Browse evidence-based analysis of health-related claims and assertions
Working out until you're exhausted might make your body release more growth hormone and testosterone, which could help your muscles grow — but we’re not sure if these hormones actually cause the growth.
Mechanistic
You can make your muscles grow bigger by lifting very light weights if you restrict blood flow to your arm or leg — it tricks your body into thinking you’re lifting heavy.
When you lift weights until your muscles burn and feel fatigued, the buildup of waste products might help your muscles grow bigger, but the main reason they grow is still from the physical force you're using.
Starting your workout with big lifts like squats and bench presses doesn’t make you stronger or change your body differently than starting with small lifts like leg extensions — as long as you train hard for 12 weeks.
Descriptive
No matter the order of exercises, people who were already trained got much stronger after 12 weeks of lifting — all groups improved a lot.
Doing isolation exercises before compound lifts (like leg extensions before squats) doesn’t make you stronger or change your body more than doing the lifts in a different order, as long as you’re already trained.
When athletes are trying to lose weight by eating fewer calories, eating more protein (about 2.3 grams per kilogram of body weight) helps them keep more of their muscle compared to eating less protein (about 1 gram per kilogram).
People with more active brown fat burn over twice as many extra calories after eating carbs as people with less active brown fat — this could explain why some people stay leaner even when eating the same food.
Quantitative
People with more active brown fat burn more calories after eating carbs — the more active their brown fat, the more energy they burn.
Correlational
Eating fatty foods doesn’t make your body burn many extra calories — and your brown fat doesn’t seem to help with it.
Eating a high-protein meal makes your body burn more calories afterward than eating carbs or fat — but this doesn’t depend on how active your brown fat is.
After eating carbs, people with more active brown fat keep burning extra calories for the full two hours afterward, not just right after the meal.
Some people have much more active brown fat than others—up to 10 times more—based on how much glucose their fat tissue takes up after cold exposure.
Just because CrossFit and weightlifters jumped about the same height doesn’t mean they’re equally powerful — the test might not have been sensitive enough to spot a real difference.
People who do CrossFit and people who lift weights end up with about the same size leg muscles after years of training — the type of workout doesn’t seem to change muscle growth much.
People who do CrossFit, lift weights, or just stay active all generate about the same peak power when jumping — no one group is clearly stronger or more powerful than the others.
The way your muscles fire when you do leg presses vs. leg extensions matches up with which muscles end up getting bigger after training.
People who do CrossFit-style workouts can jump higher than people who just exercise casually, but they don’t jump noticeably higher than people who lift weights regularly.
Leg presses make your butt and inner thigh muscles bigger, but leg extensions don’t affect those muscles at all.
Muscles don’t grow evenly — some parts get bigger than others, and different muscles in the thigh respond differently to the same exercise.
Causal
Drop sets make you lift more total weight, but that doesn’t mean you get stronger or bigger all over — just in one specific part of one muscle.
Drop sets don’t make the side muscle of your thigh bigger than regular sets — no matter where you measure it.
Even though drop sets make you do more total work, they don’t make you stronger than regular sets when you’re just starting out with leg extensions.
Doing leg extensions with drop sets (going to failure, then lowering the weight and going again) makes the front part of your thigh muscle bigger in the upper and middle areas, but not the bottom part or the side muscle.