Objectives This study aimed to investigate the association between forward bending of the trunk and low-back pain intensity (LBPi) among blue-collar workers in Denmark as well as whether the level of social support modifies the association.

Methods In total, 457 workers were included in the study. The forward bending of ≥30° was computed from accelerometer recordings for several consecutive days during work, categorized into long (highest tertile) and short–moderate (remaining tertiles) duration. LBPi was measured on a 0–10 scale and categorized into low (≤5) and high (>5) pain. Self-reported social support was categorized into low, moderate, and high levels. Multi-adjusted logistic regressions estimated the association between forward bending and LBPi and the effect modification by social support.

Results Forward bending and LBPi were not significantly associated but modified by social support. Workers with low social support and long duration of forward bending had higher likelihood of high LBPi [odds ratio (OR) 2.97, 95% confidence interval (95% CI) 1.11–7.95] compared to workers with high social support and long duration of forward bending. Among workers with low social support, workers with long duration of forward bending had higher likelihood of high LBPi (OR 3.28, 95% CI 0.99–10.90) compared to workers with short–moderate duration of forward bending. Among workers with high social support, workers with long duration of forward bending had reduced likelihood of high LBPi (OR 0.39, 95% CI 0.16–0.95) compared to workers with short–moderate duration of forward bending.

Conclusions Social support modifies the association between objectively measured forward bending and LBPi among blue-collar workers.

Key terms accelerometry; back pain; bending of the trunk; blue-collar worker; body posture; cross-sectional study; diurnal measurement; forward bending; inclination; low-back pain; musculoskeletal disorder; occupational physical activity; pain; physical activity; physical demand; risk assessment; social support; workload