Lifting light weights for nine weeks didn't make people stronger on a machine that tests muscle power at different speeds, and in fact, their performance slightly dropped — while heavy lifting kept their strength steady.

Both heavy and light weight training, done until exhaustion, didn’t change how hard participants could push or pull in a static muscle test after nine weeks.

If young, healthy guys lift weights for 12 weeks, their muscles get stronger at moderate speeds — like kicking or swinging — and they can generate 13% to 32% more force, no matter how they did the lifting.

Lifting heavier weights for nine weeks made young men stronger in a max lift test than lifting lighter weights, even when both groups worked until they couldn't do another rep.

If you lift heavy weights (85% of your max) instead of light ones (30% of your max) for nine weeks, you’ll get stronger on exercises like squats and deadlifts—even if your muscles don’t grow any bigger than if you’d lifted light weights.

Lifting heavier weights might help you get stronger a bit more than lifting lighter weights, but the difference is so small that we can’t be sure it’s real — it could just be luck.