This is a very rare condition but in some cases, intense exercise can actually cause hematuria. It is thought that this might be to do with dramatic dehydration, or perhaps damage to the bladder that goes unnoticed.
It could also be due to damage that is caused by the internal organs being jolted violently during activity, or by the breakdown of red blood cells during sustained aerobic exercise.
While this can occur in any kind of exercise, the most common type of athlete to be affected by this condition is runners. It could also be noticed in activities that involve particularly extreme exercise – such as crossfit which is infamously harsh on the body.