Should You Calculate Your Muscle Mass?

You probably know about how much you weigh. You may even know your approximate body fat percentage. But do you know what your muscle mass is? Here's how to find out and why it's important.

Brock Armstrong
7-minute read
Episode #487
Photo of a woman holding a dumbbell
The Quick And Dirty
  • "Muscle Mass" refers to all of the body’s muscle tissue but most often it is used to refer to the skeletal muscle.
  • Calculating your percentage of muscle mass can help you monitor and maintain your health.
  • Paying attention to your muscle mass gets more and more important as you age.
  • It is difficult and expensive to calculate muscle mass accurately, but you can estimate it using the YMCA formula. 

Before we dig in, here is a little body composition primer. The term “muscle mass” refers to the total amount of soft muscle tissue in the body. Then, your "body mass" is made up of two components, body fat and lean body mass. Most of us know what body fat is (if not check my article all about it) but the second component, lean body mass, includes muscle mass, as well as bones and bodily fluid (mostly water). 

Muscle mass (or your muscles) are the part of your body that help you move, balance, and stand and sit with good posture. They also aid your organs in a number of your biological functions. 

The three main types of muscles found in the body are:

  • smooth muscle (your internal organs)
  • cardiac muscle (your heart)
  • skeletal muscle (the stuff I tend to write about a lot)

Put these all together and you have the body’s muscle mass. Although, in most conversations on this topic, muscle mass usually focuses on skeletal muscle. Perhaps this is out of vanity or perhaps it's because we can exert the most control over those muscles—you decide. 

If you've been told that you have low muscle mass, that simply means that you have a lower than average amount of muscle compared to other people of the same age and gender. And if you've been told that you have high muscle mass—yep, you guessed it—you have more muscle then most people your age and gender. And we'll look at those averages later. 

When you are given this information, it's usually in conjunction with your body composition (during a Dexa Scan or maybe an MRI). Your body composition is usually a ratio of your muscle mass to your body fat mass. We’ll get into the reasons why you may want to measure this later. 

What is muscle mass for?

As I said, skeletal muscle plays a major role in mobility and movement, but muscles also play a vital role in supporting overall health, especially as we age. 

Muscles store glycogen (carbohydrates), which they use as fuel every time you ask them to move. This is especially handy when the carbohydrate in your blood (your blood sugar) runs out. That is when your muscle mass essentially acts as a reserve gas tank—you keep it full by eating carbohydrates, and then empty when you exercise. 

Healthy muscle to fat ratio creates what is referred to as a virtuous circle.

Exercising your skeletal muscles, in all the wonderful ways that I discuss in many of my Get-Fit Guy articles, can increase your body’s strength, mobility, and balance. Plus, a healthy muscle-to-fat ratio creates what is referred to as a virtuous circle. 

  • A healthy level of skeletal muscle allows you to do effective movement and exercise
  • Which maintains the muscle and helps minimize excess fat storage
  • Which increases your ability to move and exercise
  • Which maintains a healthy level of skeletal muscle
  • And so on!

So, as you can guess, increasing (or at least maintaining) your skeletal muscle, and also improving the quality and strength of your muscles, will not only allow you to continue to do the movements you love but can allow you to do them better, more frequently, and more efficiently.

Calculating muscle mass

A number of years ago, home bodyweight scale manufacturers started selling products that promise to tell you not only how much you weigh but also your body fat and muscle mass percentages. These scales use what is called Bioelectrical Impedance. They were pretty unreliable when they first arrived on the scene, and they 've only improved a little today. But aside from these simple home devices, it is possible to determine how much of a person’s body is made up of muscle, fat, and other components.

It is possible to estimate muscle mass percentage at home without a a costly trip to the hospital or the local sports physiology lab.

The most accurate avenues for measuring your body composition use expensive medical equipment like DEXA Scans, MRIs, or 3D body scans. But the good news is that it is possible to estimate muscle mass percentage at home without a a costly trip to the hospital or the local sports physiology lab.

The most simple version relies on first calculating your body fat percentage and subtracting that number from 100. This overly simplistic formula is rather flawed, though. As we know, there is more stuff in our body that just fat and muscle. Stuff like guts, bones, and the water in our blood make up a particularly large portion of our human meat sacks. So although this calculation can give you a number that you can track over time, noting any positive or negative changes, it doesn't give you an accurate measurement.

Aside from investing in a super fancy scale, 3D body scanner, or paying a lab to run the tests, the US military has a popular formula (known as the YMCA formula) that does a pretty good job of estimating body fat percentage. Using this formula involves the fun procedure (not!) of measuring the circumference of several body parts. 

Once you have those measurements, you can use them to determine your circumference value (CV). Then, your CV and height are located on a chart with some precalculated body fat percentage estimates listed for you. Once you've found that, you can use this number to estimate your lean body mass percentage. You can use this online calculator to do the math.

