When untrained young men lift weights until they can't lift anymore, their calf muscles grow bigger by 7-14%, no matter how heavy the weights are. This shows that pushing hard is what makes muscles grow, not how heavy the weight is.

When untrained young men lift lighter weights many times until they can't lift anymore, it builds just as much muscle in their calf muscles as lifting heavier weights fewer times. Both ways made their muscles about 10% bigger after 8 weeks.

If you do push-ups or bench presses with light weights until you can't do another rep, twice a week for two months, your arms and chest will grow just as much — so push-ups can be just as good as gym machines for building muscle, if you push yourself just as hard.

When people lift weights until they can't anymore, their muscles grow just as much whether they use heavy or light weights, as long as they push to their max. This shows that how hard you try matters more than how heavy the weights are.

When lifting lighter weights, you need to push until you can't do any more reps to build as much muscle as lifting heavy weights. But with heavy weights, you can build a lot of muscle without pushing to total exhaustion.

You can build muscle just as well lifting light weights as heavy ones — as long as you push yourself until you can’t do another rep.