If you're a young adult and you lift weights for 8 weeks—whether you use free weights like dumbbells or machines at the gym—you'll end up with about the same muscle growth and strength gains in your arms and legs, no matter which one you pick.

If you lift weights using machines, you'll get stronger on those machines more than if you use free weights—your strength gains depend on what equipment you train with.

Whether you lift weights the old-fashioned way or use machines, you’ll gain the same amount of strength and muscle size—if you’re doing the same exercises and you’re a healthy adult between 18 and 60.

Lifting free weights and using weight machines both help you build muscle in about the same way—neither one is clearly better than the other.

Doing push-ups with light weights until you can't do more doesn't make your biceps bigger, but doing the same kind of light-weight bench presses does — so your arms respond differently to these two exercises.

When beginners do arm curls and triceps exercises with a little swing to lift heavier weights, their arms grow just as much as when they do the movements slowly and strictly—even though they lift way more total weight with the swing.