I had a hard 5K run at Parkrun on Saturday -- warning -- too much information to follow!!)
I try to make sure that I am hydrated well - but that invariably leads to the problem of wanting to visit the little boys room halfway during a 5K run. So I generally make sure that I am well emptied out before the run starts -- but perhaps this is not a good idea -- because after this hard run where I have to admit to pushing myself almost past the bounds -- I passed blood in my urine immediately after the run. It happened again on arrival home -- but went away after that.
Internet research all recommends a visit to the Dr - which I will do tomorrow - as it can be caused by all kinds of nasties -- BUT , previously unknown to me, it is apparently quite a common problem for runners!! Nobody including the Medicos knows why it happens - but the most common conjecture is that it is possibly caused by having a totally empty bladder before intense exercise ( plus also of course dehydration) . I don't think that I was dehydrated - however there wasn't a lot of urine flow -- so who knows?? I don't think that my Doctor will -- he still believes that a runners Max HR is 22-age!!