Electromyography Analysis: Comparison of Maximum Voluntary Contraction Methods for Anterior Deltoid and Trapezius Muscles

Electromyography (EMG) analysis techniques are widely used in ergonomics and biomechanical studies for analyzing the demand of a job, comparing different tasks, and ergonomics design. To perform such analyses, the EMG data must first be normalized to maximum voluntary contractions (MVC). Normalized EMG data not only allows comparisons to be made between different tasks, but it also informs about how active muscles are relative to their maximum capabilities. Different MVC exercises have become accepted as a standard only by their wide use. However, systematic research on the effectiveness of different MVC methods are still needed to identify the exercises that will produce the true maximum contraction levels of muscles. The purpose of this study was to compare the accepted MVC methods in the literature for the anterior deltoid and trapezius muscles to newly proposed MVC methods. Eight participants were recruited from the Louisiana State University (LSU) population. The proposed MVC for the anterior deltoids involved positioning the shoulders at 90o flexion with fixed straps wrapped around the distal end of the upper arm. In this position, participants were asked to exert upward forces against the straps while attempting to use only the shoulder muscles. The proposed MVC for the trapezii involved performing lateral raises at 100o shoulder abduction against fixed chains. These MVC methods were compared to their respective accepted MVCs in the literature. The proposed MVC for the right and left anterior deltoids resulted in 58% and 46% higher EMG levels, respectively, than the accepted MVC. The proposed MVC for both the right and left trapezii produced 68% higher EMG levels than the accepted MVC. The new MVC methods were found to allow the production of more accurate EMG signals of the maximum contraction levels.