In a balance board test 3 students were tasked to balance a one mtr long board over a fulcrum point. At each end of the board were electrodes that registered on a counter the number of touch downs.
All 3 students endured different circumstances. One was blind folded. The other had their horizon blocked the third no restrictions and as much practice as they liked.

the test last 20 mins and a record made of their official count.

All three were invited back one week later and the test repeated.

All 3 showed an improvement of at least 50% over the previous results.

The conclusion was that the brain continues to process information and tasks long after said task is finished. And skill is acquired over building muscle memory (which in reality is the brain processing a task)

But what also came of the test was that massive gains are made in the first portion of the test which quantitive advances tailing off exportentially as fatigue sets it.

conclusion. Training whilst tired is a flawed return on effort expended.