Health Claims

If you're already used to lifting weights, using free weights or machines won't make a noticeable difference in how much stronger you get or how fast you can push the weight after 8 weeks of training.

Descriptive

If you're a young guy who already trains regularly and you spread your protein across either three or five meals a day — as long as the total protein is the same — you'll likely gain about the same amount of muscle and strength either way.

Correlational

If you lift weights and eat lots of protein, you’ll likely build more muscle and get stronger than if you just do one or the other—because together, they work better than alone.

Correlational

When you lift weights, your muscles release special signaling molecules that might help your body build bigger muscles and get stronger overall.

Correlational

People who do strength training like lifting weights may live longer because studies show they’re less likely to die from any cause compared to those who don’t.

Correlational

If you lift weights and eat more protein, you’ll likely build bigger muscles and get stronger than if you just lift weights without eating extra protein.

Mechanistic

Lifting weights helps people build bigger, stronger muscles, probably because it makes their muscles produce more protein and release helpful signaling molecules that help them grow and work better.

Mechanistic

Even though leucine (a protein building block) turns on muscle-growth signals in the body, if you're already eating enough protein, taking extra leucine won't make you stronger, bigger, or recover faster.

Mechanistic

Taking leucine supplements won’t help healthy, fit young people build more muscle than taking a sugar pill, even if the supplement is strong enough to trigger a muscle-growth signal in the body.

Causal

Taking leucine supplements won’t make you stronger in the gym if you’re already a healthy, trained young adult lifting weights—even if you take up to 5 grams a day for a couple of months.

Causal

Taking leucine supplements won't help you recover faster from tough workouts if you're already fit and healthy — your muscles will bounce back just as well with a fake pill.

Causal

Taking extra leucine pills won’t help you build more muscle, get stronger, or recover faster from weight training if you’re already eating enough protein.

Causal

Whether you're a seasoned gym-goer or just starting out, lifting free weights and using machines are just as good for building strength and muscle—your experience level doesn’t make one better than the other.

Descriptive

Lifting free weights and using weight machines both make your muscles grow about the same amount if you're a healthy adult between 18 and 60—even though they feel different when you use them.

Descriptive

Using weight machines for upper-body workouts might help you get stronger faster than using free weights, but for legs, both methods work about the same—maybe because machines make it easier to focus on the muscles without worrying about balance.

Causal

If you lift weights with your own body and free weights, you'll get stronger at doing just that — not necessarily at using machines. And if you train mostly on machines, you'll get better at those machines. Your body learns the exact movement you practice.

Mechanistic

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.

Descriptive

Some people’s muscles grow way more than others when they lift weights, and this might be because their muscle cells make more of the tiny machines (ribosomes) that help build muscle protein.

Mechanistic

If you lift weights until you can’t do another rep, your muscles will grow about the same no matter how heavy the weights are—but you’ll get stronger faster if you lift heavier weights.

Quantitative

Lifting weights more often each week helps you build bigger muscles and get stronger, but after a certain point, you don’t gain much extra strength—though your muscles can still grow. If you keep the same total amount of lifting, doing it in more frequent, lighter sessions helps strength more than muscle size.

Correlational

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.

Causal

When you lift weights, it's the pulling force on your muscles—not the tears or burn—that makes them grow bigger, and scientists think a specific molecular signal inside the muscle cells is behind this growth; other things like soreness or muscle burn probably don't cause the growth on their own.

Mechanistic

Taking leucine supplements won’t help young athletes build more muscle, get stronger, or recover faster—even though leucine is known to trigger a muscle-growth signal in the body.

Causal

Taking 3 to 5 grams of creatine every day can help your muscles store more energy, making you stronger, more powerful, and better at building muscle when you lift weights—without making you gain fat.

Causal