ABSTRACT
The upper and lower portions of the trapezius muscle and the 4th, 5th and 6th bundles of the serratus anterior muscle were studied electromyographically during shoulder and pectoral girdle movements, in ten adultmales, aged 18 to 28 years, with no history of shoulder pathology. For this study a Nicolet Electronmyograph and surface electrodes were used. The signals were recorded as root mean square (RMS) values, expressedin microvolts. Wilcoxon and Friedman tests were done to a 5 (per cent) significance level. The results showed that there were no differences in the behaviour of the serratus anterior muscle bundles. In the shoulder abduction and flexion movements, the upper portionof the trapezius acted simultaneously with the serratus anterior muscle. In horizontal abdunction and adduction movements there was no prevalence of any of the muscles studied. In shoulder elevation, the upper portion of the trapezius muscle showed preponderant activity over its lower portion and over the serratus anterior muscle bundles. In the shoulder depression the activity of the lower portion of the trapezius muscle predominated over the serratus anterior muscle bundles, and the least activity was exhibited by the upper portion of the trapezius muscle.