How does one rationalize the different uses of body composition for performance, appearance, and health? To assist the CMNR in responding to these questions, a workshop was convened on February , , that included presentations from individuals familiar with or having expertise in current military recruitment and retention criteria, military task performance, body composition and physical performance, racial or ethnic differences in body composition, and gender differences in body composition and physical performance.

The invited speakers discussed their presentations with Committee members at the workshop and submitted written reports. The Committee met after the workshop to discuss the issues raised and information provided.

Committee members later reviewed the workshop presentations and drew on their own expertise and the scientific literature to develop the following summary, conclusions, and recommendations. The rationale for physical standards for accession and retention in the military, according to Army regulation AR is ''.

to insure that all personnel are able to meet the physical demands of their duties under combat conditions and present a trim military appearance at all times'' AR , Current physical standards place upper limits on body fat as assessed from anthropometric measurements, including height, weight, skinfold thicknesses, body diameter measurements, and body circumference measurements.

Body composition in terms of body fat mass BFM and lean body mass LBM is calculated from these measurements. Anthropometric measurements are used because they are inexpensive to obtain, relatively easily learned, and adaptable to field conditions.

For accession, personnel are initially screened by height and weight. Standard tables have been developed for ease of use by field commanders and recruitment staff to identify personnel who fall outside acceptable values of weight-for-height. These standards differ among the military services, based on the perceived needs of each service, and are included in Appendix A.

If an individual is identified as not meeting acceptable standards of weight-for-height, an assessment of body composition by anthropometric techniques is performed.

The formulas used for determining body composition also differ among the services Appendix A. The Army uses a combination of height, weight, and circumferences of neck and waist in men and of height, weight, and circumferences of neck, forearm, wrist, and hips in women to calculate percent body fat.

The rationale for these particular measurements is based on studies done at the U. Army Institute for Environmental Medicine USARIEM on 1, men and women Vogel et al. The Navy uses height, weight, and circumferences of neck and waist for men Hodgdon and Beckett, a , and height, weight and circumferences of neck, waist, and hips in women Hodgdon and Beckett, b.

The Marines use measurements of height, weight, and neck circumference for men Wright et al. The Air Force uses height, weight, and biceps measurements for men Fuchs et al. For the Army and Navy, the weight-height and body fatness standards for admission allow a greater degree of overweight than do the standards for retention.

The rationale for this policy is that high levels of physical activity during basic training result in a loss of body fat and a gain in LBM in the overfat individuals. Thus military recruits can be accepted that exhibit higher body weight for their height than will subsequently be permitted by retention standards.

For the U. Air Force and recently the U. Marine Corps 1 retention standards are also used for accession. It is generally accepted that body weight 20 percent above the population standard of height for weight is obesity. Although the military services differ in their acceptable standards, all services have clearly stated weight control and physical fitness programs that are detailed in their retention standards Appendix B.

On the basis of these measurements and medical review, they are assigned to a program of diet and exercise for a specific time period that varies with each service.

At set time intervals, the individual's progress is reviewed, and the weight control program is evaluated. For all services, there is a specific total time limit established for an individual to meet the requirement prior to final evaluation for separation.

Individuals who do not lose sufficient weight or body fat are discharged from the service. Physical performance standards follow a similar procedure. However, also of concern here is that individuals who do lose weight and meet the service retention standards are at high risk to regain this weight with advancing age.

Numerous studies have documented an increase in body weight and percent body fat with increasing age Borkan et al.

There is also evidence that excessive body fat is not necessarily a lack of personal discipline as stated in AR but a chronic disease of complex and multifactorial origins Bray, , , A genetic component is involved Bouchard et al.

According to this hypothesis, when individuals attempt to lose weight below a set level, body defense mechanisms come into play that limit the amount of weight lost unless there are major changes in lifestyle, eating, and exercise Keesey, ; Keys et al.

Studies in humans have shown that there is frequently minimal or no relationship between food intake and body fatness for individual people Thomas et al. Because a number of recent articles have reviewed methods for assessing human body composition Buskirk, ; Heymsfield and Waki, ; Lukaski, ; Smalley et al.

This section will begin with a brief review of the operational definitions used in this report, followed by an overview of methods for assessing body composition as directly applied to the military services. Body composition, in the context of these proceedings, refers to the relative proportion of lean body mass LBM and body fat mass BFM within the body.

LBM can further be subdivided into muscle mass, body water, and bone mass. These two approaches are commonly referred to as a two-compartment model LBM and BFM or a four-compartment model BFM, muscle mass, body water and bone mass for assessing body composition.

