Body Composition and Physical Performance Applications for the Military Services (1990) / Chapter Skim
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9 Associations Among Body Composition, Physical Fitness, and Injury in Men and Women Army Trainees
9 Associations Among Body Composition, Physical Fitness, and Injury in Men and Women Army Trainees
Pages 141-174
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From page 141... ...
Thus an understanding of the interactions among body composition, physical fitness, training, and injuries is an essential foundation for policies governing both body composition and physical fitness. In the following background material, the links between body composition and physical fitness made in Army regulations and policy will be reviewed, and components of physical fitness deemed to be essential to the Army's mission will be enumerated.
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From page 142... ...
The emphasis on physical fitness in both the selection and retention process seems appropriate because soldiers must have enough stamina and strength to perform a wide variety of physically demanding tasks such as marching with loads, digging fox holes, scaling walls, and loading artillery shells. Physical fitness and appropriate body composition are achieved and maintained through physical training.
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From page 143... ...
Body composition explains only 5 to 30 percent of the variance in endurance performance measured by maximum oxygen uptake or timed run distance and even less of other factors, such as sit-ups, push-ups, or vertical jumps (Cureton et al., 1979; Jette et al., 1990; Vogel and Friedl, in press)
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From page 144... ...
As a foundation for decision making, this paper will examine data from two epidemiologic studies of male and female Army trainees that were conducted by the U.S. Army Research Institute of Environmental Medicine and that provide further insight into the following areas: · the relationship of percent OF and BMI with physical fitness and their relative importance as predictors of physical fitness in male and female Army trainees; · the degree of association of percent BE and BMI with risks of training related injuries in men and women; · the degree of association between physical fitness and risks of injury in men and women; · the degree of association between past physical activity or training and current risks of injury; · the relative importance of different parameters of body composition, physical fitness, and physical training (activity)
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From page 145... ...
Also, roughly 5 percent of men and 7 percent of women trainees were lost from follow-up due to discharge from the Army or transfer to another unit. Both studies were conducted in two phases: a prescreening phase, which consisted of a series of body composition and physical fitness measures along with a questionnaire, and a followup phase, which included a medical records review.
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From page 146... ...
Physical fitness was assessed with the Army physical fitness test, which was taken within the first 3 days of the onset of basic training. Measures taken were 1-mile run or 2-mile run times and the number of sit-ups and push-ups performed in a 2-minute time period.
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From page 147... ...
A stepwise multiple regression model was developed to predict mile run times for men and women from other physical measurements and questionnaire data at Fort Jackson in 1984. Changes in R2 values from the stepwise regression output were interpreted as indicators of the amount of
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From page 148... ...
To control for the influence of body composition and physical fitness on the risks of injury for women compared to men, Mantel-Haenszel chisquares stratified on percent BF and mile run times, respectively, were performed. Finally, a stepwise logistic regression was also performed to determine the most important factors contributing to the risk of injury in a model where the effects of multiple factors were controlled for simulta neously.
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From page 149... ...
Comparing men and women, the men were taller, heavier, and had higher BMIs than women in both 1984 and 1988, while women had higher percentages of BF. In both years, men ran faster and performed more push TABLE 9-1 Mean Descriptive Characteristics and Physical Fitness Test Results of Men and Women Army Trainees at Fort Jackson, South Carolina, in 1984 and 1988 Men Women Variable n Mean (SD)
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From page 150... ...
TABLE 9-2 Body Composition and Fitness Variable Medians, Quartile Cutoff Points, and Ranges for Men and Women Army Trainees at Fort Jackson, South Carolina, 1984 * Variable Median Quartile Cutoff Point Range Men Percent body fat 16.6 Q1 13.1 7-29 Q3 20.6 Body mass index (kg/m2)
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From page 151... ...
