When I was a track coach, I designed most of my practices to focus on interval training. Instead of running the entire distance of the races my runners participated in, they would run only a fraction of those distances at speeds that would total a personal record.
The idea is that you train your body and your mind to run at a certain speed. If you run the full distance during practice, but your pace is slower than your personal record then you train your body and mind to run slower.
A 400m runner, for example, might run intervals of 200m or 100m at a speed that puts them on pace to run a second faster than their current personal record.
I’m trying to decrease my 5k time. When I ran intervals of a mile and half a mile at a faster pace, I increased my speed for the later longer runs. Why? Because my mind was used to running at a certain speed.
The same goes for anything really.
You can write faster during longer periods of time if you are used to writing quickly in short bursts.
The same could go for any kind of art or sport