Because the main concern of the military is LBM and BFM as related to performance, the two-compartment model is generally used by the services. However failure to account for differences in bone density can lead to systematic errors in measurements, so the two-compartment model must be used with caution when applied to an individual.

Fat-free mass FFM refers to the portion of the body remaining after all fatty substances are extracted. For the purposes of this report, FFM will be used interchangeably with LBM. The most commonly used anthropometric assessments are height, weight, skinfold thicknesses, body diameter, and body circumference measurements.

Numerous previous studies in the literature have used combinations of anthropometric measurements to estimate body fat. It is well recognized that there are problems with this approach. A major criticism of the use of anthropometric data to calculate body fat is that the formulas are based on population data, and when such formulas are used to calculate body fat of an individual, a significant error may result Lukaski, In other words, the formula may have a small error when predicting body fat for a population but a greater error for predicting body fat for a given individual.

Another problem with anthropometric measures is observer error. Hodgdon Chapter 4 discussed the difficulty of training military personnel to accurately measure skinfolds and body circumferences.

After performing trial skinfold measurements, only 24 percent of personnel were proficient. However, 68 percent of trainees had reached proficiency after only 45 measurements of body circumferences. In cross-validation studies, the standard errors for the formulas used by the different services ranged from 3.

Thus, based alone on errors in measurement and inherent individual differences, these data indicate that it would be possible to inappropriately target an individual for separation or to reject a new recruit.

Due to these concerns, the military should consider the importance of validation of their measurements through multiple observations on each individual. When measurements of height and weight are combined with measurements of waist and hip circumferences, a better assessment of long-term health risk may be obtained.

Increasing evidence suggests that the deposition of fat in the abdominal area, particularly in the intraabdominal depots, is associated with a variety of diseases including hypertension, diabetes mellitus, hyperlipoproteinemias, and increased cardiovascular risk NIH, Using these measurements to screen recruits at accession may help select individuals with lower long-term risk for health problems.

Using them in older military personnel also may identify individuals, with or without obesity, who are at increased health risk, and who should receive special attention for weight or body fat reduction. Densitometry has generally been considered the standard against which all other techniques for measuring body composition are compared.

However, the formulas on which this method is based were calculated originally from carcass analysis of only seven individuals Brozek et al. In this procedure, which assumes the two compartments of LBM and BFM, the density or specific gravity of the body is measured by weighing the body in air and under water, with correction made for residual air in the lungs Behnke et al.

The relative proportion of the two compartments is calculated, with assumptions made about the density of the two compartments. The density of the body fat is assumed to be constant.

Although interstitial muscle fat has a slightly higher density than depot fat, this assumption does not usually lead to a significant error. Much more of a problem is the assumption of a density for LBM, because it can be quite variable depending on age, race, physical activity, gender, and possibly other variables, such as bone mass.

Underwater weighing has also not been well standardized. For example, the influence of age, gender, race, and ethnic group has not been evaluated. The relatively greater lean mass, particularly bone mass, that is present in many Blacks further adds to the inaccuracy of the formulas for this population.

The Committee recognizes that underwater weighing could eventually be improved if the two-compartment model in present use applied densities for lean body mass that are specific for age, gender, and ethnicity. As with the calculation of body composition from anthropometric data, underwater weighing measurements may have significant error.

The technique requires special equipment and highly specialized training, which limit its use to specialized facilities. Expensive equipment and the time required to train technical staff, coupled with the fairly long time it takes to do a measurement of a single individual, precludes this technique from being useful for accession or retention screening of military personnel.

The principle on which bioelectric impedance analysis BIA is based is that lean tissue conducts electricity better than does fat tissue. Electrodes are placed on the arms and legs, and a low-level current is run through the individual. Impedance—resistance to the flow of electricity—is measured, and the percent body fat is calculated by a formula Segal et al.

This technique has been standardized for several populations, but as with the techniques mentioned above, it is less accurate when used in a given individual. Some training is required to achieve reasonable reproducibility, and there is significant interobserver variation. Segal et al. It would appear that BIA, particularly with the most modem equipment, is preferable to anthropometry.

However, BIA as commonly used at present, does not give any information on regional fat distribution which may be of military interest and importance. More research is needed to validate this technique. Several techniques described in the literature are more accurate than the techniques described above, but the expense of purchasing costly equipment or the time required to perform the measurements may not make their use feasible by the military services.

