Electromyographic study of the trapezius (pars superior) and serratus anterior (pars inferior) muscles in free movements of the shoulder.

The trapezius (pars superior) and serratus anterior (pars inferior) muscles were analyzed in 25 adult volunteers from both sexes with a 2-channel TECA TE4 electromyograph with single coaxial needle electrodes. It was observed that in elevation and lowering of the shoulders, the trapezius shows preponderant activity. During retraction, both muscles are inactive, and during protraction, only the serratus anterior is inactive.