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1 Introduction and Background THE COMMITTEE'S TASK The Committee on Military Nutrition Research (CMNR, the Commit- tee) of the Food and Nutrition Board (FNB), Institute of Medicine (IOM), National Academy of Sciences (NAS), was asked by the Department of Defense to review and comment on the current physical criteria for recruit- ment and retention of personnel in the various military services. These criteria are largely based on direct measurement of height and weight, on indirect assessment of body composition, and on the subjective criteria of a trim military appearance. With the advent of a more diverse military popu- lation in terms of ethnic origins and increasing numbers of women, there was concern about the applicability of the existing standards to the diverse pool of volunteers. The seven principal questions the CMNR was asked to address were: 1. Can or should physical performance assessments be used as criteria for establishing body composition standards in the services? 2. What is the relationship between body composition and performance? 3. The services currently use a maximal body fat standard. Should they also establish a minimum fat-free or lean body mass standard? 4. What factors should be considered in setting body composition stan- dards? 5. Are performance and body composition standards redundant? 6. If performance criteria exist, are weight-fat standards needed? 7. How does one rationalize the different uses of body composition for performance, appearance, and health? 3
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4 BODY COMPOSITION AND PHYSICAL PERFORMANCE To assist the CMNR in responding to these questions, a workshop was convened on February 6-7, 1990, that included presentations from individu- als 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 work- shop 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. CURRENT PHYSICAL STANDARDS FOR ACCESSION AND RETENTION IN THE MILITARY The rationale for physical standards for accession and retention in the military, according to Army regulation (AR) 600-9 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 600-9, 19861. 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 mea- surements. 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. Accession Standards 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 val- ues 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 composi- tion also differ among the services (Appendix A). The Army uses a combi- nation 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.S. Army Institute for Envi
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INTRODUCTION AND BACKGROUND s ronmental Medicine (USARIEM) on 1,126 men and 266 women (Vogel et al., 19881. The Navy uses height, weight, and circumferences of neck and waist for men (Hodgdon and Beckett, 1984a), and height, weight and cir- cumferences of neck, waist, and hips in women (Hodgdon and Beckett, 1984b). The Marines use measurements of height, weight, and neck cir- cumference for men (Wright et al., 1981) and measurements of height, weight, flexed biceps, forearm, neck, waist, and thigh circumferences for women (Wright et al., 1980~. The Air Force uses height, weight, and biceps measurements for men (Fuchs et al., 1978) and height, weight, and forearm measurements for women (Brennan, 19741. Retention Standards For retention, military personnel are evaluated on a regularly scheduled basis for height, weight, and/or body circumference and are required to perform a test of aerobic fitness (Appendix B). 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.S. Air Force and recently the U.S. Marine Corpse retention standards are also used for accession. PROCEDURES USED BY THE MILITARY SERVICES FOR FAILURE TO MEET PHYSICAL OR PERFORMANCE STANDARDS 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). Typically, when individuals fail to meet the weight/height standard at the regularly scheduled evaluation, they are further assessed for body fat using anthropometric measurements. On the basis of these measure- ments and medical review, they are assigned to a program of diet and exer- cise for a specific time period that varies with each service. At set time inter ~Effective June 1, 1992 the U.S. Marine Corps began using the height, weight, and body fat retention standards (Marine Corps Order 6100.10A with Change 1) for both retention and accession of personnel.
