Objective To observe the effect of aerobic exercise of different intensities on type Ⅱ collagen,glycosaminoglycan (GAG) and chondrocyte apoptosis in rabbits modeling knee osteoarthritis (OA),so as to explore the preventive effect and its possible mechanism.Methods Twenty healthy New Zealand white rabbits were randomly divided into Groups A,B,C and D,each of 5.Group A was allowed free activity in a cage for 9 weeks.Group B was allowed free activity for 4 weeks,then an OA model was established using papain and confirmed via MRI 1 week later,Another 4 weeks of free activity were then allowed.Groups C and group D were given running training for 20 minutes a day at 0.5 km/h,3 times a week,and then 20 minutes a day at 1.5 km/h,5 days a week on a treadmill for 4 weeks.Nine weeks later,all 4 groups of rabbits were killed and the articular cartilage damage of each group was compared using Mankin scoring,and expression of type Ⅱ collagen,GAG content and chondrocyte apoptosis in the cartilage.Results After the intervention,the average Mankin score,expression of type Ⅱ collagen and GAG content of groups B,C and D were significantly lower than those of group A,and all of those values in group B were significantly lower than those of group D.After 9 weeks the chondrocyte apoptosis rate of group A was significantly lower than that of the other groups,and that of groups C and D was significantly lower than that of group B.Conclusion Aerobic exercise may prevent knee articular cartilage degeneration through inhibiting reduction in the amount of type Ⅱ collagen and GAG in the cartilage matrix.It may be related to decreasing the chondrocyte apoptosis.