. Nutr., 30, 326-33.
3 Astrand, P.-O. (1992) Influences of biological age and selection. In: Shephard, R.J. and Astrand, P. -O (eds), Endurance in Sport, pp. 285-89. London: Blackwell Scientific Publications. 4 Bortz, W.M., IV and Bortz, W.M. II. Aging and the disuse syndrome - effect of lifetime exercise. In
Optimization of human performance
Harris, S., Harris, R. and Harris, W.S. (eds), Physical Activity, Aging and Sports, Vol. H.- P,
Program and Policy, pp. 44-50. Albany, N.Y.: Center for the Study of Aging.
5 Kraus, H. and Raab, W. (1961) Hypokinetic diseases -- diseases produced by the lack of exerc Philadelphia: Thomas.
6 Bove, A.A. (1979) Heart and circulatory function in exercise. In: Lowenthal, D.T., Bharadwaja,
Oaks, W.W. (eds), Therapeutics Through Exercise, pp. 21--31. New York: Grune & Strattoi 7 Saltin, B., Blomquist, G., Mitchell, J.H., Johnson, R.L., Jr., Wildenthal, K. and Chapman, C.B.
Response to exercise after bed rest and after training. Circulation, 38(7), 1.
8 Erick, H., Knottinggen, A. and Sarajas, S.H. (1963) Effects of physical training on circulation at i
during exercise. Am. J. Cardiol., 12, 142.
9 Saltin, B., Blomquist, G., Mitchell, J.H., Johnson, R.L., Jr., Wildenthal, K. and Chapman, C.B.
Responses to exercise after bed rest and after training. Circulation, 38(8), 1.
10 Clausen, J.P. (1977) Effect of physical training on cardiovascular adjustments to exercise. Ph
Rev., 37, 779.
11 Scheuer, J. and Tipton, C.M. (1977) Cardiovascular adaptations to physical training. Ann. Rei Physiol., 39, 221.
12 Ritzer, T.F., Bove, A.A. and Lynch, P.R. (1977) Left ventricular size and performance followir term endurance exercise in dogs. Fed. Proc., 36, 447.
13 Miller, P.B., Johnson, R.L. and Lamb, L.E. (1965) Effects of moderate exercise during four w( bed rest on circulatory function in man. Aerosp. Med., 38, 1077.
14 Oscai. L.B., Williams, B.T. and Hertig, B.A. (1968) Effect of exercise on blood volume. J. A Physiol., 24, 622.
15 Hanson, J.S., Tabakin, B.S., Levy, A.M. and Nedde, W. (1968). Long term physical training ;
cardiovascular dynamics in middle aged men. Circulation, 38, 783.
16 Becklake, B., Frank, H., Dagenais, G., Ostiguy, G. and Guzman, C. (1965) Age changes in myo
function and exercise response. Prog. Cardiovasc. Dis., 19, 1-21.
17 Templeton, G., Platt, M., Willerson, J. and Weisfeldt, M. (1979) Influence of aging on left vent
hemodynamics and stiffness in beagles. Circ. Res., 44, 189-94.
18 Gottlieb, S.O., Gottlieb, S.H., Ashuffs, S.C., Baumgardner, R., Mellits, E.D., Weisfelt, M.L. a Gerstenblith, G. (1988) Silent ischemia on Holter monitoring predicts mortality in high risk infarction patients. J.A.M.A., 259, 1030-5.
19 Dustan, H. (1974) Atherosclerosis complicating chronic hypertension. Circulation, 50, 871. 20 Gribbin, B., Pickering, T., Sleight, P. and Peto, R. (1971) Effect of age and high blood presst baroflex sensitivity in man. Circ. Res., 29, 424.
21 Bristow, J., Honour, A., Pickering, G., Sleight, P. and Smith, H. (1969) Diminished baroflex sen; in high blood pressure. Circulation, 39, 48.
22 Papper, S. (1973) The effects of age in reducing renal function. Geriatrics, 28, 83-7.
23 Lane, C., Bloch, D. and Jones, S. et al. (1986). Long distance running, bone density, and osteoar
J.A.M.A., 255, 1147-51.
24 Shock, N. (1977) Systems integration. In: Finch, C. and Hayflick, L. (eds), Handbook of the Bio1 Aging, pp. 639-665, New York: Van Nostrand Reinhold.
25 Cummings, S., Kelsey, J. and Nevitt, M:C. and O' Dowd, K.J. (1985) Epidemiology of osteop and osteoporotic fractures. Epidemiol. Rev., 7, 178-208.
26 Basmajian, J. V. and De Luca, C. J. (1985). Muscles Alive. Baltimore: Williams & Wilkins. 27 Milliman and Robertson, Inc. (1987) Health risks and behavior: The impact on medical costs. C Data Corporation.
28 Lane, N., Bloch, D., Jones, H., Marshall, W., Wood, P. and Fries, J. (1986) Long distance rut bone density and osteoarthritis. J. A. M. A., 255, 1147-51.
29 Felig, P. and Koivisto, V. (1979) The metabolic response to exercise: Implications for diabete Lowenthal, D.T., Bharadwaja, K. and Oaks, W.W. (eds), Therapeutics Through Exercise, pp.
New York: Grune & Stratton.
30 Pollock, M. and Wilmore, J. (eds). (1990) Exercise in Health and Disease: Evaluation and
Prescription for Prevention and Rehabilitation. Philadelphia: W.B. Saunders.
