Lean body mass: Definition, Calculation & Importance

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What is lean body mass?

The body is composed of two elements: lean body tissue (i.e. muscles, organs, bones and blood) and body fat (or adipose tissue). The proportion of these two components in the body is called body composition. This is far more important than total weight.

For example, two people may weigh the same, but have a different body composition. Athletes usually have a smaller percentage of body fat and a higher percentage of lean weight than less physically active people.

In this post you’ll find the answers to the following questions:

    • What is lean body mass?
    • How to calculate lean body mass?
    • What is the importance of knowing your lean body mass
    • Why it’s so important to have more lean body mass?
    • What is the difference between lean body mass and free fat mass?
    • How genes affect lean body mass?
    • What is the best possible approach to increase lean body mass (decrease body fat mass)?

Definition of lean body mass (lean body weight)

Lean body mass is defined as the total weight of the human body minus the weight of all the fat. Essentially lean body mass includes muscle, bone, organs, and water.

lean body mass diagram

Simply put, lean body mass is comprised of everything in your body besides body fat.

Lean body weight usually ranges from 60 to 90 percent of body weight. Athletes often have lean body weight percentages between 81 and 91 percent for women and 84 and 94 percent for men. While this is normal for trained individuals, it’s lower than the average for healthy individuals.

Calculating lean body mass

First you have to determine your body fat percentage using one of the methods for measuring body fat percentage. There are several ways to determine how much body fat you are carrying. Each has its pluses and minuses.

Once you know your body-fat percentage, it’s easy to calculate your lean body mass (LBM). Simply subtract it from 100 to determine your percentage of lean body tissue. From there, multiply that percentage by your current weight to get your total amount of lean body mass. For example, let’s say that you use one or more of the methods we listed in our previous article to find out that you have 30 percent body fat. That means you have 70 percent lean body tissue. Then you take 70 percent of your total body weight (multiply it by 0.7) to get your lean body mass.

The formula below outlines how to calculate one’s fat mass and lean body mass:
1. Body fat % x scale weight = fat mass
2. Scale weight − fat mass = lean body mass

For example: We have a 200 pound (90.7 kg) athlete with only 10% body fat. His fat mass and lean body mass would be calculated as such:

1. 0.10 (body fat %) x 200 (scale weight) = 20 pounds of body fat
2. 200 pound (scale weight) − 20 (pounds of body fat) = 180 pounds of lean body mass

The remaining 180 pounds (200 total pounds – 20 pounds of fat weight = 180 lbs.) is muscle, organs, bones, water, etc.  Researchers call the remaining 180 pounds lean body weight (LBM) – the amount of body that is NOT fat!

lean body mass percentage

Leaner is better: percentage of lean body tissue is decreasing from left to right

Importance of knowing your lean body mass

Knowing your body fat percentage also allows you to calculate your lean body weight, which is essentially all parts of your body that aren’t fat. Knowing your lean body mass will help you calculate precisely how much protein you should be eating on a daily basis, another crucial metric that will help you enormously in your quest for optimal health.

Importance of having more lean body mass

The key word is metabolism. Fat isn’t biologically active tissue; it doesn’t do much of anything except keep you warm. Muscle, on the other hand, is constantly working, even when you’re not. It is constantly sucking calories and generating heat. The more muscle you have, the more energy you use, even when you’re doing nothing more active than tying your shoes.

Which takes us back to weight training. It has a direct effect on weight loss because it burns a tremendous amount of calories while you’re doing it. At the same time, the muscle you build with lifting jacks up your resting metabolic rate, the calories your burn every minute of every day.

Also, maintaining lean body weight as you age will help you to:

  • Combat obesity;
  • Protect against diabetes and insulin resistance;
  • Recover much faster from illness or disease;
  • Keep your bones strong and healthy;
  • Reduce your risk of falls and fractures;

Fat-free mass Vs Lean body mass

Fat-free mass (FFM) is the weight of all body components except fat and is primarily made up of the
skeletal muscles and bone, including minerals, protein, water, and fat-free organ weight. The term FFM
is often used interchangeably with lean body mass (LBM).

However, LBM includes essential fat and FFM does not. Essential body fat is the fat associated with the internal organs, central nervous system, and bone marrow. Without fat in these areas, the body cannot function properly. Approximately 70% of the FFM is made up of water.

How genes affect lean body mass?

Your natural body type dictates to some extent how much fat you carry and how readily you store it. For example, if you are an ectomorph or mesomorph, you are naturally lean and will be able to achieve a lower body-fat percentage than an endomorph who stores fat easily.

But, whatever your natural body type, you can still achieve a lower body-fat level and more defined physique through consistent hard training and healthy eating. The important point is to decide on a level that is realistic for your build and shape.

How to increase lean body mass?

Anaerobic exercise (e.g., resistance training, sprint training) increases and helps maintain lean body mass, which is the most metabolically active tissue in the body. This raises and helps sustain RMR (resting metabolic rate) during weight loss and weight management.

Aerobic workouts are fine; every smart exercise plan includes them since cardio training builds your cardiovascular system and decrease body fat. But aerobic exercise mainly effects the expenditure of calories. Pumping iron, on the other hand, literally changes your body’s composition. It builds lean muscle, kicks you to a higher metabolic rate, and burns fat faster and more efficiently that anything else. Therefore, weight training is essential to lose fat and to maintain lean body mass. The truth is if a person has limited time, we would recommend weight training over aero­bics any day.

However, the best possible approach would be doing both together. This will put you on the fast track to a leaner, tighter body.

1 pound of muscle vs 1 pound of fat

About Author

Hey! My name is Kruno, and I'm the owner and author of Bodybuilding Wizard. I started this website back in late 2014, and it has been my pet project ever since. My goal is to help you learn proper weight training and nutrition principles so that you can get strong and build the physique of your dreams!

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