Exercise may result in increased laxity in the knee. Anterior translation in 40 normal knees, 33 consecutive anterior cruciate ligament-deficient knees, and 30 randomly chosen anterior cruciate ligament-reconstructed knees was measured using the KT-1000 arthrometer before and after the participants ran for 15 minutes on a neutral-incline treadmill. A single observer blinded to the status of each knee tested all participants. There was a significant increase in anterior translation in the normal (mean, 0.75 mm), anterior cruciate ligament-deficient (mean, 0.62 mm), and anterior cruciate ligament-reconstructed knees (mean, 0.25 mm) after exercise. In addition, the amount of anterior translation after exercise was significantly different when these groups were compared with each other. Post hoc analysis using Tukey's procedure indicated that anterior translation in the anterior cruciate ligament-reconstructed knee was significantly less than in the normal and anterior cruciate ligament-deficient knees. Therefore, repetitive loading exercise contributes to an increase in anterior translation in normal, anterior cruciate ligament-deficient, and anterior cruciate ligament-reconstructed knees, and the anterior cruciate ligament-reconstructed knee does not respond to repetitive loading in the same manner as a normal knee.