When you lift weights for a long time, some muscles like your chest can grow bigger than they do right after a workout, but this doesn't happen with your arm muscles like biceps.

Your muscles can actually swell up bigger right after just one workout than they do after training consistently for several weeks.

Scientists aren't sure if the temporary muscle puffiness you get after working out is a good sign that your muscles will actually grow bigger over time. It might work for some muscle groups but not others, so we need more studies to figure this out.

After really intense arm exercises that strain the muscles, some people can get serious swelling that lasts over two weeks, spreads down to the hand because of gravity, and gets so big it shocks both the person and doctors who don’t expect it from just working out.

When trained men do strength exercises, their muscles get about 13.5% bigger right after because they fill with fluid. Certain workout styles make this happen more than others.

When you first start lifting weights, your muscles might look bigger right away—but that’s mostly because they’re swollen from tiny tears and fluid buildup, not because they’re actually growing stronger or larger for good.