Have you ever misloaded a barbell?
Added more weight than you intended to but lifted it like normal?
Have you ever been out running, knackered, feeling the energy dwindle only to see a familiar face smile at you and you take off afresh?
Ever been doing a conditioning session or partake in a tough event and been ready to drop to your knees, until you see your competitors flag and you get a renewed power?
In each example nothing physical changes.
You haven't suddenly produced any extra ATP, the fuel that drives muscle contraction.
What you have done is changed your perceptions.
The energy to perform is all neural, it's all in the head.
It's closer to you taking the brakes off than it is accessing a reserve tank.
Imagine if you could change your perceptions permenantly?
Every time you pass a perceived limit, celebrate it.
Brag about it.
This will make it permanent.
There's some funky neuroscience behind this involving dopamine.
But the result at a practical level is that you now know you are better, and can go there again.
Your perceived limit has been pushed out.
And you know that you can push it even further, if you're humble enough and smart enough