Reliability of SEMG measurements for trunk muscles during lifting variable loads in healthy subjects

Summery Objective The reliability of surface electromyography (SEMG) derived parameters is of high importance, but there is distinct lack of studies concerning the reliability during dynamic contractions. Particularly, the similarity index reliability has not been investigated during functional task yet. The purpose of this study was to evaluate the reliability of trunk muscle activities measured by means of surface electromyography during lifting tasks over repeated trials within a day. Methods Seven volunteers were assessed twice a day. SEMG signals were recorded bilaterally from seven trunk muscles. Intra class correlation coefficients (ICC) and standard error of similarity index, magnitude and timing were calculated. Results Investigation of ICC and correlation between trials showed that similarity index (ICC 0.73 – 0.97, correlation 0.6 – 0.95) is more reliable and repeatable than muscles magnitude (ICC 0.41 – 0.69, correlation 0.54 – 0.65) and it’s timing (ICC 0.41- 0.69, correlation 0.31 – 0.74) while timing had the least reliability. Conclusion Similarity index can be mentioned as an appropriate motor control index and evaluation of muscle recruitment pattern should be done by considering similarity index and magnitude.