Sprint athletes get a much bigger spike in their growth hormone after a hard 30-second sprint than endurance athletes do — their bodies react differently because of their training.

Doing really intense sprints gives your body a big, quick boost in growth hormone—up to 17 times more—which helps protect your muscles and burn fat.

When athletes do their hardest sprints, how fast they go and how much lactic acid builds up in their blood can explain most of why their growth hormone spikes — it’s closely tied to how intensely their body is working.

During prolonged exercise, the intensity of the workout and whether a person is a trained runner or not account for about one-third of the differences in how much growth hormone their body releases.

Men who regularly train for endurance sports show higher and longer-lasting increases in growth hormone during and after long workouts compared to men who do not train for endurance sports.

Even if your muscles get a big burst of growth hormone right after lifting weights, that doesn’t mean you’ll grow bigger muscles over time—some people who got way more of this hormone didn’t grow more muscle than others.