2008 Volume 23 Issue 2 Pages 215-218
In this study we investigated the power spectra characteristics of surface electromyograms of the muscles of the shoulder circumference (deltoid, latissimus, biceps and infraspinatus muscles) in response to reductions in maximum voluntary contraction (MVC) from 100% to 50% and 25%. We found a significant reduction in frequencies with decline in %MVC in the latissimus muscles and biceps. On account of this, it was considered that the activities of the thick, type II muscle fibers decreased with the decline in %MVC, leading to the lower of the frequencies. On the other hand, we found a significant increase in frequencies accompanying %MVC decline in the deltoid and infraspinatus muscles. We assume that the frequencies of the deltoid and infraspinatus muscles reach peaks at relatively low levels of contraction, and that there are unique characteristics of degree of contraction and movement in modes of action.
