Why building muscle matters for metabolic health

Any exercise improves metabolic health, but building muscle has unique benefits. Here's why resistance training should be part of your workout plan.


Whether you’re a bodybuilder or not, your muscles are massive—together, skeletal muscle would be the largest organ in your body, taking up 40% of your total body weight. And they’re not just crucial for walking, picking up things, and every other way you move. Muscles also may reduce your risk for cardiovascular diseasediabetes, and early death—and improve your metabolic health.

That’s because muscles process lots of glucose: more than 80 percent of the glucose is from food. “Larger muscles process more glucose, and when you use your muscles, insulin sensitivity is increased through a cascade of events,” says Dominic D’Agostino, PhD, associate professor in the Department of Molecular Pharmacology and Physiology at the University of South Florida Health Morsani College of Medicine.

As little as two strength-training sessions per week can help build more muscle to amplify these beneficial processes and increase your protection against disease. Here’s a summary of some benefits that strength and muscle can give your metabolic health and some simple, realistic recommendations anyone can apply to improve muscle mass.

How Muscle Mass and Strength Training Improve Metabolic Health

When you work out and grow muscle, the muscle cells use more glucose with less need for insulin (this is due to a few different factors—more detail below). Less insulin is good: Too much can lead to “insulin resistance,” when cells aren’t as responsive to insulin and blood glucose rises to dangerous levels that can lead to prediabetes and, eventually, Type 2 diabetes.

The opposite of insulin resistance is insulin sensitivity—when you’re more insulin sensitive, your body processes more glucose more efficiently, with less insulin. Research shows that both strength training and building muscle mass improve insulin sensitivity:

  • In a 2020 study from the Journal of Diabetes Research that analyzed more than 3,100 men, those who reported zero strength training were 2.4 times more likely to be insulin resistant than men who do 1-2 hours of strength training per week.
  • In older adults, 3-6 months of moderate strength training improved insulin resistance by as much as 30 percent.
  • Even when young people have “detrimental” fat deposits—like deep, rock-hard visceral fat in the abdomen and organs, and fatty deposits in the liver, both of which are associated with Type 2 diabetes risk. In one study, the third of people with the highest muscle mass under the fat had 45 percent better insulin sensitivity than the third with the lowest muscle onboard.

Muscles also improve how your body uses glucose in ways that don’t require insulin at all by building mitochondria that have more capacity for glucose, releasing chemicals that increase your base levels of glucose uptake, and even changing the type of fat in your body into a form that uses more energy at rest. Together, these insulin-dependent and -independent processes add up to more glucose processed—so less insulin needs to be released to normalize blood glucose levels. Here’s an overview of some of the ways muscle improves glucose disposal and metabolic health.

Muscle Mass and Strength Training Increase the Number of Glucose Transporters

Glucose transporters are protein molecules that act like glucose gateways to the cells—they create a pathway where glucose can be moved from the bloodstream into cells and turned into cellular energy.

One of these proteins, called GLUT-1 transporters, is expressed in most cells. When there are more of them, more glucose gets moved into cells to be processed. Training a muscle increases the number of GLUT-1s, D’Agostino explains.

“If you exercise a mouse or a human really hard for two weeks, the density of GLUT-1 transporters will increase,” he says. “So at rest, you’ll be pulling in more glucose,” without needing insulin to tell your cells to start doing so.

Lifting weights also impacts another glucose transporter called GLUT-4. These transporters aren’t always on the surface of cells, like GLUT-1. Instead, they must be moved to the edges of cells, where they start ferrying glucose in from the bloodstream. Strength training—especially doing intense, fast moves or controlling weight as you lower it, which both overload your muscle—triggers this translocation process, D’Agostino explains, resulting in more glucose being processed by your muscle cells.