These techniques include dual photon absorptiometry, neutron activation, whole body potassium 40 counting, electromagnetic conductance, and body water measurement by radioactive or stable isotopes.

Advances in the development of multicompartmental chemical approaches to the determination of body composition in humans have recently been summarized by Heymsfield and Waki Most of these techniques would be of great research interest for validating simple measurements that can be used on a large scale in the military, but they are less practical for routine use.

Of these methods, only dual photon absorptiometry has potential for routine use as a secondary measure of body composition by the military see review in Chapter Like many new techniques additional validation studies are needed.

This equipment also requires a substantial financial investment and specially trained personnel to operate. Many studies have documented an increase in body weight and percent body fat with increasing age, at least over the age range of active duty military personnel Borkan et al.

For the majority of people, LBM decreases with age and body fat increases with age, even if body weight does not change. This fact is recognized by the military's age-adjusted standards for body weight, body fatness, and performance. Alterations in body composition with age also exacerbate the problem of differences in accession versus retention standards for excess body weight and body fatness.

The rationale for the difference between accession and retention standards in some branches of the military appears to be related to high levels of physical activity during basic training, which usually produce losses in body fat and gains in LBM.

Obese individuals who do not lose sufficient weight or body fat are discharged from the service. However, individuals who lose weight and meet the service retention standards may be at increased risk to regain this weight with advancing age, may encounter increasing difficulty in achieving the body fatness standards, and may consume more resources in the form of weight reduction programs or in administrative costs for separation from the service.

Women have a higher percentage of body fat than do men. Frisancho has documented the gender-related difference in body composition based on data from the National Health and Nutrition Examination Survey NHANES I and II.

For individuals 25 to 54 years old of average frame, fiftieth percentile triceps skinfold thicknesses ranged from 11 to 15 mm for men and 19 to 30 mm for women depending on height and weight. The corresponding ranges for subscapular skinfold thicknesses were 13 to 18 mm for men and 12 to 29 mm for women.

Lohman reviewed data on skinfolds and body density and the relationship to body fatness and concluded that skinfolds predict body density with standard errors of measurement close to that expected based on known biological and technical factors.

Most of the error was associated with variance related to age and gender. The biological variation in predicting body fat from densitometry was estimated at 3.

Based on densitometry, Smalley et al. These results from the general U. population thus provide the rationale for current gender differences in body fat standards in the military services.

The majority of studies evaluating body composition have been done in Caucasians. Many investigators have recognized that the methods currently used do not accurately predict body composition in Blacks, and their applicability to other racial and ethnic groups, such as Asians, Hispanics, and Native Americans is uncertain Malina, ; Mueller et al.

A number of speakers at this workshop discussed the problems of measurement of body composition in racial and ethnic groups see Chapters 6 , 10 , 11 , and There is general agreement that Blacks have relatively greater bone mineral mass, and there is some evidence that muscle mass may be different in Blacks and Caucasians Cohn et al.

Formulas for calculating body composition that have been developed predominantly from Caucasians or even from mixed groups may not adequately predict body composition in racial and ethnic subgroups. The problem is further complicated by marked differences in body composition depending on socioeconomic status Bray, ; Cohn, a; Goldblatt et al.

Some of the observed differences in body composition may also be explained by the fact that the socioeconomic status of Blacks on the average is lower than that of Whites. Evaluating differences in ethnic groups is also complicated because new immigrants have smaller stature and lower body weights than do later generations see Chapter The rationale for current standards for body weight and body composition in the military is that these measures are correlated with performance of military duties, appearance, and overall health.

In contrast to past standards, which were designed to exclude underweight or chronically ill individuals from active duty, the primary concern of the current standards is to address excess weight in the military population. Specifically, excess weight or body fatness is thought to impair military performance.

Since and particularly since , weight standards have been used to ensure that all personnel are able to meet the physical demands of their duties under combat conditions and to present a ". trim military appearance" AR , The Army further states that excessive body weight ".

denotes a lack of personal discipline, detracts from military appearance, and may indicate a poor state of health, physical fitness, or stamina" AR , The relationship of body weight and composition to performance in the military is addressed below and a discussion of appearance standards follows.

Indicators of physical performance currently used by the military services are shown in Table The relationship of body weight and various components of body composition to successful performance of these activities varies with the activity.

In most tasks involving physical work, objects—including the body—must be moved through space. The greater the body weight in general, the more energy that must be expended simply to move the body see Chapter 7. Cureton et al. These authors found with this added-weight model that with increased body weight there was a decrease in running performance.