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6 BODY COMPOSITION AND PHYSICAL PERFORMANCE vats, 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 in- crease in body weight and percent body fat with increasing age (Borkan et al., 1983; Bray, 1976~. There is also evidence that excessive body fat is not necessarily a lack of personal discipline as stated in AR 600-9 (1986) but a chronic disease of complex and multifactorial origins (Bray, 1976, 1978, 1989~. A genetic component is involved (Bouchard et al., 1990; Stunkard et al., 1990), and some investigators (Keesey, 1980) believe there is a level of body weight that is defended from change under equilib- rium conditions. 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, 1980; Keys et al., 1950~. 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., 1961~. METHODS FOR ASSESSING BODY COMPOSITION Definition of Terms Because a number of recent articles have reviewed methods for assessing human body composition (Buskirk, 1987; Heymsfield and Waki, 1991; Lukas- ki, 1987; Smalley et al., 1990), a detailed review of methodology will not be presented here. This section will begin with a brief review of the operational definitions used in this report, followed by an overview of methods for assess- ing body composition as directly applied to the military services. Body composition, in the context of these proceedings, refers to the rela- tive 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 system- atic errors in measurements, so the two-compartment model must be used with caution when applied to an individual. Fat-free mass (FFM) refers to
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INTRODUCTION AND BACKGROUND 7 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. Anthropometric Measurements 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 an- thropometric 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, 1987~. In other words, the formula may have a small error when predicting body fat for a pop- ulation 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 accu- rately measure skinfolds and body circumferences. After performing 150 trial skinfold measurements, only 24 percent of personnel were proficient. However, 68 percent of trainees had reached proficiency after only 45 mea surements of body circumferences. In cross-validation studies, the standard errors for the formulas used by the different services ranged from 3.63 percent to 5.17 percent. Thus, based alone on errors in measurement and inherent individual differences, these data indicate that it would be possible to inap- propriately 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 measure- ments of waist and hip circumferences, a better assessment of long-term health risk may be obtained. Increasing evidence suggests that the deposi- tion 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, 1989~. 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 with- out obesity, who are at increased health risk, and who should receive spe- cial attention for weight or body fat reduction. Densitometry Densitometry has generally been considered the standard against which all other techniques for measuring body composition are compared. How
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8 BODY COMPOSITION AND PHYSICAL PERFORMANCE ever, the formulas on which this method is based were calculated originally from carcass analysis of only seven individuals (Brozek et al., 1963; Forbes et al., 1953; Siri, 1956~. In this procedure, which assumes the two compart- ments 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., 1942; Keys and Brozek, 1953~. 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 exam- ple, the influence of age, gender, race, and ethnic group has not been evalu- ated. 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 even- tually be improved if the two-compartment model in present use applied den- sities 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 tech- nique 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. Bioelectric Impedance Analysis 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., 19881. 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. The equipment is relatively inexpensive (about $3,000-$5,000), and thus impedance measurement would be feasible as a technique for screening for accession or retention of per- sonnel. Segal et al. (1988) found that the accuracy of this method is not significantly better than the results achieved with anthropometric measure
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INTRODUCTION AND BACKGROUND 9 meets, but Lukaski et al. (1985), and Kushner and Schoeller (1986) reported that BIA is superior. It would appear that BIA, particularly with the most modern equipment, is preferable to anthropometry. However, BIA as com- monly used at present, does not give any information on regional fat distri- bution which may be of military interest and importance. More research is needed to validate this technique. Options Requiring Major Equipment or Time 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, elec- tromagnetic conductance, and body water measurement by radioactive or stable isotopes. Advances in the development of multicompartmental chem- ical approaches to the determination of body composition in humans have recently been summarized by Heymsfield and Waki (19911. Most of these techniques would be of great research interest for validating simple mea- surements 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 101. Like many new techniques additional validation studies are needed. This equipment also requires a substantial financial investment and specially trained personnel to operate. FACTORS THAT MAY INFLUENCE BODY COMPOSITION Age 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., 1983; Bray, 19761. 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. Alter- ations in body composition with age also exacerbate the problem of dif- ferences 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 usual- ly 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.
