Muscle Mass Index Vs. BMI: Build Muscle To Live Longer

UCLA researchers found that people with greater muscle mass percentages live longer than those who have less muscle. Here are all the details and what they mean for you!

If you have been searching for the fountain of youth, I have some good news: it's been found! No, it's not hidden in some Florida swamp, it's actually somewhere between the dumbbells and the pull-up bar. Nope, I'm not kidding: The University of California, Los Angeles (UCLA) has published some exciting new research that suggests older adults with more muscle mass are less likely to die prematurely than those with less muscle.3

These findings add to a growing pile of evidence that overall body composition is a better predictor of all-cause mortality than overall weight or body mass index (BMI).3 So what does this mean for my fellow meatheads? Muscle mass seems to be an important predictor of life expectancy, and maintaining lean muscle mass well beyond middle age can increase your life span!3

A Massive Study

Total body mass includes both fat and muscle. Each of these tissue types has a different effect on the metabolism, so researchers at UCLA tested the hypothesis that greater muscle mass—and the metabolic stimulus it provides—is associated with a lower mortality rate in older adults.1

Study subjects were measured using bioelectrical impedance. Because muscle and fat have different water content, electrical currents flow through them at different rates. Bioelectrical impedance is the measure of how much fat or muscle mass a person has based on the speed of those electrical currents.

"Muscle mass seems to be an important predictor of life expectancy, and maintaining lean muscle mass well beyond middle age can increase your life span!"

Based on the results, researchers calculated each subject's muscle mass relative to his or her height. This value is called a muscle mass index, defined as muscle mass divided by height squared. In 1988-1994, 3,659 people—males over 55 and females over 65—were surveyed for their muscle mass index. In 2004, researchers determined how many individuals had died from natural causes and correlated it with their muscle mass index.3

The results were clear: People with more muscle mass were less likely to die of natural causes. Total mortality was significantly lower in the 25 percent of individuals with the greatest muscle mass index compared to the 25 percent of individuals with the lowest.1

The findings of this study are significant because they reveal a glaring issue in how the medical community measures health and longevity: BMI.

The BMI Lie

Traditional criteria for obesity and obesity-associated health risks are calculated using the body mass index (BMI). These guidelines are faulty and wildly inaccurate. BMI is calculated from a person's height and weight, defined as mass in kilograms divided by height in meters squared. In no way does BMI calculate a person's body fat directly.2

Imagine a man who is 5-foot-9 and weighs 260 pounds. At that height and weight, the man would have a BMI greater than 40, placing him in the third and most severe tier of obesity. What the BMI doesn't tell you is that this man could be a professional bodybuilder on stage at the Olympia. He has low body fat and has a lean mass percentage bigger than you or I could even imagine. This BMI error doesn't occur only in professional bodybuilders . Well-muscled people are often given higher BMIs and the subsequent "medical" diagnosis of being overweight or obese.

The Centers for Disease Control and Prevention (CDC) and health care organizations use BMI to assess individuals because it is inexpensive and easy to calculate,2 not because it is the most effective method to predict true body composition or health risks. Diagnosing a person as obese or overweight should come from the percentage of fat mass and muscle mass a person has. It's a much more accurate and effective way to measure health risk.

What It All Means For You

This study demonstrates the importance of muscle mass in overall life expectancy and highlights the necessity to look beyond total body mass when assessing health.1 "In other words, the greater your muscle mass, the lower your risk of death," says Dr. Arun Karlamangla, the study's co-author. "Thus, rather than worrying about weight or body mass index, we should be trying to maximize and maintain muscle mass."3

Building muscle mass is important in decreasing metabolic health risks.3 Therefore, adding some muscle and increasing your BMI by increasing your overall body weight could actually improve your health and decrease your risk of premature death.

"Building muscle mass is important in decreasing metabolic health risks."

Considering the support of these findings, measurements of muscle mass relative to body height should be added to criteria health care professionals use to diagnose and treat patients.3 Dr. Preethi Srikanthan, lead researcher in the study, says, "So many studies on the mortality impact of obesity focus on BMI. Our study indicates that clinicians need to be focusing on ways to improve body composition, rather than on BMI alone."3

The next time you step on the scale and worry about what the resulting number means to your health, think about the composition of your overall weight. If you don't already know it, get your body fat percentage tested by a qualified trainer and, most importantly, start building more muscle!


  1. American Journal of Medicine, The. Muscle Mass Index As a Predictor of Longevity in Older Adults. Volume 127, Issue 6, Pages 547–553, June 2014
  2. Centers for Disease Control and Prevention: Division of Nutrition, Physical Activity, and Obesity, National Center for Chronic Disease Prevention and Health Promotion. About BMI for Adults. 9/13/2011. Web. Acessed 5/29/2014
  3. Rivero, Enrique. Older adults: Build muscle and you'll live longer. UCLA Health Systems. 3/13/2014. Web. Accessed 5/29/2014

Recommended For You

Rig For Pain: Ashley Horner's Full-Body Circuit Workout

You're about to go on one wild ride! Join fitness athlete Ashley Horner as she takes you through her favorite circuit workout. Try not to puke!

How 4 Letters Can Spell Fitness Success

If you've been spinning your wheels at the gym, get familiar with F.I.T.T. to help you customize your workouts and achieve your goals!

The Best Female Athlete You've Never Heard Of

Camille Leblanc-Bazinet is one of the top 10 CrossFitters in the world. Check out how she trains, how she eats, and how she prepares to perform at the highest level.