EMG POWER SPECTRUM AND INTEGRATED EMG OF ANKLE PLANTERFLEXORS DURING STEPWISE AND RAMP CONTRACTIONS

The aim of this study was to investigate whether the median frequencie s (MF) of the electromyogram (EMG) and the integrated EMG (IEMG) of hi stochemically differentiated ankle planterflexors, the gastrocnemius a nd soleus, were force dependent. Bipolar intramuscular wire electrodes were used to measure EMG of the soleus (SO), medial head of gastrocne mius (GM), and lateral head of gastrocnemius (CTL) during ramp (single ongoing contractions) with the force increasing linearly from 0 to 10 0% of maximum voluntary contraction (MVC) and stepwise (steady force l evels) ankle planterflexion at 10, 20, 30, 40, 60, and 80% MVC. EMG an d force were measured simultaneously. Power spectral analysis of these signals was performed to calculate MF on 1024-point by fast Fourier t ransform (FFT) technique. IEMG value of each muscle was also obtained at the same levels of force. While IEMG of three heads of triceps sura e in both stepwise and ramp contractions increased significantly with increasing force, MF values of GL during stepwise contraction increase d significantly (20, 40, 60, 80% MVC). These results suggest that the sensitivity of EMG power spectrum might be influenced by the proportio n of fast twitch muscle fibers, which histochemically corresponds to t ype (II) fibers. (C) 1997 Tohoku University Medical Press.