Cumulative load as a risk factor for back pain. The association between cumulative load (biomechanic load and exposure time integral over the entire work experience) and back pain was investigated in a group of institutional aides with physically stressful jobs. A questionnaire/interview was conducted with 161 of these institutional aides. The point prevalence of back pain in this sample was 62%. Men had worked a mean duration of 14.3 years and women 11.6 years at the time of the onset of the first pain episode. Every job performed was analyzed by the use of a two-dimensional static mathematical model. The compression and shear at the thoracolumbar and lumbosacral discs were computed by the use of a biomechanic model. Cumulative compression and shear were significantly higher in institutional aides with pain compared with those without pain (P less than 0.05-0.01). The pain group was similar to the no-pain group in age, weight, and height. 