Browse evidence-based analysis of health-related claims and assertions
When you eat a high-protein, no-carb, high-fat diet, your body starts burning more fat and produces a lot more ketones — a sign your body is switching to fat for fuel.
Causal
When you eat a high-protein diet with no carbs but lots of fat, you feel less hungry and more full than when you eat the same amount of protein but with some carbs.
Whether you stick to a fixed rest time or rest as long as you feel you need to, it doesn’t seem to make a big difference for building muscle.
Correlational
You don’t need to take shorter breaks to build muscle than you do to get stronger—both can be done with the same rest times if you lift the same amount of weight and do the same number of reps.
Even though short breaks between sets lower your testosterone-to-cortisol ratio, that doesn’t mean you’ll grow less muscle—this ratio doesn’t reliably predict muscle gains.
Mechanistic
Even though lifting weights with short breaks makes your body release more growth hormone, that doesn’t mean you’ll grow bigger muscles over time.
Taking longer breaks between sets of weightlifting doesn't hurt your muscle growth—you might even grow more muscle with longer breaks than with very short ones.
Both Nordic curls and stiff-leg deadlifts make your entire hamstring group bigger after 9 weeks of training—Nordic curls make them grow a bit more.
Descriptive
The study didn’t measure muscle growth at all — so saying these squats make muscles bigger is a guess, not a finding.
In stiff-leg deadlifts, the size of the biceps femoris muscle (back of the thigh) seems to matter more for getting stronger at other exercises—unlike the other hamstring muscles.
When you restrict blood flow to your thigh while squatting, your muscle gets much less oxygen — no matter how you move your knee.
Keeping your knees bent longer during squats (without locking them) makes your thigh muscle work harder and use up more oxygen than fully straightening your legs — especially when blood flow is restricted.
Even when your hamstrings get bigger from training, that doesn’t really predict how much stronger you’ll get at the other exercise—so bigger muscles don’t mean much more strength in this case.
Nordic curls make one part of your hamstring (semitendinosus) grow more, while stiff-leg deadlifts make another part (semimembranosus) grow more—so different exercises target different muscles in the same group.
Even short, locked squats (8 seconds) can make your thigh muscle very low on oxygen — but only if you keep your knees bent and restrict blood flow.
Doing two different hamstring exercises—Nordic curls and stiff-leg deadlifts—makes you stronger at both, even if your muscles don’t grow the same way, meaning muscle growth isn’t what’s making you stronger in the other exercise.
When you do squats without fully straightening your knees and restrict blood flow, your thigh muscle gets much less oxygen during the exercise than when you're just sitting still.
Legs get stronger faster than arms when you start lifting weights—arms take longer to catch up.
Quantitative
The common advice to rest only 30–90 seconds between sets to build muscle might need updating — longer breaks (over a minute) seem to help a little, but not enough to be sure it’s worth changing your routine.
Even though these guys lifted really heavy weights almost every day for five months, not a single one got hurt.
When measuring overall body muscle growth by weight (like with DXA scans), longer breaks between sets don’t help — and might even seem to hurt a little — probably because these scans can’t tell the difference between muscle and water or other tissues.
People get noticeably stronger in just 4 weeks of heavy weightlifting—even before their muscles get bigger—because their nerves learn to fire better.
Whether you push your muscles to complete exhaustion or stop a few reps short doesn’t change how much longer rest periods help your muscles grow — the benefit stays about the same either way.
Even though these guys got a lot stronger from lifting weights, their weight and body fat didn’t change much—they just got more muscle without losing fat.