Relationship Between Body Fat and Physical Fitness in Army ROTC Cadets

Transcription

1 MILITARY MEDICINE, 181, 9:1007, 2016 Relationship Between Body Fat and Physical Fitness in Army ROTC Cadets Carly L. Steed, MFN, RD*; Benjamin R. Krull, MFN, RD ; Amy L. Morgan, PhD ; Robin M. Tucker, PhD, RD ; Mary-Jon Ludy, PhD, RD ABSTRACT The Army Physical Fitness Test (APFT), including timed push-ups, sit-ups, and run, assesses physical performance for the Army. Percent body fat is estimated using height and circumference measurements. The objectives of the study were to (a) compare the accuracy of height and circumference measurements to other, more accepted, body fat assessment methods and (b) determine the relationships between body composition and APFT results. Participants included Reserve Officer Training Corps (ROTC) cadets (n = 11 males, 2 females, 21.6 ± 3.5 years) from a midwestern university). At one visit, percent body fat was assessed using height and circumference measurements, airdisplacement plethysmography, and bioelectrical impedance analysis. APFT results were provided by the ROTC director. All assessment methods for percent body fat were strongly associated (r 0.7, p < 0.01), implying that height and circumference measurement is a practical tool to estimate percent body fat of ROTC cadets. Total APFT score was not associated with any body fat assessment method. Push-up number was negatively associated with percent body fat by all assessment methods (r 0.8, p = 0.001), although run time was positively associated (r 0.6, p < 0.05). This suggests that percent body fat may be an important variable in determining or improving cardiovascular and muscular endurance, but not APFT performance. INTRODUCTION Performance in combat has been of great importance for the United States and its military assets since the formation of the first U.S. Army, even before the signing of the Declaration of Independence. The U.S. Army s physicalfitness, height, weight, and body-fat standards are enforced through military regulations under the Army Weight Control Program (Army Regulation 600 9). 1 The Army Physical Fitness Test (APFT) is the current method by which the Army measures the physical performance capabilities and general health and well-being of service members. 2 The APFT is a scored test and consists of three evaluated events: the push-up, the sit-up, and the 2-mile run. Each event is scored on a scale of 0 to 100 for a total possible score of 300. To receive a passing evaluation, a soldier must complete each event with a minimum of 60 points. 3 Depending on the age and sex of a soldier, there are normalized standards. For example, a passing score of 60 in each category for a 17- to 21-year-old male would include 42 push-ups in 2 minutes, 53 sit-ups in 2 minutes, and a 2-mile run in 15 minutes 54 seconds (with *School of Family and Consumer Sciences, Bowling Green State University, 201 Family and Consumer Sciences Building, Bowling Green, OH School of Family and Consumer Sciences, Bowling Green State University, 101 Family and Consumer Sciences Building, Bowling Green, OH School of Human Movement, Sport and Leisure Studies, Bowling Green State University, 213 Eppler South, Bowling Green, OH Department of Food Science and Human Nutrition, Michigan State University, 2110 South Anthony Hall, 474 South Shaw Lane, East Lansing, MI Department of Public and Allied Health, Bowling Green State University, 135 Health Center, Bowling Green, OH AMSUS The Society of Federal Health Professionals, 2016 doi: /MILMED-D the required number of push-ups and sit-ups decreasing with age and in females, although allowable run time increases). 3 However, there has been a debate as to whether the APFT is an accurate measure of soldiers health and physical performance. 2 Comparison between soldiers APFT scores and their body composition (fat mass vs. fat-free mass) is one method of determining whether the APFT is an accurate measure of physical health. Body composition, in terms of fat and fat-free mass, can be an important predictor of health because of the link between excess fat mass, chronic disease, and physical performance. 4 An elevated fat mass negatively influences athletic performances that involve movement or projection of the body, such as running, jumping, or vaulting. 4 There are multiple ways to assess body composition. These methods include hydrostatic weighing, height and circumference measurement, air-displacement plethysmography, and bioelectrical impedance analysis. 4 Although hydrostatic weighing, or underwater weighing, is considered the gold standard of measuring body composition, this method can be difficult to measure, time consuming, and unpleasant for test participants who have to expel all of the air from their lungs while underwater. 5 Air-displacement plethysmography differs from hydrostatic weighing by using air to measure body volume rather than water. It is considered the practical gold standard, since the measurement is quick, noninvasive, requires minimal technical expertise, and is reliable and accurate. 6 The bioelectrical impedance analysis method works by sending a low-level current through the body while measuring how the current impedes different types of tissue. The device is often portable, and it is also a quick, noninvasive method that is inexpensive when compared to several of the other body composition tests (e.g., hydrostatic MILITARY MEDICINE, Vol. 181, September