7.5 Q1 6.83 5.5-10.9 Q2 7.27 Q3 7.73 Q4 8.38 2-Mile run (minutes) 16.4 Q1 14.60 11.4-26.0 Q2 15.67 Q3 16.56 Q4 17.83 Sit-ups 45 Q 1 34 2-85 Q2 41 Q3 47 Q4 54 Push-ups 29 Q 1 19 1-87 Q2 26 Q3 32 Q4 40 Women Percent body fat 27.00 Q1 23.50 15.8~2.6 Q2 25.86 Q3 27.90 Q4 30.10 Body mass index (kg/m2)
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From page 152... ...
The magnitude of the correlations between body composition measures and endurance performance and their degree of significance was greater for men than women in both years. For men, roughly 7 to 28 percent of the variance in mile run times can be explained by percent BF, while only 1 to 3 percent of the variance among women's times can be explained on this basis.
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From page 153... ...
with Entry Level Physical Fitness, and Correlations of Run Times With Sit-ups and Push-ups, Men Army Trainees, Fort Jackson, South Carolina Correlation r p n 1984 Percent BF with: 1-Mile run .27 .009 77 Sit-ups -. 1 7 .05 1 97 Push-ups -.1 1 .057 96 BMI with: 1 -Mile run .
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From page 154... ...
and Body Mass Index (BMI) with Entry Level Physical Fitness, and Correlations of Run Times With Sit-ups and Push-ups, Women Army Trainees, Fort Jackson, South Carolina Correlation r p n 1984 Percent BF with: 1 -Mile run .12 .075 135 Sit-ups -.14 .035 158 Push-ups -.02 .410 133 BMI with: 1-Mile run .00 .478 135 Sit-ups -.02 .393 158 Push-ups -.10 .116 133 1-Mile run time with: Sit-ups -.24 .002 133 Push-ups -.01 .445 109 1988 Percent BF with: 1 -Mile run.16 .004 339 2-Mile run.12 .022 342 Sit-ups-.11 .000 605 Push-ups-.18 .003 686 BMI with: 1 -Mile run.13 .017 339 2-Mile run.09 .079 342 Sit-ups-.03 .405 686 Push-ups-.08 .041 606 1-Mile run time with: Sit-ups-.23 .000 536 Push-ups-.26 .000 467 2-Mile run time with: Sit-ups-.22 .000 353 Push-ups-.21 .000 314 the direction of correlations of BMI with sit-ups and push-ups was also negative, their magnitude was small (less than r = 0.21.
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From page 155... ...
The relationship and trends in time for the 2-mile run versus quintile of percent BF for men and women, respectively, are similar to those seen for the 1 mile. Patterns of relationship of quintile of BMI and mean run times for men
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From page 156... ...
and Body Mass Index (BMI) for Women Army Trainees, Fort Jackson, South Carolina, 1988 Significantly different from Q1 Q2 Q3 Q4 Variable Mean SD n 1-Mile Run BF quintile Q1 lean 10.4 1.84 73 Q2 10.2 1.60 74 Q3 10.5 1.81 59 Q4 10.6 1.91 63 QS fat 11.2 2.17 70 *
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From page 157... ...
The final multiple regression model explained 37 percent of the variance in endurance performance of men trainees as measured by run times (p < .000)
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From page 158... ...
In 1984, over 90 percent of all musculoskeletal complaints for both men and women were due to lower extremity injuries, and in 1988 about 85 percent of the injuries of men and women were lower extremity training-related injuries, such as stress fractures, patellofemoral syndrome, achilles tendonitis, and ankle sprains. Body Composition and Injury Tables 9-8 and 9-9 display the risks of injury for men by quartile (1984)
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From page 159... ...
For women in 1988 the extreme quintiles of BMI were at the greatest apparent risk, but only the lowest two quintiles were in significantly greater jeopardy, 42.5 percent risk, compared to the fourth quintile, which had the lowest risk: 30.7 percent (risk ratio = 1.3, p = .011. Physical Fitness and Injury The relationship between physical fitness and injury is more pronounced and more directional than that for body composition and injury.
