F response analysis of motor disorders of central origin.

Antidromically activated motor responses (F waves) were analyzed. In series of 15 responses recorded from the calf and abductor pollicis brevis muscles, cross-correlation (r) values were obtained for latency and duration (r lat-dur), latency and amplitude (r lat-amp), and amplitude and duration (r amp-dur). In 38 normal subjects, significant (P less than 0.05) negative correlations tended to be found for r lat-dur and r lat-amp with significant positive correlations for r amp-dur. These data differed (generally P less than 0.001) from those obtained in 32 patients with motor disorders of central origin based either on evaluation of the proportion of individual studies with statistically significant correlations or on comparison of the means of the z transformations of the r values. Similar data from 20 patients with slowed motor conductions also differed significantly from those with central abnormalities but not from control subjects. The data indicate that F responses are altered by central motor system disorders and suggest that specific patterns of F response r values may be related to specific types of dysfunction.