When you lift heavy weights, your muscles get stronger partly because your brain learns to control them better, not just because the muscles themselves grow bigger. Lighter weights don't have the same effect.

When young guys who don't usually exercise lift heavy weights, their muscles get more efficient at using nerves to move, but this doesn't happen when they lift lighter weights.

When you lift heavy weights, your muscles get more efficient at using less energy for the same effort, while lifting lighter weights doesn't change much. It's like upgrading your muscles to work smarter, not harder.

Lifting heavier weights makes your brain and nerves work better to help you get stronger faster than lifting lighter weights, especially for guys who are new to working out.

Lifting heavy weights until you can't lift anymore makes young male athletes much stronger than lifting lighter weights over 8 weeks, showing that heavier loads train muscles and nerves better.

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.