The truth about how weights lifted translates into calories burned.

The claim: Strength training will help you build muscle and boost your metabolism. It’s a winning proposition for any woman vying to maintain a healthy weight without counting calories—or spending an obscene amount of hours sweating it out in the gym.

There are countless reasons to lift weights and build strong muscles, including injury prevention, improved bone density, and a lower risk for type 2 diabetes and other diseases—not to forget that bad-ass feeling you get when you can haul a giant piece of furniture up the stairs all by yourself. Another often-cited benefit to strength training is that it will increase your metabolism. But how much does your metabolism increase with strength training? The answer depends on many different factors.

The truth is, the speed of your metabolism is largely determined by many elements beyond your control.

Your basal metabolic rate (BMR)—the calories you burn just to live—is driven by a host of factors, including your sex, genetics, and age, Tim Church, M.D., professor of preventative medicine at Pennington Biomedical Research Center at Louisiana State University, tells SELF. Research published in the medical journal PLOS ONE also shows that the size of your internal organs plays a huge role in why some people burn more calories at rest than others—in fact, the study found that 43 percent of the differences between people’s metabolic rates can be explained by organ size.

The largest determiner of your metabolic rate is actually your total body mass. “The more cells, even fat cells, in your body, the more furnaces you have burning at any given time,” Dr. Church says. Think of it this way: It takes more juice to charge your tablet than it does to charge your phone. People who are taller and have a larger bone structure, therefore, will have a higher BMR than people who are shorter and have a slimmer build. While you can control your body mass to some extent by gaining or losing weight, you can’t change your height or your bone structure. All in all, most of a person’s BMR is determined by genetic factors, Dr. Church says.

Building more muscle mass is one thing that can increase a person’s metabolic rate.

Estimates suggest that every pound of muscle burns roughly six calories per day at rest, Dr. Church says. That’s about three times as many calories as a pound of fat, which burns roughly two calories per day.

So how does that play out in the real world? Well, if, for example, a woman adds 10 pounds of muscle and loses 10 pounds of fat, she’ll burn 40 extra calories per day. Forty calories a day isn’t nearly as significant as a dietary change could be, but for people who are looking to lose weight, it can still make a minor difference over the long term.

It’s important to remember that since everybody is different, these estimates are just that. How the numbers work out for each person will definitely vary. So many factors—like genetics, hormones, sleep, and diet—can change the rate at which our bodies burn calories. And some people may have a harder time than others when it comes losing fat or gaining muscle—again, there are so many factors at play and our body chemistries are all different. Strength training is important for many, many, many other reasons (more on that later), but if you’re looking to increase your metabolism, it’s important to have realistic expectations and know that strength training can make a difference, but probably won’t drastically affect how many calories you burn from one day to the next.

More muscle will likely lead to longer, more intense workouts, which can further increase how many calories you burn.

When people talk about wanting to increase their metabolism, they usually mean that they want to burn more calories. So we should note that by simply having more muscle, you’ll also burn more calories during workouts. That’s because you’ll be able to work harder and longer.

“Gaining muscle through resistance exercise means you can do more. You can work out harder and hike steeper trails,” sports dietitian Marie Spano, M.S., R.D., C.S.C.S., tells SELF. “This will lead to an increase in calories burned. Now, that’s significant.”

If you’re not concerned with how many calories you burn, then it’s still encouraging that strength training can improve your sports performance. (And again, there are countless benefits of exercise that have nothing to do with calories, weight, or metabolism.)

After a strength-training session, your metabolism stays elevated through a process called excess postexercise oxygen consumption (EPOC). But the effect isn’t huge.

EPOC is more commonly known as the afterburn effect. It refers to all of the oxygen (and energy, in the form of calories) that your body takes in and uses after exercise to help repair your muscles and recover.

Research shows that strength training is especially effective at raising EPOC. That’s because, generally speaking, strength-training sessions cause more physiological stress to the body compared to cardiovascular exercise, even higher-intensity cardio intervals. However, it’s worth noting that overall exercise intensity is what makes the biggest impact on EPOC. So squats, deadlifts, and bench presses with heavy weights are going to be much more effective at raising EPOC compared to bicep curls and triceps extensions with light weights.

How much of a difference does EPOC make? Well, in one research study of young women, basal metabolic rate spiked by 4.2 percent 16 hours following a strength-training session that lasted an hour and 40 minutes—the equivalent of burning an extra 60 calories, on average. That’s a long workout, and 60 extra calories isn’t exactly huge. Plus, EPOC is not a permanent boost. Research suggests it may last anywhere from 12 hours to a few days, depending on the workout and who is doing it. The calories you burn through EPOC can add up over time, especially if you’re lifting weights three or four times a week, but all in all, it doesn’t have a very big effect on your metabolism.

In the end, the exact EPOC boost you get from your strength-training workouts depends on the exercises you perform, weights you use, reps and sets you perform, rest you take, and total time you spend sweating it out—not to mention your genetics and current fitness level and muscle mass.

As we age, we lose muscle mass, so strength training is essential for maintaining it—and a healthy metabolism.

Research shows that starting as early as age 30, the body begins to slowly lose muscle mass, with women losing up to 15 percent of their total-body muscle per decade by age 50. Apart from declines in strength, that declining muscle mass comes with a declining metabolism, Emilia Ravski, D.O., a sports medicine specialist with Hoag Orthopedic Institute in California, tells SELF. This decline in metabolic rate is actually one driving factor of the weight that women generally tend to put on after we naturally hit our peak muscle levels in our 20s, research from Tufts University suggests.

However, through a targeted total-body strength-training program, it’s possible to not only prevent muscle loss, but actually increase your muscle mass (and keep your metabolism up) throughout your life.

In other words, while strength training might not increase your metabolism very much, it can help you maintain your metabolism as you age.

The best way to build muscle mass and get the biggest metabolic boost: Perform compound movements and lift heavy.

If you want to train to build muscle mass, focus on integrating at least three strength-training workouts into your weekly exercise routine and prioritizing large, compound movements—which require multiple muscle groups to work at once—over small, isolation exercises.

“Throwing in a few bicep curls into your training is helpful, but it won’t have the same impact as pull-ups,” Spano says. Squats, deadlifts, shoulder presses, lunges, rows, and bench presses are all great options for stimulating the most muscle growth possible with each and every rep.

Similarly, lifting weights that are heavy enough that you can eek out only 6 to 12 reps per set with proper form will help increase muscular size as opposed to muscular endurance. Compound exercises make it possible to lift heavier, so the two pair nicely. “Don’t be afraid to go heavy,” Spano says.

Strength training is amazing for your health and overall fitness. Building muscle might not boost your metabolism very much, but that shouldn’t discourage you from lifting weights.

At the end of the day, yes, strength training does impact your metabolism, but any boost you get will be minimal and completely secondary to all of the other health benefits of strength training. Any change in metabolism or increase in calorie burn will vary widely from person to person, and depends on so many factors: your genetics, eating habits, health conditions, what workout you do that day, how much sleep you’re getting, and even how stressed you are on any given day. But incorporating a couple of strength training sessions into your fitness routine is worth doing no matter what—you’ll feel yourself get stronger, and put yourself in a position to say healthier throughout life. Those are the best, most promising benefits to work for.

This article originally appeared in SELF Magazine

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