Scientific Aspects in the Preparation of Elite Athletes
Gideon B. Ariel, Ph.D.
Biomechanics is the study of the motion of living things and, as an established
discipline, it has evolved from a fusion of the classical disciplines of
anatomy, physiology, physics, and engineering for measuring and evaluating
performances. Biomechanics, then, is built on a foundation of knowledge and the
application of basic physical laws. Although anything which moves be it human or
machine can be quantified, the application of biomechanics has been successfully
applied to great athletes and their world record performances.
Previously, it was common practice to assess athletes in terms of muscular
strength, cardiovascular capacity, body composition, or other tests performed on
individuals. Individually or collectively, these tests inadequately defined or
determined elite qualifications. Biomechanics affords a productive approach to
the quantification and assessment of performances of elite athletes.
A biomechanical movement analysis system provides a means to quantity motion
utilizing input information from visual inputs (either video or film), as well
as additional quantitative measures such as, electromyography (EMG) and force
platforms. The theoretical bases of the video technique 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. (1)
The movement analysis system provides a means for measuring human motion based
on a technique of processing multiple high-speed film or video recordings of a
subject's performance (2,3,4). This technique demonstrates significant
advantages over other common approaches to the measurement of human performance.
First, 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 athlete need not be aware that data is
being collected. Second, 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 athlete.
Activities in the gymnasium, field, or any sporting facility 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 centimeters or of many meters, 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, although special applications may require very high-speed
cameras, powerful lenses, and high levels of illumination. Determination of the
problem, error level, degree of quantification, and price will all affect the
input device selection. Fourth, film data can be collected during international
competition far from the analyzing location and, at a later date, the events can
A typical kinematic analysis consists of four distinct phases. The initial step
involves "grabbing" the image from the film by means of appropriately programmed
software utilizing a specialized board and storing the data in the computer's
memory. This eliminates any further need for the video apparatus. The image
sequence is then retrieved from computer memory and is displayed, one frame at a
time, on the digitizing monitor. The grabbed image can be enhanced or altered in
several ways, including zooming the whole frame or a defined, isolated portion
of the view. Changing the size may help the digitizer to more accurately
determine a particular joint which in the original view could not be identified;
(4) 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; (5) the
speed of each of the cameras (frames/second) must be accurately known, although
the speeds do not have to be the same; and (6) some event or time signal must be
recorded simultaneously by all cameras during the activity in order to provide
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
discussed previously. 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 to 30 degrees can be
accommodated while introducing almost negligible error. A panning camera option
is also available.
Digitizing is the second phase of analysis. Initially, the video image is
captured by the computer and stored in memory. This eliminates any further need
for the video apparatus. The image sequence is then retrieved from computer
memory and is displayed, one frame at a time, on the digitizing monitor. using a
video cursor, the location of each of the subject's body joints, such as ankle,
knee, hip, shoulder, elbow, is selected. 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. This 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. It is performed, however, under
computer control and the digitizing of video images is computer assisted. User
participation in the digitizing process, however, provides an opportunity for
error checking and visual feedback which rarely slows the digitizing process
adversely. A trained operator with a reasonable knowledge of anatomy and a
consistent pattern of digitizing can rapidly produce high-quality digitized
images. Because all subsequent information is based on the data provided in this
phase, it is essential that the points are selected precisely. However, an
automated digitizing option is available.
The computation phase of analysis is performed after all camera views have been
digitized. The purpose of this phase is to compute the true three-dimensional
image space coordinates of the subject's body joints from the two-dimensional
digitized coordinates of each camera's view. Computation is performed using a
direct linear transformation. This transformation 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 small amount
of timing information provided by the user. This information includes starting
and ending points if all the data are not to be used, as well as a frame rate
for the image sequence that may differ from the frame rates of the cameras used
to record the sequence.
When transformation is complete, 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 cubic and
quintic splines as well as a Butterworth second-order digital filter (5,6,7).
Smoothing may be performed automatically by the computer or interactively with
the user controlling the amount of smoothing applied to each joint. In addition,
error measurements from the digitizing phase may be used to optimize the amount
of smoothing selected. At the completion of smoothing, the true threedimensional
body joint displacements, velocities and accelerations have been computed on a
continuous basis throughout the duration of the sequence.
At this point, optional kinetic calculations may be performed to complete the
computation phase. Body joint displacements, velocities and accelerations are
combined with body segment mass distribution to compute dynamic forces and
moment at each of the body joints. muscular contribution to these forces and
moments can then be computed by selectively removing the inertial and
gravitational kinetic components.