For men, you must measure the circumference of your abdomen and neck (your CV is abdominal circumference minus neck circumference).

For women, you measure the circumference of the waist, hip, and neck (your CV is waist circumference plus hip circumference minus neck circumference).

While the US military does appear to use this method, it's definitely most applicable to a more specific portion of the population and not outliers (like athletes) or even certain ethnicities (much like the BMI measurement). This is mostly due to the fact that the circumference measurements do not take into account muscle size or where certain populations carry their body fat (in relation to a predominantly caucasian population).

If you are really interested in knowing your exact body composition, magnetic resonance imaging (MRI) is the gold standard.

If you are really interested in knowing your exact body composition, magnetic resonance imaging (MRI) is the gold standard. An MRI uses strong magnets to create an accurate image of your insides. The bummer is that these scans are very expensive, which makes them not very practical for most of us.

The more practical version is the dual-energy X-ray absorptiometry (DEXA) scan. It uses two low-energy X-ray beams that create separate images of the two components in your body, including soft tissue and bone. The results of this test can also identify any weaknesses in your bone density and help measure visceral fat, a type of fat the body stores around certain internal organs that can indicate cardivascular health risks.

Unfortunately, there is not a lot of data on what a "good" amount of muscle mass should be. The best source of reliable, average information is in a research study from the Journal of Applied Physiology. In this study, researchers used a whole-body magnetic resonance imaging (MRI) protocol to examine the influence of age, gender, body weight, and height on skeletal muscle (SM) mass and distribution in a large and heterogeneous sample of 468 men and women. These are their results:

Muscle mass percentage averages for men

Age Muscle mass percentage
18–35 40–44
36–55 36–40
56–75 32–35
76–85 < 31

Muscle mass percentage averages for women

Age Muscle mass percentage
18–35 31–33
36–55 29–31
56–75 27–30
76–85 < 26

If you know your muscle mass percentage, you can use these tables to see how you stack up against an average person. 

Why knowing your muscle mass is useful

Muscle mass percentage can be an indicator of health. Generally speaking, the greater your muscle mass, the more positive the health benefits. To a point, anyway. When you start to resemble a balloon animal, the health benefits have all but disappeared. (So think Dr. Banner, not the Hullk.)

Over our lifetime time, muscle mass naturally declines. This reduction, called sarcopenia, begins at about age 30.

Over our lifetime time, muscle mass naturally declines. This reduction, called sarcopenia, begins at about age 30. After that, we continue to lose three to five percent of our muscle mass every decade. It’s not hard to imagine how this muscle loss will reduce your physical function and increase your risk of injury. It can even make everyday activities like walking (even short distances) or climbing the stairs more difficult or impossible.

The percentage of muscle mass definitely varies between people and is dependent on several factors like how fit the person previously was, their general body size, and their gender.

By keeping an eye on your muscle mass and working to maintain a healthy amount of muscle mass, you can help yourself stay mobile and strong. Maintaining a good amount of useful muscle on your body can also help you maintain a healthy body weight. This is because of that virtuous cycle I mentioned earlier—a higher percentage of muscle mass encourages a lower percentage of body fat.

Also, the types of exercise that build muscle have also been shown to increase bone density. Then there are clinical trials that have found that resistance training can improve symptoms of depression. And finally, a 2014 study published in the American Journal of Medicine found that older adults with more muscle mass live longer than those with less.

Building muscle mass

The key to building muscle is to adequately stress the muscle and the neuromuscular connections, then allow the muscle to recover while eating enough healthy food to feed the new muscle. And then, repeat!

The best exercises for full-body muscle growth are exercises that require you to use multiple joints. For example, a combination of squats, cleans, deadlifts, and bench presses can be very effective at helping your entire skeletal system get stronger. If you need some instruction and inspiration, check out my Workout of the Week videos at BrockArmstrong.com/youtube.

Remember that you don’t have to hit a gym and lift huge weights to build muscle. You can do bodyweight exercises, use elastic resistance bands, or use objects around your home to challenge your muscles enough to stimulate them to get bigger. 

Finally, there are many articles here in the Get-Fit Guy archives that will help you build enough muscle to stay fit and healthy for years to come. 

Even if you don’t want to measure your muscle mass, it is important to maintain it. So, feel free to skip the measuring part and jump straight to the building part and kick off that virtuous cycle—more muscle means more movement, which means more muscle, and so on.

About the Author

Brock Armstrong

Brock Armstrong is a certified AFLCA Group Fitness Leader with a designation in Portable Equipment, NCCP and CAC Triathlon Coach, and a TnT certified run coach. He is also on the board of advisors for the Primal Health Coach Institute and a guest faculty member of the Human Potential Institute. Do you have a fitness question? Leave a message on the Get-Fit Guy listener line. Your question could be featured on the show.