Biomechanical effects of fatigue during continuous hurdle jumping

Jumping drills that include several successive take-offs are popular in many sports events. An understanding of the effects of fatigue on biomechanical parameters during continuous jumping drills is important when selecting drills and their durations for sports training. 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 (age 20-26 years). 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. Knee angular data were recorded by an electrical goniometer for determination of angular displacement and velocity. The jumping was videotaped sagittally to determine the location of the centre of mass at different phases of contact and flight, as well as to calculate the movement amplitude for the centre of mass. The EMG activity was monitored using surface electrodes, full-wave rectified and averaged for a pre-contact period of 55 ms as well as for the eccentric and concentric phases of contact for the M. rectus femoris, vastus lateralis and vastus medialis. 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.(ABSTRACT TRUNCATED AT 250 WORDS)