Morisada Makoto, Okada Kaoru, Kawakita Kenji
Department of Physiology, Meiji University of Oriental Medicine, Nantan-city, Kyoto 629-0392, Japan.
Eur J Appl Physiol. 2006 Aug;97(6):681-6. doi: 10.1007/s00421-006-0225-6. Epub 2006 Jun 13.
The purpose of this study was to investigate the in vivo relation between muscle hardness during an electrically induced contracting state and neuromuscular functions (M-wave and developed tension). Sixteen Sprague-Dawley rats were deeply anesthetized with urethane. Muscle hardness was measured quantitatively at the mid-portion of the gastrocnemius (GS) muscle during tetanic contractions induced by electrical stimulation (50 Hz, 100 micros duration) of the sciatic nerve or of the muscle directly. The M-wave was recorded with a pair of wire electrodes inserted into the muscle, and the developed tension was monitored with a push-pull gauge. Muscle hardness, M-wave amplitude and developed tension increased rapidly with the onset of nerve stimulation. Similar but intensity-dependent increases in muscle hardness and tension were observed following direct tetanic stimulation of the muscle. The hardness measured during nerve stimulation was correlated with the amplitude of the M-wave (r = 0.62, P < 0.0001) and the developed tension (r = 0.85, P < 0.0001). These phenomena were suppressed by pancuronium treatment (2 mg/ml, i.v.). These results suggest that muscle tension might be the most important factor for transcutaneously measured muscle hardness induced by tetanic muscle contraction.
