Lean Body Mass and Muscle Mass — What’s the Difference? (2024)

A healthy fitness routine and diet may vary based on your goals. Some want to build strength and add lean muscle. Meanwhile, others are more interested in losing fat and gaining muscle mass. Whatever your motivation is, our body composition is complex, unique, and challenging to assess. There are too many factors at play and people often confuse them, especially the difference between lean body mass and muscle mass.

In this article, we’ll explain muscle mass and lean body mass meaning, see how they differ, and why they are so crucial for overall health. We’ll also explore how to measure them, so let’s dive right in.

It’s vital to clarify that there is no such thing as lean muscle simply because each muscle is lean. However, people use this term interchangeably with lean body mass, which is wrong.

Namely, lean body mass, or simply lean mass, is synonymous with fat-free mass. This term refers to your overall weight minus the nonessential fat — it includes the weight of your organs, skin, ligaments, tendons, body water, bones, and muscle mass.

Calculate it using the following equation:

Lean Body Mass (LBM) = Total Weight - Muscle Mass

Since lean body mass comprises various components, even a small weight change can affect it. Then again, organs don’t change, and while bone density decreases over the years, it doesn’t significantly affect the lean body mass weight. Therefore, the only areas to keep an eye on are muscle mass and body water.

Muscle mass is the muscle weight or the soft tissue in the body. It is also made of other components, too, such as fat, water, and bone.

A human’s body has three different types of muscles:

Muscle mass is the total amount of muscle tissue in the body. Whenever people talk about gaining muscle, they're actually referring to their skeletal muscle mass.

It is because this is the only type of muscle a person can control and grow with proper diet and exercise. If you keep them healthy and strong, you can increase the body’s mobility, strength, and balance.

Before measuring your lean body and muscle mass, you must consider one key factor — water. Water makes up a large portion of a person’s lean body mass. In fact, two-thirds of an individual's lean body mass is water (intracellular and extracellular), while the rest is dry lean mass (bone minerals, protein).

Therefore, it is possible to measure your lean body mass incorrectly since you must factor in your hydration levels, overall diet, and physical activity, all of which can fluctuate significantly during the day.

The same applies to muscle mass, as a muscle can contain up to 79% of water. The percentage can increase even more with resistance training, so you may be misled into thinking you have built up your muscles. In this case, what happened was that you only experienced a quick lean mass gain, but it didn’t change your muscle mass.

Measuring your muscle mass is extremely difficult because you must consider a person’s height, weight, age, gender, and ethnicity. Therefore, getting accurate results can be tricky.

However, we do know that the average muscle mass for adult males aged between 18 and 35 is 40%–44% and 31%–33% for females of the same age group. The numbers are 2%–3% lower for both males and females in the 36–55 age group.

Measuring your lean body mass is equally hard, and you must analyze your entire body composition to get accurate results. This means that only a trained professional can do it, using several methods:

Working on your lean body mass will lead to improved metabolism since they are interdependent. Studies have shown that people with higher lean body mass burn more calories at rest.

High lean body mass has been linked to lower risks of chronic diseases, such as stroke, cancer, and heart conditions, in both men and women.

Additionally, having a high lean body mass automatically means improved bone density and a higher muscle mass, essential components of strength and power.

A person's muscle mass percentage can serve as an indicator of their health. Muscle mass naturally declines with age, and this decrease, called sarcopenia, can make everyday activities more challenging.

Maintaining healthy muscle mass is essential, as it improves metabolic function. Muscular people burn more calories at rest than those with less muscle mass because they have a higher resting metabolic rate (RMR). Consequently, maintaining a healthy weight and preventing weight gain can be easier with a higher RMR.

With more muscle mass, we can boost insulin sensitivity, meaning our body uses insulin more effectively and controls blood sugar levels. We will also have a greater capacity for endurance and strength activities. Moreover, greater muscle mass reduces the risk of injuries and increases bone density.

Although genetics plays a critical role in determining our muscle mass, we can increase it by incorporating a proper diet, resistance training, adequate protein intake, and sufficient rest and sleep periods.

This implies lifting weights, using resistance bands, and doing exercises to challenge the muscles. Protein repairs muscles and supports their growth, so consuming between 1.2 and 2.0 grams per kilogram of body weight daily is advised. Incorporate rest periods and have a good night’s sleep to repair muscles and promote their growth.

Also, avoid extreme diets, as they can only lead to the loss of muscle mass and lean body mass.