2013 study concluded that one reason strength training moves these GLUT-4 transporters is due to a molecule called AS160. When insulin is sent to the cells, a substance called Akt phosphorylates AS160. This releases the GLUT-4s, previously held in place by AS160, so the transporters can move to the edges of the cells and let glucose in. People with diabetes and insulin resistance have impaired AS160 phosphorylation, requiring more insulin to move the GLUT-4 transporters. Since strength training improves this process, it improves insulin sensitivity—less insulin is needed to move the GLUT-4s.

Strength Training and Muscle Mass Spur Myokine Production

Strength training causes more release of proteins called myokines that interact with other organs in your body. Some myokines deal with energy metabolism, insulin secretion, and other beneficial aspects of metabolic health:

Strength Training Boosts Mitochondria Function

Organelles in your cells called mitochondria use glucose to make ATP, the energy currency of your cells. Cardio like slow, steady Zone 2 exercise, is known for building more mitochondria, resulting in more glucose uptake from the blood. Whether resistance training makes more mitochondria isn’t totally clear, but it makes the ones in your muscles function better. Research has found that people with more muscle mass who strength train have a higher ceiling for ATP production compared to their baseline ATP production than physically active people who don’t lift. This, scientists concluded, shows that the mitochondrial function in the strength trainees was better: They could produce more overall energy—and use more glucose—than the non-strength-trained people.

Another factor to consider: Even if the muscle cells built by strength training have fewer mitochondria in each cell than those built from walking, a larger muscle has more muscle cells overall, D’Agostino says. That means a bigger, more muscular powerlifting athlete may have more total mitochondria than a smaller, ultra-conditioned runner. This doesn’t mean a powerlifter is “healthier” than a runner or vice versa—the bigger athlete with more mass could just use more glucose at rest on an overall level.

Muscles Increase Your Metabolic Rate—But Not By Much

You may have heard that building muscle will let you burn more calories at rest. One popular trope says that for every pound of muscle you gain, you’ll burn an extra 50 calories per day.

That’s an exaggeration of almost 10 times the actual effect. Multiple studies (here’s one from 2010 and a review from 2013) have examined the resting metabolic rate effects of skeletal muscle and found that while muscle does burn more calories than fat, it’s not a huge difference. According to these studies, one pound of skeletal muscle burns five to six calories per day while at rest. So adding 10 pounds of pure skeletal muscle will burn 50 to 60 extra calories per day at rest; an equivalent amount of fat will burn around 20 calories.

Science-Supported Strategies to Build More Muscle

Barbells and dumbbells are great, but there are lots of methods for building muscle, in and out of the gym: strength exercises with resistance bands, calisthenics exercises like pushups and air squats, and weighted moves with dumbbells, kettlebells, barbells, and other implements can all challenge your muscles and make them bigger and stronger so you reap these metabolic benefits. Popular fitness apps like Nike Training Club, Ladder, and Peloton are also good entry points.

Before starting any strength training regimen, talk to your doctor about what’s safe for you, especially if you have any pre-existing health conditions. If you’re a beginner, aren’t comfortable performing strength exercises on your own, or if you just want some ideas on which of the many strength training methods you might enjoy the most, consult with a certified personal trainer: Your local gym may offer a free training session for first-timers, so you can learn moves and see if you like working with a pro, or would rather go it alone.

Whatever your chosen method, follow the five scientific strategies below to maximize your muscle (and metabolic) gains…

 1. Start With Two Total-Body Workouts Per Week

When you’re starting, less is more: Doing fewer weekly strength sessions affords you more flexibility on which days you can work out—and it’s easier to stick to your plan. Two workout days, separated by at least one rest day, is enough. In a 2004 study of more than 8,000 men, those who worked out 1-2 times per week for nine years reduced their risk of dying by 59 percent compared to those who didn’t work out.

