Understanding Muscle Mass: What It Is, How to Measure It, and Why It Matters

Muscle mass is an important indicator of strength, mobility, and overall physical function. While it’s difficult to measure precisely, understanding its role in your body can help you make informed decisions about your health and fitness.

What Is Muscle Mass?

Your total body mass is made up of two main components: body fat and lean body mass. While the terms “lean body mass” and “muscle mass” are sometimes used interchangeably, they are not the same.

Lean body mass includes:

•  Muscle mass (skeletal, smooth, and cardiac muscle)
•  Bones
•  Bodily fluids

When people talk about muscle mass, they typically mean skeletal muscle, which plays a key role in mobility, balance, and strength.

Low vs. High Muscle Mass

•  Low muscle mass means you have less muscle than the average person in your age and gender group.
•  High muscle mass means your muscle percentage is above average.
• You can have high or low muscle mass regardless of your overall body fat percentage.

Muscle Mass Percentage: What’s Normal?

Muscle mass percentages vary depending on factors like height, ethnicity, and fitness level. While there isn’t much reliable data, a 2000 study in the Journal of Applied Physiology provides a reference point.

Average Muscle Mass Percentages for Men

• 18–35 - 40–44%
• 36–55 - 36–40%
• 56–75 - 32–35%
• 76–85 - < 31%

Average Muscle Mass Percentages for Women

• 18–35 - 31–33%
• 36–55 - 29–31%
• 56–75 - 27–30%
• 76–85 - < 26%

These figures provide a general idea, but new research is needed for more accurate benchmarks.

How Muscle Mass Is Measured

There’s no simple way to determine your exact muscle mass percentage. While calculators, formulas, and scales claim to measure it, these methods aren’t always reliable.

Methods to Estimate Muscle Mass

1. Using Body Fat Percentage

You can estimate your lean body mass by measuring your body fat percentage with a body fat scale. These scales use bioelectrical impedance to send a small electrical current through your body, estimating your fat percentage.

To estimate lean body mass:

•  Step on a body fat scale (many require you to input your height, weight, gender, and age).
•  Subtract body fat percentage from 100% (e.g., if you have 30% body fat, your lean body mass is 70%).

Since muscle is only one part of lean mass, this method doesn’t provide an exact muscle mass measurement.

2. U.S. Military Formula

The U.S. military estimates body fat percentage using circumference measurements.

•  Men: Measure your abdominal and neck circumference. Subtract neck from abdominal measurement.
•  Women: Measure your waist, hip, and neck circumference. Use the formula: waist + hip - neck = circumference value (CV).

This method provides an estimate but doesn’t account for muscle density.

3. MRI Scan (Most Accurate Method)

Magnetic Resonance Imaging (MRI) is the gold standard for measuring muscle mass. It works by scanning your muscles using strong magnets.

While highly accurate, MRI scans are expensive and not practical for routine tracking.

Benefits and Drawbacks of High Muscle Mass

Benefits of High Muscle Mass:

•  Slower muscle loss with age: Muscle mass naturally declines after age 30. Higher muscle mass helps prevent sarcopenia (age-related muscle loss).
•  Increased metabolism: Muscle burns more calories than fat, improving metabolic rate.
•  Longevity: A 2014 study in the American Journal of Medicine found that people with more muscle mass tend to live longer.

Potential Downsides of High Muscle Mass:

•  Finding well-fitting clothes can be difficult due to increased body size.
•  Higher caloric intake is required to maintain muscle mass, which may be costly or inconvenient.
•  Some athletes experience reduced flexibility, though this varies based on training style.

Drawbacks of Low Muscle Mass

There are no real benefits to low muscle mass. Some theories suggest that excess fat may provide an energy reserve, but this is hypothetical.

Risks of Low Muscle Mass:

•  Increased risk of injury and disability
•  Reduced mobility and strength
•  Higher risk of metabolic disorders like diabetes and osteoporosis
•  Slower recovery after surgery or illness
•  Higher risk of early death

How to Build and Maintain Muscle Mass

While muscle naturally declines with age, it’s never too late to build and preserve it through exercise and proper nutrition.

1. Strength Training

Strength training is the most effective way to increase muscle mass.

•  Bodyweight exercises (push-ups, squats)
•  Resistance bands
•  Weightlifting (dumbbells, barbells, weight machines)
•  High-intensity interval training (HIIT)
•  Pilates

Aim for two to three strength training sessions per week. Cardio also plays a role in maintaining muscle health and preventing age-related loss.

2. Nutrition for Muscle Growth

Muscle-building requires adequate protein intake and balanced nutrition.

•  Protein: 10–35% of daily calories should come from protein. High-protein foods include:
•  Carbohydrates: Essential for fueling workouts. Should make up at least 50% of daily calories if training regularly.
•  Healthy fats, vitamins, and minerals are also crucial for muscle recovery.

Limit processed foods and focus on whole, nutrient-dense options.

Final Thoughts

Muscle mass is a key part of overall health, impacting strength, metabolism, and longevity. While it’s difficult to measure precisely, tracking body fat percentage and focusing on strength training can help you maintain a healthy balance.

By combining exercise and good nutrition, you can build and preserve muscle mass at any age, improving both physical function and long-term health.

If you’re unsure about your body composition, consult a fitness professional or healthcare provider for personalized guidance.