Patients with chronic pain are generally thought to be physically unfit and less active. Hence, physical reconditioning programs are traditionally proposed to such patients as part of their comprehensive rehabilitation program. Traditional physical fitness evaluation is often implemented in patients with low-back pain. However, most methods have not been validated in that context. We recall and discuss earliest findings in the field of physical fitness tests in patients with low-back pain. Maximal physical tests can be reliable when testing conditions are well defined, standardized and controlled. Reliability, however, does not imply validity. Maximal physical tests as applied to patients with pain should indeed be considered as multidimensional since performance to such tests is often limited by psychological factors as fear-avoidance. Hence, maximal physical tests do not allow valid evaluation of physical fitness in most patients with pain. To obtain valid unidimensional fitness assessment in such patients, submaximal testing should be preferred, which is only possible for cardiorespiratory endurance and body composition assessment. We present our personal contribution to the field. Most of this contribution can be found in 7 previously published papers that are included in our manuscript: • Nielens, H. and L. Plaghki. Evaluation of physical adaptation to exercise of chronic pain patients by a step-test procedure. The Pain Clinic. 1:21-28, 1991 • Nielens, H. and L. Plaghki. Perception of pain and exertion during exercise on a cycle ergometer in chronic pain patients. Clin J Pain. 10:204-209, 1994 • Nielens, H., V. Boisset, and E. Masquelier. Fitness and perceived exertion in patients with fibromyalgia syndrome. Clin J Pain. 16:209-213, 2000 • Nielens, H., T. M. Lejeune, A. Lalaoui, J. P. Squifflet, Y. Pirson, and E. Goffin. Increase of physical activity level after successful renal transplantation: a 5 year follow-up study. Nephrol Dial Transplant. 16:134-140, 2001 • Nielens, H. and E. Masquelier. The role of exercise in the treatment of fibromyalgia: An overview. Int Sportmed J. 2:1-8, 2001 • Nielens, H. and L. Plaghki. Cardiorespiratory fitness, physical activity level, and chronic pain: are men more affected than women? Clin J Pain. 17:129-137, 2001 • Nielens, H., D. Cornet, and F. Rigot. Maximal versus submaximal testing protocols to evaluate fitness of patients with chronic low back pain; abstract. Med Sci Sports Exerc. 34, 2002 We developed an original submaximal cycle ergometer test that allows calculation of an original Physical Working Capacity index, the PWC65%/kg and an original Rate of Perceived Exertion index, the RPE65%. We evaluated the reliability and the validity of the PWC65%/kg as a cardiorespiratory endurance index. We also present and discuss our results obtained in chronic pain patients with those indexes. Clearly, male patients with severe chronic pain are more affected than females in terms of physical fitness and activity, probably due to socio-cultural factors. Exertion perception of most patients with low-back pain and/or sciatica seems normal. However, females with fibromyalgia present with a very significant distortion of exertion perception. Physical reconditioning combined with education seems helpful in most patients with chronic pain directly through fitness improvement but also through the major cognitive change it contributes to generate.