Effects of 4, 8, and 12 Repetition Maximum Resistance Training Protocols on Muscle Volume and Strength.

If you do the same total amount of lifting, whether you lift heavy weights for fewer reps or lighter weights for more reps, you'll build about the same amount of muscle as a beginner.

If you do the same total amount of weightlifting work, lifting heavy weights a few times or lighter weights more times gives about the same muscle growth in the chest for beginners doing bench press, showing that the total work matters more than how many reps you do.

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 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.

Lifting weights in a certain way (doing 4 sets of 8 reps) gives the same muscle and strength benefits as another method (7 sets of 4 reps) in young men who are new to training, but it takes almost half the time per workout.

When untrained young men lift weights with different heavy loads but equal total work, their chest muscles grow about the same amount—around 10-11% bigger.