It is widely accepted that synovial inflammation is a feature of OA [11–13]. Clinically, exercise is effective in improving symptoms of OA in the chronic phase [14, 15]. On the other hand, it is well known that exercise in the inflammatory phase leads to exacerbation of symptoms . However, it is still unknown how exercise affects synovitis. Thirdly, we examined if low amounts of MIA injection induced synovitis and how strenuous running affected synovitis, if at all.