Physical exercise and low back pain. 
Campello M; Nordin M; Weiser S 
Occupational & Industrial Orthopaedic Center (OIOC), Hospital for Joint
Diseases, New York University Medical Center, New York 10014, USA. 

Scand J Med Sci Sports, 1996 Apr, 6:2, 63-72 
Health care providers often prescribe exercises as treatment for
nonspecific low back pain. However, the effectiveness of this treatment is
poorly documented in the literature. While the evidence suggests that
exercise in general is beneficial, there is a lack of knowledge about the
types, frequency and duration of exercises that should be prescribed and
at what stage of injury they are most helpful. In addition, few studies have dealt with exercise treatment alone rather than in combination with other treatments, making it hard to decipher the unique contribution of exercise.
Inadequate study designs also make conclusions difficult. Conversely, the
literature clearly shows that inactivity has detrimental effects (i.e. delayed return to normal activity, and negative physiological and psychological effects) for low back pain patients.