title: Gender differences in neck/shoulder muscular patterns in response to repetitive motion induced fatigue.
abstract: Previous studies have associated amplitude and frequency characteristics of the electromyogram (EMG) to the risk of developing musculoskeletal disorders (MSDs) with repetitive tasks. However, few studies have investigated whether EMG variability and between-muscle activity characteristics may be associated with MSD risk. Twenty-six healthy volunteers (13 men, 13 women) performed a repetitive pointing task at shoulder height until scoring 8 on a Borg CR-10 scale. Electromyographic (EMG) signals were recorded from six neck/shoulder muscle sites. EMG amplitude (RMS), variability and mutual information (MI) among muscle pairs were computed. Muscle fatigue was evidenced by increased EMG RMS of four muscles (Upper Trapezius (UT): +17%; supraspinatus (SUPRA): +28%; middle deltoid: +13%; biceps brachii: +38%) and increased SUPRA variability. Correlations between minute 1 patterns and endurance time indicated that in women, initially high variability in UTR (r=0.79) and SUPRA (r=0.71) predicted higher endurance, whereas in men, initially low MI in LT-UT (-0.69) and in LT-SUPRA (-0.77) pairs predicted high endurance. Significant correlations suggest that variability and between-muscle patterns may be associated with fatigue and injury mechanisms, in a gender-specific way. Differing fatigue mechanisms between genders could help explain gender differences in injury mechanisms.
authors.affiliation: McGill University, 475 Pine Avenue West, Montreal, Quebec H2W 1S4, Canada.
authors.forename: Larissa
authors.initials: L
authors.lastname: Fedorowich
authors.forename: Kim
authors.initials: K
authors.lastname: Emery
authors.forename: Bridget
authors.initials: B
authors.lastname: Gervasi
authors.forename: Julie N
authors.initials: JN
authors.lastname: Côté
mesh_terms: D000328:Adult; D001132:Arm / Q000502:physiology*; D005260:Female; D006801:Humans; D008297:Male; D009068:Movement / Q000502:physiology*; D009119:Muscle Contraction / Q000502:physiology*; D018763:Muscle Fatigue / Q000502:physiology*; D009334:Neck Muscles / Q000502:physiology*; D004856:Postural Balance / Q000502:physiology*; D012737:Sex Factors; D012785:Shoulder Joint / Q000502:physiology*; D013647:Task Performance and Analysis
keywords: EMG; Endurance; Functional connectivity; Mutual information; Upper limb; Variability