THE ROLE OF MONOARTICULAR AND BIARTICULAR MUSCLES DURING CONTACT CONTROL LEG TASKS IN MAN

From an analysis of cycling, it was hypothesized that mono- and bi-articular muscles may have different roles in the control of contact control tasks. The aim of the present study is to find experimental evidence for this hypothesis. On a special dynamometer, subjects were instructed to exert a force in a prescribed direction while the forceplate was either fixed (isometric) or slowly moving downwards (isokinetic). Joint positions, reaction forces and EMG-activity from six upper leg muscles were recorded. All subjects performed the tasks very accurately with a stereotyped muscle activation pattern. Comparing the mean EMG-values for the isometric and isokinetic condition, the mono-articular muscles showed a significantly higher activity in the dynamic situation, whereas the activity of the biarticular muscles was similar for both conditions. For the antagonistic biarticular muscles, a linear relationship was found for the difference in their EMG-activity (Rectus Femoris-Hamstrings) and the difference in hip and knee joint moments. Apparently, the two biarticular muscles function in a reciprocal way to regulate the distribution of net moments about the joints, whereas the activation of the mono-articular muscles appeared to depend on the type of task.