- The objective of this study was to analyze the performance of knee muscles in the affected and nonaffected sides of ACL patients as well as with healthy asymptomatic subjects. Fifty-four males, 27 with asymptomatic knees and 27 patients with tear in ACL were included in the study. Subjects performed concentric knee extension and flexion efforts at 60°/s and 180°/s on a Biodex isokinetic dynamometer. Isokinetic peak torque, angle to peak moment of quadriceps (Q) and hamstring (H), and hamstrings/quadriceps ratio (HQR) were measured. There was a significant decline in the mean strength of Q at 60°/s for the involved side compared with either the uninvolved side or with that of the healthy subjects, but not in H. There was also a significant decrease in mean Q strength at 180°/s of the involved side of ACL patients compared with the healthy young males. There was a significant difference in mean angle to peak moment of Q at 180°/s in the healthy group compared with the involved side of the patients and a significant difference for the same parameter in H at 60°/s in the involved compared with the healthy group and uninvolved sides of the ACL patients. There was no significant difference in hamstrings/quadriceps ratio between the groups. It was concluded that the effect of ACL tear on H strength is significantly less than that on the Q one year post-injury. Angle to peak moment offers original and practical information for the determination of individual performance in post ACL injury patients.