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 three
dimensions. 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.
Hard copies of these displays can also be produced for reporting and
Results can also be reported graphically. Plots of body joint and segment linear
and angular displacements, velocities, accelerations, forces and moments can be
produced in a number of format options. An interactive graphically oriented user
interface makes the selection and plotting of such results simple and
straightforward. In addition, results may also be reported in numerical form.
All quantities that can be selected for graphing may also be printed in tables
of body motion parameters. Results can also be exported for processing with
other software applications, such as spreadsheets, graphic packages, and
The preceding discussion has described a computerized biomechanical system which
can be utilized for the quantification of activities and performance levels. The
need to identify and measure a task with subsequent application and evaluation
for elite athletes and their training program was raised in the introduction as
an important need.
One example for the application of biomechanical analyses to elite sports
occurred during the Third IAAF World Championships in Tokyo in 1991 in the long
jump competition between Mike Powell and Carl Lewis. Both of these outstanding
athletes broke the longest existing world record in athletics, Bob Beamon's 8.9m
jump. The purpose of this study was to analyze the components of the jumping
techniques during different phases of one of each athlete's performances: Mike
Powell (8.95m) and Carl Lewis (8.91m).
Three consecutive parts of the jump were considered: (1) approach, (2) take-off,
(3) flight and landing.
The basic or generalized biomechanical characteristics for both athletes are
Table 1: Parameters of long jump
|Official distance (m)
|Effective Distance (m)
|Wind Velocity (m/s)
|Average Running Speed between:
|11-6m. to the board (m/s)
|6-1m. to the board (m/s)
|The Length of the:
|Third-last Stride (m)
|Second-last Stride (m)
|Last Stride (m)
|CM Horizontal Velocity (m/s)
|CM Vertical Velocity (m/s)
|Angle of Projection (degrees)
|Angle of Body Lean (degrees) at:
|Maximum CM Height (m)
|Height of CM at Touch-down (m)
|Horizontal Distance between the CM and Foot Mark (m)
It should be noted that the actual results used in this analysis were achieved
under different ambient conditions, the most important being the difference in
the wind speed. According to official measurements, Lewis' jump was assisted by
a favorable wind of considerable velocity. It is very difficult to give a
reliable assessment of the relative contribution of the wind speed to the jump
distance, although the most prudent estimates suggest that the favorable wind
was responsible for at least 10 to 15 cm in Lewis, final result. Although this
factor should be considered in evaluating the actual value of the results
obtained, for this paper the main task will be to examine the biomechanical
aspects of the performance.
The most pronounced differences in the jumping techniques for the two athletes
are clustered within the last two strides preceding the take-off. Attention
will, therefore, be restricted to that portion of the jump.
The first athlete to be evaluated was Mike Powell. The length of Powell's
second-to-the-last stride was 2.74 m, which placed it near the lower boundary of
the statistical interval for high performance jumpers. Shortening of the stride
was clearly seen on the video recording and showed a breaking of the running
tempo at this stride. The flight phase of this stride marked the beginning of
the lowering of the center of mass in preparation for the final push. This
motion was accompanied by a decrease in both horizontal and vertical velocities
of the center of mass. Nevertheless, this "shortened" stride allowed Powell to
attain a very straight body position, nearly vertical, with a slight offset of
the support leg and a stiff landing. There was virtually no flexing in the knee
joint and with the prevailing "straight-downwards" motion, the toe was forward.
This allowed Powell to enter the last stride with no reduction in velocity by
powerfully swinging the left, or leading leg, and with an active thrust of the
The flight phase of the last stride started, consequently, with a very high
horizontal velocity of the center of mass (11.8 m/s), but with zero vertical
velocity due to the knee flexors absorbing the impact. During the flight, the
position of Powell's center of mass dropped by 8 cm, reaching it's absolute
minimum of 97 cm and the angle of the trunk changed rapidly. The landing of the
take-off leg was marked by it's very long forward offset from the projection of
the center of mass. The landing of the take-off leg was very stiff, with active
body motion forward-upward. Instead of an eccentric motion in both the hip and
the knee joints, both joints worked in a concentric mode with high angular
velocities at the hip (1100 deg/s at the interval from 160 to 188 degrees) and
lower and decreasing angular velocities at the knee which, in this case,
performed as the only impact absorbing element. The knee performed actively as
well as with the angle changing from 160 to 178 degrees. At this phase, the
velocity of the lead leg began to increase in an undulating motion. After
passing the vertical, the motion of the swing leg prevailed. The angles in the
support leg changed considerably, although with lower angular velocities. Thus,
the final push was performed mostly by the motion of the swing leg. The final
surface interaction was characterized by dramatic changes in the center of mass
velocity. The horizontal velocity of the support leg decreased by more than 2
m/s, but at the expense of the vertical velocity increase of 4.26 m/s, which was
largely assisted by the very energetic motion of the pelvis at this stage. The
resulting take-off angle was 24.6 degrees.
