When beginners lift weights for 10 weeks, doing fewer reps with heavier weights (like 4 or 8 reps max) builds more strength than doing more reps with lighter weights (12 reps max), even if the total work is the same.

When men lift weights, doing more reps with lighter weights (like 12 reps max) gives less strength improvement than doing fewer reps with heavier weights (like 4 or 8 reps max), even if the total workout effort is the same.

Lifting heavier weights makes untrained men much stronger than lifting lighter weights over 8 weeks, even if both types of training are done until you can't lift anymore.

If you're a young guy who already lifts weights, doing workouts until you can't do another rep for 12 weeks will make your legs and shoulders just as strong whether you use light or heavy weights—but for the bench press, heavy weights make you stronger than light ones.

When people lift lighter weights many times (12 reps max), their muscles get bigger and that's why they get stronger. But when lifting heavier weights fewer times (4-8 reps max), their strength comes more from their brain and nerves learning to use muscles better, not from bigger muscles.

If you lift the same total amount of weight, lifting heavier weights (80% or more of your max) makes you stronger in a single big lift than lifting lighter weights—but lifting very light weights and light weights (under 60%) give you about the same strength gains.