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10 BODY COMPOSITION AND PHYSICAL PERFORMANCE 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. Gender Women have a higher percentage of body fat than do men. Frisancho (1984) 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 (1981) reviewed data on skinfolds and body density and the relationship to body fatness and con- cluded that skinfolds predict body density with standard errors of measure- ment 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 3.8 percent for the general population (Lohman, 1981~. Based on densitome- try, Smalley et al. (1990) reported that men and women averaged 20.9 + 7.6 percent and 26.3 + 9.4 percent body fat, respectively (n = 363~. These results from the general U.S. population thus provide the rationale for current gender differences in body fat standards in the military services. Race and Ethnic Group The majority of studies evaluating body composition have been done in Caucasians. Many investigators have recognized that the methods current- ly 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 (Marina, 1971; Mueller et al., 1987; Mueller and Malina, 1987; Zillikens and Conway, 1990~. 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 13~. 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., 1977a,b; Hampton- et al., 1966; Merz et al., 1956; Pollitzer and Anderson, 1989; Schutte et al., 1984; Seale, 1959; Trotter and Hixon, 1974; Zillikens and Conway, 1990~. Formulas for calcu- lating body composition that have been developed predominantly from Cau
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INTRODUCTION AND BACKGROUND 11 casians or even from mixed groups may not adequately predict body com- position in racial and ethnic subgroups. The problem is further complicated by marked differences in body composition depending on socioeconomic status (Bray, 1976; Cohn, 1977a; Goldblatt et al., 1965~. 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 13~. BODY WEIGHT, COMPOSITION, AND PHYSICAL PERFORMANCE The rationale for current standards for body weight and body composi- tion in the military is that these measures are correlated with performance of military duties, appearance, and overall health. In contrast to past stan- dards, which were designed to exclude underweight or chronically ill indi- viduals 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 1960 and particularly since 1976, 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 600-9, 1986~. 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 600-9, 1986~. The relationship of body weight and composition to performance in the military is addressed below and a discussion of appearance standards follows. Does Being Overweight Impair Military Performance? Indicators of physical performance currently used by the military ser- vices are shown in Table 1-1. The relationship of body weight and various components of body composition to successful performance of these activi- ties varies with the activity. Running ability, sit-ups, and push-ups 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. (1978) (Chapter 5) used weight belts and shoulder har- nesses to add weights to normal volunteers in good physical condition.
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12 Cal Ct Ct o .~ a, 4 - U) . - Ct Cal .~ CQ so o Ct CON Cat 4- Cal Ct A o ¢ * ;^ A ¢ a ~ ¢ I I I I I I I I I I I I I I O ~ g ~ O g 3 Cal .- ~ 1 1 1 11 1 CM au o ~. - V) ~ ·- ·-U. ~ Cal 1 1 1 ~1 1 1 1 11 -°° ° ~ ~ ° an Cal Cal Cal ¢ 1 1~- 1 1~ 1 1 1 1 1 1 1 o .- o. ~ ~ ~ ~ o r ~o o oo ~ ~ ~ o ~ ~ ~ ~ ~ ~ ~ ~ ~ can In us . c' ~ ca c~ °° ~ ~ ~ 1 1 ~ 1 1 1 1 ~ ~ °= ~ ~ ~ O O O ~1 If) O O O °° 1 1 ° 1 1 1 °° 1 1 O O O . - 00 0 ~.. ...... CiD CQ -- CO CC ~1 1 1 ~1 1 1 U ~1 1 0 ~ ~1 ~O (D a ~ 1 1 V) 1 1 1 ~1 1 ~ ~ ~) 1 ;^ ;^ ~ ;^ ;^ .= ~ ~t4~ E ~_ ~0 eE e c~ - c~ ._ .= ._ .= ~_ a' ._ o 4_ c~ a> c°~ ~ ~ c~ ·_ cld ~ .e 3 ~04u, ° .=a~ o~ ~· c, a ~c/~) a.) '~ ' ~ ~ .5:: c.~ c 3 c ~ ~ c O a: O ~ ° - = ~ = o ~o o ~ · ~ eO c o ~ c o ~ v} - ~ ~ ~ ~ c~ ~ c~ ~ st ct ;> ~ . - ~ · :> ~ ~ ~ - ~ ~ :: o ~ ~ ~ o ~ lo-, o ~ =~e ~ ·c~ u) ~ ct 'n '~ ~ · - o .= ¢ v ~ - ~ ~ ~ * -~ ~'m o
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INTRODUCTION AND BACKGROUND 13 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 perfor- mance model used by Cureton et al. (1978) is valid. Studies conducted by Vogel and Friedl, and separately by Harman and Frykman (see Chapters 6 and 7), also suggested that excess weight dimin- ishes running performance and that, conversely, lower body weight is asso- ciated 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 poor- ly and underweight individuals do relatively well on PT tests, the usefulness of these measures as a predictor of military performance is limited. Load carrying ability and lifting 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 per- formed reasonably well in load carrying ability as assessed by 20-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 under- weight individuals perform relatively poorly on these tasks, while over- weight individuals generally perform adequately, perhaps due to their rela- tively greater LBM. However, both load carrying and lifting ability, as well as performance during running, sit-ups, and push-ups, are impaired in sig- nificantly obese individuals. RELATIONSHIP OF LEAN BODY MASS VERSUS BODY FATNESS TO PERFORMANCE OF PHYSICAL TASKS As noted above, the compartments of the body may be divided into LBM and BFM. The standard measures of body weight and body mass index (weight/height2) may give a misleading picture of actual body compo
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4 BODY COMPOSITION AND PHYSICAL PERFORMANCE sition. 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 distin- guishing 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 individu- als of similar LBM, but greater body weight. Harman and Prykman (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 capaci- ty, treadmill run time, and 12-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 perfor- mance 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.
