Browse evidence-based analysis of health-related claims and assertions
Even though lifting weights makes your muscles bigger and more active, those changes don’t explain why you get stronger—meaning something else, like how your nerves coordinate movement, might be more important.
Mechanistic
You can’t just count how many reps you do to know if your workout is good enough — how long your muscles are under strain matters just as much, maybe more.
Descriptive
When people who’ve never lifted weights before train their chest and arms with the same total muscle tension time, the back part of their triceps (near the elbow) grows more than the middle or shoulder-end parts.
When two different ways of lifting weights are adjusted so that the total time your muscles are under strain is the same, both ways lead to about the same strength gains and muscle growth in people who haven’t trained before.
The link between muscle mass or calorie burn and how much you eat gets weaker the older you get.
Correlational
How much fat a person has doesn’t seem to affect how much they eat, but how much muscle they have or how many calories they burn does.
Older adults who burn more calories each day tend to eat more, but this link gets weaker as they get older.
Older people with more muscle tend to eat more, but this link gets weaker as they get older.
When people eat more protein, their blood shows higher levels of a waste product called urea, which means their body is breaking down more protein than when they eat more carbs.
Causal
When people eat more protein and fewer carbs, their bodies hold onto more protein instead of breaking it down and losing it, which means they’re building or maintaining muscle better.
Eating a diet high in protein and low in fat makes your body burn about twice as much energy after meals compared to eating a diet high in carbs and low in fat.
Even if your hormones spike a lot right after your first few workouts, that doesn’t mean you’ll grow more muscle or get stronger later on.
Whether you rest 1 minute or 2.5 minutes between sets, your strength gains in squat and bench press end up being about the same after 10 weeks of training.
If you rest longer between weightlifting sets (2.5 minutes instead of 1 minute), your arms grow bigger over 10 weeks — even if your strength doesn’t change.
When you lift weights and rest only 1 minute between sets, your body releases more stress and sex hormones right after the workout — but only at the very start; after a few weeks, this effect goes away.
If you want to get stronger at squats, doing squats is way better than doing leg extensions — but if you want to get stronger at leg extensions, both exercises work about the same.
Squats make the outer thigh muscle bigger near the knee more than leg extensions do, but both exercises build it similarly higher up on the thigh.
Doing leg extensions for 8 weeks makes the front thigh muscle bigger along its whole length more than doing squats, especially near the knee.
To grow your quads, biceps, and triceps best, it helps to stretch the muscle more during exercise—either by going all the way down or starting the movement early.
When you squat or move your legs wide, using a full motion helps your butt and inner thighs grow more than only doing the top half of the movement.
Doing exercises through a full motion or starting the movement with a shorter motion (but not ending with it) helps your muscles grow more in your thighs and biceps than doing only the last part of the movement.
The way your muscles fire when you do leg presses vs. leg extensions matches up with which muscles end up growing bigger after training.
Leg presses make your butt and inner thigh muscles bigger, but leg extensions don’t affect those muscles at all.
Doing leg presses and leg extensions for 12 weeks both make your main thigh muscles bigger in about the same way, but only leg extensions make the front part of your thigh (rectus femoris) grow significantly.