Kinetics of the lower extremities during drop landings from three heights.

In this study, the landing preferences of gymnasts (n = 6) and recreational athletes (n = 6) were determined by comparing the changes in lower extremity kinetics of drop landings performed from three heights (0.32-1.28 m). Net joint moments and work done on the extensor muscles of the ankle, knee, and hip were selected as variables representative of the demand placed on the muscles responsible for controlling flexion and dissipating the load. Kinematic and kinetic two-dimensional data were acquired simultaneously using high-speed film (202.4 fps) and a force plate (1000 Hz). Reaction forces and lower extremity joint motions were used to calculate net joint forces, net joint moments powers, and work done on the extensor muscles of the ankle, knee, and hip. Results indicated that the extensor joint moments tended to peak earlier after contact with increases in velocity, but the temporal sequence of events was maintained independently of velocity or group. As impact velocity increased, net peak extensor moments and work done on the extensor muscles significantly increased. Significantly larger ankle and hip peak extensor moments were observed for the gymnasts across velocities as compared to the recreational athletes. No significant differences in work done on the extensor muscles were noted between groups. Significant interaction effects indicate that gymnasts chose to dissipate the loads at contact by using larger ankle and hip extensor moments at higher impact velocities than the recreational athletes, whereas recreational athletes chose to adjust their strategy by using greater degrees of hip flexion (McNitt-Gray, Int. J. Sport Biomech, 7, 201-204, 1991) and longer landing phase durations than the gymnasts. The greater demands placed on the ankle and hip extensors by the gymnasts, as compared to the recreational athletes, may be explained by the need to maintain balance during competitive gymnastics landings or, perhaps, by the inability of recreational athletes to produce larger extensor moments at the ankle or hip during landings from great heights.