Effects of ischemia on myo-electrical signal characteristics during rest and recovery from static work.

Twenty male college students served as subjects for a study which investigated how artificially-induced ischemia, with and without muscular fatigue, affects the: 1) input/output (IEMG/Force) relationship, and 2) power density spectrum of EMG signals during submaximal static contractions. In the first experiment, subjects maintained constant-force (60% MVC) static handgrip contractions for 55 sec. Following exercise, EMG mean power frequency (MPF) was significantly (P less than 0.05) reduced and EMG amplitude (rmsEMG) was significantly (P less than 0.05) increased. With circulation intact during 5 min recovery, MPF and rmsEMG values returned to pre-exercise levels. With ischemic recovery, MPF remained significantly (P less than 0.05) lower than pre-exercise values, while rmsEMG returned to approximately normal levels. In the second experiment, subjects performed either 3 sec ramp (90 N/sec) or constant-force (40% MVC) contractions immediately before, during the final 3 sec of, and 1, 3, 5 and 10 min after a 10 min tourniquet application. No statistically significant differences (P greater than 0.05) in the IEMG/Force slope coefficients, IEMG/Force ratios or MPF were observed for subjects performing either static ramp or constant-force contractions following temporary ischemia. Results suggest that reduced blood flow may contribute to fatigue-induced EMG changes. However, in the absence of motor activity, ischemia is an insufficient stimulus to cause either increased amplitude or frequency shift of the EMG signal during static contractions.