Health Claims

We don't really know for sure if doing exercises with more or fewer reps left in the tank helps you build more muscle, because scientists are just guessing how many reps people had left based on how the studies were written.

Correlational

If you lift weights with different levels of effort—whether you stop just before failure or push almost to failure—you’ll still gain about the same amount of strength, as long as you’re doing the same total amount of work and using the same weight.

Correlational

When you lift weights and push yourself almost to the point of not being able to do another rep, you’re more likely to build bigger muscles than if you stop earlier — even if you’re lifting the same weight or doing the same number of sets.

Correlational

If you're trying to figure out how much muscle you build from each workout, you need to account for how long you've been training and how long the program has been going—otherwise, the numbers won't make sense.

Causal

We don’t know yet if doing more than 20 sets of weight training in one session helps you get stronger or if it’s just too much and stops helping—so don’t assume there’s a clear cutoff point where more sets stop being useful.

Descriptive

Doing more sets in a workout helps you get stronger and bigger, but after a certain point, extra sets don’t help much—especially for strength. You hit your sweet spot for strength with fewer sets than you need for muscle growth.

Quantitative

How you count your weightlifting sets—whether you count every little part or just the full sets—can change how we think about how much lifting helps you get stronger versus bigger muscles.

Causal

Doing more sets of weightlifting in one session can help you build bigger muscles and get stronger, but after a certain point, doing even more sets doesn’t help much—around 2 sets is enough for strength, and 11 sets is enough for muscle growth.

Correlational

If you lift weights the same total amount each week, it probably doesn’t matter much whether you do it in 2 big sessions or 5 small ones—your muscles will grow about the same either way.

Causal

When you lift weights more often or heavier, your strength goes up fast at first but then slows down a lot quicker than your muscles growing — so strength gets tired of extra work sooner than muscle size does.

Quantitative

When you're lifting weights, whether you do exercises that target one muscle at a time or ones that work multiple muscles together can change how well we can guess how much muscle you'll build or how much stronger you'll get—and using a special way to measure the workload (called 'fractional') works best for making those guesses.

Quantitative

If you lift weights more often each week, you’ll likely get stronger faster—but that doesn’t always mean your muscles will get bigger. Strength and muscle growth might not follow the same rules.

Correlational

Lifting weights more often each week helps you build more muscle—but only up to a point. After a certain amount, you don’t get much extra benefit, so there’s a sweet spot for the best results.

Correlational

Some people’s genes might make them build a little more muscle from weight training than others, but these specific genes don’t explain much of why some people get way stronger than others.

Correlational

Some people who lift weights and end up with more of a certain protein in their muscles tend to grow bigger muscles, but not everyone sees this link—some people with lots of the protein don’t grow much, and others with less do.

Correlational

Some people who get really strong from weight training might have special tiny molecules in their muscles that help boost a protein involved in muscle growth, but we’re not sure how or if this really works yet.

Mechanistic

Some people get much stronger and build more muscle from weight training than others—this might be because their muscle cells grow more new nuclei, but not every study agrees on this.

Mechanistic

People who get much stronger from weight training tend to make more of the cellular machinery (ribosomes) that helps build muscle, while those who don’t get as strong show little to no change in this machinery.

Mechanistic

Some people get much bigger and stronger from weight training than others—even when they do the exact same workouts—because everyone’s body responds differently to exercise.

Descriptive

Whether you're new to lifting weights or have been doing it for years, when you eat your protein around your workout doesn't seem to make a big difference in how strong or muscular you get—but there just aren't many studies on people who already train regularly.

Correlational

Most of the studies in this review didn’t give the same amount of protein to people in the exercise group and the control group, so it’s probably not when they drank their protein shake that made them grow muscle—it’s just that they ate more protein overall.

Causal

If two people eat the same total amount of protein each day, it doesn’t matter whether one drinks a protein shake after the gym and the other drinks it at breakfast—both will gain muscle and strength about the same, but there’s not much research on this yet.

Causal

Eating protein right before or after your workout doesn't give you extra muscle gains if you're already getting enough protein throughout the day—so you don't need to rush your shake right after lifting.

Causal

If you're lifting weights and want to build muscle, eating at least 1.6 grams of protein per kilogram of body weight every day is the biggest factor that helps — more protein means better results, and when you eat it doesn't matter as much.

Causal