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.

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.

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.

When men who lift weights start training, doing more reps with lighter weights causes a bigger short-term boost in certain hormones compared to lifting heavy weights for fewer reps. But this hormone boost gets smaller the longer they keep training.

In guys who lift weights regularly, doing more reps with lighter weights and short breaks gives a bigger boost in growth hormone early on (by week 3) than doing fewer reps with heavier weights and longer breaks—but by week 10, that difference goes away.

If you're a guy who lifts weights, doing more reps with lighter weights (which spikes your hormones more) doesn't build more muscle or strength over 8 weeks than lifting heavier weights with fewer reps—even though the hormone changes look different.