title: Fatigue development in the finger flexor muscle differs between keyboard and mouse use.
abstract: OBJECTIVE
  The aim of the present study was to determine whether there were any physiological changes in the muscle as a result of intensive computer use.
  
  
  METHODS
  Using a repeated measures experimental design, eighteen subjects participated in four different 8-h conditions: a control (no exposure) condition and three exposure conditions comprised of 6 h of computer use (keyboard, mouse, and combined keyboard and mouse use) followed by 2 h of recovery. In each condition, using 2 Hz neuromuscular electrical stimulation, eight temporal measurements were collected to evaluate the fatigue state (twitch force, contraction time, and ½ relaxation time) of the right middle finger Flexor Digitorum Superficialis (FDS) muscle before, during, and after computer use.
  
  
  RESULTS
  The results indicated that 6 h of keyboard, mouse, and combined mouse and keyboard use all caused temporal fatigue-related changes in physiological state of the FDS muscle. Keyboard use resulted in muscle potentiation, which was characterized by approximately 30% increase in twitch force (p < 0.0001) and 3% decrease (p = 0.04) in twitch durations. Mouse use resulted in a combined state of potentiation and fatigue, which was characterized by an increase in twitch forces (p = 0.002) but a prolonging (11 %) rather than a shortening of twitch durations (p < 0.0001).
  
  
  CONCLUSIONS
  When comparing mouse and keyboard use, the more substantial change in the physiological state of the muscle with mouse use (potentiation and fatigue compared to just potentiation with keyboard use) provides some physiological evidence which may explain why mouse use has a greater association with computer-related injuries.
authors.affiliation: Department of Industrial and Systems Engineering, Northern Illinois University, DeKalb, IL, USA, jaykim@niu.edu.
authors.forename: Jeong Ho
authors.initials: JH
authors.lastname: Kim
authors.forename: Peter W
authors.initials: PW
authors.lastname: Johnson
mesh_terms: D000328:Adult; D001696:Biomechanical Phenomena / Q000502:physiology; D003201:Computers; D004558:Electric Stimulation; D004576:Electromyography; D005260:Female; D005385:Fingers; D006801:Humans; D008297:Male; D009119:Muscle Contraction / Q000502:physiology*; D018763:Muscle Fatigue / Q000502:physiology*; D018482:Muscle, Skeletal / Q000503:physiopathology*; D055815:Young Adult
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