Examination of Carl Lewis' jump yielded different movement patterns. Lewis
commenced the preparation for the final push during the support phase of the
second to last stride. This is expressed in the lowering of the center of mass
by 3 cm. Lewis left the surface interaction with noticeable forward trunk lean
and a high horizontal velocity of the center of mass (11.8 m/s). At the same
time, the vertical component of the center of mass speed was negative. The next
stride was considerably longer than the statistical average by more than So cm.
During this elongated stride, the position of the center of mass was lowered by
10 cm. and the trunk was nearly vertical. During this stride, the left knee
absorbed the impact with the change in the knee angle approximately 10 degrees.
The center of mass reached it's absolute minimum in height at 94 cm. With the
knee flexed, active extension of the left hip was attained with the angle
changing by 19 degrees and the angular velocity reaching 600 deg/s. The right
hip swung at an angular velocity of 850 deg/s in order to assist the raising of
the body from the deeply bent stride.
At that moment, the center of mass began it's upward motion. After passing the
vertical, the motion of the segments became less active. The raising of the
center of mass was achieved mostly by the extension in the hip, with a nearly
constant knee angle. Some gain in the vertical speed of the center of mass was
achieved due to the foot push. With minimal vertical speed, the last stride was
very short (1.88 m) and with a negligible flight phase. The height of the center
of mass was maintained constant. This body position was made possible by placing
the support leg on the surface with a downward vertical motion without a
pronounced "thrust" and with a very fast inward motion of the hips with the
angular velocity of this motion reaching 1250 deg/s. The next phase of the final
push was characterized by a whip-like motion of the swing leg and the extension
of the support leg in the knee. The change in the height of the center of mass
during the last interaction was 26 cm. The horizontal speed dropped by 1.4 m/s
(from 10.5 to 9.1), and the gain in the vertical speed was 3.37 m/s. The
take-off angle was 20.3 degrees. It should be noted here that the angle in the
knee of the support leg at the moment of take-off was only 158 degrees,
which demonstrated "under extension". This observation suggests the presence of
a concealed reserve in the performance recorded.
The flight techniques used by both athletes were practically identical. They
both employed a 3 1/2 steps of "run-in-the-air" and the maximum elevation of the
center of mass was 2.05 m for Powell and 1.84 m for Lewis.
Comparison of the individual techniques employed by the two athletes leads to
the conclusion that the fundamental distinction lies in the different approach
used in the run and take-off phases. The athlete who maximizes the velocity and
the direction of the take-off while, at the same time, maintaining the optimum
combination of body spatial positions, angular movements, and the relative
movements of the segments will produce the longest jump. Powell and Lewis used
different techniques during the take-off phase of the jump: (1) between the
velocity and the height of the center of mass, and (2) between the accumulated
muscle force and kinematics of the speed transformation in order to achieve the
maximum efficiency with precise timing.
The "jump formula" of Powell might be
summarized as follows:
- Shortened second-to-last stride
- Vertical lead leg landing
- Stiff landing of the take-off leg with a large offset
- Incorporating the pelvis in the locomotion due to powerful trunk muscles
- Energetic swing. The lowest center of mass position was reached in the
beginning of the last surface interaction
- Considerable loss in the horizontal velocity with compensation in a large
gain in the vertical component.
The "jump formula" of Lewis can be summarized as follows:
- Significant elongation of the second-to-last stride
- Early lowering the center of mass
- Entering a very short last stride with zero vertical velocity
- A very short last stride
- Take-off with fast inward hip motion.
Comparison of the original video recordings of the two attempts described above
and confirmed by the biomechanical quantification indicate that there are
sufficient differences to consider these jumps as belonging to different jumping
styles. One of the most fundamental differences lies in the timing of the
beginning of the center of mass upward motion. It is this point which defines
how long or how short the process of the transformation of speed will take and,
consequently, how the type of motion will be executed. Lewis started the motion
much earlier and divided the process of the speed transformation between two
strides. As a result, this process was not accompanied by application of
accumulated momentum in a single high force surface interaction. Conversely,
Powell preserved all the momentum gained until the last surface interaction and
converted it into the launch
velocity of a single motion.
