This prospective controlled study examined changes in fitness, health, and work ability after a work-oriented physical fitness course arranged for lumberjacks experiencing low back pain but being still at work. The 1-week courses were designed to activate exercising during leisure time and consisted of fitness tests, various types of exercise, and lectures. Eighty-seven lumberjacks participated in the courses and 61 subjects served as controls. Questionnaire data obtained before and 1 year after the course were available for 78 (90%) of the course participants and 41 (67%) of the controls. In the intervention group, perceived fitness, health, and work ability improved and ergonomic strain at work decreased. Both groups reported an increased frequency of leisure-time physical activity. There were between- group differences in the development of fitness, health, distress symptoms, and subjective work ability, whereas the changes in physical activity, back and musculoskeletal symptoms, or ergonomic strain did not differ between the groups. In a 6-month follow up, muscle function improved in the intervention group, but no change was observed in aerobic capacity. There was a tendency of the number of back pain-related sickness leaves, but not of their duration, to develop more favorably in the intervention group, when data from the year before and the year after the course were compared.