I read that this can happen (visible blood in the urine) when you exercise strenuously - like after a long run and/or if your bladder is half full (or so) at the time and the exercise involved the crashing of the walls of the bladder banging into each other continuously in a rapid "back and forth" motion - it can cause bleeding.

I imagine this would be all the more so with an inflamed bladder which is already irritated and tender or had suffered through a UTI.