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.

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.

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.

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.

Even if your hormones spike after a tough workout, that doesn’t mean you’ll grow bigger muscles or get stronger over 12 weeks of training — the spike and the results don’t seem to go together.

Even if you lift heavy or light weights for 12 weeks, your body’s short-term hormone spike after each workout doesn’t change—and that means those hormone surges probably aren’t why your muscles get bigger or stronger over time.