When young guys who don't work out do leg exercises until they can't do any more for 10 weeks, lifting lighter weights and heavier weights both build muscle about the same amount.

If you're new to lifting and using light weights, you need to push your muscles until they can't do another rep to grow them bigger—otherwise, even doing more reps won't help.

If you're lifting heavy weights, you don't need to push to absolute exhaustion to grow your muscles—stopping just before failure works just as well, as long as you're lifting heavy enough.

If you lift light weights but push them until you can't do another rep, you can grow your muscles just as much as someone lifting heavy weights—so long as you're putting in the same total effort.

When guys who’ve never lifted weights before train their legs for 15 weeks, the more their muscles grow, the stronger they get—so muscle growth is mostly why they get stronger.

When guys who’ve never lifted weights before start training their legs for 15 weeks, the more their thigh muscles grow, the stronger they get—so muscle growth is probably why they’re getting stronger, not just better at lifting.