According to another study of ours, 0.1 mg MIA induced punctate depressions on the surface of cartilage and cartilage erosion proceeded with time in Wistar rats . In our current results, additional running advanced cartilage degeneration induced by 0.1 mg MIA in only the tibial cartilage, not in the femoral cartilage. In the tibial side, cartilage degeneration induced by MIA was observed around the apex part of the tibia, which was not covered with the meniscus. Therefore, the apex part of the tibia cartilage was possibly sensitive to the mechanical stress induced by strenuous running. In the femoral side, while cartilage degeneration by MIA was observed in the posterior part, mechanical stress would affect an extensive area, not a focal area, of the femoral condyle cartilage. This might reduce the influence of mechanical stress in the femoral cartilage.