The changes in oxygen consumption and running time reported in Cureton's study were similar to those seen with cross-sectional studies done with volunteers with different body weights. These results suggest that an added-weight-based performance model used by Cureton et al.

Studies conducted by Vogel and Friedl, and separately by Harman and Frykman see Chapters 6 and 7 , also suggested that excess weight diminishes running performance and that, conversely, lower body weight is associated with relatively better running performance.

Because sit-ups and push-ups involve lifting the body, these studies indicate that increased body weight is associated with lesser performance.

Therefore, as supported by the work of Harman and Frykman Chapter 7 , smaller, lighter-weight individuals do well with these tasks of muscular strength and endurance. Unfortunately, performance on the standard physical training PT test does not correlate well with measures of military performance, because there is little need for unloaded running, sit-ups, or push-ups in normal daily military activity.

Although overweight individuals do relatively poorly and underweight individuals do relatively well on PT tests, the usefulness of these measures as a predictor of military performance is limited.

Unlike measures in the PT tests described above, load carrying ability and lifting have a more direct relationship to military performance. Harman and Frykman Chapter 7 noted that moderately overweight individuals performed reasonably well in load carrying ability as assessed by km marches with packs.

In contrast, underweight individuals frequently underperformed. These authors noted that LBM was the best predictor of load carrying and lifting abilities, as discussed below.

These authors also described studies of the ability to push loads and produce torque and concluded that underweight individuals perform relatively poorly on these tasks, while overweight individuals generally perform adequately, perhaps due to their relatively greater LBM.

However, both load carrying and lifting ability, as well as performance during running, sit-ups, and push-ups, are impaired in significantly obese individuals. As noted above, the compartments of the body may be divided into LBM and BFM.

Some of the speakers noted that being underweight and overfat is a problem that may be more significant than overweight as a predictor of poor military performance, which further emphasizes the importance of distinguishing overweight from overfatness.

The data are quite clear that the best correlations of all aspects of physical performance are with LBM. Cureton Chapter 5 found that exercise performance of fit, normal-weight individuals decreased with increasing weight added by a weight belt and shoulder harness.

Their performance was similar to that of obese individuals of similar LBM, but greater body weight. Harman and Frykman see Chapter 7 discussed the relationship of LBM in a variety of tasks relevant to military performance.

LBM was the best predictor of performance capability as assessed by maximal aerobic capacity, treadmill run time, and minute run distance. These studies pointed out that body fatness was not a strong predictor of run time on an individual basis.

Fatness was associated with longer load carrying time to cover a given distance, and LBM was associated with faster load carriage time. Thus, lean individuals with a small LBM, or obese individuals with a high body fatness, would be expected to do poorly on load carrying tests. These studies also found a low but positive correlation of percent body fat with lifting ability, probably because individuals with more fat tend to have greater LBM.

As described above, LBM is positively associated with the ability to push, carry, and exert torque. LBM was a better predictor of performance ability with these tasks than was percent body fat.

There was a weak trend for fatter people to push and exert torque better, probably because they could use their fat mass to generate momentum. Harman and Frykman Chapter 7 concluded that minimum LBM standards may be more important to military performance than are maximum percentage body fat standards.

They suggested that recruits should be required to meet standards for both minimum LBM and maximum percent body fat. They further suggested that recruits be required to pass physically demanding performance tests that closely simulate military tasks before entry into the service.

Many police and fire departments currently require such tests before accession. There is a lower level of physical performance for the average woman versus the average man, due in large part to the lower LBM and not to differences in body fat. Cureton see Chapter 5 evaluated running performance in men versus women and found that most of the difference in performance could be explained by the differences in LBM, but there were also differences in energy efficiency during running.

He stated that other investigators have not found this difference in running efficiency, so more research is needed to determine if all of the differences in performance between men and women. can be explained on the basis of differences in LBM, or if there are more fundamental differences in muscle function.

In contrast to the findings above, Jones et al. Chapter 9 found that increased body fatness had a weak but positive correlation with lower run times in women trainees.

The explanation for this finding is not clear, but may relate to the greater LBM of the somewhat fatter women. By having more stringent body fat standards for women, women inducted into military service are selected for performance abilities closer to those of men than to those typical of the average American woman.

These less-fat women service personnel may be better able to carry out the tasks involved in normal military operations. Jones et al. Army trainees at Fort Jackson, South Carolina, in two studies in and Women trainees suffered significantly more injuries than did men 50 percent versus 27 percent.

