Study design: Prospective case series with historical controls (normative data).

Objectives: To compare the aerobic fitness level of patients with chronic low back pain (CLBP) with healthy controls matched for gender, age, and level of sport activity and to evaluate the association of the difference in aerobic fitness level with pain intensity, duration and degree of disability, fear of injury, and level of activity during work, including household and leisure time.

Summary and background data: Controversy exists whether patients with CLBP have a lower level of aerobic fitness and whether this level may partly depend on the patients' activity level.

Methods: A total of 108 CLBP patients completed questionnaires regarding pain, disability, fear of injury, and activity level and performed a modified Astrand submaximal cycling test. The maximum oxygen consumption (VO2max) was calculated and compared with normative data. Multiple linear regression analysis was performed with the difference of the level of aerobic fitness as dependent variable.

Results: VO2max could be calculated in 78% of the patients. Both men and women with CLBP had significant lower VO2max than the healthy referents (10 mL/kg LBM x min(-1) and 5.6 mL/kg LBM x min(-1) respectively, P < 0.001), and this difference was significantly greater in men (P = 0.03). Multiple regression analysis showed that the level of aerobic fitness was not associated with the presumed variables. The patients who stopped the test prematurely were older (P = 0.02) and more disabled (P = 0.01).

Conclusion: CLBP patients, especially men, seem to have a reduced aerobic fitness level compared with the normative population. No explanatory factor for that loss could be identified.