The relationship between resistance exercises and muscle
strength has been known for centuries. In ancient Greece, Milo the wrestler used
progressive resistance exercises to improve his strength. His original method consisted of
lifting a calf each day until it reached its full growth and this technique provides
probably the first example of progressive resistance exercises.
Today, it is well documented in the 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. These attempts to produce a better means of rehabilitation or a
physiologic edge in sporting activities have only scratched the surface of the cellular
mechanisms and physiologic consequences of muscular overload.
Muscular strength may be defined as the force that a muscle
group can exert against a resistance in a maximal effort. In 1948, Delorme (35) 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
regimens for producing muscle hypertrophy and those for producing muscle power. (66) He
concluded that the number of repetitions for each set of exercise determines the different
characteristics of the various training procedures.
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,
the Oxford technique, the double and triple progressive super set systems, and many
others. Each system's effectiveness has been supported and refuted by numerous
Berger concluded that six to seven repetitions three times
a week was best for developing dynamic strength (13). Research conducted by Steinhause
emphasized the need to increase the intensity, not the amount, of work in order to develop
maximum strength. (88)
In more recent studies pertaining to exercise, Pipes and
Wilmore compared isokinetic training with isotonic strength training in adult men (77).
According to their findings with isokinetic contractions at both low and high speeds, the
isokinetic training procedure demonstrated marked superiority over the isotonic methods.
(Note: This study was not a valid study and do not accept its merit).
In 1972, I introduced the dynamic variable resistance
(DVR) exercise principles in 1968, which resulted in the variable resistance
exercise equipment (3-7). For the first time biomechanical principles were employed in the
design of exercise equipment.
Owing to ambiguity in the literature concerning certain
physiologic terms and differences in laboratory procedures, the following terms are
- Muscular strength: the contractile power of muscles as a
result of a single maximum effort.
- 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.
- Isometric training: a muscular contraction of total
effort but with no visible limb movement (sometimes called static training).
- Isotonic training: raising and lowering a submaximal
load, such as a weight, a given number of times (sometimes called dynamic training).
- 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.
- Concentric contraction: an isotonic contraction in which
the muscle length decreases (that is, the muscle primarily responsible for movement
- Eccentric contraction: an isotonic contraction in which
the muscle length increases (that is, the muscle primarily responsible for movement
- Muscle overload: the workload for a muscle or muscle
group that is greater than that to which the muscle is accustomed.
- Repetitions: the number of consecutive times a particular
movement or exercise is performed.
- Repetition maximum (1 RM): the maximum resistance a
muscle or muscle group can overcome in a maximal effort.
- Sets: the number of groups of repetitions of a
particular movement. or exercise.
- Variable resistance exercise: as the muscle contracts,
the resistance changes in a predetermined manner (linear, exponentially, or as defined by
- 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).
In most existing exercise equipment today and in the
previously cited research, resistive training was performed with "tools" that
lack intelligence. That means the equipment was "unaware" that a subject was
performing an exercise on it. For example, the equipment employed in the study conducted
by Pipes and Wilmore assumed certain velocities on the isokinetic modality used. However,
verification of the speed was impossible since a closed loop feedback and sensors were not
used, as they do not exist on the equipment employed (Note: This was unacceptable study in
the field). However, with the advent of miniaturized electronics in computers, it is
possible today to join exercise equipment with the computer's artificial intelligence. For
the first time it is possible for the equipment to adapt to the user rather than for the
user to adapt to the equipment.
Another 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. 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
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 that place little stress on the neuromuscular system
had little effect on the functional capacity of the skeletal muscles; however, they 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.
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 are
results of rotational motion of the links, which are made of 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 performance are force,
displacement, and 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 center 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
In any athletic performance, 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 centers to produce the correct forces at the appropriate time.
Since most athletic events are ballistic movements 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.