These injury rates, however, did not correlate with body fatness. In both men and women, there was instead a significant correlation of injury rate with body mass index BMI. Individuals at the lowest quartile and the highest quartile of BMI had significantly greater injury rates than did individuals in the middle two quartiles.

Jones also found that greater aerobic fitness, as measured by 1-mile and 2-mile runs, was strongly associated with a decreased risk of injury. However, he pointed out that despite the correlation between poor fitness and injury and between poor fitness and fatness, there was no correlation between fatness and injury.

Chapter 9 speculated that women and men with a low BMI do not have sufficient muscle mass to endure vigorous physical training under the conditions present in military basic training programs.

Again, this seems to suggest that the absolute amount of LBM is a critical factor and provides justification for assessment of LBM and physical performance ability in military recruits before accession.

BMI is related to all causes of mortality and increased morbidity from specific diseases such as cardiovascular disease, hypertension, and diabetes mellitus. Bray reviewed a number of prospective and retrospective studies that included data on the effects of being overweight on health.

Bray concluded that fat distribution, particularly increased abdominal fat, was a more important risk factor than overweight for morbidity and mortality. Mortality ratio and body mass index.

Data from the American Cancer Society study have been plotted for men and women to show the relationship of body mass index to overall mortality. In particular, as shown in Figure , there is an increased risk of hypertension, gall bladder disease, and diabetes with increased abdominal fat.

The percentage of the population affected increases with greater obesity. Given the high cost of obesity in terms of health risk, Bray recommended large-group behavior modification in the work place as the most cost-effective treatment for obesity.

Relationship of the abdominal waist to gluteal hips circumference ratio to various risks of obesity. Copyright , George A.

Bray, M. Used by permission. Body fat distribution may be more important than total body weight or body fatness as a risk factor for several diseases including hypertension, diabetes, and cardiovascular disease.

Increased abdominal fat, as assessed by a high waist-to-hip circumference ratio increases health risk for these diseases. Complicating these observations is the fact that body fat distribution differs among racial and ethnic groups Cohn et al. Few studies have addressed the health risks of different racial and ethnic groups with similar degrees of abdominal overweight.

Evaluation of ethnic group differences is complicated by the fact that new immigrants have a smaller stature and lower body weights than do later generations see Chapter Furthermore, some of the factors that are said to predict health risks are different among ethnic groups.

Haffner et al. Stevens et al. Recent research Dowling and Pi-Sunyer, also indicates ethnic variability of these risk factors. More research is needed in this area. Part of the rationale for a body composition that is, body fat standard in the military is that, according to AR and similar statements from the other services, all personnel are to ''.

present a trim military appearance at all times'' AR , A "trim military appearance" is a subjective criterion that is difficult to define in any scientific sense. Currently, this determination is made by local commanders who are not provided with standardized criteria on which to base their decisions.

Although there would be little trouble finding consensus among multiple observers on grossly obese or overweight personnel in terms of meeting an appearance standard, a direct generalizable relationship between body fat content and military appearance is not likely to be observed. Some overweight and overfat individuals "carry their weight better" than others depending on skeletal structure, body type, and body fat distribution.

Some individuals who fail to meet the body composition standard may even be of normal weight but are overfat and have a lower LBM. Caution must therefore be exercised in making subjective assessments of a trim military appearance.

For individuals who fail to meet performance standards or subjective standards of trim military performance, appropriate therapy and administrative actions for weight reduction and weight control are warranted within military guidelines.

Anthropometric techniques such as circumferences or skinfold measurements, currently in accordance with published procedures, should be used as the first assessment of body fat burden. Reliance on these data is appropriate where individuals agree and respond to a weight reduction program involving modest calorie restriction and moderately increased physical activity.

However, more accurate and reliable techniques for assessing body fat burden should be used when any of the following conditions exist:.

The recommended techniques for measuring body fat under these circumstances include underwater weighing, body volume measurement, total body water measurement, or total potassium 40 40 K measurement, although these methods, as noted earlier, have limitations.

The procedures described above also are subject to some minor risk, which should be described to the patient. For some individuals, compliance with necessary conditions for underwater weighing is difficult or impossible because of an inherent fear of being submerged in water.

Some individuals who suffer claustrophobia will be unable to comply with 40 K measurements. Others are likely to object to the administration of substances for total body water measures. It is recommended that informed consent be obtained before any of these procedures are performed to avoid possible legal action.

However, refusal to participate should not interfere with administrative actions. The standards for weight and body fatness for accession and retention in the military services are significantly different for men and women. The standards recognize that women have a higher percent body fat than men; the Department of Defense standard levels of body fatness are 20 percent for men and 26 percent for women.

