ABSOLUTE MUSCLE FORCE DETERMINATION

Abstract

An absolute muscle force is applied when the muscle is activated to its fully extent, what normally doesn't happen in voluntary actions. It is believed that interpolated electrical stimulation (ES) during maximum voluntary contraction (MVC) is capable to fully activate the muscle. Six sport students volunteered the study. They were asked to perform isometric knee extensions at different activation levels (go%, 90%, and 100% of MVC) and were then transcutaneously electrically stimulated (quadriceps muscle) with equal ES amplitude, set to the individual tolerance threshold. Four volunteers additionally performed 100% MVC knee extensions with different ES amplitudes (80%,100%, and 120% of the tolerance threshold). In all subjects the interpolated ES elicited an additional force growth, over the actual voluntary level. Results showed that in the first experiment the force was growing according to the voluntary activation level almost linear. In the second experiment different ES amplitudes exhibited no statistically significant differences in force levels. It is concluded that interpolated ES enables, already at the submaximal ES amplitude, to achieve a stable force level, which can not be further elevated with a rising of ES amplitude and which might correspond to the absolute force of the agonists. A comparison to the MVC force would reveal an activation deficit. Because of the substantial force improvements in comparison to the MVC, interpolated ES can be used to study a single muscle andlor muscle group sensitiveness to the joint acceleration.