Effect of skin temperature on RMS amplitude of electromyogram and mechanomyogram during voluntary isometric contraction.

The aim of this study is mainly to elucidate the relation between the modification of skin temperature and MMG signal properties depending on the contractile force. Ten healthy male volunteers, aged 22.8 +/- 0.7 (mean+/-SE) years, participated in this study. EMG and MMG signals were recorded during voluntary isometric contraction (20, 40, 60, and 80% MVC) of biceps brachii muscle under a skin temperature of 34 degrees C (control), 28 degrees C (cooling), and 40 degrees C (heating), respectively. A significant difference of MVC during elbow flexion was not recognized among the thermal conditions. Root mean square values of EMG and MMG (i.e., rms-EMG and rms-MMG) increased depending on the contractile level (P< 0.01). In the heating condition, the rms-MMG progressively increased in response to an increase of up to 60% MVC, however, it was nearly unchanged at a contractile force higher than 60% MVC The rms-EMG was not significantly influenced by the skin temperature. The rms-MMG significantly increased depending on the skin temperature at each contractile level (P< 0.01). There were significant interactions between contractile force and skin temperature for rms-MMG (P< 0.01). In conclusion, by modification of passive muscle temperature, rms-MMG was significantly altered in comparison with MVC and rms-EMG, which might be reflective of the changes of the mechanical contractile properties of muscle fibers.