The aims of this study were to conduct a comparative investigation of muscle function between patients with low back pain (LBP) and healthy persons, and to determine whether intensive rehabilitation can change back muscle contraction synergy. Twenty healthy persons and 20 patients with chronic LBP were asked to perform symmetrical and asymmetric tasks. The patients with LBP were tested in the weeks immediately before and after 12 weeks of LBP rehabilitation. Tasks include "carrying" weights up and down and with a 45 degrees left rotation. Eight-channel surface electromyographic electrodes were placed on the surface of paraspinal muscles over the lumbar region. Correlations between the right and left corresponding muscles and between values before and after treatment were determined. Lifting capacity for patients with LBP were also measured before and after treatment. Results from electromyographic profiles showed that the muscle activity strategies varied between healthy persons and patients with LBP. The correlation coefficients for spinal muscles have shown very reproducible intrasubject muscle contraction synergies. Unbalanced electromyographic patterns found in patients with LBP given symmetrical tasks were not affected by rehabilitation treatment.