As an OA model in rats, 15 km of running was insufficient and 30 km of running induced OA but only 50% of the rats completed the regimen. This is the first report to reveal dropout rate in 30 km of running. To induce OA in rats, 30 km of running in 6 weeks is currently popular but some modifications are required to reduce the dropout rate. Beckett et al. reported that over 30 km running distances were required to induce OA progression in 3 weeks . Even though the drop off rate was not mentioned in this paper, it might increase because 30 km of running in 3 weeks seems more stressful.