We don't really know for sure if doing exercises with more or fewer reps left in the tank helps you build more muscle, because scientists are just guessing how many reps people had left based on how the studies were written.

When you lift weights and push yourself almost to the point of not being able to do another rep, you’re more likely to build bigger muscles than if you stop earlier — even if you’re lifting the same weight or doing the same number of sets.

Progressive increases in strength within the 6–12 repetition range under consistent training conditions are a reliable proxy for skeletal muscle hypertrophy.

When healthy adults lift weights, doing more sets each week and focusing on slowly lowering the weight helps build bigger muscles.

If you get much stronger—like more than 20% stronger—on an exercise you’ve been doing for a long time, it probably means your muscles got bigger, not just your brain getting better at telling your muscles to work harder.

Whether you lift weights slowly or quickly, you’ll likely gain about the same amount of muscle—so don’t stress over the speed, just keep lifting.