"Turns" analysis in the physiological evaluation of neuromuscular disorders

A previously described technique of automatic analysis of the electromyogram during isometric voluntary contraction has been used to investigate the biceps and triceps muscles of 18 patients with various neuromuscular disorders. Three modifications in the method were made: at each electrode position the data were computed at 10%, 20%, 30% and 50% of the maximum force; the duration of contraction was reduced from 5 s to 2 s; and the diagnosis was based on analysis of the plots of turns and mean amplitude per turn versus percentage of maximum force. These modifications resulted in increased sensitivity, the ability to evaluate motor unit abnormality at different force levels, and a quantitative assessment of the degree of involvement of antagonist muscles. The data indicate that motor units recruited at lower force levels may be involved preferentially in myopathies, and also that the involvement of pairs of flexor and extensor muscles in neuromuscular disorders is not always uniform.