D22 Dynamics / Forces

Topic

This dynamic analysis determines the forces and torques that cause the observed movement of the athlete—in contrast to kinematic analysis, which describes the movement geometry alone without considering the causative forces.

Conversely, inverse dynamics utilizes both kinematic data (specifically the acceleration of each body segment) and measured external forces acting on the athlete to calculate—using Newton-Euler equations applied to each segment individually—the internal joint moments and joint reaction forces at each of the athlete's joints. Consequently, this calculation proceeds from the most distal segment (such as the foot) toward the most proximal segment (such as the trunk), rather than in the reverse direction.

A force platform, on the other hand, directly measures the ground reaction force exerted during each step, as well as the point of application of that force on the platform's surface.

Forward dynamics, conversely, begins with the athlete's muscle forces to predict the resulting movement—operating in the exact opposite direction of the inverse dynamics approach previously described. Because forward dynamics involves predicting complex movements, the calculations are computationally more demanding; consequently, this method is primarily reserved for movement simulation rather than for the direct analysis of previously recorded movement. Consequently, the athlete's segmental position—measured via the kinematic analysis established by another model in this set—combined with the ground reaction force and point of application measured by the force platform, collectively determine the final net joint torque, joint reaction force, and final joint power for each of the athlete's joints. The fact that the final joint power at a specific joint is higher means that the joint contributes more forcefully to energy transfer along the athlete's entire kinetic chain—the very same kinetic chain defined by another model in this set.

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