Single motor unit F-waves in the thenar muscles studied by the multichannel surface EMG

The thenar motor units (MUs) were studied by the multichannel surface electromyography (EMG) technique. The median nerve was stimulated at the wrist by repetitive submaximal stimulation. Three hundred consecutive evoked responses were recorded from the thenar muscles of 5 healthy volunteers with a 32 channel matrix-type multielectrode. Seven channel F-wave waveforms in a selected electrode array were classified using a template-matching method. The F-wave parameters, amplitudes, latencies and muscle fiber conduction velocities (MFCVs), were calculated to evaluate the properties of single MU F-wave. Most of the F-waves (93.3%) were composed of a single motor unit action potential (MUAP). The numbers of MU classified from single MU F-waves in 5 subjects were 11, 8, 13, 13 and 13, respectively. Many of them (84.5%) were originated from the abductor pollicis brevis (APB), and there were a few MUs originated from the flexor pollicis brevis (FPB). Significant correlations were found between F-wave amplitudes and latencies in 3 subjects.