Browse evidence-based analysis of health-related claims and assertions
Deep squats make young tennis players explode off the ground faster than shallow squats—after 8 weeks, they get about 20% faster at pushing heavy weights quickly, while shallow squats only help by 10%.
Causal
Deep squats don’t make leg muscles bigger than shallow squats if you do the same number of reps and same weight—muscle growth is about total work, not how deep you go.
For young tennis players, doing deep squats instead of shallow ones for 8 weeks makes them faster and stronger when pushing off the ground, and helps them lose body fat—without making their leg muscles bigger than shallow squats do.
The way your muscles fire when you do leg presses vs. leg extensions matches up with which muscles end up getting bigger after training.
Descriptive
People who do CrossFit might jump a little higher than weightlifters, but the difference is so small it could just be random chance.
Correlational
Whether you do CrossFit or lift weights regularly, your thigh muscles end up about the same size after years of training.
People who do CrossFit, lift weights, or just stay active all generate about the same peak power when jumping — no one group is significantly stronger or more explosive.
People who do CrossFit-style workouts can jump higher than regular active people, but they don’t jump noticeably higher than people who lift weights regularly.
People who have been doing serious workouts like CrossFit or weightlifting for years have bigger leg muscles than people who just stay active without formal training.
Just eating more protein doesn’t make you less hungry — but if you take out carbs and add fat instead, you feel much less hungry.
If you eat a high-protein, no-carb diet for two days, your body starts making a lot of ketones — enough to be in ketosis. But if you eat carbs with the same protein, you don’t.
Whether you eat a high-protein diet with carbs or without carbs, your body burns about the same number of calories — carbs don’t make you burn more energy.
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.
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.
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.
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.