Regression analysis of fatigue at various shoulder postures in sitting

Abstract

The purpose of this study is to investigate the level of fatigue of shoulder muscle in various working postures in sitting. An experiment was designed to evaluate the six shoulder muscles at nine shoulder postures including 30 degrees of adduction/abduction, and neutral postures as well as 60, 90, and 120 degrees of shoulder flexion. Thirteen subjects participated in the experiment to collect MVC (Maximum Voluntary Contraction) and MPF (Mean Power Frequency) of SEMG (Surface Electromyography). The participants maintained the shoulder posture in each of nine pre-determined flexion and abduction/adduction shoulder angle for 60 seconds. A regression was calculated out of 60 data points of MPF values, and the slope value was used as fatiguing rate of individual muscle. It was found that a certain muscle was fatigued fast at particular posture compared to other muscles, which would mean that a certain shoulder muscle at particular posture could be more exposed to the risk of musculoskeletal disorders than other muscles. © 2011 Taylor & Francis Group.