However, criteria for accession and retention are not equal for men and women who have a level of fatness that exceeds the standards.

For accession into the Army, 16 to 20 year old men can be approximately 37 percent above the medium-frame "desirable" weight from the Metropolitan Life Insurance Tables see Appendix C , but 18 to 20 year old women can be only 6 percent above the medium-frame "desirable" weight.

Differences in accession standards for men and women also exist for the Navy and Air Force. Retention standards for the Army are more strict for women. Although men aged 17 to 20 can be 14 percent over "desirable weight" to remain in the Army, women aged 17 to 20 can be only 5 percent over see also Appendix B.

Current weight criteria suggest that approximately 29 percent of women Army recruits are not acceptable for accession versus only about 3 percent of men recruits see Chapter 3.

As indicated earlier, women accepted into military service are selected for performance abilities that are closer to those of men than to those of the average American woman.

These less-fat women in the services with a greater LBM may be better able to carry out the tasks involved in normal military operations. A second rationale for stricter criteria for women is the perception that women have more injuries due to increased body fat.

This rationale may derive from the perception that overweight and increased body fat are associated with an increased risk of injury. However, Jones et al. In both women and men, injuries were associated with both the highest and lowest BMI quartiles.

These data suggest that low weightfor-height individuals are prone to injury and that individuals with heavier body weights, regardless of fatness, are prone to injury.

Women suffered significantly more injuries than men The reasons for this result are not clear, but Jones speculated that women and men with a low BMI do not have sufficient muscle mass to endure vigorous physical training under the conditions present in military basic training programs.

Again, this finding seems to suggest that the absolute amount of LBM is a critical factor and provides justification for assessment of LBM and physical performance ability before accession. The current body fat standard in the military appears to discriminate against women.

The Services recognize that women have a higher percent body fat and allow for these differences between men and women. However, standards for women allow less excess over "ideal weight".

These major differences in standards for men and women discriminate against women. Although female soldiers may be fatter in absolute terms than male soldiers, they are required to have a greater percent LBM in relationship to a gender-specific mean than are men soldiers.

However, it is also true that the physical performance standards in the military discriminate against men in that higher performance levels are required for male soldiers than for female soldiers.

As mentioned above, LBM correlates positively with physical performance, and therefore it is a better predictor of physical performance than is BFM, which has a weak negative correlation with performance.

Paradoxically, fatter women may perform physical tasks better than less fat women because they have a higher LBM. The question of the appropriateness of current body fat standards for men and women in the military cannot be answered separately from the question of whether there should also be a minimum standard for LBM.

These issues become of increasing importance as women move into more military occupation specialties as an outcome of the Persian Gulf War and societal trends. Effective June 1, the U.

Marine Corps began using the height, weight, and body fat retention standards Marine Corps Order Turn recording back on. National Library of Medicine Rockville Pike Bethesda, MD Web Policies FOIA HHS Vulnerability Disclosure. Help Accessibility Careers.

Fat mass is the amount of body fat. Fat-free mass is all the lean tissues in your body like muscles, organs, bone, water, etc.

Body mass index BMI is another popular term used in the medical and health community to describe body measurements. Body composition is different from body mass index because BMI focuses on how your whole body weight compares to your height.

BMI is calculated by taking total body mass in kilograms kg and dividing it by height in meters m squared. The number is then put into a chart to find the category. The BMI categories include:. Many athletic people with high muscle mass and low body fat percentage may fall into the overweight or obese categories.

Body composition and body fat percentage may better predict health risks than simple obesity classification based on BMI. A healthier body composition is a higher percentage of lean tissue and a lower percentage of body fat.

Body composition is important because it can give you a better idea of your health risk, especially if you fall in the overweight or obesity category for BMI because you have more muscle and lean tissue.

Body composition is measured using tools to estimate your body fat percentage. The ways to measure body composition vary. Some are more accessible but may be less accurate, while others may be harder to access and more accurate.

Here are different ways body composition is measured. Skinfold measurements use a special type of caliper tool designed to measure the thickness of a skinfold. It's done by gently pinching the skin and fat under the skin on several body parts.

Skinfold measurements are usually done on the following:. This type of measurement is accurate. However, there is a large possibility of "user error" if the person performing the test doesn't have proper training. Body circumference or waist circumference measurements are a simple and easy way to estimate body fat.