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INTRODUCTION AND BACKGROUND 15 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 in- ducted 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. RELATIONSHIP OF BODY COMPOSITION AND INJURY Jones et al. (1988) evaluated the association of fatness, fitness, and injury among U.S. Army trainees at Fort Jackson, South Carolina, in two studies in 1984 and 1988. Women trainees suffered significantly more inju- ries than did men (50 percent versus 27 percent). These injury rates, how- ever, 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. Jones et al. (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. RELATIONSHIP OF BODY COMPOSITION TO HEALTH BMI is related to all causes of mortality and increased morbidity from specific diseases such as cardiovascular disease, hypertension, and diabetes mellitus. Bray (1989) reviewed a number of prospective and retrospective studies that included data on the effects of being overweight on health. Both general data from the American Cancer Society (Figure 1-1) and a study from Norway indicated that a minimum mortality was associated with a BMI between 22 to 25 kg/m2 for both men and women. Bray con- cluded that fat distribution, particularly increased abdominal fat, was a more important risk factor than overweight for morbidity and mortality.
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16 2.5 o 2.0 to - ~ 1.5 o 1 .0 BODY COMPOSITION AND PHYSICAL PERFORMANCE Digestive & Pulmonary Disease i Mod Cardiovascular Gall Bladder ~Vor/~ : ~ Low: MEN 0 WOMEN ~ IF- - i~,,# _ .~.. :.:.: ......... : ~F.: :.:: : Very High 20 25 30 35 40 BODY MASS INDEX (kg/m2) FIGURE 1-1 Mortality ratio and body mass index. Data from the American Can- cer Society study have been plotted for men and women to show the relationship of body mass index to overall mortality. At a body mass index below 20 kg/m2 and above 25 kg/m2 there is an increase in relative mortality. The major causes for this increased mortality are listed along with a division of body mass index groupings into various levels of risk. [Adapted from Lew and Garfinkel (1979~. Copyright 1976. George A. Bray, M.D. Used by permission.] In particular, as shown in Figure 1-2, 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 obesi- ty. Given the high cost of obesity in terms of health risk, Bray recom- mended large-group behavior modification in the work place as the most cost-effective treatment for obesity. 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 distribu- tion differs among racial and ethnic groups (Cohn et al., 1977a,b; Hampton et al., 1966; Merz et al., 1956; Schutte et al., 1984; Seale, 1959; Trotter and Hixon, 1974; Zillikens and Conway, 19901. Few studies have addressed the health risks of different racial and ethnic groups with similar degrees of
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INTRODUCTION AND BACKGROUND 60 50 LO (a) 40_ J lo 11 <, 30 By LIJ 10 O- Severe Obesity - HYPERTENSION Moderate ,. Obese A< ~o~ Severe Obesity GALL BLADDER DIABETES FAX Moderate X- X Obesity <.72 .73-.76 .77 .80 ~ 81 WAIST TO HIP RATIO RISK LOW | MODERATE | HIGH 1. 7 FIGURE 1-2 Relationship of the abdominal (waist) to gluteal (hips) circumference ratio to various risks of obesity. [Data from Blair et al. (1984~. Copyright 1988, George A. Bray, M.D. Used by permission.] 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 131. Furthermore, some of the factors that are said to predict health risks are different among ethnic groups. Haffner et al. (1986) showed that increased abdominal fat, which is a major risk factor in Caucasians, does not carry the same risk for Hispan- ics. Stevens et al. (personal communication) have shown that a high waist/ hip ratio is not associated with higher mortality in Black women studied in the Charleston Heart Study. Recent research (Dowling and Pi-Sunyer, 1990) also indicates ethnic variability of these risk factors. More research is needed in this area.
