Browse evidence-based analysis of health-related claims and assertions
When young men did leg extensions with a slow upward motion and drank a protein shake right after, their fast-twitch muscle fibers got noticeably bigger—but this didn’t happen if they did the slow downward motion or drank sugar water instead.
Correlational
Doing exercises where you push the weight up (concentric) makes more muscle repair cells grow than doing exercises where you lower the weight slowly (eccentric), at least in young men training for 12 weeks.
Which leg exercise you choose matters: leg extensions grow the front thigh muscle more, squats grow the lower outer thigh more and make you stronger at squats—but both help you get stronger at leg extensions.
Causal
Even if you only do squats, you still get almost as strong at leg extensions as someone who only does leg extensions—so squats aren’t useless for that movement.
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 lower part of the outer thigh muscle grow more than leg extensions do, probably because squats involve more hip and knee movement together.
Doing leg extensions makes the front thigh muscle grow more evenly along its length than doing squats, which don’t stimulate that muscle as much.
The side muscle of your thigh doesn’t grow any more with drop sets than with regular sets—no matter where you measure it.
Drop sets don’t make you do more reps or sets, but they let you lift heavier weights for more total work—which is probably why your muscle grows more in some spots.
Quantitative
When guys who never lifted weights before started doing leg workouts for 15 weeks, their thigh muscles got 12.7% bigger—and super-precise MRI scans proved it, showing this tech is great for tracking muscle growth.
When scientists look at how one person changes over time—like how their muscles grow and get stronger together—they find a super strong link. But when they compare different people to each other, that link looks much weaker.
When guys who’ve never lifted weights start training, most of their strength gains come from their muscles getting bigger—not from their brain and nerves getting better at telling muscles to work harder.
When guys who’ve never lifted weights before start training, the more their thigh muscles ‘fire up’ during max efforts, the stronger they tend to get—both in holding a heavy position and in lifting one heavy weight.
When guys who’ve never lifted weights before train their legs for 15 weeks, the more their muscles grow, the stronger they get—so muscle growth is mostly why they get stronger.
Single-leg lunges helped both legs get better at turning quickly, but double-leg squats only helped the stronger leg.
Both training methods made athletes jump higher and turn faster, but didn’t make them run straight-line sprints any faster.
Single-leg lunges helped athletes slow down better with their weaker leg after turning, more than double-leg squats did.
Both types of training made athletes stronger and more powerful, but squats with both legs made them significantly more powerful in the squat than lunges did.
Doing squats with both legs on a special machine for six weeks made the outer thigh and outer calf muscles grow more than doing single-leg lunges.
Doing single-leg lunges with a special machine for six weeks made the inner thigh and inner knee muscles grow more than doing regular squats with both legs.
How much your butt muscles 'fire up' during your first hip thrust or squat doesn’t tell you how much they’ll grow over time — the feeling during the workout isn’t a reliable guide to results.
Doing squats or hip thrusts helps you get stronger at deadlifts and pushing against a wall about the same amount — neither exercise gives you a big edge over the other for these other movements.
If you want to get stronger at squats, you need to squat; if you want to get stronger at hip thrusts, you need to do hip thrusts. Training one doesn’t make you much stronger at the other.
Squats build your thigh muscles (quads and inner thighs) more than hip thrusts do, because squats involve more knee and hip movement that engages those muscles more.