The influence of strenuous running on OA remains a matter of controversy. There are 8 reports (including this one) describing the influence of strenuous running on articular cartilage in Wistar rats (Table 1) [5, 19–24]. Thirty km of strenuous running was harmful without other OA inductions in all four papers [5, 19, 20, 24]. Fifteen km of strenuous running with other OA inductions was also harmful in two papers in addition to this one; two other papers reported running as beneficial. Cifuentes et al. reported that 15 km of running over 8 weeks was beneficial in the knee injected with 1.2 mg MIA . The difference between the study by Cifuentes et al. and ours was the time from MIA injection to the start of strenuous running. Cifuentes et al. started strenuous running just after MIA injection, while we did 1 week after injection at which time synovitis was already induced.