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From page 160... ...
BOVEE, AND JOSEPH J KNAPIK TABLE 9-9 Risk of Musculoskeletal Injury by Quintile of Percent Body Fat, Body Mass Index, and Run Time for Men Army Trainees, Fort Jackson, South Carolina, 1988 Relative Risk Confidence Variable Risk (%)
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From page 161... ...
The association between run times and injury risk was not so distinct for women in 1988. The risk ratio of the slowest two quintiles was contrasted with the fastest three, yielding a risk ratio of 1.2 (p = .02~.
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From page 162... ...
BOVEE, AND JOSEPH J KNAPIK TABLE 9-11 Risk of Musculoskeletal Injury by Quintile of Percent Body Fat, Body Mass Index, and Run Time for Women Army Trainees, Fort Jackson, South Carolina, 1988 Relative Risk Confidence Variable Risk (%)
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From page 163... ...
Stratification on several other factors, including age, race, sit-ups, and push-ups, did not affect the magnitude of the risk ratio. Two logistic regression models were also created to determine the importance of various risk factors for injury.
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From page 164... ...
Discussion These two studies at Fort Jackson provided a unique opportunity to prospectively examine the relationships among body composition, physical fitness, and injury in men and women. The assemblage of basic trainees at an Army reception station for several days prior to the onset of basic training permitted the collection of baseline data from direct physical measurements and questionnaires.
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From page 165... ...
This lower correlation probably occurred because BMI is only a surrogate measure of percent BF, and it is the inert fat tissue that detracts from weight-bearing endurance performance. BMI accounted for only 65 to 70 percent of the variance in percent BF among men trainees and between 40 and 70 percent of the variance for women trainees.
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From page 166... ...
Predicting Endurance Because of the universal requirement for soldiers to march and carry loads, models were developed to predict the endurance performance of men and women. A multiple regression model was used to determine the relative importance of multiple factors suspected of contributing to weightbearing endurance as measured by 1-mile run times.
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From page 167... ...
Association Between Body Composition and Risk of Injury hew studies have examined the association of percent BF and BMI with the risk of training-related injuries, and no studies have systematically looked at the relationship of BF and weight-bearing training injuries. A few studies of runners have examined the relationship of BMI to injuries (Blair et al., 1987; Macera et al., 1989b; Marti et al., 19881.
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From page 168... ...
Perhaps women with low percentages of BP who are still relatively fat compared to men may not have enough lean body mass to support their total body weight without undue stress. In any case, distinct and consistent patterns of relationship between percent BF or BMI and risk of injury are not evident.
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From page 169... ...
It is not surprising that a measure of weight-bearing fitness is associated with injury among Army trainees. The single most common physical stress during basic training results from weight-bearing physical training, a stress that is secondary to running, drill and ceremony, marching to and from training sites, and road marching with loads.
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From page 170... ...
These data suggest that for men recruits higher prior physical activity levels may protect against current injury when they are engaged in a uniform training program, and are performing the same amounts of exercise as individuals with less prior exposure to the stress of vigorous physical activity. Other studies have looked at runners all of whom ran different distances, in which case the "dose" or volume of running was the primary risk factor (Blair et al., 1987; Koplan et al., 1982; Macera et al., 1989b; Marti et al., 1988~.
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From page 171... ...
First, it suggests that low levels of aerobic fitness or some related factor are a primary risk factor for musculoskeletal injuries associated with military and possibly other vigorous weightbearing training activities such as running. Second, it indicates that gender per se is not the major risk factor that a crude analysis of military training injury data might imply, and that low physical fitness may be the underlying predisposing factor.
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From page 172... ...
1957. Maximal oxygen intake and its relation to body composition, with special reference to chronic physical activity and obesity.
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From page 173... ...
1989a. Age, physical activity, physical fitness, body composition, and incidence of orthopedic problems.
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