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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.
Descriptive
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.
Quantitative
What matters most for burning calories during weightlifting is whether you’re using big muscles like legs or small ones like chest—not how long you rest or how fast you lift.
You breathe the hardest not when you’re lifting, but right after you finish a set and are resting—your body is catching up on oxygen debt built up during the effort.
How long you rest between sets doesn’t usually change how long your body keeps burning calories after a workout—unless you do chest flys with long breaks, then it stops sooner.
Your body burns more calories after leg presses than after chest flys—even if you rest the same amount—because your legs use way more muscles and need more oxygen to recover.
Right after leg presses with only 1-minute breaks, your body gasps for air more intensely in the first minute than if you took 3-minute breaks—but this doesn’t happen with chest flys.
Whether you rest 1 minute or 3 minutes between sets, you burn about the same total calories—rest time doesn’t change your overall energy burn in these workouts.
After lifting heavy with your legs, your body keeps burning extra calories for about 40 minutes—but after doing chest flys with long breaks, it only lasts 20 minutes.
Doing leg presses burns way more calories than doing chest flys—even if you do the same number of reps—because your legs use more muscles and keep burning energy longer after you finish.
When doing leg presses, taking only 1 minute of rest between sets makes you breathe harder overall than taking 3 minutes, but this doesn’t happen when doing chest flys—your body handles short breaks better when using smaller muscles.
When you’re just starting out, how much total work you do matters more than how long you rest between sets—your muscles grow and get stronger either way.
Correlational
This study only looked at beginners doing one leg at a time, so we can’t say for sure if the same results would happen to experienced lifters or people training both legs together.
You don’t need long breaks between sets to get strong—just do the same total amount of work, even with short rests, and you’ll get just as strong.
The study used high-tech scans (MRI) to measure muscle growth in specific parts of the thigh, making the results more accurate than just guessing from body measurements.
If you take only 20 seconds between sets, you have to do way more sets to match the same total weight lifted as someone taking 2-minute breaks, making your workout longer and more intense.