Coordination in vertical jumping.

The present study was designed to investigate for vertical jumping the relationships between muscle actions, movement pattern and jumping achievement. Ten skilled jumpers performed jumps with preparatory countermovement. Ground reaction forces and cinematographic data were recorded. In addition, myoelectric activity (EMG) was recorded from seven leg muscles. EMG-signals were rectified and low-pass filtered to obtain EMG-levels. The latter, which were assumed to reflect activation levels, rose to a plateau in the sequence m. semitendinosus, long head of m. biceps femoris, m. gluteus maximus, m. vastus medialis, m. rectus femoris, m. soleus, m. gastrocnemius. It was attempted to link the EMG-pattern to the purpose of the push-off, namely to maximize the effective energy (Ey) of the mass center of the body (MCB). The term Ey designates the sum of the potential energy of MCB and the kinetic energy due to the vertical velocity of MCB. One of the requirements for maximization of Ey is that the mono-articular extensor muscles release as much energy as possible before toe-off occurs. It is argued that this requirement can only be satisfied if the vertical velocity differences between the proximal and distal ends of body segments reach their peaks in a sequence. The sequence that is realized by the pattern of muscular activation is upper body, upper legs, lower legs, feet. Another important requirement is that the mechanical energy released by the muscles is optimally used. This requirement can be satisfied by transportation of energy via the biarticular m. rectus femoris and m. gastrocnemius.