MMG measurement of different muscle fibers in tetanic contraction

Mechanomyogram (MMG) can evaluate the mechanical function of the muscle. The MMG is generally measured using the accelerometer and it is known that the amplitude of acceleration MMG (MMGg) decreases during tetanic contraction. In this study, the displacement MMG (MMGd) in tetanic contraction was measured using a laser displacement sensor, and the relationship among the contraction force, the MMGg and MMGd was discussed. And the contraction properties of different muscle fibers in tetanic contraction were also discussed. The tibial nerve of rat was electro-stimulated, and the isometric contraction of gastrocnemius and the soleus muscle were induced as the foot was fixed. The electro-stimulation was repeatedly done at (1) 2-100 [Hz] and had stimulation period in 1 [s] and idle period in 1 [s], and at (2) 5-50 [Hz] during 5 [s]. When the stimulation frequency increased and exceeded the threshold of frequency, tetanic contraction was caused by the continuous contraction that the muscle was compulsorily contracted by the coming stimulation before the contracted muscle once was perfectly released. (1) Tetanic contraction was caused by the fusion of muscle contraction, and made the base line of muscle force (MF-) rise. The fluctuation of muscle force (MF_-AC) gradually decreased, as the fluctuation of muscle contraction decreased. The MMGg decreased when tetanic contraction was promoted, as well as the former report. On the other hands, the base line of MMGd (MMGd_-DC) increased like the muscle force, and its fluctuation (MMGd_-AC) decreased like the MMGg_-AC. (2) When the stimulation frequency increased from 5 to 50 [Hz] the base line fluctuation of MMGd was found. Tetanic contraction promoted at 14-47.5 [Hz] in the gastrocnemius, and at 8-25 [Hz] in the soleus. The stimulation frequency in the soleus, at which tetanic contraction arised, was lower than that in the gastrocnemius.