Methods for the analysis of surface EMG in ergonomic evaluations

Disorders of the musculo-skeletal system are among the most common reasons for lowered working capacity and sick-leave in the industry. General opinion is that there exists a connection between long-term muscular work and local musculo-skeletal problems. It has been suggested that these problems are partly caused by long-term effects of sustained or too frequent muscular contractions, which lead to overloading of the passive and active elements of the musculo-skeletal system. Measurement methods capable of separating and classifying the intensity and rate of occurence of these work sequences during normal long-term work are needed especially for epidemiologic studies. Surface EMG has in ergonomic studies been used for the evaluation of both long-term and short-term muscular strain. However, many problems are connected to the use of electromyography arising mainly from the nature and complexity of the signals. In this study new methods and apparatus are proposed for the analysis of surface EMG for ergonomic field evaluations. The effects of muscular work on the musculo-skeletal system are reviewed, nature and generation of the EMG signals are analysed and typical uses of EMG and modelling schemes previously applied are reviewed. A new model and method for the analysis of EMG is also proposed. In the method EMG activity is used for the descriptive analysis of local muscular strain applying nonlinear trend analysis for the decomposition of signals. The method aims to produce a descriptive parametrisation of the EMG, which enables the classification of work done and identification of various potentially harmful work sequences, such as prolonged static work. Various parameters suitable for the classification of the decomposed EMG are proposed. The developed model and method are evaluated using laboratory measurements. A developed PC/AT-based measurement and analysis system is presented, which enables the use of the methods in practical studies.