Exercise increases BDNF, a protein that supports the growth and repair of nerve cells. It also regulates cortisol and stimulates the release of endorphins and serotonin. These are physiological changes that explain why people who exercise regularly report better mood and sharper focus.
The dose needed for mental health benefits is lower than people assume. Twenty to thirty minutes of moderate movement three to five times a week is sufficient to show measurable effects. The type of exercise matters less than the consistency.