The aim of this cross-sectional study was to compare data on the level of aerobic capacity and body composition of nonspecific chronic low back pain (CLBP) patients with normative data matched for sex, age and level of sporting activity. The study population consisted of 101 outpatients with nonspecific CLBP who had entered a rehabilitation programme. Results were as follows: the mean (standard deviation) aerobic capacity (VO[subscript 2max]) of CLBP patients was significantly (P less than 0.001) lower 7.3 (5.6) ml/kg lean body mass/min as compared with the normative data. The mean (standard deviation) body fat percentage of the patients was significantly (P less than 0.001) higher 3.9 % (5.9) as compared with the normative data. These results provide evidence of a reduced level of aerobic capacity and an increased body fat percentage in nonspecific CLBP patients compared with healthy participants.