title: Effects of concurrent physical and cognitive demands on muscle activity and heart rate variability in a repetitive upper-extremity precision task.
abstract: OBJECTIVE
  Most previous studies of concurrent physical and cognitive demands have addressed tasks of limited relevance to occupational work, and with dissociated physical and cognitive task components. This study investigated effects on muscle activity and heart rate variability of executing a repetitive occupational task with an added cognitive demand integral to correct task performance.
  
  
  METHODS
  Thirty-five healthy females performed 7.5 min of standardized repetitive pipetting work in a baseline condition and a concurrent cognitive condition involving a complex instruction for correct performance. Average levels and variabilities of electromyographic activities in the upper trapezius and extensor carpi radialis (ECR) muscles were compared between these two conditions. Heart rate and heart rate variability were also assessed to measure autonomic nervous system activation. Subjects also rated perceived fatigue in the neck-shoulder region, as well as exertion.
  
  
  RESULTS
  Concurrent cognitive demands increased trapezius muscle activity from 8.2% of maximum voluntary exertion (MVE) in baseline to 9.0% MVE (p = 0.0005), but did not significantly affect ECR muscle activity, heart rate, heart rate variability, perceived fatigue or exertion.
  
  
  CONCLUSIONS
  Trapezius muscle activity increased by about 10%, without any accompanying cardiovascular response to indicate increased sympathetic activation. We suggest this slight increase in trapezius muscle activity to be due to changed muscle activation patterns within or among shoulder muscles. The results suggest that it may be possible to introduce modest cognitive demands necessary for correct performance in repetitive precision work without any major physiological effects, at least in the short term.
authors.affiliation: Department of Occupational and Public Health Sciences, Faculty of Health and Occupational Studies, Centre for Musculoskeletal Research, University of Gävle, 801 76, Gävle, Sweden. diasrn@hig.se.
authors.forename: Divya
authors.initials: D
authors.lastname: Srinivasan
authors.affiliation: Department of Occupational and Public Health Sciences, Faculty of Health and Occupational Studies, Centre for Musculoskeletal Research, University of Gävle, 801 76, Gävle, Sweden.
authors.forename: Svend Erik
authors.initials: SE
authors.lastname: Mathiassen
authors.affiliation: Department of Occupational and Public Health Sciences, Faculty of Health and Occupational Studies, Centre for Musculoskeletal Research, University of Gävle, 801 76, Gävle, Sweden.
authors.forename: David M
authors.initials: DM
authors.lastname: Hallman
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: Afshin
authors.initials: A
authors.lastname: Samani
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
authors.affiliation: Department of Occupational and Public Health Sciences, Faculty of Health and Occupational Studies, Centre for Musculoskeletal Research, University of Gävle, 801 76, Gävle, Sweden.
authors.forename: Eugene
authors.initials: E
authors.lastname: Lyskov
mesh_terms: D000293:Adolescent; D000328:Adult; D001696:Biomechanical Phenomena / Q000502:physiology*; D003071:Cognition / Q000502:physiology; D004576:Electromyography / Q000379:methods; D005260:Female; D006339:Heart Rate / Q000502:physiology*; D006801:Humans; D009119:Muscle Contraction / Q000502:physiology*; D018482:Muscle, Skeletal / Q000502:physiology*; D012782:Shoulder / Q000502:physiology; D013647:Task Performance and Analysis; D034941:Upper Extremity / Q000502:physiology*; D055815:Young Adult
keywords: Autonomic nervous system; Cycle-to-cycle variability; Entropy; Mental demands; Pipetting