Associations between low back muscle activity, pelvic movement and low back discomfort development during prolonged standing – An exploratory laboratory study

Low back discomfort (LBD) is common in long-term standing work. The aim of this study was to investigate whether development of LBD during standing is related to lumbar muscle activity and pelvic movement. In a secondary analysis we investigated whether age, gender, and standing work habituation moderates the above-mentioned relationship. Sixty subjects (15 young females, 15 young males, 15 older males, and 15 young males habituated to standing work) were included and had to stand for 4.5 h over three periods with two seated breaks. Surface electromyography, a gravimetrical position sensor, and a numeric rating scale were used to assess lumbar muscle activity, pelvic movement, and LBD, respectively. 22 of 55 analyzed subjects (40%) reported LBD and were assigned to the discomfort developer (DD) group. The remaining subjects (non-discomfort developer: NoDD) showed a statistically significant increase of medio-lateral pelvic movement in the progression of the three standing periods. Almost no differences occurred in lumbar muscle activity (except for the 5th percentile of surface electromyography, which was higher in NoDD). No influence of age, gender, or standing habituation was found. Increased pelvic movement may protect from LBD development during prolonged standing, although differences are very small and clinical relevance is unclear.