Electromyography was used to determine the level and pattern of muscle activity of the rectus abdominus and T10, L1 and L3 erector spinae muscle in healthy subjects and patients with chronic low-back dysfunction during various postures and activities. Statistically significant differences in erector spinae activities were found between groups for the Valsalva maneuver and for portions of the sit-up exercise. Comparisons between the 4.5 and 16-kg lifts completed with bent and straight knees showed few differences during actual lifts, but the patients with chronic dysfunction maintained an increased level of activity when lifts had been completed.