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8 BODY COMPOSITION AND PHYSICAL PERFORMANCE BODY COMPOSITION AND MILITARY APPEARANCE Part of the rationale for a body composition (that is, body fat) standard in the military is that, according to AR 600-9 and similar statements from the other services, all personnel are to ". . . present a trim military appear- ance at all times" (AR 600-9, 1986~. A "trim military appearance" is a subjective criterion that is difficult to define in any scientific sense. Cur- rently, this determination is made by local commanders who are not provid- ed 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. ASSESSING BODY COMPOSITION FOR INDIVIDUALS WHO FAIL TO MEET MILITARY STANDARDS For individuals who fail to meet performance standards or subjective standards of trim military performance, appropriate therapy and administra- tive 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 in- creased physical activity. However, more accurate and reliable techniques for assessing body fat burden should be used when any of the following conditions exist: · the level of body fat burden is disputed, · the individual routinely engages in heavy physical activity and/or par- ticipates in body building or physically demanding sports, · the individual appears to be making a sincere effort to lose weight but shows little or no progress, or · the individual resists or fails the appropriate weight loss program and is being separated from service. The recommended techniques for measuring body fat under these cir- cumstances include underwater weighing, body volume measurement, total
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INTRODUCTION AND BACKGROUND 19 body water measurement, or total potassium 40 (40K) 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 40K 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. How- ever, refusal to participate should not interfere with administrative actions. COMMENTS ON BODY COMPOSITION STANDARDS 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 1959 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. (1988) conducted studies during basic training at Fort Jackson, South Carolina, and found no association between fatness and injury in either women or men. In both women and men, injuries were associated with both the highest and lowest BMI quartiles. These data suggest that low weight
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20 BODY COMPOSITION AND PHYSICAL PERFORMANCE for-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 (50.5 percent versus 27.4 percent). 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. How- ever, 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 relation- ship 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 per- formance. 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 spe- cialties as an outcome of the Persian Gulf War and societal trends. REFERENCES AR 600-9. 1976. See U.S. Department of the Army. 1976. AR 600-9. 1983. See U.S. Department of the Army. 1983. AR 600-9. 1986. See U.S. Department of the Army. 1986. Behnke A. R., Jr., B. G. Peen, and W. C. Welham. 1942. The specific gravity of healthy men: Body weight divided by volume as an index of obesity. J. Am. Med. Assoc. 118:495-498. Blair, D., J. P. Habicht, E. A. Sims, D. Sylwester, and S. Abraham. 1984. Evidence for an increased risk for hypertension with centrally located body fat and the effect of race and sex on this risk. Am. J. Epidemiol. 119:526-540. Borkan G. A., D. E. Hulls, S. G. Gerzof, and A. H. Robbins. 1983. Age changes in body composition revealed by computed tomography. J. Gerontol. 38:673-677. Bouchard C., A. Tremblay, J. P. Depres, A. Nadeau, P. J. Lupien, G. Theriault, J. Dussault, S. Moorjani, S. Pinault, G. Fournier. 1990. The response to long-term overfeeding in identical twins. N. Engl. J. Med. 322:1477-1482.
