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Does body mass define Soldier’s fitness level?

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UNITED STATES

04.12.2022

Courtesy Story

Defense Centers for Public Health-Aberdeen

By V. Hauschild, MPH, Army Public Health Center, Clinical Public Health and Epidemiology Directorate
ABERDEEN PROVING GROUND, Md. – The Department of Defense recently updated its 20-year-old policy that establishes body composition and physical fitness standards for active-duty service members to ensure optimal physical readiness.

The revised DoD Instruction 1308.03 states all service members “will maintain physical readiness by possessing the necessary body composition and aerobic and anaerobic fitness … to successfully perform in accordance with their service-specific requirements, missions, and military specialties.”

The cornerstone of the policy is the body fat standard that defines the acceptable body composition range for active-duty service members. The percent of a person’s body fat, or “%BF,” is a scientifically valid physical indicator for assessing health status.

“Scientific evidence supports the same military %BF standards as had been recommended by the previous version of the policy,” says Dr. Bruce Jones, a medical doctor and chief scientist for the U.S. Army Public Health Center’s Clinical Public Health and Epidemiology Directorate. “The policy update clarifies how simpler measurements may be used to estimate a service member’s %BF and makes allowances based on fitness tests.”

The DOD policy differentiates standards for men and women due to well-established physiological gender differences in body fat. The standard stipulates that active-duty men must maintain %BF between 18 and 26, and women must maintain %BF between 26 and 36.

“The most common way to estimate the amount of a person’s body that is fat is called the body mass index,” says Jones. “BMI is calculated using a person’s height and weight. It is a quick, inexpensive, and scientifically-accepted screening tool to identify overweight and obese individuals.”

BMI is used by the National Institutes of Health, the World Health Organization, the Centers for Disease Control and Prevention, and many healthcare practices to determine a person’s obesity classification and risks of long-term health impacts and death. The four classification levels, which apply to all men and women of the general population who are more than 20 years of age, define a BMI less than 18.5 as underweight, a BMI between 18.5 and 24.9 as normal or healthy, a BMI between 25 and 29.9 as overweight, and a BMI over 30 as obese.

BMI has compared relatively well with the more accurate measures of %BF, such as air-displacement plethysmography, water displacement, or dual-energy x-ray absorptiometry.

While BMI has value as a screening tool, it poses limitations as an exact measurement of body fat for some individuals, says Jones.

For example, because BMI does not reflect how fat is distributed, the index can’t identify those who carry most fat in their waists, which can mean greater adverse health risk. A waist circumference measurement may provide an indication of long-term health risk but will be misleading if not adjusted for height.

Also, BMI does not account for lean body mass, which is the portion of a person’s weight from body components other than fat, including muscles. Because of this, a very fit muscular person who weighs the same as a non-muscular, thick-waisted person of the same height will have the same BMI!

It is also possible for a healthy, muscular person to have a BMI that is slightly above the NIH/WHO/CDC “normal” range and not be truly “overweight.” Studies have shown that persons who fall into this category represent a small percentage of the overall population, and they usually exceed acceptable or normal BMI standards only slightly.

Because all of the NIH/WHO/CDC BMI classifications apply to adults, regardless of their age, fitness, or gender, the Army sets its own standards for Soldier acquisition and retention.

Army standards, referred to as weight-for-height standards, differ slightly from the NIH/WHO BMI classifications in that the former include a small portion of men whose BMI would place them in the NIH/WHO/CDC “overweight” range. This adjustment, which extends the “normal” range for Soldiers to a BMI of 27.5, accommodates the potential greater muscle mass of some Soldiers.

Tyson Grier, an APHC Injury Prevention Branch kinesiologist who has studied the use of BMI among Soldiers, says that despite the Army’s adjustment, a higher BMI generally indicates more fat mass, not more muscle mass.

“A Soldier with a BMI between 25 and 27.5 places them in the low end of the general population overweight BMI category, but their %BF may meet the DOD standard,” says Grier. “However, we still have other Soldiers who exceed standards.”

According to the APHC’s 2020 Health of the Force report,17% of Soldiers are classified as obese according to the WHO/NIH classifications (HoF pages 20-21). These service members do not meet the DOD or Army standards.

Another APHC IPB expert, Dr. Joseph Pierce, says while BMI and the adjusted Army weight-for-height standards provide an important measure of optimal physical readiness, there are tradeoffs between body composition and types of fitness.

“Soldiers with higher BMIs tend to perform better on strength and power tests, such as lifting heavy objects, but not as well on aerobic endurance tests, such as running two miles, while Soldiers with lower BMIs perform better on aerobic events like running.” says Pierce, lead author of a recent study of BMI and fitness capabilities among Soldiers.

Soldiers with very low BMI have also been found to have higher injury rates across physical fitness levels, says Jones. This finding underscores the risks of being underweight and the need to ensure weight control efforts do not result in excessive dieting and weight loss.

While DODI 1308.03 establishes the parameters of body composition required for all active-duty military personnel, it also allows for a range of body sizes and fitness testing necessary to meet service-specific needs.

Very importantly, says Jones, the updated policy now permits the military services to make allowances for their members who fail the body composition standards but perform exceptionally high on their physical fitness test. The policy does not stipulate how each service will implement this change, but excelling at fitness tests may allow some Soldiers to exceed the body fat standards.

The policy also requires the Army, Air Force, Navy, and Marine Corps to maintain physical fitness programs and monitor the number and types of injuries each year to ensure personnel can perform their duties in a manner that reduces the risk of fitness-training-related injuries. The policy allows each service to determine its own fitness testing methods and standards to meet its unique mission needs.

For its fitness testing, the Army chose the Army Combat Fitness Test to replace its 40-year-old Army Physical Fitness Test. The recently revised, six-event ACFT includes gender- and age-adjusted standards, and replaces the leg tuck with the plank.

Military personnel should maintain a %BF as specified by DODI 1308.03 and the applicable service-specific procedures to optimize their health and readiness:

• Review this BMI Factsheet to better understand BMI, and recognize that since muscle weighs more than fat, improving fitness and increasing muscle mass may not always result in weight loss.
• Achieve the weekly military physical activity Performance Triad, or P3, target goals.
• Refer to P3 tips for nutrition, sleep, and activity.
• Utilize Army Wellness Centers to assist with weight management goals, including monitoring of body fat using their specialized body fat assessment equipment called BodPods.
• Because being underweight can lead to higher injury risk, and excessive or overly rapid weight loss can be dangerous, seek advice from your healthcare provider or designated professional through your local AWC.

The U.S. Army Public Health Center focuses on promoting healthy people, communities, animals, and workplaces through the prevention of disease, injury, and disability of Soldiers, retirees, family members, veterans, Army civilian employees, and animals through population-based monitoring, investigations, and technical consultations.