NORMALIZATION OF SURFACE EMG AMPLITUDE FROM THE UPPER TRAPEZIUS MUSCLE IN ERGONOMIC STUDIES - A REVIEW

Surface electromyographic (EMG) amplitude from the upper trapezius mus cle is widely used as a measure of shoulder-neck load in ergonomic stu dies. A variety of methods for normalizing EMG amplitude from the uppe r trapezius (EMGamp(ut)) have been presented in the literature. This i mpedes meta-analyses of, for instance, upper trapezius load in relatio n to development of shoulder-neck disorders. The review offers a thoro ugh discussion of different normalization procedures for EMGamp(ut). T he following main issues are focused: output variable, location of ele ctrodes, posture and attempted movement during normalization, load and duration of reference contractions, signal processing and test-retest repeatability. It is concluded that translations of EMGamp,, into bio mechanical variables, for example relative force development in the sh oulder or in the upper trapezius itself, suffer from low validity, esp ecially if used in work tasks involving large and/or fast arm movement s. The review proposes a standard terminology relating to normalizatio n of EMGamp,, and concludes in a concrete suggestion for a normalizati on procedure generating bioelectrical variables which reflect upper tr apezius activation.