Exercise boosts brain function because the human animal is an integrated being composed of two elements, mind and body.
The body affects the mind. The mind affects the body. They have a reciprocal relationship.
Your mind is affected by exercise because:
Exercise oxygenates the blood and the blood oxygenates the mind.
Exercise causes the brain to release hormones, such as endorphins, growth hormone and other mood elevators.
Exercise is controlled and coordinated by the mind, and thus causes the mind to think in coordinated ways.
Intense exercise, such as heavy weightlifting necessitates the mind to fire off billions of neurons at a single moment, and thus trains the brain to switch itself on - on demand.
In other words, intense training improves the minds ability to focus and concentrate and put forth efforts centred upon a single point.
I know nothing more valuable than the ability to switch yourself on and off, on demand.
Control your mind, and you control your personal reality.