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INTRODUCTION AND BACKGROUND 2 Bray, G. A. 1976. The Obese Patient. Philadelphia: W. B. Saunders. Bray, G. A. 1978. Definition, measurement, and classification of the syndromes of obesity. Int. J. Obesity 2:99-112. Bray, G. A. 1989. Obesity: Basic considerations and clinical approaches. D.M. 35:476-537. Brennan, E. H. 1974. Development of a binomial involving anthropometric measurements for predicting lean mass in young women. M. S. thesis. Incarnate Word College, San Antonio, Tex. Brozek, J., F. Grande, J. T. Anderson, and A. Keys. 1963. Densitometric analysis of body composition: revision of some quantitative assumptions. Ann. N. Y. Acad. Sci. 110:113- 140. Buskirk, E. R. 1987. Body composition analysis: The past, present and future. Res. Quart. for Exercise and Sport 58:1-10. Cohn, S. H., C. Abesamis, S. Yasumura, J. F. Aloia, I. Zanzi, and K. J. Ellis. 1977a. Com- parative skeletal mass and radial bone mineral content in black and white women. Metabolism 26:171-178. Cohn, S. H., C. Abesamis, I. Zanzi, J. R. Aloia, S. Yasumura and K. J. Ellis. 1977b. Body elemental composition comparison between black and white adults. Am. J. Physiol. 232: 419-422. Cureton, K. J., P. B. Sparling, B. W. Evans, S. M. Johnson, U. D. Kong, and J. W. Purvis. 1978. Effect of experimental alterations in excess weight on aerobic capacity and distance running performance. Med. and Sci. Sports 10:194-199. Dowling, H. J., and F. X. Pi-Sunyer. 1990. Effects of race and body fat distribution on fat cell morphology and glucose tolerance. Am. J. Clin. Nutr. 51:512 (Abstract). Forbes, R. M., A. R. Cooper, and H. H. Mitchell. 1953. The composition of the adult human body as determined by chemical analysis. J. Biol. Chem. 203:359-366. Frisancho, A. R. 1984. New standards of weight and body composition by frame size and height for assessment of nutritional status of adults and the elderly. Am. J. Clin. Nutr. 40:808-819. Fuchs, R. J., C. F. Their, and M. C. Lancaster. 1978. A nomogram to predict lean body mass in men. Am. J. Clin. Nutr. 31:673-678. Goldblatt, P. B., M. E. Moore, and S. J. Stunkard. 1965. Social factors in obesity. J. Am. Med. Assoc. 192: 1039- 1044. Haffner, S. M., M. P. Stern, H. P. Hazuda, J. Pugh, J. K. Patterson, and R. M. Malina. 1986. Upper body and centralized adiposity in Mexican American and non-Hispanic whites: Relationship to body mass index and other behavioral and demographic variables. Int. J. Obes. 10:493-502. Hale, L. A. ed. 1990. Proceedings Report: National Conference on Military Physical Fitness 1990. Washington, D.C.: President's Council on Physical Fitness and Sports. Hampton, M. C., R. L. Huenemann, L. R. Shapiro, B. W. Mitchell and A. R. Behnke.1966. A longitudinal study of gross body composition and body conformation and their associa- tion with food and activity in a teenage population: anthropometric evaluation of body build. Am. J. Clin. Nutr. 19:422-435. Heymsfield, S. B., and M. Waki. 1991. Body composition in humans: Advances in the devel- opment of multicompartmental chemical models. Nutr. Rev. 44:97-108. Hodgdon, J. A., and M. B. Beckett. 1984a. Prediction of percent body fat for U.S. Navy men from body circumferences and height. Report no. 84-11. San Diego, Calif.: Naval Health Research Center. Hodgdon, J. A., and M. B. Beckett. 1984b. Prediction of percent body fat for U.S. Navy women from body circumferences and height. Report no. 84-29. San Diego, Calif.: Naval Health Research Center. Jones, B. H., R. Manikowski, J. A. Harris, J. Dziados, S. Norton, T. Ewart, and J. Vogel. 1988. Incidence of and risk factors for injury and illness among male and female Army basic
