OBJECTIVE The aim of this study was to analyze the effect of running retraining on the recovery of the knee's functional and muscular properties after anterior cruciate ligament (ACL) reconstruction. METHODS Eighty-five athletes who had undergone ACL reconstruction surgery were selected randomly to receive, or not to receive, controlled running training based on interval training and speed exercises. The effect of retraining was measured by the evolution of the knee's isokinetic strength deficit and progress (at angular speeds of 60 and 180 degrees /s), the knee laxity parameters and the score on the Lysholm Knee Scale from the 4th to the 6th month after the surgery. Forty subjects were retrained and compared with 40 control-group subjects. The effect of the retraining program was studied in terms of the type of ACL reconstruction and the effect of time. RESULTS After retraining, no difference was found for isokinetic knee strength deficit and progress, knee laxity and Lysholm Knee Score. The isokinetic strength deficit was influenced mainly by the type of ACL reconstruction. CONCLUSIONS It would seem that running retraining has an insufficient effect on the muscular and functional recovery after ACL reconstruction, despite the fact that this type of training is well-tolerated.