Lifting heavy weights (80% of your max) makes your thigh and arm muscles grow much bigger than lifting light weights (20% of your max) when you do the same total workout over 12 weeks.

Lifting heavier weights (80% of your max) builds bigger muscles faster than lifting lighter weights (20% of your max) when you do the same total work, with thigh muscles growing about 20% more and arm muscles growing about 25% more after 12 weeks.

If you're a young man who already trains regularly, doing more sets with lighter weights for 6 weeks can make your thigh muscle grow a little bigger — but doing fewer sets with heavier weights won't make it grow at all.

Lifting weights at different effort levels (from light to heavy) all made muscles bigger and stronger in men over 12 weeks, but the lightest effort wasn't as good as heavier ones.

Your muscles don’t get bigger or smaller right after a single workout, no matter how hard or how many reps you do.

If untrained adult men lift weights twice a week for 8 weeks, doing 4-6 sets of 8-12 reps until they can't do any more, their upper arm muscles will get bigger - this is measurable with ultrasound or other imaging.