For me it's training, despite what some people like to say, people who are extremely well trained can pull feats of seemingly superhuman nature without having any superpowers.

Such as dodging a bullet, catching a cannonball with your gut, or resisting the blade of a spear with your core muscles.

Even though these things have been done in real life by real people, if you do it in character as anyone who doesn't have superhuman abilities, you're a shitlord and everyone complains.

Basically, what it breaks down to from what I've seen, is that training is used as a metric for how much better of a fighter you are than anyone else. And that's the end of training.