Browse evidence-based analysis of health-related claims and assertions
When guys who’ve never lifted weights before start training, their muscles get stronger partly because their brain gets better at telling the muscles to fire harder — but most of the strength gain still comes from the muscles actually getting bigger.
Correlational
When guys who’ve never lifted weights before start training their legs for 15 weeks, the more their thigh muscles grow, the stronger they get—so muscle growth is probably why they’re getting stronger, not just better at lifting.
People with a certain version of the ACTN3 gene bounce back faster after intense workouts that strain muscles, like downhill running, so they might be able to train more often without getting as sore.
Causal
Whether you have the 'speed gene' (RR) or not (XX), your muscles recover and stop getting as sore after doing jump training twice — your genes don’t change how well you bounce back.
Descriptive
People with a specific version of the ACTN3 gene (the R version) tend to get much more muscle sore and weak after jumping exercises and take longer to bounce back than people with the other version (the X version), like their muscles just can’t handle the stress as well.
Even if you don’t lift heavier weights over time, just doing regular arm workouts for 8 weeks can make your triceps muscles noticeably bigger—way more than just sitting around.
Quantitative
Even if you lift the same weight every time without making it heavier, your arms can still get noticeably bigger in just two months — at least when you're just starting out and you're a young woman.
If you're a young woman just starting weight training, slowly lifting heavier weights over time will make your triceps (the back of your arms) grow about twice as much as just doing the same workout over and over.
We don’t really know if variable resistance training works well for athletes or over long periods—most studies have only looked at beginners and for a few months at most.
Doing varied weight workouts might hurt your muscles a little less than doing the same routine over and over—but you still gain just as much muscle, meaning you don’t need to feel wrecked to get stronger.
Mechanistic
Some people think mixing up your leg workouts (like changing weights or angles) might make all parts of your quadriceps grow better than doing the same routine over and over—but right now, science hasn’t proven this for sure.
Using machines or bands that change how hard they feel as you move might make your muscles work more evenly during an exercise, but that doesn’t always mean you’ll grow bigger muscles faster than with regular weights—especially if you’re just starting out.
If you're new to lifting weights, whether you switch up your weights and reps (variable training) or stick to the same routine (conventional training), you'll build muscle at about the same rate—neither method is better than the other for getting bigger muscles in the first few months.
The more you work each muscle group per week—with the right exercises that really engage the muscle—the more your muscles will grow, and this is the #1 thing that matters for building muscle.
If you get much stronger—like more than 20% stronger—on an exercise you’ve been doing for a long time, it probably means your muscles got bigger, not just your brain getting better at telling your muscles to work harder.
When you move your muscles through their full stretch and contraction during exercise—like fully lowering and raising a dumbbell—you build more muscle than if you only move partway, because the muscle gets stretched under load, which seems to trigger better growth.
Lifting heavier weights over time doesn’t directly make your muscles grow—it just shows your body has already recovered and built new muscle from past workouts.
To keep getting bigger and stronger muscles, you gotta slowly make your workouts harder over time—either lift heavier weights, do more reps, or do more sets.
When you lift weights or push against resistance, your muscles get stronger and bigger because they're trying to handle the stress—this is exactly why people do strength training.
Changing up your workout routine all the time—like switching exercises every week—won’t make your muscles grow bigger than sticking to the same routine, even if you do more total work in the varied version.
When you keep working out, your muscles get used to it and don’t get as sore or damaged each time—so you can train harder and more often, which helps you build more muscle over time.
When you do the same weight workout more than once, your muscles get better at handling it — so next time, you’re less sore and damaged.
When your muscles get damaged from intense exercise, they start breaking down more protein and stop building new muscle as well, which makes you recover slower and feel weaker in your next workout.
Lifting weights makes your muscles start building more protein right after the workout, and mixing up your routine a little bit gives your muscles a tiny extra boost right after lifting—but in the long run, both routines build about the same amount of muscle.