BACKGROUND: As the articular cartilage has a special anatomical position, its function is often affected by movement. Whether exercise training can promote the cartilage repair still needs to be confirmed. OBJECTIVE: To investigate the effects of different intensities of treadmill exercises on the repair of full-thickness articular cartilage defects in rats. METHODS: Forty rats were selected, and the models of full-thickness articular cartilage defects (3.2 mm in diameter) on the femoral surface were made with a orthopedic drill, followed by randomized into model, low-, moderate- and high-intensity exercise groups (n=10 per group). The rats in the model group were allowed free cage activity. The rats in the low-intensity exercise group exercised on the platform, and the platform speed was 8.2 m/min; rats in the middle-intensity exercise group exercised on the 5° treadmill, and the speed was controlled at 15.5 m/min; rats in the high-intensity exercise group exercised on the 10° treadmill, and the speed was controlled at 26.7 m/min. RESULTS AND CONCLUSION: The levels of serum matrix metalloproteinase-3 and inhibitor of matrix metalloproteinase in the latter three groups were significantly lower than those in the model group at 8 weeks after exercise (P < 0.05), and the level was the lowest in the moderate-intensity exercise group (P < 0.05). In the moderate-intensity exercise group, there were fibrous tissues in the defect area, which were connected with the adjacent cartilage, and the repair effect was superior to that in the other three groups. To conclude, moderate-intensity treadmill exercise can promote the repair of full-thickness knee cartilage defects in rats, thereby improving functional recovery of the rat knee joint.