OBJECTIVETo evaluate the effects of treadmill running exercise of different intensity on early repair of full-thickness defects on the patellofemoral articular surface and the changes in the expressions of matrix metalloproteinase-3 (MMP-3) and tissue inhibitor of metalloproteinase-1 (TIMP-1) in SD rats.

METHODSTwenty-four male SD rats with full-thickness defects on the patellofemoral articular surface were randomly assigned into sedentary control (SED) group and low-, moderate- and high-intensity running groups (LIR, MIR, and HIR groups, respectively). The running groups were trained on treadmill for 6 consecutive weeks. Blood samples were collected to detect serum MMP-3 and TIMP-1 levels using ELISA before and after the experiment, and the femoral trochlea were collected to assess tissue repair by gross appearance scoring and O Driscoll histological scoring with Safranine O-Fast Green staining and Toluidine blue staining.

RESULTSIn rats in SED group, the defect was filled with hyaline articular cartilage-like tissues, as compared to fibrous tissues in LIR and MIR groups and subchondral bone damage in HIR group. The SED group scored the highest and HIR group the lowest among the 4 groups in gross appearance scoring and O Driscoll histological scoring. No significant differences were found in MMP-3 or TIMP-1 levels among the groups before training (P>0.05), but after 6 weeks of training, serum MMP-3 and TIMP-1 levels differed significantly among the 4 groups (P<0.05), and all the 3 running groups had a significantly higher MMP-3 level than the control group (P<0.05). After the 6-week training, TIMP-1/MMP-3 ratio was significantly higher in SED group than in the 3 running groups, and was the lowest in HIR group.

CONCLUSIONBoth low- and moderate-intensity exercise failed to promote resurfacing of full-thickness cartilage defects on the patellofemoral articular surface in rats, and high-intensity exercise even induces subchondral bone damage. The expression of MMP-3 and TIMP-1 is related to exercise, and the TIMP-1/MMP-3 ratio reflects the extent of tissue repair.