Lifelong moderate running training increases the incidence and severity of osteoarthritis in the knee joint of C57BL mice

Background: Inbred C57BL made mice express a high incidence of spontaneous osteoarthritis of the knee joint at the age of 18 months. We used this strain of mice to find out the effects of life‐long, moderate running exercise on the health of articular cartilage and the incidence of osteoarthritis. Methods: Male mice (294) were divided into controls and runners. The runners were trained daily between 2 and 18 months of age. The speed was 13.3 m/min and the distance on a flatbelt treadmill was 1,000 m/day. The mice were sacrificed at the ages of 2, 6, 10, 14, and 18 months. The Knee joints were sectioned in frontal direction and the osteoarthritic changes were graded using a conventional light microscope. The reproducibility of the grading method was tested by calculating extended k‐coefficient for the results of six researchers. Results: The incidence of osteoarthritis at the age of 18 months increased from 72% in controls to 88% in runners in the medial tibial condyles (P<0.05), and from 80 to 96% in the lateral tibial condyles (P < 0.001). The incidence of the most severe osteoarthritic changes rose from 16% in controls to 38% in runners in the medial tibial condyles, and from 4 to 36% in the lateral tibial condyles. Conclusion: According to our results, the moderate, long‐lasting running exercise accelerates the development of osteoarthritis in the knee joints of C57BL mice. © 1995 Wiley‐Liss, Inc. Copyright © 1995 Wiley‐Liss, Inc.