The twenty-minute rule

Most advice about exercise assumes you have an hour, a gym and a change of clothes. Most students have none of these on a school day.

That is why researchers keep returning to a smaller number: twenty minutes. Twenty minutes of moving hard enough to breathe faster is long enough to raise your heart rate, improve how you sleep, and sharpen attention for the next lesson. It is also short enough to fit into a break, which is the part that matters. A plan you can follow on a bad day beats a plan you follow only on good ones.

The second idea is that the twenty minutes do not have to arrive together. Three bursts of seven minutes bring most of the same benefit. Walking quickly up four flights of stairs counts. So does standing up every half hour during homework, which sounds too small to matter until you add up a week.

What does not work is the weekend repair job. Sitting still for five days and then playing football for three hours on Sunday leaves the body less prepared, not more, and carries a higher chance of injury. The body responds to how often you move, not to how impressive a single session looks.

None of this is a reason to stop playing sport properly. It is a reason to stop treating twenty minutes as too small to bother with. For a student with a crowded timetable, twenty minutes is not the compromise. It is the whole plan.