INCREASED CENTRAL DRIVE DURING FATIGUING CONTRACTIONS OF THE PARASPINAL MUSCLES IN PATIENTS WITH CHRONIC LOW-BACK-PAIN

In low back pain patients the paraspinal muscles demonstrate excess fa tigability. Whether the cause is ''central' as could result from impai red motor unit recruitment due to poor motivation or fear of pain, or ''peripheral'', and caused by defects in the contractile apparatus, is unknown. Using surface electromyography in conjunction with a standar dized isometric fatigue test, this study investigates the mechanisms c ausing paraspinal muscle dysfunction in patients with both nonsurgical and postsurgical chronic low back pain. During the fatigue test norma l subjects and both patient groups exhibited electromyographic increas es. These were significantly greater in both patient groups, indicatin g increased central drive to their muscles. These findings may suggest that patients' excess fatigue is peripheral in origin, with increased central drive arising secondary to muscle wasting or denervation, alt hough a central activation defect has not been excluded. Impaired phys ical performance in low back pain patients does not seem to be caused by lack of central drive.