The aim of this study was to compare the kinematic pattern and the segmental movement co-ordination when the trunk segment was constrained in different positions during plyometric rebound jumps. Nine skilled volleyball players, experienced in plyometric training, were asked to perform a random series of maximal rebound jumps, using three different seat arrangements (90°, 135°, and 180°) in a pendulum swing device. From two-dimensional filming, performed in a right sagittal plane at 200 Hz, it was possible to calculate ankle, knee, and hip displacements; velocities; and muscle-tendon lengths. The subjects showed similar ankle and knee angles between experimental conditions. The hip joint angle differed significantly between conditions. Only the muscle-tendon lengths of the biarticular muscles spanning the knee/hip were affected by the seat arrangement variations. Significantly greater knee angular velocities were observed in the upright sitting posture (90°). The hip was consistently the first joint to extend. The ankle and knee joint reversals were not invariant, regardless of the seat arrangement. The movement co-ordination strategy did not differ across postural variations.
The authors are with the Department of Exercise and Sport Science at Manchester Metropolitan University, Hassal Road ST7 2HL, Alsager, Stoke-on-Trent, UK.