GROUP SPECIFIC BEHAVIOR OF BIARTICULAR UPPER LEG MUSCLES EXEMPLIFIED BY SLEDGE

Abstract

The biarticular skeletal muscles represent a much considered topic in current research. Concerning these muscles, not only Lombard's paradox is of special interest. Some authors refer to their energy-transferring function and others have observed an increase of activity in M. biceps femoris after a special training. By means of so-called sledge jumps, we have experimentally examined the behavior of M. biceps femoris for two groups, jumpers and non-jumpers, whose task was to push the sledge with different loads and different speeds. The results clearly show a specific behavior of the muscles for each group — which seems to affect the muscle coordination and has crucial influence on the shape of the ground reaction force. Due to nearly equal kinematic conditions, Lombard's paradox could apply for both groups. However, the amount of training seems to be an essential parameter. The jumpers activate the M. biceps femoris during the entire contact phase and during the shortening as well as the stretching of the leg. Thus the force shape becomes smoother and shows fewer fluctuations. Despite positive geometrical conditions, not all subjects use this muscle from the beginning of the movement. In this context, neural pathways, inhibitions or coupling processes are decisive factors. All that indicates that the controlling of the muscle can only be achieved by an appropriate training.