Even though people who swing weights use their whole body more, their upper arms don’t get any thicker than those who lift strictly—so the extra movement doesn’t help build more arm muscle.

When beginners do arm curls and triceps exercises with a little swing to lift heavier weights, their arms grow just as much as when they do the movements slowly and strictly—even though they lift way more total weight with the swing.

Even if you cheat a little to lift heavier, your muscles still grow just as well—so maybe the key to building muscle isn’t perfect form, but just getting your muscles to work hard enough.

People who’ve never lifted weights before gain muscle much faster than those who’ve trained before—even if they do the same workout.

People grow muscle at very different rates — but each person tends to grow their arms and legs similarly, no matter what weight they use. This means your genes and biology matter more than how heavy your weights are.

Some people’s muscles grow a lot with training, others don’t—but if one person’s arms grow, their legs usually grow similarly, meaning your body’s natural response is more important than which muscles you train.