Background. Previous studies suggest that prolonged sitting at work is a risk-factor for neck-shoulder pain (NSP). However, a majority of studies on the association between occupational sitting and NSP have relied on cross-sectional designs and self-reported measurements of sitting time. Our aim was to determine the extent to which occupational sitting time, assessed using accelerometry, is associated with the 1-year time course of NSP intensity among blue-collar workers.

Methods. Our study included 494 Danish workers (female n=220) from three occupational sectors: cleaning (n=96), manufacturing (n=356) and transportation (n=42). At baseline, sitting was monitored continuously for several working days (mean (SD) wear time: 2.6 (0.9) days) using accelerometers attached to the thigh and trunk. During the following 12 months, data on self-reported NSP intensity (NRS scale, range 0-10) were collected on a monthly basis using SMS tracking. Repeated measures ANOVA adjusted for gender, occupational sector, seniority, and pain at baseline was used to examine the association between per cent time spent sitting (at work and leisure) and changes in NSP across time.

Results. We found a significant interaction between occupational sitting at baseline and the time course of NSP (F(11,491)=6.37, p=0.01), which remained significant with adjustment for covariates (F(11,464)=6.64, p=0.01). We found no main effect of occupational sitting on NSP (p>0.05). Categorizing sitting time revealed that more sitting at work was accompanied by larger reductions in NSP over time. The effect of time on NSP was stronger in the high sitting group (F(11,162)=30.4, p<0.0001) than in the low (F(11,162)=4.9, p=0.05) and moderate (F(11,167)=5.10, p=0.02) sitting groups. We found no association between leisure-time sitting and NSP (p>0.05).

Discussion. In contrast to previous studies, our results indicate that prolonged sitting is associated with a favourable prognosis of NSP across one year in workers. The clinical significance of this result needs to be examined further