Even if you lift heavier weights with your muscles mostly bent, you don’t grow bigger muscles than if you lift lighter weights with your muscles stretched out — the stretch matters more than how heavy the weight is.

Just stretching your muscle under light weight won’t make it grow — you need to push hard while it’s stretched out, like doing a bicep curl slowly at the bottom where it’s fully extended.

Lifting weights when your muscles are stretched out more (like at the bottom of a squat or a full bicep curl) tends to make them grow bigger than lifting with your muscles mostly shortened, as long as there's still resistance pushing back when they're stretched.

Doing a full squat or starting a bicep curl from the bottom makes your muscles grow more at the far ends (like the top of your thigh or the outer part of your bicep) than doing partial reps from the top.

When you stretch your muscles fully during workouts, the ends of the muscles grow more than the middle parts — the stretch makes the muscle ends bulk up more than the center.

If you lift light weights but push them until you can't do another rep, you can grow your muscles just as much as someone lifting heavy weights—so long as you're putting in the same total effort.