Doing exercises where you push the weight up (concentric) makes more muscle repair cells grow than doing exercises where you lower the weight slowly (eccentric), at least in young men training for 12 weeks.

When you lift weights or put extra stress on your muscles, tiny repair cells called satellite cells usually wake up and get busy—this helps your muscles grow bigger, but sometimes muscles can still grow even if these cells don’t activate.

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.

Lifting weights slowly (eccentric) or quickly (concentric) both make your quads stronger in about 10 weeks — and you don’t need to be sore or damaged to 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.

Some people get much stronger and build more muscle from weight training than others—this might be because their muscle cells grow more new nuclei, but not every study agrees on this.