CHANGES IN SURFACE ELECTROMYOGRAM PARAMETERS IN RAT SKELETAL MUSCLE AFTER STRENUOUS ECCENTRIC EXERCISE

Abstract

PURPOSE: The purpose of this study was to examine the effects of strenuous eccentric exercise on the surface electromyogram (EMG) parameters. METHODS: The right tibialis anterior (TA) muscles of anesthetized male wistar rats (n = 5) were subjected to 300 (60 times, 5 sets) controlled eccentric contractions induced by electrical stimulation from surface electrodes. The contralateral TA muscle was used as a normal control. Three days after eccentric exercise, isometric peak torque and surface myoelectric signals during twitch contraction induced by electrical stimulation via the peroneal nerve were measured in control and exercised TA muscles. EMG parameters such as 1) muscle fiber conduction velocity (MFCV), 2) integral electromyogram (iEMG), 3) the maximum correlation coefficient and the amplitude ratios between the different neighboring channels were calculated using surface array electrodes to evaluate the conductive waveform properties of action potentials. Exercise-induced muscle fiber degeneration was quantified in transverse sections stained with hematoxylin- eosin (HE). RESULTS: Intense muscle damage (87.7 ± 10.9%) was observed in exercised TA muscles. The isometric peak torque was significantly decreased in exercised TA muscles (2.34 ± 0.25 mN∼Nm) compared with control TA muscles (0.37 ± 0.09 mN∼Nm). Furthermore, a slgnificant decrease in iEMG was observed in exercised TA muscles. There was thus a significant correlation between iEMG and peak torque (r = 0.80). MFCV was significantly increased in exercised TA muscles (4.77 ± 0.09 m/sec) compared to control TA muscles (4.25 ± 0.26 m/sec). The maximum correlation coefficient and the amplitude ratio between the different neighboring channels did not differ in control and exercise TA muscles. CONCLUSION: In conclusion, despite a decrease of amplitude for myoelectric signal during muscle contraction, the characteristics of conductive waveform were maintained in degenerated skeletal muscles after eccentric exercise.