Browse evidence-based analysis of health-related claims and assertions
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.
Correlational
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.
Descriptive
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.
Causal
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.
When untrained young men lift heavy weights three times a week for five months, they get much stronger—some exercises more than double their original strength.
Taking a little longer break between sets of weightlifting (more than a minute) might help your arms and legs grow slightly bigger, but the difference is so small it might not even matter in real life.
The common advice to rest 30–90 seconds between sets to build muscle might need updating — resting a bit longer (over a minute) might help a little, but not enough to be sure it’s worth changing your routine.
When measuring overall body muscle growth with scales that can’t tell muscle from water or bone, resting longer between sets doesn’t seem to help — and might even look worse than resting shorter, but that’s probably because the measurement isn’t accurate.
Whether you push your muscles to complete exhaustion or stop a few reps short doesn’t change how much rest you need between sets to grow muscle.
Resting more than a minute and a half between sets doesn’t seem to help your muscles grow any more than resting for about a minute — after that, extra rest doesn’t add benefit.
Taking a bit more than a minute between sets when lifting weights might help your arms and legs grow slightly bigger, but the difference is so small it might not matter much in real life.
Men and women gain muscle at roughly the same rate when they train the same way—women just start with less muscle, so they gain less in absolute numbers.
If you're new to lifting weights, you can expect to gain about 3 pounds of muscle in the first few months—but after that, gains get much slower, and you won't become a bodybuilder without drugs.
Muscles don’t grow bigger by filling up with water or energy stores—they grow by adding more contractile proteins that actually make you stronger.
Mechanistic
The burning feeling and muscle pump you get during a workout don’t make your muscles grow—those are just side effects, not the reason your muscles get bigger.
The spike in 'muscle-building hormones' after a workout doesn’t make your muscles grow bigger—your muscles grow because of the lifting itself, not the hormone rush.