Browse evidence-based analysis of health-related claims and assertions
Lifting heavier weights (fewer reps) leads to bigger strength gains than lifting lighter weights (more reps), even if both are done until exhaustion.
Causal
Whether you lift light weights with lots of reps or heavy weights with few reps—so long as you push until you can’t do another rep—you’ll build muscle about the same amount.
Even people in their 50s and 70s can get much stronger and activate their muscles better after 12 weeks of heavy weight training — age doesn’t stop them from improving.
Descriptive
Whether you train both legs together or one at a time, your thigh muscles grow about the same amount after 12 weeks of heavy lifting.
Quantitative
People who train both legs together show bigger increases in muscle electrical activity during double-leg lifts than those who train one leg at a time, suggesting their nervous systems become more active during those movements.
When people train one leg at a time, that leg gets much stronger than the other leg, even if the other leg didn’t do any training.
Doing leg exercises with both legs at the same time for 12 weeks makes you stronger at lifting with both legs together, while doing them one leg at a time makes you stronger at lifting with each leg separately.
The outer part of your calf and the deeper calf muscle don’t grow better with either straight-knee or bent-knee calf raises — they respond similarly to both.
Not all parts of your thigh and calf muscles grow the same way — some parts grow better with certain exercises, so doing different types of lifts can help you build muscle more evenly.
Doing calf raises with your knees straight (standing on toes) makes the inner part of your calf muscle grow more than doing them with your knees bent (seated), because the muscle is stretched more.
Pushing a heavy leg press machine makes the outer part of your thigh muscle grow more than doing leg extensions, because it puts more overall stress on that part of the muscle.
Doing leg extensions (kicking your leg out while sitting) makes the front thigh muscle right above your knee grow more than doing leg presses (pushing a heavy platform with both legs).
There are only a few small, short studies on this topic, and many didn’t even track whether people stuck to their workout plans — so we can’t trust the results very much.
Even if you lift light or heavy weights, if you push until you can’t do another rep, your muscles end up using nearly all the same fibers — so they grow similarly.
Mechanistic
One study with women showed a much bigger muscle growth difference than the others — all of which were only with men — suggesting sex might matter, but we need more studies to know for sure.
All the studies looked only at leg muscles in young people — we don’t know if the same results apply to arms, women, or older adults.
Whether you lift light weights or heavy weights until you can’t do another rep, your muscle fibers don’t seem to grow significantly more with one than the other — but we can’t be sure because the results are too uncertain.
Just because one exercise makes your muscles 'fire' more during the first workout doesn’t mean it’ll make them grow more over time—muscle activation during a single set doesn’t tell you what will work best for building muscle.
Whether you train with squats or hip thrusts, you’ll get just as better at deadlifts and pushing against a wall—both exercises improve real-world leg strength equally.
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 makes you better at the exact movement you practice.
Squats make your thighs bigger—especially the front and inner muscles—while hip thrusts don’t really change your thigh size, making squats better if you want to build overall leg muscle.
Doing hip thrusts or squats for nine weeks, with the same total amount of work, makes your butt muscles grow just as much—so neither exercise is clearly better for building glutes if you're new to lifting.
When you lift weights, your body’s protein-making response doesn’t change much from week to week — but it’s very different from person to person.
Just because your muscles get bigger from lifting weights doesn't mean you'll get much stronger — the two don't really go hand in hand.
Correlational