How much is too much ballbusting/cbt

I have seen many people discussing their limits in bb and some femdom video limits. But medically speaking how much or what can a guy take that doesn’t make infertile or cause any damage. Is using needles the extreme? or Is it hard twisting and squeezing? Or even hard kicks and punches/ smacks(paddles etc.)?

Or should we just stay away from bb completely to have kids?

I do love watching all cbt videos specially hard ball kicks/ punches and balls being hit with crop/paddle.

Does anyone know medically what are the limits and effects for ballbusting or any cbt methods?