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OCR for page 105
Body Composition and Physical Performance 1992.
Pp. 105-118. Washington, D.C.
National Academy Press
7
l
The Relationship of Body Size and
Composition to the Performance of
Physically Demanding Military Tasks
Everett A. Harman and Peter N. Frykman
INTRODUCTION
The most common physically demanding tasks in the U.S. Army are
lifting and carrying (including load carriage). Typical military lifting tasks
include loading artillery shells, lifting supplies onto and removing them
from trucks, moving construction components, and assembling or disassem-
bling heavy equipment. Most lifts involve raising an object from the ground
to between waist and shoulder height. Carrying is usually associated with
lifting. A soldier is generally expected to lift objects weighing as much as
50 kg single-handedly, with heavier objects lifted by more than one individ-
ual. Most of the objects lifted do not have handles. In heavy lifting jobs,
85- to 200-pound objects may be lifted and carried up to 200 yards by a
single individual. Packs in excess of 100 pounds and other heavy loads
may be lifted and carried for several miles (Myers et al., 1983; U.S. Army,
1978).
Unfortunately, large numbers of recruits have left the military because
of failure to cope with physically demanding military training and work.
Some enlisted personnel have been unable to carry out their jobs or have
become injured while lifting or carrying heavy equipment and supplies (Myers
et al., 1983~. An important question one must ask is whether military
screening tests are effective in excluding from service individuals likely to
be either ineffective in performing their assigned tasks, or prone to injury
due to physical weakness.
105
OCR for page 106
106
EVERETT A. HARMAN AND PETER N. FRYKMAN
Aside from the standard physician's examination, the main physical
screening tool for entry into the-U.S. Army is a table of maximal body
weight-for-height (accession standard AR 40-501) (K. E. Friedl, U.S. Army
Research Institute of Environmental Medicine, unpublished data). Exces-
sive body weight-for-height is used to infer obesity. The Army physical
fitness test, which is based on age-specific standards for push-ups, sit-ups
and 2-mile run time is not an entry screening test and is not administered
until after the start of basic training. A lifting test on a stack-type weight
machine is administered to potential recruits to help advise them whether
they might have difficulty performing physically demanding jobs, but it is
never used to exclude anyone from a military occupational specialty.
Associations Among Body Fat, Load Carriage Ability,
and Running Performance
A sound theoretical basis exists for believing that excess body fat (BF)
is detrimental to performance. Adipose tissue mainly serves the purpose of
energy storage. It is noncontractile and cannot assist in force generation.
Yet it has mass and weight, which increases the force-generation require-
ments of the muscles for support of body segments against gravity and to
overcome inertia during acceleration (Boileau and Lohman, 19774. Accord-
ing to Newton's second law, force equals mass times acceleration, so that
acceleration equals force divided by mass (Meriam, 19781.
Force = Mass x Acceleration
Acceleration = Force / Mass
(1)
For an individual with a given amount of muscle tissue and force-genera-
tion capability, fat deposits increase the mass and thus the weight and iner-
tia of body segments. Table 7-1, based on calculations using equation 1,
shows that for a given amount of force applied to an object, a 10 percent
TABLE 7-1 Loss in Acceleration
with Increase in Mass Given a
Fixed Force
Increase
in Mass (%)
10
20
30
40
Decrease
in Acceleration (%)
9
17
23
29
OCR for page 107
BODY SIZE/COMPOSITION AND MILITARY TASKS
107
increase in the object's mass reduces acceleration by 9 percent. A 20
percent increase in mass reduces acceleration by 17 percent, and so on. BF
then reduces the rate at which the body can be accelerated, as when speed
or direction are rapidly changed.
For endurance activities, where rate of energy production is a limiting
factor, fat weight is detrimental because the work performed in raising an
object to a given height is proportional to its weight, and energy required is
directly related to work performed. The body's center of mass is raised
repeatedly during locomotion. From a simplified point of view the net
power output during running equals body weight times the vertical center of
mass travel per stride divided by the time per stride. Increasing either body
weight or the vertical travel of the center of mass raises the power require-
ment. Also, with all else being equal, a more rapid stride frequency-
which results in a shorter stride time in which the work of raising the body
is performed increases power output. Because sustainable maximal power
output is limited by one's anaerobic threshold, when an individual's body is
fatter, it cannot be raised and lowered as frequently as when it is leaner,
unless it is raised a shorter distance per stride. All else being equal, the
lowering of either stride frequency or vertical center of mass travel (and
thereby stride length) reduces running speed.
