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 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.

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.

When untrained young men lift heavy weights (80% of their max), their muscles and nerves become more efficient at lighter tasks, needing less effort over time. Lifting lighter weights (30% of max) doesn't give this same benefit.

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.

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.