General state and pain threshold of rats
During the experiment, no rats in any of the groups died. The control rats had well-grown fur that was white and shiny. The fur of the rats with OA appeared haggard and yellow, and they exhibited signs of irritability. Within one week of the MIA injection, the OA rats showed a limp, but their movement gradually improved after three weeks. The OA+HIIT rats also exhibited limp movement and irritability one week after the MIA injection. After six weeks of HIIT training, it was expected that the OA+HIIT rats would show improved movement in their right knee joint, but four rats suffered from serious infections in their paws and tails. The OA+C-A1 and OA+C-A1+HIIT rats showed a limp during the first week after the MIA injection, but their condition gradually improved after the third week. After six weeks of HIIT training, the fur of the OA+C-A1+HIIT rats became shiny, but three rats had severe infections in their paws and tails. The body weight of the rats in each group increased significantly over the feeding period, with no significant difference in the rate of weight gain (P > 0.05, Figure 2 A, C).
OA rats manifested a lower threshold when the von Frey test stimulated the hind paw. OA rats exhibited significantly decreased MWT from the third and tenth week compared with control rats, but HIIT treatment reversed the OA-induced trend (P  < 0.001, Figure 3 B). There was no significant difference in the MWT of rats in each group before MIA injection ( > 0.05). From the seventh to tenth week, the MWT of OA+HIIT rats was significantly higher than that of OA rats (seventh week: P  < 0.01; eighth to tenth week: P  < 0.001). The MWT of OA+C-A1 rats was significantly lower than that of OA rats (P  < 0.05). At the eighth to tenth weeks, the MWT of OA+C-A1+HIIT rats was significantly lower than that of OA+HIIT rats (P < 0.05, Figure 2 B, D).