Voluntary muscle strength in hemiparesis: distribution of weakness at the elbow.

Maximal voluntary strength (torque) of the flexors and extensors of the elbow was measured in 56 normal subjects and 18 hemiparetic subjects. In normal subjects the ratio of extension to flexion strength averaged 55% and did not differ significantly between sides or sexes. The ratio of maximal extensor to flexor strength on the clinically unaffected side of hemiparetic subjects was the same as that for the normal subjects but it was significantly increased on the affected side. This increase indicates that the elbow flexors were relatively more weakened than the extensors on the hemiparetic side, a conclusion contrary to conventional clinical teaching. The increase in the ratio was not the result of co-contraction of either muscle group. A possible physiological basis for the observed distribution of weakness is suggested.