Both electrical stimulation and electromyographic biofeedback have been shown to be more effective than voluntary isometric exercise alone in the recovery of quadriceps femoris muscle force following anterior cruciate ligament (ACL) reconstruction. In a comparison of these two modalities, 30 patients with ACL reconstruction were randomly assigned to either a group receiving electrical stimulation in conjunction with voluntary isometric exercise or a group receiving biofeedback in conjunction with voluntary isometric exercise. Following 6 weeks of a rehabilitative exercise protocol, the quadriceps femoris muscle isometric peak torque in the operative limb was compared with that in the nonoperative limb. A t test of independent samples indicated that the biofeedback group recovered a significantly greater percentage of their nonoperative limb's peak torque than did the electrical stimulation group. Measurements of active knee extension were taken at weeks 1, 2, 4, and 6 of the exercise program. A two-way analysis of variance (groups x weeks) indicated no significant difference between the rate at which each group recovered full active extension. The authors concluded that biofeedback is more effective than electrical stimulation in facilitating the recovery of peak torque and that biofeedback is comparable to electrical stimulation in the recovery of active knee extension.