Abstract des Autors

In the present study, effects of continuous hurdle jumping on myoelectrical (EMG) activity, ground reaction forces, vertical movements of the body's centre of mass and knee joint angle kinematics were studied among eight male volleyball players. The subjects jumped hurdles (height 0.65 m) continuously for 45 s with bilateral foot contacts. All of the take-offs were performed from force-platforms which registered the three components of ground reaction force. The two middle take-offs in both directions were used for further analysis. The ground reaction forces and knee angular data were used to determine the eccentric and concentric phases of contact. The average EMG activity of the knee extensor muscles during the eccentric and concentric phases of contact increased during the jumping drill. The kinetic and kinematic parameters did not show any statistically significant change during the eccentric phase, whereas during the concentric phase the contact time, knee angle at take-off, knee angular displacement, time taken to attain peak knee angular velocity and vertical movement amplitude for the centre of mass increased and the average resultant ground reaction force decreased. Statistically significant changes were noted after the first 12-18 take-offs. It is suggested that the changes reported show fatigue effects in motor unit recruitment, in their firing characteristics or in the transfer of mechanical energy from the eccentric to the concentric phase of contact. Verf.-Referat