Muscular rest and gap frequency as EMG measures of physical exposure: the impact of work tasks and individual related factors

Ergonomics. 2000 Nov;43(11):1904-19. doi: 10.1080/00140130050174536.


Owing to an orderly recruitment of motor units, low threshold type I fibres are presumed to be vulnerable in contractions of long duration. To study load on these fibres muscular rest was registered as the time fraction of electromyographic (EMG) activity below a threshold. Moreover, the frequency of periods with muscular rest, EMG gaps, was derived, since a low gap frequency has been shown to be a risk factor for musculoskeletal disorders. Trapezius EMG was registered in 24 female hospital cleaners, 21 female office workers and 13 male office workers during one working day. Cleaners have a high risk of neck/shoulder pain and had much less muscular rest than office workers measured as a percentage of total registered time (median value = 1.5%, range = 0.2-13% vs. median value = 12%, range = 0.0-32%, respectively). Gap frequency showed no difference between the two occupational groups. Both measures displayed a wide inter-individual variation. For the cleaners, some of the variance was explained by body mass index (BMI) and age, with lower values of muscular rest for older subjects with a high BMI. Among the office workers, low values of muscular rest and a high gap frequency were registered in subjects with a low subjective muscular tension tendency. Gender, strength, smoking, job strain, employment time and musculoskeletal symptoms had no impact on either EMG measure.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Adult
  • Case-Control Studies
  • Electromyography*
  • Female
  • Humans
  • Male
  • Middle Aged
  • Muscle, Skeletal / physiology*
  • Neck Pain / etiology
  • Neck Pain / physiopathology*
  • Neck Pain / prevention & control
  • Occupational Exposure / adverse effects
  • Occupational Exposure / analysis*
  • Shoulder Pain / etiology
  • Shoulder Pain / physiopathology*
  • Shoulder Pain / prevention & control
  • Statistics, Nonparametric
  • Sweden
  • Task Performance and Analysis
  • Weight-Bearing / physiology