High tension surface EMG

This paper considers the relationship between various averages of the high interference EMG and these parameters and the resulting tension. Isometric contraction and static conditions are assumed. At first it is assumed that only motor units belonging to a single type are present. In this case muscle tension is proportional to the extrapolated expression for the low interference EMG. Proportionality between tension and spike frequency, reported by some investigators, is obtained if the twitch tension of recently recruited motor units increases with advancing recruitment only very slowly. Proportionality between tension and r.m.s. EMG is obtained, if the twitch of newly recruited unit increases approximately proportionally with tension. The relation between force and EMG parameters changes in the region of the highest voluntary forces, where all available motor units are recruited and the only mechanism for controlling force is the firing frequency. At high interference levels integrated and r.m.s. EMG are intrinsically proportional to one another. In the final paragraph it is shown, that the conclusions obtained apply also to inhomogeneous muscles.