When young and older men do short, super-intense bike or sprint workouts, the young guys get better at using oxygen during exercise, but the older guys don’t — their bodies just don’t respond the same way.

Older men in their 60s and 70s didn’t get better at using oxygen during exercise after three weeks of intense sprinting, but younger men did—so aging might make it harder for your body to improve aerobic fitness from short, intense workouts.

Short, intense bursts of exercise (like sprinting) can boost heart and lung fitness just as well as longer, steady workouts — and take way less time.

After just three weeks of short, intense bike or sprint workouts, older men between 63 and 72 got better at bouncing back from muscle tiredness caused by repeated hard exercise — their muscles recovered faster and felt stronger afterward.

Both short, intense sprints and steady, moderate workouts boost teenage boys' stamina just as much after six weeks — either way, their bodies get better at using oxygen.

For young adults who exercise a bit, doing a quick 9-minute sprint workout leads to bigger drops in muscle power—like how high you can jump or how strong your legs and arms feel—compared to other similar workouts using burpees or steady hard exercise.