It uses a tape measure to see how wide around specific body parts are. Circumference is often assessed on body parts like the waist, arms, chest, thighs, and hips. Research suggests carrying more weight on your abdomen is associated with an increased risk for health problems.

The circumference method helps assess the risk for disease based on the weight you carry on your belly. However, this method may not be the best if your goal is to assess your overall body fat percentage because it only measures the circumference and not the percentage of fat and muscle.

The dual energy X-ray absorptiometry scan, known as a DEXA scan , uses low-energy X-rays to accurately measure the weight of bone, muscle, and body fat. After the scan, you receive an assessment of your bone density , body fat percentage, and mass of each body part.

Many professionals consider the DEXA scan the gold standard for measuring muscle mass. However, it can be harder to find a place to have a DEXA scan done depending on where you live, and it may be a more expensive option. Hydrostatic weighing measures the water displacement when someone is fully submerged in water.

Hydrostatic weighing was long considered the gold standard for assessing body composition until other methods, like DEXA scans, were developed. While this method is accurate, some people find it difficult to stay submerged in water long enough for the assessment, and it may not be accessible.

A bioimpedance analysis BIA uses a painless, low-energy electrical current to assess fat mass, muscle mass, and hydration water mass. Muscle contains more water than fat, so it conducts the energy current better than fat. Fat tissue impedes the movement of the current.

The BIA scanner can assess body composition based on how the energy moves through the body. This test tends to cost less and may be easier to find than other types of scans.

However, the accuracy of this assessment changes based on how hydrated you are. If you drink too much water before the test, you could appear leaner than you are. Some other methods of assessing body composition include:. The best way to improve your body composition is to make healthy changes, like:.

Eating a diet full of highly processed foods that provide large amounts of sugar and fat is associated with gaining weight and body fat. Moving more and exercising regularly helps improve body composition. Research shows all types of exercise programs helped improve the body composition of people who were sedentary.

The results showed strength training programs that develop the whole body had the biggest impact on body composition and improving bone density. Here are some tips to help you increase your physical activity.

The amount of time you sleep and your sleep quality can greatly impact your body composition. A study found poor sleep quality was associated with:.

Here are some tips to help increase your sleep quality:. In addition to the above lifestyle changes, other changes that may help your body composition include:. Body composition is a measurement of the amount of body fat and lean tissue in your body.

Body composition can be measured with tests like skinfold assessment, DEXA scan, body circumference, hydrostatic weighing, and bioimpedance analysis.

In addition, you may be able to improve your body composition by focusing on lifestyle changes like a healthy diet, exercise, sleeping better, and managing stress.

Body composition can give you a better understanding of your current fitness and health level. In addition, repeating the body composition test over time can help you track your progress on your wellness journey. Many calculations for finding healthy body weight use factors like age, sex, and height.

These measures can be limited and provide an estimated range. Still, finding your height on a BMI chart can give you an idea of what a healthy weight may be for you. Strength training and interval training may have a bigger impact on raising your muscle mass and lowering your body fat percentage.

Centers for Disease Control and Prevention.

For adults over 20 years old, BMI typically falls into one of the above categories see table above. UC Davis Health School of Medicine Betty Irene Moore School of Nursing News Careers Giving. menu icon Menu. Sports Medicine. Enter search words search icon Search × Enter search words Body Composition UC Davis Sports Medicine UC Davis Health.

UC Davis Health Sports Medicine Learning Center Body Composition. Body composition. Fundamentals With respect to health and fitness, body composition is used to describe the percentages of fat, bone and muscle in human bodies.

DXA body composition analysis Dual X-ray Absorptiometry DXA is a quick and pain free scan that can tell you a lot about your body. Composition analysis available.

Example analysis from a DXA scan PDF Fat: function, metabolism and storage Although body fat endures a negative reputation, fats and lipids play critical roles in the overall functioning of the body, such as in digestion and energy metabolism.

Health and performance considerations From a performance stand point, excess body fat lowers your work to weight ratio, This means that a heavier person would consume more energy per minute of work resulting in a lower energy economy during activity.

Assessing body composition Assessing body fat can be done using the following methodologies: Hydrostatic weighing, skinfold assessment and bio-electrical impedance.

Body Mass Index BMI BMI is often mistaken as measurable guide to body fat. However, these methods are not always readily available, and they are either expensive or need to be conducted by highly trained personnel.

Furthermore, many of these methods can be difficult to standardize across observers or machines, complicating comparisons across studies and time periods. BMI is calculated the same way for both adults and children. The calculation is based on the following formulas:.

