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...

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.

Training one limb with resistance exercises can improve the speed at which the opposite, untrained limb generates force, without making the muscle bigger or stronger overall. This suggests the improvement comes from changes in how the nervous system controls the muscle, not from physical muscle growth.

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.

After four weeks of one-sided leg training with restricted blood flow, the opposite leg does not become stronger or develop larger muscles, even if the trained leg does.