Lifting heavier weights is much better than lifting lighter weights for building muscle strength in healthy young adults, because it trains your muscles and nerves to work together more effectively for maximum power.

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.

Lifting heavier weights (fewer reps) leads to bigger strength gains than lifting lighter weights (more reps), even if both are done until exhaustion.

If you're a healthy young adult lifting weights, lifting heavier weights (fewer reps) helps you get stronger faster than lifting light weights (more reps), but lifting medium weights works almost just as well as heavy weights — the difference isn't big enough to say for sure.

Lifting heavy weights until you can't lift anymore makes young male athletes much stronger than lifting light weights over 8 weeks, even if both make muscles grow about the same size.

Older adults doing light weight lifting twice a week for 12 weeks can get about 20% stronger, even if they don't push themselves to their absolute limit every time.