With the metric system, the formula for BMI is weight in kilograms divided by height in meters squared. Because height is commonly measured in centimeters, divide height in centimeters by to obtain height in meters.

Calculate BMI by dividing weight in pounds lbs by height in inches in squared and multiplying by a conversion factor of For adults 20 years old and older, BMI is interpreted using standard weight status categories.

These categories are the same for men and women of all body types and ages. BMI is interpreted differently for children and teens, even though it is calculated using the same formula as adult BMI.

The CDC BMI-for-age growth charts take into account these differences and visually show BMI as a percentile ranking.

These percentiles were determined using representative data of the US population of 2- to year-olds that was collected in various surveys from to Obesity among 2- to year-olds is defined as a BMI at or above the 95 th percentile of children of the same age and sex in this to reference population.

For example, a year-old boy of average height 56 inches who weighs pounds would have a BMI of For more information and to access the CDC Growth Charts. For adults, the interpretation of BMI does not depend on sex or age. Read more about interpreting adult BMI.

The correlation between the BMI and body fatness is fairly strong 1,2,3,7 , but even if two people have the same BMI, their level of body fatness may differ The accuracy of BMI as an indicator of body fatness also appears to be higher in persons with higher levels of BMI and body fatness While, a person with a very high BMI e.

According to the BMI weight status categories, anyone with a BMI between 25 and However, athletes may have a high BMI because of increased muscularity rather than increased body fatness. In general, a person who has a high BMI is likely to have body fatness and would be considered to be overweight or obese, but this may not apply to athletes.

People who have obesity are at increased risk for many diseases and health conditions, including the following: 10, 17, For more information about these and other health problems associated with obesity, visit Health Effects.

A comparison of the Slaughter skinfold-thickness equations and BMI in predicting body fatness and cardiovascular disease risk factor levels in children. et al. Body fat throughout childhood in healthy Danish children: agreement of BMI, waist circumference, skinfolds with dual X-ray absorptiometry.

Comparison of body fatness measurements by BMI and skinfolds vs dual energy X-ray absorptiometry and their relation to cardiovascular risk factors in adolescents. Comparison of dual-energy x-ray absorptiometric and anthropometric measures of adiposity in relation to adiposity-related biologic factors.

Association between general and central adiposity in childhood, and change in these, with cardiovascular risk factors in adolescence: prospective cohort study.

BMJ , , p. Estimates of excess deaths associated with body mass index and other anthropometric variables. Wilkinson DJ, Piasecki M, Atherton PJ. The age-related loss of skeletal muscle mass and function: Measurement and physiology of muscle fibre atrophy and muscle fibre loss in humans.

Ageing Res Rev. Schnurr TM, Gjesing AP, Sandholt CH, Jonsson A, Mahendran Y, Have CT, et al. PLoS ONE 11 11 : e Karastergiou K, Smith SR, Greenberg AS, Fried SK.

Sex differences in human adipose tissues - the biology of pear shape. Biol Sex Differ. University of Houston. Center of Wellness Without Borders. The 3 somatotypes. Wells JC, Fuller NJ, Dewit O, Fewtrell MS, Elia M, Cole TJ. Four-component model of body composition in children: density and hydration of fat-free mass and comparison with simpler models.

Am J Clin Nutr. Kravitz L, Heyward VH. The University of New Mexico. Getting a grip on body composition.

Nuttall FQ. Body mass index: obesity, BMI, and health: A Critical review. Nutr Today. By Jill Corleone, RD Jill is a registered dietitian who's been learning and writing about nutrition for more than 20 years.

Use limited data to select advertising. Create profiles for personalised advertising. Use profiles to select personalised advertising. Create profiles to personalise content. Use profiles to select personalised content.

Measure advertising performance. Measure content performance. Understand audiences through statistics or combinations of data from different sources. Develop and improve services. Use limited data to select content. List of Partners vendors. Breaking Down Diet Culture. By Jill is a registered dietitian who's been writing about nutrition, health, and fitness for more than 20 years.

Jill Corleone, RD. Learn about our editorial process. Learn more. Medical Reviewers confirm the content is thorough and accurate, reflecting the latest evidence-based research. Content is reviewed before publication and upon substantial updates.

Medically reviewed by Rachel Goldman, PhD, FTOS. Learn about our Medical Review Board. Table of Contents View All. Table of Contents. What is Body Composition? What is Body Fat? Body Composition vs. How to Measure Body Composition. Factors to Consider. Changing Your Body Composition.

Frequently Asked Questions. Body Image: What It Is and How to Improve It.