Effects of partial occlusion of circulation on frequency and amplitude of surface electromyography

We examined two distinct questions. First, would the amplitude and frequency changes characteristic of fatigue produced by an isometric exercise be produced by fatiguing isotonic exercise? Second, are the frequency shifts produced during fatiguing exercise the result of increased metabolite concentration? Ten subjects (five men and five women, aged 22-43 years) performed two sets of 25 biceps curls at between 50 and 60% of their maximal voluntary contraction (MVC). One set was performed with the circulation to the arm unimpaired (NO); during the other set, a blood pressure (BP) cuff held midway between systolic and diastolic pressure was used to partially occlude (PO) circulation. Both the NO and PO conditions produced significant changes in root mean square (rmsEMG) of the amplitude and the mean power frequency (MPF) of the signal. Both the increase in amplitude and the downward shift in MPF of the frequency power spectrum characteristic of fatigue were significantly greater for the PO versus NO condition (PO = 29.47 Hz, NO = 7.39 Hz). These results indicate that the changes in amplitude and frequency characteristic of fatigue observed during isometric exercise can be produced to a lesser degree during dynamic exercise. In addition, these changes can be amplified by addition of occlusion caused by external compression. Because the compressive force used for occlusion allowed blood flow into the working muscle while impairing venous return, this degree of change appears to be directly related to reduced metabolite washout.