When young men do isometric leg exercises for 12 weeks, their thigh muscles get bigger—and that bigger muscle size helps explain about 1 in 5 of their strength gains, even if their nerves aren’t getting better at telling muscles to work harder.

If you're already fit and lift weights, doing 5 to 10 sets per muscle group each week will make you stronger—but doing more than that (like 15 to 20 sets) won't make you any stronger, no matter how hard you push.

If you're already fit and lift weights, doing anywhere from 5 to 20 sets per muscle group each week will make you stronger and build more muscle — and it doesn't matter much which number you pick within that range.

When guys who’ve never lifted weights before start training, their muscles get stronger partly because their brain gets better at telling the muscles to fire harder — but most of the strength gain still comes from the muscles actually getting bigger.

If you train a muscle three times a week instead of once, and you end up doing more total work, you’ll get stronger and bigger muscles—better than if you kept the same total work.

After doing 12 weeks of static strength exercises, whether your quadriceps muscle fibers change their angle doesn’t seem to affect how much stronger you get.