Resistive Excercising Methods
There is a significant difference between various resistive
training methods. As far as isotonic and isokinetic exercises are concerned, for example,
in the isotonic exercises the inertia, that is, the initial resistance, has to be overcome
first, then 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 else 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 programs utilize isokinetic training to recondition injured limbs 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
In isotonic resistive training, if more than one repetition
is to be used, one must use submaximal overload on the initial contractions in order to
complete the required repetitions. Otherwise, the entire regimen will not be completed,
owing to fatigue. Berger and Hardage studied this problem by training two groups of men
with 10 RM. One group trained following the standard Berger technique while the other
group used one repetition maximum for each of the ten repetitions. This was accomplished
by progressively reducing the weight for the next repetition in a manner that paralleled
the fatigue of the muscle. The results showed that the intensity of the work seemed to be
the important factor in strength increases, since the maximal overload group showed
significantly greater strength gains than did the standard 10 RM group.
Based on these findings, it would seem appropriate to
assume that a modality that can adjust the resistance so that it parallels fatigue to
allow the maximum RM for each repetition would be superior to the currently available
equipment. Berger accomplished this function by removing weight from the bar while the
subject trained. This is neither the most convenient nor the most practical method. With
the aid of the modern computer, this function can be performed automatically.
Another drawback with current isotonic types of resistive
exercises is that with the aid of inertia, due to the motion, the resistance changes
depending on the acceleration of the weight and the body segments. In addition, since
overload on the muscle changes due to both biomechanical levers and the length-tension
curve, the muscle can obtain maximal overload only in a small portion of the range of
motion. To overcome this shortcoming in resistive training, several companies have
manufactured strength training devices that have "variable resistance"
mechanisms in them. However, these "variable resistance" systems increase the
resistance in a linear fashion and this linearity does not truly accommodate the
individual. When including inertial forces to the variable resistance mechanism, the
accommodating resistance might be canceled by the velocity of the movement.
There seem to be unlimited training methods and each system
is supported and refuted by as many "experts." In the past, the problem of
validly evaluating the different modes of exercise was rendered impossible because of the
lack of the proper diagnostic tools. For example, in the isotonic type of exercise the
investigator does not know exactly the muscular effort and the speed of movement but knows
only the weight that has been lifted. When a static weight is lifted, the force of inertia
is 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
very poorly verified. The rotation of a dial to a specific location does not guarantee the
accuracy of subsequently generated velocity. In fact, discrepancies as great as 40 per
cent are found when verifying the velocity of the bar.
The Intelligent Excercise Machine
In all of the previous descriptions of exercise equipment,
the user has had to determine the amount of resistance and the number of repetitions
desired. The reason the user made the choices was, of course, that the exercise equipment
itself was inherently incapable of any intellectual participation. However, with the
advent of computers, it became possible to design exercise equipment with artificial
intelligence enabling the computerized machine to select the best exercise method based on
each individual user. Thus, the user need not be an expert in any biologic, physiologic,
or exercise area, since the exercise machine is programmed with information from many
scientific fields, thus correctly benefiting the different individual users.
The exercise machine described herein is the result of the
application of many unique, innovative features and mechanisms to the long-established
fields of resistive exercise or training for athletics, rehabilitation, and physical
fitness. The underlying principle behind these innovations is that of a
computer-controlled feedback or servomechanism that is able to maintain any desired
pattern of force and motion throughout the range of each exercise, regardless of the
magnitude or rate of force applied by the person exercising. The advantages of an
intelligent feedback-controlled mechanism over existing resistive exercise mechanisms are
First, all systems that employ weights as the mechanism for
resistance have major drawbacks in four or more areas, as follows:
- biomechanical considerations,
- risk of injury, and
- uni-directional resistance.
The biomechanical considerations are the most important for
exercise equipment and have been previously explained. Inertia is the property of
resisting any change in motion; because of this property, it requires a greater force to
begin moving weights than it does to keep them moving in a constant manner. Similarly,
when the person exercising slows his motion at the end of an exercise movement, the
weights tend to keep moving until slowed by gravity. This phenomenon reduces the required
force at the end of a motion sequence. This property 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 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. Injury could easily result if the weights fell
back to their resting position accompanied by the concomitant motion of the bar or the
handle attached to the weights. If the person exercising happened to lose his grip, or was
unable to hold the weights owing to exhaustion or imbalance, serious injuries could and
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 that employ springs,
torsion bars, and the like are able to overcome the inertia problem of weight-based
mechanisms and can partially overcome 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.