Complex goal-directed human movements consist of a series of phases with multiple objectives. Knowledge of the relationship between control and dynamics during flight and subsequent contact phase is essential for improving landing performance without sustaining injury. The purpose of this study was to 1) model the relationship between the flight phase control, the center of gravity (CG) trajectory and the reaction force during contact with the landing surface and 2) determine how control of the lower extremities prior to contact, as observed experimentally, influences the reaction force during impact. Simulated landings with fixed joints resulted in greater reaction force magnitudes and longer times-to-peak force than observed experimentally. Landing simulations with progressive increases in knee extensor torque prior to touchdown reduced the relative velocity between the CM and the legs ("pull-up") and resulted in a) more vertical shank positions at touchdown, b) greater rates of vertical and horizontal impulse generation c) greater peak forces during the contact phase and d) greater reductions in the CGVy and CGVx during the initial part of the contact phase. A multi-link model of a gymnast and a model of the gymnastics mat were developed and experimentally validated. Modification of the knee joint torque prior to touchdown simulated the leg "pull-up" behavior often observed prior to contact (McKinley et al., 1992; McNitt-Gray et al., 2001). These results support the hypothesis that modifications in flight phase control provides a mechanism for regulating the magnitude of the reaction forces experienced during contact.
© Copyright 2004 Annual Meeting of the American Society of Biomechanics. (Presented on poster September 9-10, 2004 at the ASB meeting in Portland). All rights reserved.