PURPOSE:

The present study was designed to investigate the effects of lower limb joint kinetics on energy cost during jumping.
METHODS:

Eight male middle and long-distance runners volunteered for the study. The subjects were asked to repeat vertical jumps at a frequency of 2 Hz for 3 min on a force platform in three different surface inclination conditions: Incline (+8°), Level (0°), and Decline (-8°). Sagittal plane kinematics were obtained using a high-speed video camera. Simultaneously, ground reaction forces and EMG of the lower limb muscles were recorded. Energy cost was calculated using steady-state oxygen uptake, respiratory ratio, and vertical distance of the body.
RESULTS:

In all conditions, energy cost correlated positively with total mechanical work of the knee joint (r = 0.636, P < 0.01), but negatively with total mechanical work of the ankle joint (r = -0.584, P < 0.01). The muscle-tendon complex length of the gastrocnemius and soleus muscles were significantly longer in incline than in level and decline. The gastrocnemius muscle showed different activity pattern in decline as compared with the incline and level conditions.
CONCLUSIONS:

The present study revealed that the ankle and knee joint kinematics and, therefore muscles' coordination are associated with energy cost during repeated vertical jumping. The lower limb joints contributed different efficiencies to generate the same total mechanical work in repeated vertical jumping on different surface inclinations. Energy cost was smaller when mechanical work was mainly done by ankle joint. Whereas, when the ankle joint did less mechanical work, the knee and/or hip joints compensated for the lack of mechanical work of the ankle joint and energy cost was increased.