Muscular and Systemic Correlates of Resistance Training-Induced Muscle Hypertrophy

When people who’ve never lifted weights before start training, some gain just a little muscle—like half a kilo—while others gain a lot, up to three kilos, in about two to three months.

After working out with weights, the levels of certain hormones in the blood don’t predict whether a guy will gain more or less muscle over 16 weeks — so those hormones probably aren’t the main reason some people grow bigger muscles than others.

When young guys who’ve never lifted weights before train with weights for 16 weeks, those whose muscles develop more androgen receptors tend to grow bigger muscles—and this receptor increase might explain about a quarter of why some people grow stronger or bigger than others.

When young men lift weights, if a specific protein in their muscles gets activated strongly exactly 5 hours after working out, they tend to build more muscle over the next 4 months—so this protein spike might tell us who’s going to grow the most from training.

After a tough workout, your body releases a chemical called IL-6, and people who gain more muscle tend to have more of it—but it’s probably just a side effect, not the reason your muscles grow.

When young guys who don’t work out start lifting weights, their muscles grow more because of changes inside the muscle itself—like more hormone sensors and activation signals—rather than because of hormones floating in their blood.