Athletics can be likened to a spectrum. On one side of the spectrum are esthetic events such as gymnastics, diving, and figure skating where success depends on the ability of the athlete to create movements that are visually pleasing to the referees. In the middle of the spectrum are the endurance activities for which the athlete tries to maintain muscular contractions for long periods of time at submaximal intensity levels. The explosive activities, such as sprinting, jumping and throwing, include events in which the athlete tries to achieve maximal, coordinated power.

Biomechanical analysis provides a technique for the investigation of the particular event in order to

• Understand,
• Correct or improve, or
• Create the ideal model of performance.

Analysis of the performer and subsequent comparison with the ideal model can provide feedback to the athlete concerning deviation from the optimum and, hence, continued performance enhancements.

A video-based biomechanical analysis treats the human body as a series of moving links; upon which muscular, gravitational, inertial, and reaction forces are applied. The physical and mathematical model for such a system, although complex, is well defined. The system provides a means of measuring human motion based on the processing of two or more simultaneously acquired video recordings of a subject's performance. This technique demonstrates a significant advantage because it is noninvasive. No wires, sensors, or markers need be attached to the subject (although markers can be used if automatic digitizing is desired). In fact, the subject can be completely unaware that data are being collected which would be the situation if video recordings are made during actual competitions. Cameras can be taken to the location of the activity and positioned in any convenient manner, so as not to interfere with the subject.

A typical performance analysis assessment consists of four distinct phases:

1. Data Collection,
2. Digitizing,
3. Computation, and
4. Presentation of Results.

Data collection consists of video recordings of an activity made using two or more cameras, stationary or panned.

In the digitizing process, two methods can be used:

• Manual and
• Automatic.

The automatic process requires reflective markers to be placed on the athlete's joint centers while the manual technique requires human decisions regarding the determination of each joint center location for each of the film's frames.

Following the digitization, the computation phase of analysis computes the true three dimensional image space coordinates of the subject's body joints. The computation is performed utilizing the two-dimensional digitized coordinates from at least two cameras view which have been selected for use. Computation is performed using a direct linear transformation, or the newer and more powerful Physical Parameters Transformation, to determine the true image space locations in three dimensions.

When transformation is complete, a smoothing or filtering procedure is performed on the image coordinates to remove small, random digitizing efforts and to compute body joint velocities and accelerations. Smoothing algorithms include polynomial, cubic and quintic splines, as well as various filters. At the completion of smoothing, the true three-dimensional body joint displacements, velocities, and accelerations have been determined on a continuous basis throughout the duration of the sequence.

At this point, optional kinetic calculations can 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 moments 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 body motion can be presented in both still frame and animated stick figure; movements in three dimensions. Results can be reported numerically in tables, exported to external mediums such as spreadsheets, and graphically. Plots of body joints and segments, linear and angular displacements, velocities, acceleration, forces and moments can be produced in a number of format options.

The preceding discussion has illustrated the use of biomechanical quantification of movement analysis in assessing functional capacity. The technique can be performed with papers, pencils, erasers and large amounts of time or with newer, enhanced technologies incorporating computers and integrated hardware-software. In addition to PC desktop computerized biomechanical systems, it is now possible to perform most of these procedures with a portable, 2 Kg. notebook computer. With the technological innovations of the future, there would seem to be no limit except, perhaps, human reluctance.

While the biomechanical assessment technique just discussed measures functional capacity, it can also be measured directly by resistive dynamometry devices. An ideal system would employ computerized feedback control of both resistance and movement during the exercise. This intelligent dynamometer; would allow the machine to dynamically adapt to the activity being performed rather than the traditional approach of modifying the activity to conform to the limitations of the machine. With this type of equipment, the coach could examine the results of the biomechanical motion analysis and, with his or her knowledge and experience of the sport and the individual athlete, determine the most appropriate training regimen at that time for that person. Concentration on strength acquisition may be important during the off season while speed and strength maintenance are paramount within the competition period. These choices can be made and subsequently modified by the coach.

Case studies in applied biomechanics demonstrate the importance of considering the true patterns of motion in determining efficient performance. One of the most important parameters in training is the ability to allow the performer to achieve a movement pattern of resistance or the pattern of motion experienced by the user during the actual activity. The ability to modify the pattern by reprogramming the dynamometer can be determined by the individual. Standard isokinetic equipment cannot fulfill these requirements.

The value of applying the principles of biomechanics to the assessment of functional performance has been demonstrated. Movement analysis provides the means to quantity human activity and to provide insight into the mechanisms that contribute either to superior or inferior levels of performance. In addition, a technology has been presented that permits exercise and rehabilitation patterns to biomechanically duplicate the target activity as measure of function capacity.