A comprehensive 4-week inpatient treatment including intensive physical training was evaluated in 194 chronic low back pain patients of whom 101 were working and 79 were on sick leave. Physical performance was assessed by measurements of spinal mobility, isometric trunk flexion and extension strength, and isokinetic lifting strength. Outcome was evaluated by a functional capacity index and work status changes reported at a 12-month follow-up. There was a 30-50% average increase in physical performance during treatment. At the 12-month follow-up the functional capacity index showed an average increase from 35.4 to 39.3 points (score range 24-48). At follow-up 28% of the sicklisted patients had returned to work and of those employed before treatment 14% were on sick leave. Associations between outcome and the improvement in physical measurements and their level at discharge were determined by stepwise multiple and logistic regression analyses. Among the physical measurements only increase in spinal mobility was associated with functional capacity index in women and return to work in both men and women at the 12-month follow-up. The overall results showed that intensive physical training and improved physical performance did not play crucial roles in the rehabilitation of chronic low back pain patients, at least when return to work was used as the outcome criterion.