Skeletal Muscle vs Muscle Mass

Muscle Mass Overview

It's not uncommon to hear people starting out in the gym, or even gym veterans, say things like, "I want to tone/sculpt and lose weight", or, "I want to gain lean muscle". Though the terminology isn't 100% there, any knowledgeable, seasoned expert can translate these commonly heard expressions, too:

"I want to tone/sculpt and lose weight" --- "I want to lose fat and maintain muscle."

"I want to gain lean muscle" ---- "I want to build muscle mass".

There's no such thing as lean muscle. There is such thing as lean body mass, which includes the weight of your-

  • organs
  • skin
  • bones
  • body water
  • muscle mass

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Unlike the expression of "lean muscle", Lean Body Mass correctly exemplifies the term by describing your body minus fat, also known as "Fat-Free Mass".

man using dumbbells to do pushups 

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Concerning Muscle Mass, you have three different types of muscles, visceral, skeletal, and cardiac.

Visceral muscles, the weakest of all the muscles, are small and found inside internal organs and inside blood vessels.

Cardiac muscles are located only in the heart and help pump blood throughout your body.

Skeletal muscles are the only muscles, using soft tissue to compose muscle controlled consciously, contracting and expanding to create movement.

They are the strongest in the body and are developed when incorporating fitness into our daily routines. When someone is talking about muscle mass, they are talking about skeletal muscle mass. T

he same can be said for when talking about body composition; we must remember that it contains fat mass + muscle mass + bone mass, not exclusively muscle and water or fat and muscle.

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What Is Skeletal Muscle Mass?

man jogging alongside beach

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Skeletal muscles are essential in critical movements, such as bending your arm to pick up your coffee or squatting down to pick up the remote that fell on the floor. Skeletal muscle accounts for 40% of total body weight and is known for playing diverse and crucial physical and metabolic roles in humans (6).

Muscle mass essential refers to skeletal muscle and the various way it helps with your body's mobility, balance, and strength. The percentage of muscle mass can be an important indicator of health, as, over time, your muscle mass naturally declines, referred to as sarcopenia, making everyday activities more difficult and increasing health risks in older persons.

Maintaining a healthy muscle mass, especially in older adults, has been found to counteract mental health issues, such as depression (1). A healthy percentage of skeletal muscle mass is normally acquainted with low body fat percentages and, therefore, lower health risks in relation to obesity. 

How To Calculate Muscle Mass


Muscle mass includes the size of your skeletal, smooth (visceral), and cardiac muscles.

You won't be able to get an accurate measurement of your muscle mass without expensive technology. An MRI (magnetic resonance imaging) is the most accurate form of calculating your muscle mass percentage.

During an MRI scan, the machine uses strong magnets to briefly rearrange your body's hydrogen atoms to release energy in order to calculate your muscle mass.

Another method that can be used is bioelectrical impedance analysis (BIA), which sends a small and safe electrical signal through your feet and into the body, helping to calculate your body composition percentages.

DEXA (dual-energy x-ray absorptiometry) is also used to measure skeletal muscle mass, though much more expensive and not as widely accessible as, say, an MRI, and some have a high-risk factor for radiation exposure (8).

Another study that had previously reported the correlation coefficient between corresponding MRI and cadaver sections of human appendicular SM approached unity and found that the relative difference between MRI and cadaver SM measurements was 1.3% (9, 10).

Muscle Mass Averages For Men

For men, muscle mass averages range differently depending on age-

  • Age 20-39, 75%-89%
  • Age 40-59, 73%-86%
  • Age 60-79, 70%-84%

Muscle Mass Averages For Women

For women, muscle mass averages range differently depending on age-

  • Age 20-39, 63%-75.5%
  • Age 40-59, 62%-73.5%
  • Age 60-79, 60%-72.5%

Skeletal Muscle Mass and Gender

In a study using men and women from ages 18-88, it was explained why there is an increased prevalence of osteoporosis in women that may be explained by lower skeletal muscle mass compared to men, with the strong influence skeletal muscle mass has on bone mineral density (10).

Based on these discoveries, the recommendation for resistance exercise to build and maintain muscle mass, strength, and bone mineral density are highlighted for women in an attempt to decrease the risk of osteoporosis. 

