Sub-acute (4-12 weeks duration) and chronic (more than 3 months duration) low back pain (LBP) is frequent, disabling and costly. The effectiveness of usual treatments (including pain killers, anti-inflammatory drugs, spinal infiltrations, physiotherapy, spinal traction, transcutaneous electrical nerve stimulation, etc) may be not sufficient, and many patients resort to alternative therapies. Manipulative treatments represent en emerging therapy in this area, although studies assessing their effectiveness are limited and often biased. The purpose of this study is to evaluate the efficacy of two manual therapies administered by osteopaths on improving functional recovery in sub-acute and chronic low back pain less than 1 year. A standardised osteopathic manipulative treatment is compare to a placebo of osteopathic manipulative treatment.