When discussing sports nutrition and programs for gaining or losing weight, the term“lean mass”often comes up. Many people mistakenly associate it with muscle mass, when in fact it includes other components.
So, what is lean body mass? It simply refers to everything thatisn’t body fat. This means that, in addition to muscle mass, it includes bone mass, body water, and other components essential to health and the functioning of the body’s metabolism.
Between body weight, lean body mass , and fat-free mass, it’s easy to get confused. It’s important to distinguish between these concepts to understand how ourbody composition works, what lean body mass really is, and why it’s so important to athletes.
So, here's howto measure lean body mass, how to interpret it, and how to use it to track your progress during a training program.
Contents
- Why can two people of the same weight have different body types?
- The Actual Composition of Lean Body Mass
- Why is it often confused with muscle mass?
- Why are athletes interested in lean body mass?
- The same lean body mass but two levels of performance
- How has it changed over time?
- How can you track changes in your lean body mass?
- Do dietary supplements help with its development?
In a nutshell
- Lean body mass refers to everything in the body other than fat mass: muscles, bones, organs, water, and connective tissues.
- It is often confused with muscle mass, but muscles account for only a portion of lean body mass.
- Two people of the same weight can have very different physiques depending on their body composition (water, fat, muscle, bone density).
- Lean body mass is important for tracking athletic performance, particularly through indicators such asthe IMM, because it helps assess physical fitness and muscle development.
- It changes with age and physical activity: regular exercise (especially strength training) helps maintain or increase it, while a sedentary lifestyle contributes to its decline.
Why can two people of the same weight have different body types?
Body mass is defined as the total weight of the human body. It is a figure expressed in kilograms that differs from a concept of interest to nutritionists:body composition. The latter encompasses the following components:
- bone;
- water;
- Grasse;
- and muscular.
This explains why two men with a body weight of 70 kilos can havevery different body types, such as:
| Athlete A | Athlete B |
|---|---|
| more skeletal muscle | more water |
| fewer bones | high bone density |
| low glycogen | full reserves |
| not very well trained | highly trained |
Even among people of similar weight, body densities vary, which makes it difficult to estimate body composition.The body mass index (BMI)does not distinguish between these differences, resulting in different body shapes even among people of similar weight. Furthermore, this index can be skewed in cases of water retention, for example.
Weight is therefore a general measure, but it does not define actualbody composition. This is where the concepts of lean body mass and fat mass come into play.
The Actual Composition of Lean Body Mass
Many articles refer to lean mass as a component of the body, but in nutrition, it is more commonly referred to asa compartment. There are several models for studying body composition, including the physiological model, which incorporates this concept.
A compartment consists ofbody componentsthatare functionally interconnected. In nutrition, the two-compartment model is widely used and distinguishes between:
- body fat, or the total amount of triglycerides stored in fat cells;
- lean body mass, which represents the portion of body mass other than fat mass.
Lean body mass is the sum of all tissues other than adipose tissue.
Lean body mass is therefore composed of:
- water, both intracellular and extracellular;
- lean body mass, including skeletal muscle, bones, organs, skin, connective tissue, as well as minerals, protein content, etc.
Why is it often confused with muscle mass?
It is often confused with muscle mass, because muscle mass is part of lean body mass.
Furthermore, an increase in muscle mass will lead to an increase in lean body mass, but the reverse is not necessarily true. An increase in lean body mass is not necessarily linked to muscle gain. It could be due to higher hydration levels, for example.
(Add a diagram based on the image to illustrate the following formula)
Total body mass = fat mass + lean body mass ((intracellular water + extracellular water) + (dry lean mass))
| Terminology | Differentiation |
| lean body mass | total weight from which body fat is subtracted |
| muscle mass | weight of skeletal muscles |
| dry weight | lean body mass minus water |
| lean body mass | includes water and dry matter |
| lean mass | is equivalent to lean body mass |
Why are athletes interested in lean body mass?
Some athletesregularly calculate their Lean Body Mass Index (LBM)to track changes in theirbody composition.
This measurement also allows themto estimate their muscle massand adjust their training accordingly. This indicator is also useful for monitoring potential muscle loss associated with sarcopenia, a condition associated with aging.
In fact, IMM is a more accurate measure, since the portion of lean body mass that consists of skin, bones, or blood does not change significantly. Thus, any variations would be primarily related to changes in muscle mass.
For athletes, knowing their IMM is also helpful for managing their diet—for example, toadjust their protein intake.
Muscle mass is a key indicator of longevity. Therefore, tracking your lean body mass helps you maintain your physical health through proper nutrition and physical activity.
The same lean body mass but two levels of performance
Two athletes with similar lean body mass may havedifferent muscle quality. It is therefore important to distinguish between the quantity of lean body mass and its quality.
Scientific literature shows that people with the same amount of lean body mass can have different levels of strength.1 Anenergy deficit can reduce lean body mass without affecting strength levels. This demonstrates that lean body mass and strength are not directly correlated.
