Study Design. A population-based longitudinal study conducted in northwest England for a 12-month period involving adults aged 18-75 years.

Objectives. To determine physical factors related to employment that predict a new episode of low back pain.

Summary of Background Data. Most epidemiologic studies that have examined the relation between occupation and back pain have been cross-sectional or retrospective in design. Because workers who have experienced low back pain may have changed jobs or work activities, it is important to use longitudinal studies that define "exposures" before the onset of symptoms.

Methods. From adults registered with two general practices in northwest England, 1412 people who were currently in employment and free of low back pain were identified. A lifetime occupational history was recorded for all participants, with details of activities performed in each occupation. Data on consultations for low back pain during the follow-up year were collected through computerized medical records, whereas those who had not consulted with low back pain were sent another questionnaire at the end of the 1-year follow-up.

Results. An increased risk of a new episode of low back pain was found in those whose jobs involved lifting/pulling/pushing objects of at least 25 lbs, or whose jobs involved prolonged periods of standing or walking. Risks were, in general, greater in women, for a first ever episode of back pain and for back pain that led to a general practice consultation. No clear relation between years of exposure to such factors and magnitude of risk was evident.

Conclusions. Occupational activities, particularly in women, such as working with heavy weights or lengthy periods of standing or walking, were associated with the occurrence of low back pain. Short-term influences may be more important in the occurrence of new episodes rather than cumulative lifetime exposure, and emphasize that such morbidity may be avoidable.