None. There’s actually two parts to this; the injuries themselves, and the pain from those injuries.
Nearly any physical activity will eventually introduce you to managing pain. Note: “managing”, not ignoring.
Managing pain isn’t something you can teach, you can’t rationally explain it to someone. You experience pain, and push on.
This is part of the point of all those extreme endurance training exercises, it’s as much about learning to deal with discomfort and finding your actual limits as it is about physical conditioning and fitness. The trick is to inflict as much discomfort as possible (not just pain) without actually harming the participants.
Of course, this also gets warped into outright sadism by writers that don’t understand the point. So, if you’ve got a story where they’re torturing characters as “training”, that’s probably what you’re looking at.
It doesn’t make you ignore pain, but it does give you a better grasp of what pain actually means.
You can’t power through injuries. If your character’s actually been seriously hurt, they can’t ignore it. This is the point where something in their body has been damaged, and there is no way you can simply go “I’m givin’ ‘er all she’s got, Captain!” and keep fighting.
Minor cuts, scrapes, and bruises hurt, and could cause someone without any experience to think that something’s gone really wrong, but the fact is, it hasn’t. Also, remember, bruises take a few minutes to form, so they won’t really start until after the fight is already over.
Deep tissue cuts, severed tendons, torn muscles, broken bones, concussions, punctured lungs? These are things that your character will need to work around. You can’t use a broken arm to fight. It just doesn’t work anymore. The same goes for everything else on that list. These don’t automatically mean your character is out of a scene, but they’re not going to be able to continue to fight.