Functional biomechanical evaluation of industrial upper limb exoskeletons using electromyography

The main purpose of the present work is to study the application of industrial passive exoskeletons in companies of the automotive sector in order to improve the workers wellness. Biomechanical functional evaluation tests have been performed to document the real benefit that the use of these exoskeletons would bring in the reduction of efforts registered in certain muscle groups and related to the risk of musculoskeletal injury. Objective and quantitative EMG signals have been used to test three different exoskeletons. The tests have been performed in the actual under-floor workstations from Nissan plant at Zona Franca in Barcelona. From the signal four different variables have been studied: Maximum 10% EMG amplitude, maximum 50% EMG Amplitude and Root-Mean Square (RMS) of the signal, as amplitude variables to assess the muscle activation, and Mean Power Frequency (MPF), from the frequency-domain to assess fatigue. Wilcoxon signed rank test (with a significance level of α=5%) have been used to statistically report the significant differences. From the obtained results, it must be highlighted that great reductions of muscle activity are found at the shoulder area (up to 40% in deltoids). This illustrates that the studied exoskeletons are useful for preventing injuries in Under-Floor (UF) tasks such as the studied ones. Especially good results are obtained for the workstations with more aerial tasks (which imply higher abduction angles at the shoulder joint), achieving, in some cases, reductions in the deltoids above the 65%. Statistically significant reductions have been found, for at least one of the exoskeletons tested, in deltoids, triceps, upper-trapezius and latissimus dorsi. It should be kept in mind that this is a trial phase and that exoskeletons still have adverse results in specific cases. But, based on the global results obtained, it can be concluded that their usefulness will probably make them a reality very soon