BACKGROUND: Physical conditioning programs aim to improve work status for workers on sick leave. This is an update of a Cochrane Review (Work conditioning, work hardening and functional restoration for workers with back and neck pain) first published in 2003. OBJECTIVES: To compare the effectiveness of physical conditioning programs in reducing time lost from work for workers with back pain. SEARCH STRATEGY: We searched the following databases to June/July 2008: CENTRAL (The Cochrane Library 2008, issue 3), MEDLINE from 1966, EMBASE from 1980, CINAHL from 1982, PsycINFO from 1967, and PEDro. SELECTION CRITERIA: Randomized controlled trials (RCTs) and cluster RCTs that studied workers with work disability related to back pain and who were included in physical conditioning programs. DATA COLLECTION AND ANALYSIS: Two review authors independently extracted data and assessed risk of bias. MAIN RESULTS: Thirty-seven references, reporting on 23 RCTs (3676 workers) were included, 13 of which had a low risk of bias. In 14 studies, physical conditioning programs were compared to usual care. In workers with acute back pain, there was no effect on sickness absence. For workers with subacute back pain, we found conflicting results, but subgroup analysis showed a positive effect of interventions with workplace involvement. In workers with chronic back pain, pooled results of five studies showed a small effect on sickness absence at long-term follow-up (SMD: -0.18 (95% CI: -0.37 to 0.00)). In workers with chronic back pain, physical conditioning programs were compared to other exercise therapy in six studies, with conflicting results. The addition of cognitive behavioural therapy to physical conditioning programs was not more effective than the physical conditioning alone. AUTHORS' CONCLUSIONS: The effectiveness of physical conditioning programs in reducing sick leave when compared to usual care or than other exercises in workers with back pain remains uncertain. In workers with acute back pain, these programs probably have no effect on sick leave, but there may be a positive effect on sick leave for workers with subacute and chronic back pain. Workplace involvement might improve the outcome. Better understanding of the mechanism behind physical conditioning programs and return-to-work is needed to be able to develop more effective interventions.