After just three weeks of short, intense bursts of running, older men had less of a biological marker in their blood that signals stress or damage in the body—this might mean their bodies are under less strain as they age.

After a super intense sprint workout, your body releases a tiny bit of DNA into your blood — and the more tired your muscles feel afterward, the more DNA shows up. This could mean that measuring this DNA helps doctors tell how hard your muscles were pushed.

When guys who work out regularly do a 12-week strength training program, the more they train, the more DNA floating in their blood goes up — and that might be a sign their body is dealing with hidden inflammation from overdoing it.

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.

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.