The effect of postural variations in movement co-ordination during plyometric rebound exercises

The aim of this study was to compare the kinematic pattern and the segmenta l movement co-ordination when the trunk segment was constrained in differen t positions during plyometric rebound jumps. Nine skilled volleyball player s, experienced in plyometric training, were asked to perform a random serie s of maximal rebound jumps, using three different seat arrangements (90 deg rees, 135 degrees, and 180 degrees) in a pendulum swing device. From two-di mensional filming, performed in a right sagittal plane at 200 Hz, it was po ssible to calculate ankle, knee, and hip displacements; velocities; and mus cle-tendon lengths. The subjects showed similar ankle and knee angles betwe en experimental conditions. The hip joint angle differed significantly betw een conditions. Only the muscle-tendon lengths of the biarticular muscles s panning the knee/hip were affected by the seat arrangement variations. Sign ificantly greater knee angular velocities were observed in the upright sitt ing posture (90 degrees). The hip was consistently the first joint to exten d. The ankle and knee joint reversals were not invariant, regardless of the seat arrangement. The movement co-ordination strategy did not differ acros s postural variations.