Braun here from Human Precision. Exercise trains the cardiovascular system while also changing the conditions in which the brain works. Here is the useful version of what the evidence says, without pretending one habit or one score explains everything.
Immediate effects
A single session of moderate activity can change alertness, mood and blood flow. You may feel mentally clearer afterward, although fatigue from a very hard session can temporarily hurt fine performance. The effect depends on fitness, intensity, sleep, temperature and hydration.
Long-term effects
Regular activity can improve cardiovascular fitness, blood pressure, insulin sensitivity and other risk factors that influence blood vessels. The National Institute on Aging reports that physical activity is associated with healthier cognitive aging, while also being careful that not every study proves the same degree of benefit for every person.
What kind of exercise counts?
The American Heart Association recommends a weekly mix that generally totals at least 150 minutes of moderate aerobic activity or 75 minutes of vigorous activity, plus muscle-strengthening work. Walking, cycling, swimming, running, sports and many forms of active work can count. The best plan is one you can repeat and increase gradually.
Exercise is not a reaction-time shortcut
Athletes and gamers often search for ways to improve reaction time. Exercise may support attention, coordination and general health, but practicing a browser reaction task mainly makes you more familiar with that task. Use the reaction time test as a personal benchmark. Do not assume a faster click means you are safer to drive or have better neurological health.
A practical starting routine
Start with a brisk 20- to 30-minute walk most days and two short strength sessions each week. Add intensity slowly. Break up long periods of sitting. Protect sleep and recovery. People with symptoms, injuries or medical conditions should get individualized guidance before making a major change. Exercise works best as part of the same system as food quality, sleep and nicotine avoidance.
Human Precision does not diagnose cognitive, cardiovascular or neurological conditions. Speak with a qualified health professional about symptoms, medication, nicotine dependence or major lifestyle changes.