Health Claims

If you're lifting weights and want to build muscle, eating at least 1.6 grams of protein per kilogram of your body weight every day is the most important thing — and eating even more protein (like 0.5 extra grams per kg) helps you gain a little more muscle on top of that.

Causal

If you lift weights the same amount and with the same effort, holding your muscles still (isometric) builds muscle just as well as moving them up and down (dynamic).

Quantitative

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.

Causal

If you lift weights until you can’t do another rep vs. stopping just before failure, you end up doing about the same total amount of work over eight weeks — same number of reps and same weight lifted.

Descriptive

If you lift weights until you literally can't do another rep, you'll feel more tired right after than if you stop a couple reps before failure — even if you're someone who regularly lifts weights.

Causal

If you're already used to lifting weights, training until you can't do another rep gives you about the same muscle growth as stopping a few reps short—so you don't have to push to absolute exhaustion to build muscle.

Causal

When you lift weights with your blood partially restricted, your muscles might produce certain chemicals that could help them grow—but scientists aren’t sure which chemicals or if they really cause growth yet.

Mechanistic

You don’t need to be sore after a workout to build muscle, but being sore might help you build a little more muscle—no one’s sure how much, if at all.

Mechanistic

Scientists think that two proteins, Filamin-C and BAG3, might act like a sensor in muscle cells that detects when the muscle is being stretched or worked hard, and then turns on or off other signals that help the muscle grow — but they’re not sure exactly how this works yet.

Mechanistic

When you lift weights, your muscles grow because of the physical pulling and stretching forces they feel—this is thought to be the main reason they get bigger.

Mechanistic

Lifting weights makes your muscles bigger, mostly because it turns on a special signal in your muscle cells that tells them to make more protein, but other things might help too.

Mechanistic

A lot of workout studies don’t have enough participants to notice small but real muscle gains in people who already lift weights, so their results might be confusing or wrong.

Descriptive

Scientists use tape measures and skin pinches to guess how much muscle people gain from weight training, but these methods aren’t precise enough to notice small muscle gains.

Descriptive

If you're already fit and lift weights, whether you do partial reps with the muscle stretched or full reps, you'll gain about the same tiny amount of strength after 12 weeks.

Descriptive

When people who already work out build muscle, they don’t get much bigger very fast, and the gains slow down over time—so to tell if one workout plan is better than another, you’d need to study a lot of people.

Descriptive

Doing partial-range weight exercises with a longer muscle stretch can build arm and thigh muscles just as well as doing full-range exercises, as long as you’ve been training for a while and do it for 12 weeks.

Quantitative

In fitness research, nearly half of the big summary studies ignored how reliable each individual study was and treated them all the same — even tiny, shaky studies got the same weight as big, solid ones, which can mess up the final conclusion.

Descriptive

When scientists combine results from lots of fitness studies, sometimes they get really big numbers—bigger than 3.0—and this claim says almost 6 out of 10 of those huge numbers are probably mistakes because they used the wrong math formula.

Quantitative

A lot of the most popular fitness studies only looked at how people improved on their own after a workout or supplement, not how they did compared to people who didn’t do anything — which might make those treatments seem way more effective than they really are.

Descriptive

A lot of big studies that combine other studies on strength and fitness didn’t properly handle cases where the same people were measured multiple times or when one study had several groups — this made their results look more precise and important than they really were.

Descriptive

In nearly half of the most popular science reviews on strength and fitness, researchers made a math mistake—they used the wrong number to calculate how strong an exercise or supplement’s effect was. This made the effects look way bigger than they really were, and most of the super huge effects (over 3.0) were just due to this error.

Quantitative

A big review found that in most top-rated studies about strength and fitness training, about 85% made at least one common math mistake—like using the wrong numbers to show results or including results that seem way too extreme.

Descriptive

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.

Descriptive

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.

Mechanistic