title: Variability in spatio-temporal pattern of trapezius activity and coordination of hand-arm muscles during a sustained repetitive dynamic task.
abstract: The spatio-temporal distribution of muscle activity has been suggested to be a determinant of fatigue development. Pursuing this hypothesis, we investigated the pattern of muscular activity in the shoulder and arm during a repetitive dynamic task performed until participants' rating of perceived exertion reached 8 on Borg's CR-10 scale. We collected high-density surface electromyogram (HD-EMG) over the upper trapezius, as well as bipolar EMG from biceps brachii, triceps brachii, deltoideus anterior, serratus anterior, upper and lower trapezius from 21 healthy women. Root-mean-square (RMS) and mean power frequency (MNF) were calculated for all EMG signals. The barycenter of RMS values over the HD-EMG grid was also determined, as well as normalized mutual information (NMI) for each pair of muscles. Cycle-to-cycle variability of these metrics was also assessed. With time, EMG RMS increased for most of the muscles, and MNF decreased. Trapezius activity became higher on the lateral side than on the medial side of the HD-EMG grid and the barycenter moved in a lateral direction. NMI between muscle pairs increased with time while its variability decreased. The variability of the metrics during the initial 10 % of task performance was not associated with the time to task termination. Our results suggest that the considerable variability in force and posture contained in the dynamic task per se masks any possible effects of differences between subjects in initial motor variability on the rate of fatigue development.
authors.affiliation: Laboratory for Ergonomics and Work-related Disorders, Physical Activity and Human Performance Group - SMI, Department of Health Science and Technology, Aalborg University, Fredrik Bajers Vej 7 D-3, 9220, Aalborg East, Denmark. afsamani@hst.aau.dk.
authors.forename: Afshin
authors.initials: A
authors.lastname: Samani
authors.affiliation: Department of Industrial and Systems Engineering, Virginia Polytechnic Institute and State University, Blacksburg, VA, USA.|Centre for Musculoskeletal Research, Department of Occupational and Public Health Sciences, Faculty of Health and Occupational Studies, University of Gävle, 801 76, Gävle, Sweden.
authors.forename: Divya
authors.initials: D
authors.lastname: Srinivasan
authors.affiliation: Centre for Musculoskeletal Research, Department of Occupational and Public Health Sciences, Faculty of Health and Occupational Studies, University of Gävle, 801 76, Gävle, Sweden.
authors.forename: Svend Erik
authors.initials: SE
authors.lastname: Mathiassen
authors.affiliation: Laboratory for Ergonomics and Work-related Disorders, Physical Activity and Human Performance Group - SMI, Department of Health Science and Technology, Aalborg University, Fredrik Bajers Vej 7 D-3, 9220, Aalborg East, Denmark.
authors.forename: Pascal
authors.initials: P
authors.lastname: Madeleine
mesh_terms: D000328:Adult; D000704:Analysis of Variance; D001132:Arm / Q000294:innervation / Q000502:physiology*; D004576:Electromyography; D005260:Female; D006225:Hand / Q000294:innervation / Q000502:physiology*; D006801:Humans; D008297:Male; D009119:Muscle Contraction / Q000502:physiology*; D011187:Posture / Q000502:physiology*; D011597:Psychomotor Performance / Q000502:physiology*; D064171:Superficial Back Muscles / Q000502:physiology*; D013647:Task Performance and Analysis; D013997:Time Factors; D055815:Young Adult
keywords: Fatigue development; Functional connectivity; High-density electromyogram