A21 Dynamic Mode Failures

Topic

In general, an athlete experiences a failure of the dynamic mode whenever their movement pattern deviates significantly from the biomechanical mode optimal for the specific task being performed. This deviation can stem from accumulated fatigue or a specific injury—whether structural, elastic, articular, or related to motor control, as outlined in the preceding models—or from poor technique or unfavorable external conditions.

In running, however, this dynamic mode collapses precisely when the runner's leg—acting as a spring-mass system—loses stiffness (analogous to the model describing stiffness in a degenerated tendon), causing ground contact time to extend beyond the limits of the optimal dynamic mode. A further reduction in leg stiffness leads to an even longer ground contact time, thereby degrading the dynamic mode of the run.

In jumping, conversely, an incorrect takeoff angle drastically reduces both the final distance and the height of the jump. As the takeoff angle deviates further from the optimum, the final distance or height is reduced even more sharply. During a throw, however, the athlete's kinetic chain breaks down prematurely precisely when a distal segment of the chain activates before the preceding proximal segment has reached its peak velocity—a scenario similar in principle to the timing mismatch between agonist and antagonist muscles found in another model in this set. Consequently, this premature activation dissipates the throwing energy rather than effectively transferring it to the final distal segment. If the distal segment activates even earlier—before the proximal segment reaches peak velocity—the energy of the throw dissipates even more forcefully without being transferred to that distal segment.

Therefore, given this deviation from the optimal biomechanical pattern, the athlete's dynamic movement is analyzed by comparing their observed kinematic and kinetic parameters against the reference parameters of the correct biomechanical pattern. This deviation is quantified either as the root-mean-square error between the athlete's observed trajectory and the optimal reference trajectory, or as the difference between a key observed dynamic parameter (such as a runner's leg stiffness, flight time, or takeoff angle) and its expected reference value—much like the ratio of produced force to expected force used in another model in this set to quantify muscle force loss. The further the observed dynamic parameter deviates from its expected reference value, the greater the resulting quantified deviation for that dynamic movement becomes.

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