People who want to get stronger might need to train differently than people who want to build bigger muscles, but we don’t have good ways to measure how close to failure they should go—so right now, it’s hard to give clear advice on how to train for each goal.

When young adults train really hard until they can’t do another rep, it doesn’t matter whether they’re working their arms, legs, or doing squats vs. bench presses — the results for muscle growth and strength stay pretty much the same.

When lifting lighter weights, pushing until you can't do any more reps helps build more muscle than stopping early. But with heavier weights, pushing to failure doesn't give much extra muscle growth compared to stopping a bit sooner.

Lifting lighter weights really close to failure might build muscle just as well as lifting heavy weights, but the evidence isn’t strong enough to say for sure — it might depend on how you combine weight and effort.

When lifting lighter weights, pushing until you can't lift anymore helps build bigger muscles, but this doesn't happen with heavier weights. Heavier weights always build more strength than lighter ones, no matter how hard you push.

When you lift weights close to your limit, your muscles grow bigger better if you leave a few reps in the tank—but that same closeness doesn’t help you get stronger as much, which suggests your body builds muscle and strength in different ways.