The association between physical workload and low back pain clouded by the"healthy worker" effect - Population-based cross-sectional and 5-year prospective questionnaire study

Study Design. A population-based cross-sectional and 5-year prospective que stionnaire study. Objective. To investigate self-reported physical workload as a risk factor for low back pain. Summary of Background Data. Both physical and psychosocial workplace factor s are considered risk factors for low back pain. However, today no consensu s has been reached regarding the exact role of these factors in the genesis of low back pain. Methods. Questionnaire data were collected at baseline for 1397 (and after 5 years for 1163) men and women aged 31-50 years at baseline. Low back pain ("any low back pain within the past year," "low back pain less than or equ al to 30 days in total during the past year," "low back pain > 30 days in t otal during the past year") was analyzed in relation to physical workload ( sedentary, light physical, and heavy physical work) using logistic regressi on and controlling for age, gender, and social group. The proportions of wo rkers changing between the workload groups over the 5-year period were anal yzed in relation to low back pain status. Results. At baseline no statistically significant differences in low back p ain outcomes were found for workers exposed to sedentary, light physical, o r heavy physical work. This was true for all age, gender, and social groups . At follow-up there was a statistically significant dose-response associat ion between any low back pain and longstanding low back pain within the pas t year and increasing physical workload at baseline also after controlling for age, gender, and social group. Subjects with heavy physical workload at baseline changed statistically significantly more often to sedentary work if they experienced low back pain for more than 30 days out of the past yea r. Conclusions. Having a sedentary job might have a protective or neutral effe ct in relation to low back pain, whereas having a heavy physical job consti tutes a significant risk factor. Because of migration between exposure grou ps (the "healthy-worker" effect), longitudinal studies are necessary for in vestigating the associations between physical workload and low back pain.