2 TABLE I. Height and Circumference Measurement Equations Males ( Log10 [Waist Neck]) ( Log10 [Height]) Females ( Log10 [Waist + Hip Neck]) ( Log10 [Height]) weighing and air-displacement plethysmography). 5 Bioelectrical impedance analysis is a reliable method of assessing body composition, but has greater variability than hydrostatic weighing and air-displacement plethysmography. 7 Body mass index is a ratio of height and weight (weight in kilograms divided by height in meter square). It is an index used to predict cardiometabolic risk. Although body mass index does not measure body fat, it is strongly predictive of percent body fat among obese individuals. 8 Among lean individuals, body mass index s association with percent body fat can be imprecise (e.g., muscular individuals with a high body mass index but low adiposity vs. individuals with a normal body mass index but increased adiposity). 8 On the basis of the body mass index, individuals are placed in weight class categories (underweight <18.5, normal , overweight , and obese 30). 9 The U.S. Army uses the height and circumference measurement method, which uses a formula to calculate percent body fat from height, neck, and waist circumferences (Table I). For women, hip circumference is also included. 3 The Army adopted this method because it requires minimal training and tools, and the results are easy to obtain. However, there is little research that evaluates the accuracy and validity of using this method compared to traditional methods. Although the height and circumference measurement provides a convenient alternative to other methods, it might not be as accurate in estimating percent body fat. 10 Because of the differences between methods (e.g., accuracy, cost, time, and ease of measurement), it is important to compare and determine which methods are optimal for use in the Army setting. This study identified the associations between APFT scores and body composition by using four established methods: body mass index, height and circumference measurement, air-displacement plethysmography, and bioelectrical impedance analysis. The first objective was to compare more widely accepted measures of body mass index, airdisplacement plethysmography, and bioelectrical impedance analysis to height and circumference measurement to determine the optimal method of assessing body composition in collegiate Reserve Officer Training Corps (ROTC) cadets. The second objective was to identify associations between APFT scores in Army ROTC cadets and body composition, as one method of confirming the validity of the APFT as an assessment of health. It was hypothesized that (a) percent body fat determined by air-displacement plethysmography and bioelectrical impedance analysis would be strongly positively correlated, whereas the percent body fat determined by height and circumference measurement and fatness, indirectly estimated by body mass index, would be weakly positively correlated with air-displacement plethysmography and bioelectrical impedance analysis results and (b) total APFT and individual scores for timed sit-ups and push-ups would be negatively correlated with percent body fat and body mass index, and timed 2-mile run would be positively correlated with percent body fat and body mass index. METHODS Participants Participants were recruited from the Army ROTC student population at a large, Midwestern University. Criteria required for participation included (a) currently enrolled in Army ROTC (Military Science and Leadership [MSL] class level I IV), (b) completed an APFT within 3 months of participation in the study, (c) at least 18 years of age, (d) not pregnant, (e) nonclaustrophobic (contraindication to airdisplacement plethysmography testing), (f) no implanted medical devices (contraindication to bioelectrical impedance analysis testing), and (g) weight less than 500 pounds (scale capacity). Informed consent was acquired before testing. As an incentive, participants who completed the experimental protocol were entered into a drawing to win one of six $25 gift certificates. Experimental Protocol All four body composition methods were conducted on each participant during one test day to minimize bias between the testing results. Participants individually performed the testing procedures for each method in a supervised laboratory. They were instructed to refrain from exercising and eating or drinking anything (other than water) for 3 hours before testing. This was to ensure body temperature and/or breathing rate postexercise, as well as the presence of food and/or beverages in the gastrointestinal tract, did not influence test results. 