Purpose. Does physical deconditioning ( loss of cardiovascular capacity and strength/endurance of paraspinal muscles) exist in patients with chronic low back pain (CLBP) and are treatments specifically aimed to reduce these signs effective? Method. Systematic literature search in PUBMED, MEDLINE, EMBASE and PsycINFO until December 2004 to identify observational studies regarding deconditioning signs and high quality RCTs regarding the effectiveness of cardiovascular and/or muscle strengthening exercises. Internal validity of the RCTs was assessed by using a checklist of nine methodology criteria in accordance with the Cochrane Collaboration. Results. There is conflicting evidence that cardiovascular deconditioning is present in CLBP and limited evidence for wasting of the multifidus muscle. No study examined the effectiveness of cardiovascular training specifically. General and lumbar muscle strengthening are equally effective as other active treatments. Only moderate evidence is available for the effectiveness of intensive low back extensor muscle strengthening compared to less intensive strengthening. Conclusion. Probably reactivation caused by active treatment and not the reconditioning itself is the important factor in the reduction of disability. Further prospective and evaluative research into the role of physical deconditioning is necessary. It seems more promising to further explore the interplay between biological, social and psychological factors.