I think that you must have misunderstood what was said. That makes no sense at all. The water in your body is lost by sweating and through urination. Unless he was saying that a person wets themselves the statement makes no sense. Working out or sparring would cause a person to sweat and thus urinate less, since the body has lost some of the water through sweating.
...
I never heard that or experienced that. You sure you got this right? People pee themselves when they have health issues like bladder control issues or are really scared as in they are about to lose their life. But a physical confrontation is rarely that serious and a kickboxing fight definitely not. A really hard kick to the bladder area can cause incontinence too but since most people don't know to kick there and it is below the belt for sports fighting this too is highly unlikely.
Because they forgot to use the bathroom before their bout.
My kickbox trainer told us that people lose some urine when theyre in a fight. like in an official fight or outside the gym. Why is that?