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22 BODY COMPOSITION AND PHYSICAL PERFORMANCE trainees. Report no. T19/88. U.S. Army Research Institute of Environmental Medicine, Natick, Mass. Keesey, R. E. 1980. A set point analysis of the regulation of body weight. Pp. 144-165 in: Obesity, A. J. Stunkard, ed. Philadelphia: W. B. Saunders. Keys, A., and J. Brozek. 1953. Body fat in adult man. Physiol. Rev. 33:245-325. Keys, A., J. Brozek, A. Henshel, O. Mickelsen, and D. R. Simpson. 1950. The Biology of Human Starvation, vol 1-2 Minneapolis, Minn.: University of Minnesota Press. Kushner, R. F., and D. A. Schoeller. 1986. Estimation of total body water by bioelectrical impedance analysis. Am. J. Clin. Nutr. 44:417-424. Lew, E. A., and L. Garfinkel. 1987. Variations in mortality by weight among 750,000 men and women. J. Chronic Dis. 32:563-567. Lohman, T. G. 1981. Skinfolds and body density and their relation to body fatness: A review. Hum. Biol. 53:181-225. Lukaski, H. 1987. Methods for the assessment of human body composition: Traditional and new. Am. J. Clin. Nutr. 46:537-556. Lukaski, H., P. E. Johnson, W. W. Bolonchuk, and G. E. Lykken. 1985. Assessment of fat-free mass using bioelectrical impedance measurements of the human body. Am. J. Clin. Nutr. 41 :810-817. Malina, R. M. 1971. Skinfolds in American Negro and white children. J. Am. Diet. Assoc. 59:34-40. Merz, A. L., M. Trotter, and R. R. Peterson. 1956. Estimation of skeleton weight in the living. Am. J. Phys. Anthropol. 14:589-609. Mueller, W. H. and Malina, R. M. 1987. Relative reliability of circumferences and skinfolds as measures of body fat distribution. Am. J. Phys. Anthrop. 72:437-439. Mueller, W. H., M. L. Wear, C. L. Hanis, S. A. Barton and W. J. Schull. 1987. Body circum- ferences as alternatives to skinfold measurements of body fat distribution in Mexican- Americans. Int. J. Obes. 11(4):309-318. NIH (National Institutes of Health). 1989. Program and abstracts of a workshop: Basic and Clinical Aspects of Regional Fat Distribution. National Institutes of Health, Bethesda, Md. September 11-13. Pollitzer, W. S. and J. J. B. Anderson. 1989. Ethnic and genetic differences in bone mass: A review with a hereditary versus environmental perspective. Am. J. Clin. Nutr. 50:1244- 1259. Schutte, J. E., E. I. Townsend, J. Hugg, R. F. Shoup, R. M. Malina and C. G. Blomqvist. 1984. Density of lean body mass is greater in blacks than in whites. J. Appl. Physiol. 56:1647- 1649. Seale, R. U. 1959. The weight of the dry fat-free skeleton of American whites and Negroes. Am. J. Phys. Anthropol. 17:37-48. Segal, K..R., M. Van Loan, P. I. Fitzgerald, J. A. Hodgdon, and T. B. Van Itallie. 1988. Lean body mass estimation by bioelectrical impedance analysis: A four-site cross-validation study. Am. J. Clin. Nutr. 47:7-14. Siri, W. E. 1956. The gross composition of the body. Pp. 239-280 in Advances in Biological and Medical Physics IV, C. A. Tobias and J. H. Lawrence, eds. New York Academy Press. Smalley, K. J., A. N. Knerr, Z. V. Kendrick, J. A. Colliver, and O. E. Owen. 1990. Reassess- ment of body mass indices. Am. J. Clin. Nutr. 52:405-408. Stunkard, A. J., J. U. Harris, N. L. Pedersen, and G. E. McLearn. 1990. The body-mass index of twins who have been reared apart. N. Engl. J. Med. 322:1483-1487. Thomas, A. M., W. Z. Billewicz, and P. Passmore. 1961. The relation between calorie intake and body weight in man. Lancet 1:1027-1028. Trotter, M. and B. B. Hixon. 1974. Sequential changes in weight, density, and percentage ash
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INTRODUCTION AND BACKGROUND 23 weight of human skeletons from an early fetal period through old age. Anal. Rec. 179: 1-18. U.S. Department of the Army. 1976. Army Regulation 600-9. "The Army Physical Fitness and Weight Control Program." November 30. Washington, D.C. U.S. Department of the Army. 1983. Army Regulation 600-9. "The Army Weight Control Program." February 15. Washington, D.C. U.S. Department of the Army. 1986. Army Regulation 600-9. "The Army Weight Control Program." September 1. Washington, D.C. Vogel, J. A., J. W. Kirkpatrick, P. I. Fitzgerald, J. A. Hodgdon, and E. A. Harman. 1988. Derivation of anthropometry based body fat equations for the Army's weight control program. Report no. T17/88, U.S. Army Research Institute of Environmental Medi- cine, Natick, Mass. Wright, H. G., C. D. Dotson, and P. E. Davis. 1980. An investigation of assessment techniques for body composition of women Marines. U.S. Navy Med. 71:15-26. Wright, H. G., C. E. Dotson, and P. D. Davis. 1981. Simple technique for measurement of percent body fat in man. U.S. Navy Med. 72:23-27. Zillikens, M. C., and J. M. Conway. 1990. Anthropometry in blacks: applicability of general- ized skinfold equations and differences in fat patterning between blacks and whites. Am. J. Clin. Nutr. 52:45-51. \
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Representative terms from entire chapter: