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  • Title: Variability of Time- and Frequency-Domain Surface Electromyographic Measures in Non-Fatigued Shoulder Muscles.
    Author: Alasim HN, Nimbarte AD.
    Journal: IISE Trans Occup Ergon Hum Factors; 2022; 10(4):201-212. PubMed ID: 36411999.
    Abstract:
    OCCUPATIONAL APPLICATIONSLocalized Muscle Fatigue (LMF) can be monitored or predicted based on the relative change in the values of surface electromyography (sEMG) measures with respect to the "fresh" or no-fatigue condition. Quantification of LMF based on relative change, though, relies on the assumption that the sEMG measures recorded in a no-fatigue condition can serve as an appropriate reference. Results of this study indicate that sEMG measures in a no-fatigue condition are affected by various work-related factors and provide further guidance on the variability of commonly used time- and frequency-domain sEMG measures to assist the ergonomist in improving the accuracy of LMF assessment. Background: Surface electromyography (sEMG) is widely used to monitor or predict localized muscle fatigue (LMF). sEMG signals are often analyzed in time and frequency domains – Root Mean Square (RMS), Mean Absolute Values (MAV), and Zero Crossings (ZC) are common time-domain measures; Mean Power Frequency (MnPF), Median Power Frequency (MdPF) and Power Frequency Bands (PFB) are the common frequency-domain measures. LMF prediction is based on the relative change in the values of these measures with respect to “fresh” or no-fatigue conditions. To our knowledge, the assumption that the sEMG measures do not change/vary under no-fatigue conditions due to factors other than LMF has not been thoroughly tested.Purpose: The goal of this study was to quantify the variability of sEMG measures in non-fatigued shoulder muscles and the implication of this variability for assessing LMF.Methods: Twelve participants performed 120 occupationally-relevant static tasks under various conditions of joint angles, anatomical planes, force levels, and force directions. sEMG data were recorded from seven shoulder muscles – supraspinatus, infraspinatus, middle deltoid, anterior deltoid, posterior deltoid, biceps, and triceps.Results: For these shoulder muscles, the variability of RMS, MAV, ZC, MnPF, MdPF, and PFB ranged from 7.9 to 11.1%, 7.1 to 10.1%, 10.2 to 11.0%, 8.6 to 11.4%, 8.7 to 12.2%, and 5.3 to 7.9%, respectively.Conclusions: Both time- and frequency-domain sEMG measures vary due to various work-related factors under no-fatigue conditions. Therefore, it is critical to consider the variability ranges of sEMG measures while monitoring or predicting LMF due to sustained exposure to work-related factors.
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