Fatigue-induced changes in myoelectric signal characteristics and perceived exertion.

Perceived exertion (RPE) has been used as a subjective indicator of exercise intensity for extremely light to supramaximal-level dynamic exercise. Little data exist on the relationship of RPE to physiological variables during sustained isometric exercise. Ten male subjects volunteered and participated in this investigation. Subjects were instructed to maintain a hand grip contraction of 50% of maximal effort until exhaustion. During this bout of exercise, electromyographic activity (EMG) and RPE values were recorded at 10 s intervals. The raw EMG signals were processed for frequency content (mean power frequency [MPF] and for signal amplitude (root mean squared [RMS]). RPE was recorded as a subjective value selected from a ten-point scale with ratio properties. Analysis of the data indicated that RPE was strongly correlated to both MPF: r2 = (-).922, and RMS: r2 = .729. These data imply that during sustained isometric exercise changes in perceived exertion are related closely to electromyographic activity of the contracting muscle.