Abstract

In addition to the utilization of muscles elastic energy enhancement of performance in exercise involving stretch-shortening cycle might be also due to simultaneous increase of myoelectrical activity. This hypothesis was tested by examining three athletes during vertical jumping exercise on force-platform with (CMJ) and without (SJ) preliminary counter-movement. Additional dropping jumps (DJ) were executed from different heights (20-100 cm). The results obtained were similar to those reported in isolated muscle and as expected, the prestretch in CMJ shifted the force-velocity curve of concentric work to the right. In two cases enhancement of performance was attributed primarily to restitution of elastic energy because myoelectrical activity was similar to that observed in SJ. In one subject increased myoelectrical activity was observed during the concentric phase of CMJ. In DJ condition the EMG activity during eccentric phase was much higher than in SJ. Therefore the high performance in this condition was attributed to both elastic energy and reflex potentiation. In eccentric work of CMJ the average force decreased with the increase of stretching speed. This phenomenon was associated with a light increase of EMG activity. The observed results emphasize that both elastic energy and reflex potentiation may operate effectively during stretchshortening cycle activity. Verf.-Referat (gekuerzt)