Energy Cost and Lower Limb Biomechanics of Repeated Vertical Jumping at Different Contact Times

The purpose of the present study was to examine the effects of the contact time on energy cost and lower limb biomechanics during repeated vertical jumping. Nine male Japanese distance runners jumped for three minutes on a force platform for a preferred and long contact time. Sagittal plane kinematics, ground reaction force, and electromyography (EMG) results were measured. The following results were obtained: 1) the energy cost was significantly smaller in the preferred than in long condition, 2) mechanical work of the ankle joint was significantly greater in the preferred than in long condition, 3) mechanical work of the knee joint was significantly greater in the long than in preferred condition. Therefore, a longer contact time alters the distribution of the mechanical work of the ankle and knee joints. This alteration may increase energy cost in the long condition.