SOFTENING OF THE LATERAL CONDYLE ARTICULAR-CARTILAGE IN THE CANINE KNEE-JOINT AFTER LONG-DISTANCE (UP TO 40KM DAY) RUNNING TRAINING LASTINGONE-YEAR/

The effects of long distance running training (up to 40 km/day) on the biomechanical properties of young canine articular cartilage were inv estigated using in situ indentation creep technique. The stiffness of articular cartilage was determined in the form of instantaneous and eq uilibrium shear moduli. The rate of cartilage deformation was also com puted. Microspectrophotometric and polarized light microscopic analyse s were made for determination of local glycosaminoglycan content and c ollagen organization, respectively. During a period of one year, the r unner dogs (n = 10) underwent a gradually increased treadmill exercise up to 40 km/day, while the littermate control dogs (n = 10) lived nor mally in their cages. The equilibrium shear modulus of articular carti lage decreased significantly by 12 to 14% (p<0.05) in the lateral, but not in the medial, condyles of femur and tibia. In the lateral condyl es of the runner dogs, the deformation rate of cartilage increased by 16% (p<0.05). Consequently, the articular cartilage response to runnin g training was site-dependent. The simultaneous changes of the equilib rium shear modulus or the retardation time spectrum and the glycosamin oglycan content confirm the key role of proteoglycans in modulating th e cartilage equilibrium stiffness and creep rate. The changes in the i nstant shear modulus appeared to be predominantly related to the alter ations in the organization of the superficial collagen network. Althou gh the running training did not create cartilage damage, we assume tha t the softening of the cartilage may with time jeopardize the ability of articular cartilage to maintain its normal structural and functiona l properties.