When untrained young men lift weights until they can't anymore three times a week for six weeks, and they do the same total amount of work, their muscles grow about the same amount whether they lift heavy or light weights.

When untrained young men lift weights until they can't anymore, both heavy and light weights make their muscles grow about the same amount (6% bigger) if they do the same total work. This goes against the common belief that heavier weights are always better for muscle growth.

Lifting weights until you can't do any more reps, whether with light or heavy weights, makes muscles grow bigger in fit young men after 8 weeks. It shows that pushing to your limit is what really matters for growth, not how heavy the weights are.

If you lift weights until you can’t do another rep—whether you use heavy weights or light ones—you’ll end up with about the same muscle growth after nine weeks, as long as you’re putting in the same effort and number of reps.

If you're a guy who already works out regularly, doing 5, 10, 15, or even 20 sets of exercises per muscle group each week won't make your muscles grow any bigger than the others—after 6 months, they all end up looking about the same.

If you're already fit and lift weights, doing 5 to 20 sets of exercises for each muscle group every week won't make you grow bigger muscles any more or less than any other number in that range.