11 The protocol was approved by the human subjects review board associated with the university where data collection took place. Anthropometric Measurements Anthropometric measurements collected included height, weight, and circumferences. Neck and waist circumferences were measured in all participants, with hip circumference measured in women only. Participants were required to wear compression shorts/tops and swim caps on arrival to the test site. Shoes, socks, jewelry, and hair accessories were removed before testing. Apparel guidelines were put in place to promote measurement and testing accuracy. 12 Height was measured to the nearest 0.5 inch using a calibrated stadiometer, as mandated in the Army protocol for body composition assessment. 1 Participants were required to stand upright with heels together, head straight, and back touching, but not leaning against, the measuring device. Once in the proper position, the researcher lowered the 1008 MILITARY MEDICINE, Vol. 181, September 2016

3 measuring level, parallel to the ground, until it touched the participant s head. Weight was obtained using a calibrated electronic scale, which was coupled with air-displacement plethysmography, measuring to the nearest 0.1 kg. Circumference measurements were recorded to the nearest 0.5 inch with a measuring tape, on the basis of standards outlined in AR All measurements were taken three times; the average was used for analysis. Neck circumference was acquired by measuring the base of the neck. Waist circumference was acquired by measuring the circumference of the abdomen at the navel. Hip circumference was acquired by measuring the circumference around the greatest protrusion of the gluteal muscle, as viewed from the side. Body mass index was calculated from height and weight measurements. Calculating Percent Body Fat from Height and Circumference Measurements Upon completion of data collection, separate formulas for males and females were used to calculate percent body fat by height and circumference measurement. 1 These equations are used by the Army to determine percent body fat in soldiers (Table I). 1 Air-Displacement Plethysmography Body fat was assessed via air-displacement plethysmography (BOD POD; COSMED, Concord, California) using standard procedures to measure body volume. Calibration of the BOD POD was also performed using standard procedures. Once a participant was seated inside the chamber, two body volume measurements were taken. Using weight and volume measurements, body density was calculated and converted to percent body fat using the Siri equation. 13 Bioelectrical Impedance Analysis Body composition was measured by means of bioelectrical impedance analysis with a direct segmental multifrequency method using hand and foot electrodes (InBody 230; Biospace, Seoul, Korea). 14 Participants were required to stand barefoot on the foot plates while holding the hand electrodes during testing. Empirically derived formulas supplied by the manufacturer were used to calculate percent body fat. Statistical Analysis A sample size calculation was conducted using a repeatedmeasures analysis of variance, within-subjects factor approach with G*Power 3 statistical software (Heinrich-Heine-University, Düsseldorf, Germany). 15 Limits included 5% significance, 80% power, correlation between measures of 0.7, medium effect size of 0.25, and large effect size of 0.4. The total sample size required to detect a medium effect was 21, with 10 participants needed to detect a large effect. Statistical analysis was completed using IBM SPSS Statistics version 20 (Armonk, New York). Repeated-measures analysis of variance was performed, using one withinsubjects factor (percent body fat) to determine differences between three assessment methods (height and circumference measurement, air-displacement plethysmography, and bioelectrical impedance analysis). Pearson correlations were used to determine associations between body composition assessment methods (body mass index, height and circumference measurement, air-displacement plethysmography, and bioelectrical impedance analysis) and APFT scores (total, push-up, sit-up, and run). Data are presented as mean ± standard deviation. The α level for significance was set at p < RESULTS Participants in each rank of the Army ROTC program (year in the program) were included in this study. The 13 Caucasian ROTC cadets (MSL I freshmen [n = 2, 15%], MSL II sophomores [n = 1, 8%], MSL III juniors [n = 7, 54%], and MSL IV senior cadets [n = 3, 23%]) comprised the sample population. All participants earned passing scores on the APFT in all three evaluated events. Males appeared to have higher waist and neck circumferences and push-up number, with lower run time and percent body fat by height and circumference measurement, air-displacement plethysmography, and bioelectrical impedance analysis (Table II). Statistical