Somatosensory evoked potential changes during muscle testing.

Fifteen naive subjects with no known neurological problems were tested by means of manual muscle testing to determine two "strong" and one "weak" muscle on a limb contralateral to the stimulated side. Somatosensory evoked potentials (SEP) were then recorded from contralateral median nerve stimulation while a naive tester tested the three previously identified muscles. In all subjects the baseline (no muscle test) and control "strong" muscle test recordings were comparable while the recording from the "weak" muscle test showed increased amplitudes in contralateral layer components. These findings suggest a neurologic basis for manual muscle testing.