Even if you lift the same weight every time without making it heavier, your arms can still get noticeably bigger in just two months — at least when you're just starting out and you're a young woman.

Even if you don’t lift heavier weights over time, just doing regular arm workouts for 8 weeks can make your triceps muscles noticeably bigger—way more than just sitting around.

If you're a young woman just starting weight training, slowly lifting heavier weights over time will make your triceps (the back of your arms) grow about twice as much as just doing the same workout over and over.

If you do push-ups or bench presses with light weights until you can't do another rep, twice a week for two months, your arms and chest will grow just as much — so push-ups can be just as good as gym machines for building muscle, if you push yourself just as hard.

This claim says that lifting lighter weights until you're tired, done regularly for six weeks, can build muscle just as well as lifting heavier weights. It specifically found growth in arm and chest muscles, showing you don't always need heavy weights to get stronger.

When untrained young men lift lighter weights many times until they can't lift anymore, it builds just as much muscle in their calf muscles as lifting heavier weights fewer times. Both ways made their muscles about 10% bigger after 8 weeks.