There is something to being in the correct mindset or flow-state. There was a documentary on it following such people as world class free climbers and other athletes. Some deep sea divers who can hold their breath for ages also enter the state. It seems to be about learning to trust your body to move as it needs to.

They used brain wave monitors in various controlled environments to try and figure out what was going on, but like most things to do with the mind and how it works it's not easily explained.

You might find the documentary on Youtube searching "flow state"