A study on the low frequency oscillations in the activation of the muscle under sustained isometric task

We studied the periodicity of a relatively slow oscillation of the muscle activation, via the surface electromyogram (EMG), recorded from the Biceps and Brachioradialis muscles, under an endurance isometric task. The peaks in the Root Mean Square (RMS) of the EMG were assigned as peaks of the muscle activation; the estimate of their periodicity was checked via correlation. 32 subjects participated in different exercises involving isometric isotonic tasks, at 25%, 50% and 75% MVC (maximal voluntary contraction). The activation of the muscle under such an exercise has an overall low frequency periodicity of between 14.29 s and 16.75 s with standard deviations (sd) between 2.97 s and 5.04 s, independent of the intensity of the task and sex. They are larger for the Brachioradialis (mean 15.08-19.6 s/sd 2.59-6.3 s) than for the Biceps (mean 11.96-16.41 s/sd 1.24-4.86 s).