31 Jokl, E. (1992) Physical activity and aging. In: Harris, S.; Harris, R. and Harris, W.S. (eds), Phys,
Activity, Aging and Sports. Vol. II, pp. 12-20. Albany, New York: Center for the Study of Ag: 32 Paffenbarger, R., Hyde, R., Wing, A. and Hsieh, C. (1986) Physical activity and all-cause mortal
and longevity of college alumni. N. Engl. J. Med., 314, 605-13.
33 Kannel, W., Doyle, J., Shephard, R., Stamler, J. and Vokonas, P. (1987) Prevention of cardiovasci disease in the elderly. J. Am. Coll. Cardiol., 10, 25A-8A.
34 Dudley, G. and Fleck, S. (1987) Strength and endurance training: Are they mutually exclusive? Spy
Medicine, 4, 79-85.
35 McDonaugh, M. and Davies, C. (1984) Adaptive response of mammalian skeletal muscle to exer(
with high loads. Eur. J. Appl. Phys., 52, 139-55.
36 Delorme, T.L. and Watkins, A. L. (1948) Techniques of progressive resistance exercise. Arch. Pi
Med., 29, 645-67.
37 McQueen, I. (1954) Recent advances in the technique of progressive resistance exercise. Brit. Med 2, 328-38.
38 Hellebrandt, F. and Houtz, S. (1956) Mechanism of muscle training in man: Experimental
demonstration of overload principle. Physiol. Ther. Rev., 36, 371-6.
39 Ariel, G.B. (1973). Computerized biomechanical analysis of human performance. In: Mechanics
Sport, Vol. 4, pp. 267-75. New York: The American Society of Mechanical Engineers.
40 Wainwright, R.W., Squires, R.R. and Mustich, R.A. (1988) Clinical significance of ground react
forces in rehabilitation and sports medicine. Presented at the Canadian Society for Biomechani
5th Biannial Conference on Biomechanics and Symposium on Human Locomotion.
41 Llacera, I. and Squires. R.R. (1988) An analysis of the shoulder musculature during the forehand
racquetball serve. Las Vegas: Presented at the American Physical Therapy Association meeting 42 Susanka, P. (1990) Biomechanical analyses of men's handball. Presented at International Handbc
Federation 12th Men's Handball World Championship, Prague, Czechoslovakia, Charles Univers 43 Reinsch, C. (1967) Smoothing by spline functions. Numerische Mathematik, 10, 177-83. 44 Wood, G.A. and Jennings, L.S. (1975) On the use of spline functions for data smoothing. J. of
Biomech., 12(6), 477-9.
45 Kaiser, J.F. 1975. Digital Filters. In: Liu, D. (ed), Digital Filters and the Fast Fourier Transform, 5-79. Stroudsburg, Pennsylvania: Dowden, Hutchinson & Ross.
46 Hoy, M.G. and Marcus, R. (1992) Effects of age and muscle strength on coordination of rising froi chair. In: Woollacott, M. and Horak, F. (eds), Posture and Gait: Control Mechanisms, Vol. II, 187-90. Portland, Oregon: University of Oregon Books.
47 Teasdale, N., Stelmach, G.E., Bard, C. and Fleury, M. (1992) Posture and elderly persons: Deficit; the central integrative mechanisms. In: Woollacott, M. and Horak, F. (eds), Posture and Gait: Control Mechanisms, Vol. II, pp. 203-7. Portland, Oregon: University of Oregon Books.
48 Vamos, L. and Riach, C.L. (1992) Postural stability limits and vision in the older adult. In: Woollac M. and Horak, F. (eds), Posture and Gait: Control Mechanisms, Vol. II, pp. 212-5. Portland, Oregon: University of Oregon Books.
49 Frank, J., Patla, A., Winter, D., Prentice, S., Walt, S. and Prasad, S. (1992) Control of upright stand active, healthy elderly. In: Woollacott, M. and Horak, F. (eds), Posture and Gait: Control Mechanisms, Vol. II, pp. 216-9. Portland, Oregon: University of Oregon Books.
50 Panzer, V., Kaye, J., Edner, A. and Holme, L. (1992) Standing postural control in the elderly and v elderly. In: Woollacott, M. and Horak, F. (eds), Posture and Gait: Control Mechanisms, Vol. II, 220-3. Portland, Oregon: University of Oregon Books.
51 Craik, R. (1989) Changes in locomotion in the aging adult. In: Woollacott, M.H. and Shumway-Co A. (eds), Development of Posture and Gait across the Life Span. pp. 150-3. Columbia, South Carolina: University of South Carolina Press.
52 Williams, K. (1992) Intralimb coordination of older adults during locomotion: Stair climbing. In:
Optimization of human performance 31
Woollacott, M. and Horak, F. (eds), Posture and Gait: Control Mechanisms, Vol. II, pp. 208-11.
Portland, Oregon: University of Oregon Books.
53 Light, K.E., Tang, P.F. and Krugh, C.R. (1992) Performance differences between young and elderly
females in a step-reach task. In: Woollacott, M. and Horak, F. (eds), Posture and Gait: Control
Mechanisms, Vol. II, pp. 287-90. Portland, Oregon: University of Oregon Books.
54 Jacobs, I., Bell, D.G. and Pope, J. (1988) Comparison of isokinetic and isoinertial lifting tests as
predictors of maximal lifting capacity. European J. Appl. Physiol., 57, 146-53.
55 Ariel, G.B. (1978) Computerized dynamic resistive exercise. In: Landry, F. and Orban, W.A.R. (eds),
Mechanics of Sports and Kinanthropometry, Book 6, pp. 45-51. Miami, Florida: Symposia
56 Benson, H. (1991) University Physics. New York: Wiley & Sons.
57 Eddington, A. (1928) The Nature of the Physical World. Cambridge: New Press.