When following a two-a-week plan, it’s best if both workouts train your whole body. In a 2016 research review from Sports Medicine, scientists found that training a muscle group more than once per week was more effective than doing so once per week, even if the total amount lifted was equalized across the sessions. So instead of performing a weekly “leg day” workout where you lift 2,000 total pounds with your legs—maybe four sets of 10 repetitions with 50 pounds—and an “upper body” day where you lift 2,000 pounds with your upper body, you’ll get more benefit from working both muscle groups twice per week, lifting 1,000 pounds in each workout with your upper and lower body.

The rest between your two training sessions is essential. Your workout (and eating protein, as discussed below) kicks off the muscle growth process. But the actual muscle growth happens between your workouts while you’re recovering. So rest for at least one day between workouts.

How to apply this: Total-body workout studies use just a handful of exercises to tax all the body’s muscle groups. These exercises usually target multiple joints at once to maximize the number of muscle groups being worked—a bench press, for example, works the muscles of the chest through the shoulder joint and the triceps through the elbow joint, while a triceps pushdown isolates only the elbow joint.

Choose one or two exercises from these categories to build your total-body workout sessions:

  • Knee-dominant lower-body exercises: Squats, split squats, lunges, and the leg press machine work your quadriceps (the fronts of your thighs), as well as your calves, glutes, and the stabilization of your trunk. The hamstrings (the back of your thighs) are also involved, but to less of an extent than with hip-dominant moves.
  • Hip-dominant lower-body exercises: Deadlifts, Romanian deadlifts, step-ups, glute bridges, and rear foot-elevated split squats usually have the hamstrings and glutes as the prime movers.
  • Horizontal pressing: Bench presses, pushups, the chest press machine, and resistance band presses work your chest and triceps.
  • Pulling exercises: Horizontal seated cable or resistance band rows, lat pulldowns, barbell or dumbbell rows, inverted bodyweight rows, and pull-ups all work the muscles of your back—including the latissimus dorsi, one of the body’s biggest muscles—and your biceps. If choosing two moves from this category, go for one vertical and one horizontal pull.
  • Vertical presses: Barbell, dumbbell, or resistance band overhead presses all work the deltoids (the caps of your shoulders), as well as the chest and triceps.

2. Train Almost to Failure in Each Set

The number of repetitions of an exercise you perform in each set doesn’t matter—if you prefer doing sets of 15 leg presses with a lighter weight, or 3 to 5 with a heavier weight, both will build muscle … as long as it gets hard at the end of the set.

How hard? Aim for going within two repetitions of “momentary muscular failure,” or the point where you couldn’t perform another repetition without form breaking down. When you do this, some researchers theorize that you work all the different fibers of your muscle during the set: In the early repetitions of a set, while the exercise is still relatively easy, you’re using slow-twitch, Type I fibers. But as the set continues, these muscle fatigue and the Type II fibers—the fast-twitch ones that can create more muscle size—go to work. At the end of this kind of set, all the fibers should theoretically be worked.

To make sure you’re really getting close to failure, do the last set of an exercise all the way to failure once every few weeks, going until you can’t do another repetition. You may find, as studies have shown, that you can actually do more reps than you believe before reaching failure. Use this new “test” set as your benchmark going forward, and try to get within two repetitions of that number on your workout sets.

How to apply this: Perform sets that are 1-3 repetitions away from failure during most workouts.

3. Perform 10 to 20 Working Sets Per Week on Each Muscle

Those “near-failure” sets are working sets (e.g., not a warmup set)—and more of them means more muscle size: In a 2019 study from Medicine & Science in Sport & Exercise comparing groups that performed one, three, or five sets per exercise in three training sessions per week for eight weeks, all three groups saw similar strength gains. But the higher-volume groups gained more muscle in certain parts of the body.

To maximize muscle gain, research says doing 10 to 20 working sets per muscle group weekly. In a 2016 review published in the Journal of Sports Sciences, scientists found that for each additional near-failure training set for a muscle group in that 10 to 20 range, muscle growth increased by 0.37 percent. And while that sounds like a small number, remember that muscle growth is hard—bodybuilders aim for a few percentage points of additional muscle a year.

