The synergy of elbow extensor muscles during dynamic work in man. I. Elbow extension.

This study concerns the synergy of the elbow extensor muscles during voluntary elbow extension performed at various velocities against different intertia and in a horizontal plane. The quantity of excitation (Q) of the three heads of the triceps brachii muscle increases linearly with the external work (W). On the contrary, the anconeus Q increases rapidly for low values of W while for higher values it increases very slowly but linearly with the W. These results imply a proportionality between Q and W of the different muscles except in the case of anconeus for low values of W. Furthermore, it is shown that the position of the shoulder does not influence the relative contribution of the different muscles to W but leads to an adjustment of the activity of the long head. The different extensor muscles do not come into play simultaneously. The chronology of the muscular activities depends on velocity and inertia. The importance of anconeus activity for slow movements is pointed out, and it is suggested that there exists a specific control of the motoneurons of the different elbow extensor muscles. The limits of the concept of muscle equivalent are also discussed.