These conclusions allow us, to some extent, to speculate about the type of
physical training of the two athletes. Lewis, in effect, adapted the high speed
sprinter's techniques to the long jump. The Powell formula focused on a more
pronounced force orientation. Powell's technique required greater efforts for
the force exertion capabilities in his training. These two different approaches
might be possibly used as guidelines in selecting and structuring the training
basis for an athlete, with due consideration of the individualities, training
and competitive background.
This presentation has focused on a method for quantification of elite athletes
and a specific example of its application. The world of athletics and the
personnel who participate can easily be selected, trained, and coached through
the techniques of biomechanical analysis. Ultimately, however, the athlete is
the only individual who can actually perform; we as scientists, coaches, and
spectators can only try our best and then sit back and watch.
- G.B. Ariel, "Computerized Biomechanical Analysis of Human Performance,"
Mechanics and Sport, Vol. 4, pp. 267-275, The American Society of Mechanical
Engineers, New York, 1973.
- R.W. Wainwright, R.R. Squires, R.A. Mustich, "Clinical Significance of Ground
Reaction Forces in Rehabilitation and Sports Medicine," presented at the
Canadian Society for Biomechanics, 5th Biannual Conference on Biomechanics and
symposium on Human Locomotion, 1988.
- Llacera and R. Squires, "An Analysis of the Shoulder Musculature during
the Forehand Racquetball Serve," presented at American Physical Therapy
Association meeting, Las Vegas, June, 1988.
- P. Susanka, "Biomechanical Analyses of Men's Handball," International
Handball Federation 12th Men's Handball World Championship, Charles University,
Prague, Czechoslovakia, 1990.
- C. Reinsch, "Smoothing by Spline Functions," Numerische Mathematik, Vol. 10:
pp. 177-183, 1967.
- G.A. Wood and L.S. Jennings, "on the Use of Spline Functions for Data
Smoothing," J. of Biomechanics, Vol. 12 (6): pp. 477-479, 1975.
- J.F. Kaiser, "Digital Filters," Digital Filters and the Fast Fourier
Transform, Edited by D. Liu, pp. 5-79, Dowden, Hutchinson & Ross, Stroudsburg,
- G.B. Ariel, "Computerized Dynamic Resistive Exercise," Biomechanics of Sports
and KinanthrORometry, Edited by F. Landry and W.A.R. Orban, Book 6. pp. 45-51,
Symposia specialists, Inc., Miami, Florida, 1978.
- Ballreich R. Weitsprunganalyse. Berlin 1980.
- Bruggemann, P.,Nixdorf, E., Ernst, H. "Biomechanische Untersuchungen beim
Weitsprung. Die Lehre der Leichtathletik", Vol.4: pp.36-40, 1982.
- Dapena G. "Three-dimensional cinematography with control object of unknown
shape." J. of Biomechanics, Vol. 15: pp. 11-19, 1982.
- Fischer R. Weitsprung. "Biomechanische Untersuchungen am Schweizerischen
Weitsprungkader mittels Film-analyse und Messungen mit der
Mehrkomponentenmess-platform.11 Diplomarbeit in Biomechanik, ETH Zurich, 1975.
- Hay J.G. The biomechanics of sport techniques. New York, 1978.
- Hay, J.G., Miller, J.A. "The horizontal jumps. A report on the USOC elite
athlete project". T.Tech., 1983.
- Hay, J.G., Miller, J.A. "Techniques used in transition from approach to
take-off in the long jump." Int.J.Sport Biomech., Vol.1: pp. 174-184, 1985.
- Hay, J.G. "The biomechanics of the long jump." Exercise and svort sciences
reviews, Vol.14: 1986
- Hay, J.G., Miller, J.A., Canterna, R.W. "The techniques of elite male long
jumpers." J. Biomechanics, Vol.19: pp. 855-866, 1986
- Lees, A. "An optimised film analysis method based on finite difference
techniques." Journal of Human Movement Studies, Vol.6: pp. 165-180, 1980.
- Luthanen, P., Komi, P.V. "Mechanical power and segmental contribution to
force impulse in long jump take-off." Eur. J.Mplied Physiol, Vol. 41:pp.
- Nigg, B.M. Sprung, springen, sRrunge. Zurich, 1974.
- "Scientific research project at the games of XXIV Olympiad -Seoul 1988.11
ed. G.Bruggemann and B.Glad. international Athletic Foundation, pp. 263-301,
- Susanka, P., Stepanek, J. "Dependence of resultant sports performance on
running speed in the long jump." Prague, 1986.