testing to determine between-sex differences was not performed because of the low number of females (n = 2). Percent Body Fat Methods and APFT Scores Body mass index was calculated and percent body fat was assessed using height and circumference measurement, airdisplacement plethysmography, and bioelectrical impedance analysis for all 13 ROTC cadets. Results from height and circumference measurement, air-displacement plethysmography, and bioelectrical impedance analysis were very strongly correlated (r 0.7, p < 0.01; Table III), and percent body fat did not differ significantly between these methods (F 2,13 = 1.114, p = 0.345). Body mass index was not correlated with height and circumference measurement, air-displacement plethysmography, or bioelectrical impedance analysis. Total APFT score was not correlated with any of the body composition methods. As hypothesized, percent body fat determined by airdisplacement plethysmography and bioelectrical impedance analysis were strongly positively correlated. Contrary to the initial hypothesis, these methods were also strongly positively correlated with percent body fat determined by height and circumference measurement. The lack of correlation between body mass index and any body fat assessment method also contradicted the hypothesized relationship. Fitness Tests The number of completed push-ups demonstrated a very strong negative association with percent body fat by height MILITARY MEDICINE, Vol. 181, September

4 TABLE II. Demographics, Anthropometrics, and APFT Results Variables Male (n = 11) Female (n = 2) All (n = 13) Age (Years) 21.8 ± ± ± 3.5 Height (Inches) 70.5 ± ± ± 3.1 Weight (Pounds) ± ± ± 22.0 Waist (Inches) 32.5 ± ± ± 2.1 Neck (Inches) 15.6 ± ± ± 1.4 Hip (Inches) 40.0 ± 0 Body Mass Index (kg/m 2 ) 24.6 ± ± ± 1.6 % Body Fat by Height and Circumference Measurement 12.9 ± ± ± 6.2 % Body Fat by Air-Displacement Plethysmography 11.9 ± ± ± 7.0 % Body Fat by Bioelectrical Impedance Analysis 13.7 ± ± ± 6.0 APFT Total Score ± ± ± 18.6 APFT 2-Mile Run (Minutes) 13.3 ± ± ± 1.4 APFT 2-Mile Run (Score) 92.7 ± ± ± 10.1 APFT Sit-Up (Number) 80.2 ± ± ± 8.9 APFT Sit-Up (Score) 96.5 ± ± ± 7.6 APFT Push-Up (Number) 75.7 ± ± ± 16.3 APFT Push-Up (Score) 96.5 ± ± ± 6.2 Values are mean ± standard deviation. and circumference measurement, air-displacement plethysmography, and bioelectrical impedance analysis methods (r = 0.8, p = for all). The number of completed pushups was not associated with body mass index. The push-up score on the APFT 100-point scale was not correlated with body mass index or any measure of percent body fat. Neither the number of sit-ups completed, nor the score on the APFT 100-point scale was correlated with body mass index or any measure of percent body fat. The 2-mile run time demonstrated a very strong positive correlation with percent body fat by air-displacement plethysmography and bioelectrical impedance analysis methods (r =0.8,p = for both) and a strong positive correlation with percent body fat by height and circumference measurement (r =0.6,p < 0.05). The 2-mile run time was not associated with body mass index. There was no significant association between 2-mile run score on the APFT 100-point scale and body mass index or percent body fat by any measure. A hypothesized push-up number was negatively correlated with percent body fat, although run time was positively correlated. Contrary to hypothesized expectations, total APFT score and sit-up number were not associated with percent body fat, and body mass index was not correlated with any fitness test. DISCUSSION The outcomes of this study revealed that height and circumference measurement, air-displacement plethysmography, and bioelectrical impedance analysis were strongly correlated when comparing percent body fat. On the basis of these findings, height and circumference measurement appears to be a low-cost, reliable method of assessing percent body fat in ROTC cadets. Body mass index was not correlated with the methods of body composition assessment. This is not entirely surprising as body mass index is not a measure of percent body fat but, rather, a measure of cardiometabolic risk to which increased percent body fat may contribute. The results revealed no correlation between any method of percent body fat assessment and total APFT score. Thus, total APFT score does not reflect percent body fat, a key measure of health. Body composition is measured in athletes because physical performance often increases as muscle mass increases and body fat decreases. 4 Optimizing physical performance in TABLE III. Correlation Between Body Composition Methods and Total APFT Scores Body Mass Index Height and Circumference Measurement Air-Displacement Plethysmography Bioelectrical Impedance Analysis Height and Circumference Measurement Air-Displacement ** Plethysmography Bioelectrical Impedance Analysis *** 0.833*** Total APFT Score Correlation is significant at the **p < 0.01 and ***p < levels MILITARY MEDICINE, Vol. 181, September 2016

