Health Claims

When people who already work out do a type of lifting where the resistance changes during the movement, their muscles send out a stronger 'grow' signal right after — but that doesn’t mean they end up bigger than if they did regular lifting.

Mechanistic

If you're already fit and lift weights regularly, adding variety to your workouts or sticking to the same routine won't noticeably change the number of special muscle repair cells or their nuclei — your muscles stay pretty much the same on that front.

Descriptive

Even when you train one leg differently from the other, both legs tend to grow muscle in similar ways — which means your body’s natural biology, not the workout itself, is what really controls muscle growth.

Correlational

If you're already used to lifting weights, mixing up your routine—like changing how heavy you lift, how many reps you do, or how long you rest—won't make your muscles grow any bigger than sticking to the same routine. Both ways work about the same.

Descriptive

You don’t need to be sore after a workout to build muscle—some workouts cause less soreness but still make you just as strong and muscular as the super-painful ones.

Causal

When you first start lifting weights, your muscles get tiny tears — and the protein your body makes right after working out is mostly used to fix those tears, not to make your muscles bigger yet.

Mechanistic

You can't really grow bigger muscles until you've done about 18 weightlifting sessions—your body needs time to adapt before it starts building real muscle.

Quantitative

After about 10 weight workouts, your muscles don’t just look puffy from water anymore—they actually start getting bigger because the muscle fibers themselves are growing.

Mechanistic

When you first start lifting weights, your muscles might look bigger right away—but that’s mostly because they’re swollen from tiny tears and fluid buildup, not because they’re actually growing stronger or larger for good.

Mechanistic

When healthy young men do a tough new workout that involves lowering weights slowly (like lowering a dumbbell), their muscles get sore and some blood markers go up, but within five days, everything goes back to normal—even if they’ve never done that workout before.

Descriptive

If you train by lowering weights slowly (eccentric), you’ll get stronger at lowering weights; if you train by lifting weights up (concentric), you’ll get stronger at lifting them up — and this happens no matter how sore your muscles get.

Causal

If you do the same tough muscle workout (like lowering weights slowly) once a week for 10 weeks, your muscles stop getting sore and stop showing signs of damage—even compared to easier workouts—because your body gets used to it.

Quantitative

Lifting weights slowly (eccentric) or quickly (concentric) both make your quads stronger in about 10 weeks — and you don’t need to be sore or damaged to get stronger.

Causal

When you do a new, super tough workout that stretches your muscles (like lowering weights slowly), your body gets sore and inflamed—but if you do it again every week for 10 weeks, your muscles adapt and don’t get as damaged. The key isn’t the type of movement, it’s that your body wasn’t used to it.

Causal

Men with a lot of belly fat tend to have higher stress hormone levels during the day, but their nighttime levels stay normal—like their body’s stress clock is out of sync.

Correlational

When obese men lose weight, a specific gene in their fat cells called 11β-HSD-1 becomes less active — and this seems to happen because they’re losing fat, not because the gene caused them to gain weight in the first place.

Mechanistic

When obese men lose weight by dieting, their body doesn’t make less cortisol overall—but because they still have some fat left, the cortisol they do have is now more concentrated relative to that fat, which might trick their body into putting fat back on, especially around the belly.

Mechanistic

In men, having more of a certain gene (11β-HSD-1) active in their belly fat is linked to carrying more overall body fat, more fat around the organs, and worse blood sugar control—but it’s not just about belly fat, it’s tied to fat everywhere.

Correlational

In older men, having more of the stress hormone cortisol floating around in the blood is linked to more belly fat and worse blood sugar control—even if they’re not overweight overall—suggesting stress might be quietly hurting their metabolism.

Correlational

When you don't eat for about 3.5 days, your body switches to burning fat for energy—so it stops listening to the hormone that tells fat cells to stop breaking down, and starts listening more closely to the hormone that tells them to break down faster.

Mechanistic

When you fast for a long time, your body becomes super sensitive to a stress hormone called epinephrine that tells fat cells to break down—but this doesn’t happen because there’s more of the hormone in your blood; it’s because your fat cells just get better at responding to the same amount.

Mechanistic

When healthy adults don’t eat for 3.5 days, their bodies start breaking down fat for energy—even though the usual fat-burning hormones and blood sugar levels stay pretty much the same.

Mechanistic

When you fast for 3.5 days instead of just a day and a half, your body becomes more sensitive to the 'fat-burning' signal from adrenaline—even if the adrenaline level in your blood is exactly the same. It's like your fat cells get better at listening to the fat-burning command.

Mechanistic

When you go without eating for 3.5 days, your body starts releasing more fat into your bloodstream than after just a half-day fast—even if your insulin levels are the same—because your fat cells become less responsive to insulin’s ‘stop releasing fat’ signal.

Mechanistic