The "sweet- and sour-spot" of occupational physical activity for back pain: a prospective accelerometer study among eldercare workers.

Objectives: Both high and low levels of occupational physical activity are associated with back pain. Thus, there might be a "sweet- and sour-spot" of occupational physical activity for back pain. Our aim was to investigate if there exists an occupational physical activity "sweet- (lowest risk) and sour-spot" (highest risk) for back pain.

Methods: A total of 396 eldercare workers from 20 Danish nursing homes participated. Occupational physical activity was measured between 1-4 working days using thigh-worn accelerometry. Back pain intensity was reported monthly on a scale from 0-10 over 1-year. A zero-inflated mixed-effects model was developed regressing occupational physical activity against back pain, adjusted for confounders. The "sweet- and sour-spot" were defined as the occupational physical activity compositions (sitting, standing, light, and moderate-to-vigorous) associated with the 5% lowest and highest risk for back pain, respectively.

Results: The composition associated with the lowest risk of back pain - the "sweet-spot"- consisted of 71% worktime spent sitting, 18% spent standing, 5% spent on light physical activity and 6% spent on moderate-to-vigorous physical activity. The composition associated with highest risk for back pain -the "sour-spot"- consisted of 8% worktime spent sitting, 66% spent standing, 4% spent on light physical activity, and 21% spent on moderate-to-vigorous physical activity.

Conclusions: The "sweet-spot" of occupational physical activity for back pain among eldercare workers involves more sitting and light physical activity time, while the "sour-spot" involves more standing and moderate-to-vigorous physical activity time. Research on the occupational physical activity "sweet- and sour-spot" is needed.