Browse evidence-based analysis of health-related claims and assertions
Doing bicep curls with two different methods—either lowering the weight gradually or keeping it heavy—both made the upper arm muscles thicker in young women after 12 weeks of training.
Descriptive
Only five small studies were used, with just 120 people total — so the results are too shaky to be very confident about.
We can’t say whether light or heavy weights are better for growing muscle fibers in the thighs — we just don’t have enough good data yet, and we need more studies with more people.
Even if you lift light weights, if you go until you can’t do another rep, your muscles end up using almost all the same fibers as if you lifted heavy — which might be why both ways make muscles grow similarly.
Mechanistic
One study with women showed a big difference in muscle growth between light and heavy weights — when it was removed, the overall result became much smaller, hinting that men and women might respond differently.
Quantitative
The studies weren’t perfect, but they were decent quality overall — so the results aren’t likely wrong just because of bad methods, even if they didn’t track who stuck to the workouts.
We don’t know if most people actually stuck to their workout plans — only one study checked, so we can’t be sure the results reflect what really happened during training.
Most of the people in these studies were young men who didn’t lift weights before — so we don’t know if the results apply to women, older people, or bodybuilders.
All the studies looked only at thigh muscles — so we don’t know if the same results would apply to arms, shoulders, or calves.
We just don’t know yet if light or heavy weights make muscles grow better — the results could swing either way in future studies, so we need more research.
Lifting light or heavy weights until failure doesn’t clearly make your fast-twitch muscle fibers bigger in your thighs — the data is too mixed to say one is better.
Whether you lift light weights or heavy weights until you can't do another rep, your slow-twitch muscle fibers in your thighs grow about the same amount — but we can't be sure because the results are too uncertain.
Even though exact numbers aren’t given, the researchers noticed that rest-pause training seemed to help people get a bit stronger than regular training, just not by a lot.
No matter which way you train—rest-pause, drop sets, or regular sets—if you do the same total amount of work for 8 weeks, your upper and middle thighs grow about the same.
After 8 weeks of any kind of weight training, the lower part of the thigh doesn’t get noticeably thicker—even though the upper and middle parts do.
When people who already lift weights do drop sets or rest-pause sets instead of regular sets—while doing the same total amount of work—they don’t get bigger thigh muscles any faster or more than with normal training.
Causal
If you're already experienced with weightlifting, doing rest-pause sets (short breaks between reps) for 8 weeks might help you lift a little more weight in squats than doing regular sets, but not better than drop sets.
If you lift weights twice a week for 8 weeks and do the same total amount of work, your upper and middle thighs will get thicker — no matter what fancy technique you use.
When people do the same total amount of lifting work, whether they use rest-pause, drop-sets, or regular sets, their upper and middle thighs grow about the same.
The lower part of your thigh doesn't get noticeably thicker no matter which kind of weight training you do, if you're already trained and train for 8 weeks.
If you do your workouts with either drop sets, rest-pause, or regular sets — but do the same total amount of work — your muscles grow about the same size in your thighs.
Doing short bursts of heavy lifts with brief rests in between can make you stronger in squats a little more than doing regular sets, if you're already trained and doing the same total amount of work.
When you lift a weight you can do 15 times, for 5 sets of 10 reps, your body’s energy burn depends mostly on how much muscle you use and how tired you get—not how fast you lift or how heavy the weight is relative to your max.
To know how many calories you burn during a weightlifting session, you have to measure your breathing for at least 90 minutes after you finish—most of the burn happens after you’re done lifting.