Abstract
It has been reported that hardness palpated from the body surface is related to muscle tonus. The aim of this study, an experimental model of muscle hardness was investigated under tetanic contractions of the gastrocnemius (GS) muscle using electrical stimulation of the sciatic nerve (50Hz, 100μs, 2min) in rats (n=10). The muscle hardness was measured by a hardness meter. The M-wave was recorded from a pair of wire electrode inserted into the muscle. Muscle tension was measured by a push-pull gauge after cutting the tendon at the distal end. The M-wave and the tension of GS muscle were monitored to clarify a component of the muscle hardness. The maximum amplitude of the M-wave was observed immediately after the onset of stimulation, whereas the hardness and tension reached their maximum at 5 sec after the stimulation. The amplitude of M-wave markedly decreased compared to the hardness and tension during the stimulation. The hardness was significantly and positively correlated to tension (R=0.82, P<0.01) and the amplitude of the M-wave (R=0.63, P<0.01). After pancuronium (2mg/ml : 0.4ml, i.v.) injection, the increases in the hardness and the tension were completely suppressed. These results suggest that the muscle hardness in tetanic contractions induced by electrical nerve stimulation might mostly reflect the changes in the muscle tension. [Jpn J Physiol 54 Suppl:S118 (2004)]
