I would say don't do it before your fight or what ever physical activity you will be doing. save it for the day before or after. and definitly not during. Although it might help to distract the guy you are fighting.
Professional athletes often have rather poor sex lives. The intensity of training for an event tends to divert their attention from the normal aspects of living, including sex. But that is how it should be. When in camp if you have enough energy left at the end of the day to jerk off, that means you aren't training hard enough. Your dick should NOT be distracting you from the goals that you are trying to achieve.
I don't know if you are being serious or not, but I have heard many young boxers say that who really were serious! :shock:
tell your girl that it helps your training. I think someone here said that... Oh wait actually it was iks. He was telling his ex back in the day that he needed lots of sex because it helped his MMA training
Don't wack off in the middle of training. I got kicked out of my gym for staining the mat and mentally damaging my sparring partner.