45 high-level athletes who had suffered anterior cruciate ligament (ACL) rupture were included in this study which investigated the effect of a "reathletization" program and leucine supplementation on functional recovery following ACL reconstruction. All patients underwent the same 2-3 week rehabilitation protocol, and were randomized to either leucine or placebo supplementation. Follow-up on parameters of muscle improvement were conducted at the completion of the rehabilitation program. The results revealed that the effect of the rehabilitation program led to significant global improvement of thigh perimeter, quadriceps and hamstring isokinetic tests, and percent body fat of all athletes. Lecuine supplementation was only associated with significant increase in lower thigh perimeter compared to placebo.