Muscular rest and gap frequency as EMG measures of physical exposure: the impact of work tasks and individual related factors.
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.
Nordander
C
C
Department of Occupational and Environmental Medicine, University Hospital, Lund, Sweden.
Hansson
G A
GA
Rylander
L
L
Asterland
P
P
Byström
J U
JU
Ohlsson
K
K
Balogh
I
I
Skerfving
S
S
D000328:Adult; D016022:Case-Control Studies; D004576:Electromyography; D005260:Female; D006801:Humans; D008297:Male; D008875:Middle Aged; D018482:Muscle, Skeletal / Q000502:physiology*; D019547:Neck Pain / Q000209:etiology / Q000503:physiopathology* / Q000517:prevention & control; D016273:Occupational Exposure / Q000009:adverse effects / Q000032:analysis*; D020069:Shoulder Pain / Q000209:etiology / Q000503:physiopathology* / Q000517:prevention & control; D018709:Statistics, Nonparametric; D013548:Sweden; D013647:Task Performance and Analysis; D016474:Weight-Bearing / Q000502:physiology