Relative mRNA gene expression of proteoglycan ( PRG )4 (A) and transforming growth factor ( TGF )-β (B) relevant to lyceraldehydes-3-phosphate dehydrogenase (GAPDH) in the control (CON), low- (LIR), moderate- (MIR), and high-intensity (HIR) groups. Significantly higher mRNA gene expression of PRG4 was found in the LIR (1.03 ± 0.38) and MIR group (1.00 ± 0.12) than in the CON group (0.67 ± 0.31). However, there was significantly lower PRG4 expression in the HIR group (0.64 ± 0.09) than in LIR or MIR groups. Similar changes were found in mRNA gene expression of TGF-β. The LIR (1.13 ± 0.35) and MIR (0.89 ± 0.09) groups had significantly higher gene expression than the CON group (0.65 ± 0.20), whereas the HIR group (0.48 ± 0.08) had significantly lower expression than the LIR or MIR groups. NCA: non-contact area, TA: transitional area; CA: contact area.