5 athletes has made the need for measuring body composition (fat mass vs. fat-free mass) an essential part of an athlete s physical examination. 6 In athletic movements where projection of the body takes place, such as running, jumping, or vaulting, high percent body fat has a negative effect on performance. 4 In the current study, as percent body fat increased, 2-mile run time increased, indicating that elevated body fat slows projection of the body and may limit cardiovascular endurance. The results of this study also demonstrated that as percent body fat increased, the number of push-ups decreased, indicating that upper body strength as measured by push-ups (chest, back, or triceps) is higher in individuals with lower percent body fat. These conclusions imply that identifying the percent body fat of an athlete or soldier may be an important variable in determining or improving cardiovascular and muscular endurance but not APFT performance. However, when 2-mile run time and push-up number were normalized to the APFT 100-point scale adjusted for age and sex, these differences were no longer significant, suggesting that correlations may be an artifact of sex. Further investigation with larger sample sizes is needed to clarify this issue. Limitations A limitation of the study was the small sample size of ROTC cadets. Of the 48 available contracted ROTC cadets on campus, a total of 13 ROTC cadets volunteered to participate. There were few female participants (n =2)compared to male participants (n = 11). A larger sample size may have indicated additional statistically significant correlations between percent body fat and APFT results, as well as allowed for additional comparisons on the basis of sex, ethnicity, and rank. Another limitation may lie in the population being studied. Army ROTC cadets are required to maintain height and weight standards, as well as physical performance standards (APFT), to remain enrolled in the program. If cadets do not fall under appropriate height and weight standards, percent body fat is determined by height and circumference measurement to verify eligibility. Because of these program requirements, generally, Army ROTC cadets are considered to be in good health and physical condition. Of the 13 cadets tested, all were in compliance with current Army height, weight, and APFT standards. Quantifying an individuals physical performance can be done through a variety of methods. For the purpose of this study, the APFT was used as the only indicator of physical performance. Although the APFT is currently utilized by the Army to assess soldiers physical abilities, the fitness test only measures three components of physical fitness: cardiovascular endurance (2-mile run); muscular endurance (pushups for upper body, sit-ups for core, and running for lower body); and body composition by height and circumference measurement. Two basic components of physical fitness assessment are not measured: muscular strength and flexibility. 16 It would be interesting to assess whether body mass index and percent body fat by height and circumference measurement, air-displacement plethysmography, and bioelectrical impedance analysis are associated with muscular strength or flexibility. Potentially, field appropriate methods to evaluate the two basic components of physical fitness assessment not measured could include the vertical jump for lower body strength, grip strength for upper body strength, and the sit-and-reach test for flexibility. 16 Conclusions and Implications For this young, active population, very strong correlations between height and circumference measurement, airdisplacement plethysmography, and bioelectrical impedance analysis suggest that height and circumference measurement is a convenient and reasonable tool to estimate percent body fat of ROTC cadets. Body mass index was not correlated with body composition assessment methods and should not be used to assess adiposity in this lean, healthy population. The results also indicate that for ROTC cadets who are already within a healthy body fat range, there may be no additional benefit in decreasing percent body fat for the purpose of improving abdominal muscular performance (since sit-up number was not associated with percent body fat). Given the importance of physical performance to service personnel, additional research investigating the relationship between percent body fat and performance would be valuable. ACKNOWLEDGMENT This pilot study was supported by a Graduate Student Research Award from Bowling Green State University s School of Family and Consumer Sciences. There is no number associated with this grant. REFERENCES 1. Department of the Army: The Army Body Composition Program. Army Regulation Washington, DC, Department of the Army, Available at accessed November 10, Worden T, White ED: Modifying the U.S. Air Force Fitness Test to reflect physical combat fitness: one study s perspective. 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