How to apply this: Aim for 10 to 20 total working sets of your muscle groups (chest, back, shoulders, legs, arms) each week to maximize muscle growth. Spread across your two weekly total-body sessions, that’s 5-10 sets per muscle group in each workout.

For 10 weekly sets for your chest, that could be five sets of the same move, like a dumbbell bench press. Or it could be two sets of one exercise—like a pushup—and three of another—like an incline chest press machine. Or it could be five single sets of five different moves that you enjoy or any other permutation. Just get to 10 to 20 each week, and make sure each working set is near failure.

4. Do More Total Work Over Time

As your muscles gain strength, what used to be hard will become easy—so you’ve got to do more. In studies like this seminal 2010 review from the Journal of Strength and Conditioning Research, science has shown that to build and maintain muscle, you need to do more over time. In strength training, this concept is called “progressive overload.”

Progressive overload is applied via the total volume of your workouts (volume is the amount of weight moved multiplied by the number of repetitions performed). To progressively overload, this number needs to increase over time. For example, if you do the exercises targeting your back with 100 pounds right now, and you’re doing 10 total sets of eight repetitions each, your current weekly volume is 8,000 pounds (100 x 10 x 8).

To increase this weekly volume, one or more of those three variables needs to increase: You could do nine reps in one set, or perform a set with 105 pounds, or add a whole extra set to one workout. Even adding just one repetition to one set will increase the total volume (in this case, by 100 pounds), meaning the principle of progressive overload is being applied.

How to apply this: Log your workouts with an app—like FitNotes, which is free for Android users, or HeavySet, which is free for iPhone—that tracks your volume. When you’re starting out, you’ll gain strength fast: You’ll likely be able to increase the total volume of your workouts each session at first. Over time, this gets harder: You won’t be able to increase in each session compared to the last—at this point, try to increase the total volume each week. When that becomes impossible, try improving each month. As you progress, adding more repetitions or weight will become more difficult—eventually, simply doing the last rep “stronger”—still struggling, but finishing it with slightly more ease—may be progress. Just keep track, and keep doing more work over time.

5. Eat 0.6 to 1.4 Grams of Protein Per Pound of Body Weight Per Day

Building muscle is all about the balance between two processes: muscle protein breakdown (MPB) and muscle protein synthesis (MPS).

MPB is made up of multiple molecular pathways that tear down muscle in response to exercise, as well as for other processes in the body that require the amino acids stored in muscle protein. When MPB is greater than MPS, the balance is shifted toward breaking down muscle, and you’re in a catabolic (i.e., muscle-losing) state. When MPS is greater, you’re in an anabolic (muscle-gaining) state.

Strength training triggers MPS, but it’s not enough. Since your body can’t make all of the amino acids, to perform MPS, you need to eat protein that contains all of these “essential” amino acids. This combination of eating protein and performing resistance exercise puts the balance of MPS and MPB into anabolic territory—and you build muscle.

How to apply this: How much protein you need depends on your body weight and whether you’re eating enough calories to maintain your current weight or if you’re dieting.

The International Society of Sports Nutrition’s guidelines, based on a review of multiple studies, indicate that trainees who want to gain muscle—and are eating enough calories to maintain their current body weight—should consume 0.6 to 0.9 grams of protein per pound of body weight per day. For a 180-pound person, this would be 108 to 162 grams per day.

If you’re eating fewer calories than needed to maintain your current body weight—that is, if you’re dieting—the numbers are slightly higher: 1 to 1.4 grams per pound of body weight per day. For that same 180-pound person, this recommendation would be 180 to 252 grams per day.

Eating more protein than this may not significantly improve your results—so more is not necessarily better. In a 2014 study of resistance-trained people, those who ate two grams of protein per pound of body weight per day didn’t build more muscle than another group who ate less than one gram per pound of body weight per day.