Introduction High physical workload and unhealthy lifestyle behaviors are common among blue-collar workers, both being separate risk factors for self-rated health. It may however be that the combination of high physical workload and an unhealthy lifestyle have a stronger effect than the sum of these factors, but studies to the combined effects are scarce.

Objective To investigate the combined effects of a high physical workload and either overweight/obesity or insufficient vigorous physical activity on self-rated health.

Methods A longitudinal study was performed among 29,987 construction workers using data of two Workers’ Health Surveillance Programs. Self-reported physical workload involved strenuous work postures and manual material handling. Insufficient vigorous physical activity was defined as self-reported vigorous activity for less than 3 times per week. Overweight/obesity was measured by physical examination. Self-rated health was measured using a single item question. Logistic regression analysis was used to investigate the associations between the separate risk factors at baseline and self-rated health at follow-up. The combined effects of physical workload and overweight/obesity or insufficient vigorous activity on self-rated health were analyzed using the relative excess risk due to interaction (RERI).

Results Construction workers with strenuous work postures (OR 1.35 95%CI 1.25–1.46) or manual material handling (OR 1.29 95%CI 1.19–1.40) were more likely to report poor self-rated health at follow-up. Overweight was not associated with poor self-rated health at follow-up, but obesity (OR 1.31 95%CI 1.17–1.47) and insufficient vigorous activity (OR 1.13 95%CI 1.01–1.25) were. However, no statistically significant interaction effects were found for physical workload and obesity or insufficient vigorous activity.

Conclusions Physical workload, obesity and insufficient vigorous activity were separate risk factors for poor self-rated health, but did not appear to have a synergistic effect. Worksite health promotion interventions focusing on improvement in physical workload and lifestyle both can have beneficial health effects.