For young men who are already fit and lift weights until they can't anymore, doing lots of lighter reps builds muscle just as well as doing fewer heavy reps over 8 weeks.

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.

Lifting lighter weights many times in a row helps well-trained young men do more push-ups longer than lifting heavier weights fewer times, after 8 weeks of training.

If young men lift weights for 15 weeks, their biceps get significantly stronger—by about 20%—no matter if their body releases extra muscle-building hormones during the workout or not.

Whether you use light or heavy weights, your muscles can grow about the same amount if you train hard enough—both methods work for building muscle size.

Lifting heavy weights to the point of exhaustion three times a week for six weeks makes untrained young men much stronger than lifting lighter weights, even though both types of training build similar amounts of muscle size.