Conversely, an increase in lean body mass does not guarantee greater strength. Thedistribution of muscle fibersis partly genetically determined. However, certain muscle fibers are associated with strength and power, while others are better suited for endurance.
We are not all born with the same potential to build muscle. Again, this fact supports the idea that muscle quality varies even when mass and fiber composition are the same.
Increasing lean body mass does not automatically improve performance.
How has it changed over time?
Lean body masschangesfrom childhood through adulthood, and then decreases with age.
In addition to age, the level of physical activity is one of the factors influencing changes in lean body mass. A sedentary lifestyle leads to a decrease in lean body mass of approximately 0.35% per hour of daily sedentary activity.
For so-called low-intensity activities, no impact on body composition was observed.
In contrast,moderate-intensityactivities (+0.83% per hour of activity) andhigh-intensityactivities (+4.26%) increase the percentage of lean body mass per hour, everyday.² These figures clearly illustrate the negative impact of a sedentary lifestyle on the lean body mass ratio.
How can you track changes in your lean body mass?
There are many methods for tracking changes in body composition. Most of them start with body fat percentage and then use that to determine lean body mass. These include:
- Magnetic Resonance Imaging (MRI), which is used for medical purposes due to its high cost;
- The adipometer, better known as a skinfold caliper, uses predictive equations to calculate the thickness of subcutaneous adipose tissue at various locations on the body.
- impedance scaling, orbioelectrical impedance analysis, which works by passing a very low-intensity electrical current through the body to estimate the amount of body water in relation to lean body mass.
The problem with these methods is their variability, which results in a lack of precision.
It is recommended to conduct follow-up assessments using the same method over time.
There is also a test called DEXA, or dual-energy X-ray absorptiometry. This more accurate test uses X-rays of two different energy levels to pass through the body. The analysis report breaks down body fat, lean body mass, and bone mass.
High-quality sugar-free proteins
- Cold microfiltration
- Optimal digestibility
- Unsweetened flavor
- Without performance-enhancing substances
- Gluten-free
Do dietary supplements help with its development?
No supplement directly increases lean body mass.
Muscle growth results from amechanical stimulus—that is, resistance training. Without it, dietary supplements do not lead to an increase in lean body mass.
However, some of them create a favorable environment that makes it easier to gain lean muscle mass orlosebodyfat.
For example, whey protein and creatine promotetraining adaptations.
| Protein Powders | Créapure Creatine |
| help meet daily protein needs; stimulate protein synthesis after exercise; help limit muscle loss during a calorie deficit. | increases phosphocreatine stores; helps you sustain high-intensity training; helps ATP regenerate faster. |
These supplements promotemuscle growth. Some have even been shown to increase muscle mass.
This is true ofprotein: it promotes muscle growth by compensating for an insufficient intake. In older adults, combining protein with exercise is more effective than exercise alone.
Similarly,creatineincreases lean mass gains in individuals who perform resistance training.
A supplement helps increase lean body mass when combined with an appropriate workout routine and sufficient calorie intake.
Here is a summary that separates fact from fiction about what lean body mass really is:
| What Many People Think | What has been demonstrated |
|---|---|
| Lean body mass = muscles. | Muscles account for only a portion of lean body mass. |
| More lean body mass = more strength. | Muscle quality and other factors influence performance, given the same amount of lean body mass. |
| Losing weight increases the percentage of lean body mass. | Sometimes when you lose weight, you lose muscle. So in this case, the opposite happens. |
| A smart scale accurately measures lean body mass. | It provides an estimate that depends on other factors (hydration, meals, etc.). |
| We can talk about lean muscle mass. | This is a misnomer, since muscle is, by definition, lean. We refer to lean body mass. |
Conclusion
Lean body mass is not just a number displayed on a smart scale like the Body Scan. It refersto all thebodytissuesthat are not fat. This includes skeletal muscle mass, bones, body water, and internal organs. Changes in lean body mass provide insight into physical fitness and overall health.
Whether your goal is to build muscle, lose body fat, or stay in shape, it’s better to monitoryour body compositionrather than the number of kilos shown on the scale. Low lean body mass increases the risk of muscle loss. Conversely, a higher lean body mass indicates better metabolic function, improved muscle function, and a lower risk of age-related complications.
To effectively increase lean body mass, the top priorities are, first and foremost, toengage inregularphysical exerciseand follow a strength training program. Next, you needto meet yourproteinneedsthrough an appropriate diet (meat, fish, eggs, dairy products, or plant-based alternatives) and maintain a caloric intake consistent with your goal. Dietary supplements are a useful tool when theycomplement these fundamentals. They are not a substitute for proper training or a balanced diet.
Understanding the difference between body fat and lean body mass allows you to betterinterpretyour measurement results. It’s also a way to track how your body is adapting, rather than relying solely on the number on the scale.
