Experimental procedure: All the subjects were randomly assigned to 4 weeks training as follows: rhythmic stabilisation (RS), combination of isotonic exercises (ISO) or a control group (CON). Training was aimed at improving trunk stability and strength. Disability and back pain (Oswestry index), static and dynamic trunk muscle endurance (repetitions in flexion and extension) and lumbar mobility were measured before, immediately after 4 weeks training, and 4 and 8 weeks after training was stopped.