Muscle Mass Formulas

This formula is pulled from a method to determine human body muscle mass using the anthropometric measures of girth and skinfolds, mainly used for men (2). The equations to use is as follows, where: H = height, FG = forearm girth, CG = calf girth, CCG = corrected calf girth, TG = mid-thigh girth, CTG = corrected mid-thigh girth, ϖ = Pi.

CTG = TG - ϖ(mid-thigh skinfold/10)

CCG = CG - ϖ(calf skinfold/10)

Muscle mass (g) = H(0.0553CTG² + 0.0987FG² + 0.0331CCG²) - 2445

What Is Muscle Atrophy?

Muscle atrophy is the decrease in muscle mass. It occurs when overall rates of protein synthesis exceed the rates of protein degradation (3).

In extreme cases, progressive loss of not only muscle but also body fat mass and the overall weight is related to advanced cancers that use these sources as fuel (4).

Less intense cases can be related to aging and a sedentary lifestyle. If you are experiencing extreme symptoms, it is recommended that you see a health care professional. 

BMI and Skeletal Muscle Mass- How do they relate?

In a study, it was found that skeletal muscle density and mass were significantly associated with sex, age, and BMI (body mass index) (6). In another study, it was discovered that skeletal muscle deteriorated quantitatively and qualitatively with aging, resulting in loss of muscle strength (7).

The epidemiology of sarcopenia in the elderly is an extensive one, choosing groups based on ethnicity, culture, location, and more.

As skeletal muscle is known to play diverse and crucial physical and metabolic roles in humans, determinants such as physical activity and dietary structures play a huge role in affecting loss or gain of skeletal muscle mass as well as the combination of your basal metabolic rate compared to your caloric intake (affecting weight gain and loss).

Statistical analyses show that there is an increased prevalence of physical inactivity, which plays a big part in the loss of total-body skeletal muscle and affects the whole body by creating a higher risk of disease and injury in the elderly. 

Mortality Rates In Correlation to Muscle Mass

In 2004, researchers began a study to find the correlation between muscle mass and those that had died from natural causes. They used the value of the subject's muscle mass index, which uses muscle mass divided by height squared. The results of the study were drastic. It was discovered that the total mortality rate was drastically lower in the 25% of subjects with the greatest muscle mass index when compared to the 25% of subjects with the lowest muscle mass index (11). 

Muscle mass index can also be used as a predictor of longevity in older adults in accordance with the risks of sarcopenia. 

QuickFire FAQs 

What is a good skeletal muscle mass percentage?

For men, muscle mass averages range differently depending on age groups-

· Age 20-39, 75%-89%

· Age 40-59, 73%-86%

· Age 60-79, 70%-84%

For women, muscle mass averages range differently depending on age groups-

· Age 20-39, 63%-75.5%

· Age 40-59, 62%-73.5%

· Age 60-79, 60%-72.5%

  1. What is skeletal muscle mass?

Basically, skeletal muscle mass is the muscles you can exercises or voluntarily control in key movements such as squatting, bending, lifting, etc. 

Can you gain skeletal muscle mass?

Yes! You can gain skeletal muscle mass by exercising through resistance and strength training. 

Is skeletal muscle mass the same as lean body mass?

No. Skeletal muscle is included in lean body mass calculations. Lean body mass includes muscle mass, bones, and bodily fluid (total body water). Muscle mass normally includes skeletal muscle, smooth muscle, and cardiac muscle. 

What can you do to keep a good body composition?

To keep a good body composition, exercising regularly (strength and resistance training), eating healthy foods (and in a certain caloric and macro range according to your body and goals), hydrating frequently, reducing stress, and sleeping well all play important roles in maintaining healthy body composition. 

How do you reduce skeletal muscle?

Having a low muscle mass is not recommended as it is related to higher health risks, such as cardiovascular disease, in relation to low muscle tissue. There are ways to reduce skeletal muscle--

    1. Eating in a caloric deficit resulting in weight loss
    2. Removing strength training from your exercise routine.
    3. Replacing strength training with cardio. 

What is another name for skeletal muscle?

Another name for skeletal muscle is striated muscle. 

Is the skeletal muscle voluntary or involuntary?

Skeletal muscle is voluntary. Extending your arm to reach out and grab a cup from the shelf and then bending at the elbow to bring it closer are all voluntary skeletal muscle movements. 




kaelyn buzzo  Kaelyn is a Certified Personal Trainer and Nutrition Coach (ISSA) with a Bachelor’s degree in Creative Writing (English) and a Minor in Nutrition from the University of South Florida. Read More.