Normalization of the trapezius sEMG signal – a reliability study on women with and without neck-shoulder pain

OBJECTIVE To evaluate within- and between-days reliability of two normalization methods of surface electromyography (sEMG) recordings of the trapezius muscle. METHODS Nineteen women were allocated into 2 groups (healthy and with neck-shoulder pain). The sEMG was recorded in two sessions with 7 days in between sessions. The four portions of the trapezius muscle (the clavicular and acromial fibers of the upper trapezius, the middle and the lower trapezius) were evaluated during maximal and submaximal isometric voluntary contractions. The within- and between-days reliability of both maximal and submaximal contractions were assessed through Intraclass Correlation Coefficient (ICC(2,1) was used for within-day analyses of both maximal and submaximal contractions, and for between-days analyses of maximal contractions while ICC(2,3) was used for between-days analyses of submaximal contractions), Coefficient of Variation, Standard Error of Measurement, and Bland-Altman analysis. RESULTS In general, submaximal contractions presented higher within-day reliability, with higher ICC values (e.g., middle trapezius - mean of 0.97), smaller Coefficient of Variation and Standard Error of Measurement ranges compared to maximal contractions (ICC values, e.g. for middle trapezius - mean of 0.94) in both groups. The same pattern was observed for between-days analyses, with submaximal contractions presenting higher ICC values (e.g., middle trapezius - mean of 0.84), smaller Coefficient of Variation and Standard Error of Measurement ranges than maximal contractions (ICC values, e.g. for middle trapezius - mean of 0.73) in both groups. CONCLUSION Submaximal contractions are recommended for normalization procedures of trapezius sEMG, in both subjects with neck-shoulder pain and healthy individuals.