Mechanical properties of the take-off leg as a support mechanism in the long jump

The aim of this study was to establish the functions of the support leg in the long jump take-off with a three-element mechanical model spring, damper, and actuator The take-off motions of eleven male long jumpers, with personal bests from 6.45 to 7.99 m, were videotaped at 250 Hz and ground reaction forces were simultaneously recorded at 1 kHz. A two-dimensional 14-segment linked model was used to collect basic kinematic parameters. The spring, damper and actuator forces were determined from the displacement and velocity of the centre of mass and from ground reaction forces. Large spring and damper forces were exerted, and absorbed the impact force immediately after the touch-down. The spring force was also exerted from 25 to 75% of the take-off phase. The actuator force was dominant in the latter two-thirds of the take-off phase. Statistically significant correlations were found between the spring force impulse and the knee flexion during the take-off phase (r = 0.699, p < 0.05), and between the knee flexion and the angular velocity of the thigh at the touch-down (r = 0.726, p < 0.05). These results indicated that the jumper should retain less flexion of the take-off leg knee to increase the spring force, after a fast extension of the hip, and use a more extended knee at the touch-down to prevent excessive knee flexion.