Hi Udo, It's hard to tell for sure, but I do know that if i exercise too much, or too little for that matter, my IBD (I have UC) can backslide. When I'm in a flare I have to be very careful about how much exercise I get - much less than when in remission. I don't run but would think that the jarring effects of it could be disruptive to your inner organs, especially your colon since it's a weak spot anyway because of the IBD. I think you have to listen to your body. While in this flare I would cut back significantly on the running and possibly augement it with some walking or bicycling. Just don't stress your body beyond it's limits while flaring. It's trying to repair itself and if you put too much stress on it I can't imagine that would be good or helpful. Good luck, Elizabeth