When young guys who lift weights regularly do intense leg workouts for two weeks, those who gain more strength also tend to have bigger increases in their morning testosterone levels.

If young guys lift weights for 12 weeks, their muscle strength gains in the leg press don’t seem to be linked to how much their hormones spike right after each workout.

If young guys who lift weights do intense training every day for two weeks, their morning hormone levels might dip for a bit—but they bounce back within four days after stopping, so it’s just a short-term blip, not a long-term problem.

When young men lift weights for 12 weeks, their short-term spikes in testosterone and IGF-1 after workouts don’t seem to predict whether they’ll gain more muscle or get stronger.

If a guy who already lifts weights takes a high dose of testosterone for 10 weeks without working out, he’ll get stronger on the bench press and squat—meaning testosterone alone can make muscles stronger, even without training.

When young men do intense leg workouts, their body releases more lactate and cortisol—stress and energy chemicals—but that doesn’t mean they’ll grow bigger muscles or get stronger faster than if those chemicals stayed low.