Calibration and Adjustment Algorithm to Attenuate the Effect of Arm Orientation on an sEMG-Based Muscle Fatigue Indicator

A limit in the development of preventive interventions for musculoskeletal disorders (MSDs) of the upper limb is the lack of devices that can measure and process surface electromyography (sEMG) signals in order to provide real-time, reliable information on muscular fatigue in relation to the physical demands of the work being carried out. To keep track of the muscle fatigue level, the chosen fatigue indicator (FI) must not be sensitive to arm orientation (i.e., elevation angle and plane). The objective of this article is, therefore, to develop a calibration and adjustment algorithm to provide an FI that is not sensitive to arm orientation. First, the effect of arm orientation on our former FI indicator was verified by comparing initial (beginning of the task) FIs (IFIs) for static contractions in different arm elevation planes and angles. The results confirmed the hypothesis. A personalized calibration and FI adjustment based on current arm orientation were then proposed. The adjustment module's efficiency was first verified for different elevation planes and elevation angles separately. Using paired t-tests, we compared the IFI deviations from the baseline with and without the adjustment module. It was shown that the proposed method significantly reduces the IFI deviations from the baseline for both the elevation plane ( p = 0.005, d = 1.220) and the elevation angle ( p = 0.002, d = 1.455). Finally, a combined adjustment is presented for both the elevation plane and angle at the same time. The IFI deviations from the baseline were statistically significantly lower with the adjustment module than without it ( p < 0.001, d = 1.461).

Automated summary

The objective of this study is to develop a calibration and adjustment algorithm to provide a fatigue indicator that is not sensitive to arm orientation. The proposed method significantly reduces the deviation of the fatigue indicator from the baseline, confirming its effectiveness in addressing the issue of arm orientation sensitivity.