Chronic back pain rehabilitation in small groups: pain, disability and function a quasi-randomized trial

2-week exercise rehabilitation program. Back School based exercise involving stretching of back muscles, exercise of abdomen strenghtening, postural education, floor based exercise. Back School home-based exercises (the same exercises performed during treatment sessions) are reported in a book given at the end of the treatment. Evidence based exercise involving progressive exposure (with a progressive increase in repetitions and coordination and decrease of balance till fatigue), aerobic global exercise (involving the muscles of both legs and of the back in the way to increase the heart beat from the one at rest). Evidence based home-based exercises involves global aerobic exercises floor based exercises and auto-mobilization of peripheral nervous system, those exercises will be taught to the patients during the treatment sessions. Prescription is 5 x 1/2 hours sessions per week for 2-weeks. All directly supervised from the physiotherapist in a group format (5 people per group session). All sessions will be performed in a outpatient service of the public health system. No intervention group will completes both the back and evidence based exercises. Adherence to the intervention will be assessed through the presences to the treatment sessions and an adherence scale at follow-up assessment.