If you're lifting weights to the point where your muscles are totally tired, it doesn't matter if you use barbells, dumbbells, or machines — you'll gain muscle just the same.

If you lift weights until you're almost too tired to do another rep, you'll likely build bigger muscles—but your strength gains won't be any better than if you stopped earlier, as long as you're doing the same total amount of work and lifting the same weight.

If you lift weights with machines or with free weights and do the same amount of work at the same effort level, you’ll build muscle just as well with either one — even if you’re already fit.

Doing more sets of weightlifting seems to build muscle more reliably than how close you get to failing on each set—whether you stop short or push to exhaustion doesn’t change the muscle growth much if you’re doing the same number of sets.

You can build muscle just as well lifting light weights as heavy ones — as long as you push yourself until you can’t do another rep.

Going all the way to exhaustion on every set probably doesn't build more muscle than stopping a few reps short — both seem to work about the same.