KINETICS OF THE LOWER-EXTREMITIES DURING DROP LANDINGS FROM 3 HEIGHTS

In this study, the landing preferences of gymnasts (n = 6) and recreat ional athletes (n = 6) were determined by comparing the changes in low er extremity kinetics of drop landings performed from three heights (0 .32-1.28 m). Net joint moments and work done on the extensor muscles o f the ankle, knee, and hip were selected as variables representative o f 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 f orce plate (1000 Hz). Reaction forces and lower extremity joint motion s were used to calculate net joint forces, net joint moments, net join t moment powers, and work done on the extensor muscles of the ankle, k nee, and hip. Results indicated that the extensor joint moments tended to peak earlier after contact with increases in velocity, but the tem poral sequence of events was maintained independently of velocity or g roup. As impact velocity increased, net peak extensor moments and work done on the extensor muscles significantly increased. Significantly l arger ankle and hip peak extensor moments were observed for the gymnas ts across velocities as compared to the recreational athletes. No sign ificant differences in work done on the extensor muscles were noted be tween groups. Significant interaction effects indicate that gymnasts c hose to dissipate the loads at contact by using larger ankle and hip e xtensor moments at higher impact velocities than the recreational athl etes, whereas recreational athletes chose to adjust their strategy by using greater degrees of hip flexion (McNitt-Gray, Int. J. Sport Biome ch. 7, 201-204, 1991) and longer landing phase durations than the gymn asts. 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 lar ger extensor moments at the ankle or hip during landings from great he ights.