There is considerable evidence that fat weight can diminish running per-
formance. Cureton et al. (1978) performed experiments in which they added
weight to the trunks of runners to simulate the effects of fat weight. It was
found that the added weight systematically and significantly decreased
VO2max expressed relative to body weight (which included the added mass)
but did not decrease absolute VO2 maX nor VO2 maX relative to lean body weight.
The added weight decreased endurance time on a treadmill, the speed of
which was increased every 2 minutes, and shortened maximal distance run in
12 minutes. Fifteen percent added weight decreased the speed of the 12-
minute run by 8.6 percent. The experiment showed a negative effect on
running performance attributable to excess weight alone, independent of
any change in cardiovascular capacity. In a similar experiment, Cureton
and Sparling (1980) placed weights on each male subject to simulate the
percent BF of a paired women subject. The weighting reduced men-women
differences by about one-third for both treadmill run time and 12-minute
run distance, and by two-thirds for VO2max relative to total running weight.
Based on significant correlations of percent BF with both time required
to run a fixed distance and distance covered in a fixed amount of time,
studies have shown that fatter individuals tend not to perform as well in
unloaded running as do leaner individuals. Table 7-2 shows correlations)
1 Pearson product-moment correlations (Ferguson, 1976) were used throughout.
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108
EVERETT A. HARMAN AND PETER N. FRYKMAN
TABLE 7-2 Correlations of Percent Body Fat with Run Performance
Male Female
Study Runn* Gender rT r
K. E. Friedl 2 miles1048 M -0.36
(U.S. Army Res. 846 F ~.12
Environ. Med.,
unpublished)
M. Knapik 2 miles81 M -0.38
(U.S. Army Res.
Environ. Med.,
unpublished)
Mello et al. 2 miles44 M -0.60
(1984) 17 F ~.35
Harman et al. 2 miles32 M ~.46
(1988)
Myers et al. 2 miles751 M ~.21
(1983) 450 F -0.19
Cureton et al. 12 minutes55 M ~.30
(1979) 55 F ~.22
Fitzgerald et 2 miles1001 M ~.47
al. (1986) 2 miles253 F -0.31
*n = number of subjects
tr = Pearson product-moment correlation coefficient; negative r means fatter subjects
ran slower.
between percent fat and running performance for several reported studies.
It can be seen that the relationship between percent BF and running perfor-
mance is not strong. However, all of the studies showed some detrimental
effect of percent BF on running performance.
Women in the Army show a weaker relationship between percent BF
and running performance than do men. One reason might be that the wom-
en show less variation in percent BF, so that other factors such as cardio-
vascular status, skeletal proportion, and motivation can exert greater influ
ence.
The relatively weak association between percent BF and 2-mile run
time indicates that an individual's running ability cannot be well predicted
by fatness. There are many fatter individuals who can run faster than leaner
ones and many lean individuals who do not run as fast as expected.
Despite the fact that the 2-mile run is part of the semiannual physical
fitness test that soldiers must take, there is little evidence that unloaded
running ability relates to military performance. Running more than a mile
without a load is a task rarely demanded of a soldier. One might assume
that a soldier who can run better without a load can run better with one as
well. This may not be the case. In experiments in which the performances
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BODY SIZEICOMPOSITION AND MILITARY TASKS
109
of both load carriage and unloaded distance running have been assessed,
Knapik (U.S. Army Research Institute of Environmental Medicine, unpub-
lished data) found a correlation of only 0.16 between the 2-mile run time
and 20-km load carriage time, while Kraemer et al. (1987) found a 0.63
correlation between 2-mile run times with and without a load. One reason
for the higher correlation among Kraemer's subjects was that both run and
load carriage were conducted over the same distance and course. The 20-
km distance is much more typical of military marches and normally in-
volves considerably more walking than running.
Why is the association between performances in load carriage and run-
ning not stronger? The answer seems to be that it takes a different body
type to carry loads well than to be a good runner. Table 7-3 shows the
typical body build of competitive middle- to long-distance runners (McAr-
dle et al., 19864. It can be seen that they are slight of build and lean. Elite
runners are even more slightly built and linear than very good runners, as
shown by Bale et al.'s (1985, 1986) measurements of both men and women
distance athletes. Tanaka and Matsuura (1982) showed that simple anthro-
pometric measures of linearity and leanness account for as much variance in
running ability as do VO2max and cardiac output combined.
Not only is the leaner individual favored in unloaded distance running,
but so is the smaller individual who carries less muscle tissue. In their text
on work physiology, Astrand and Rodahl (1986) extensively discussed the
effects of body size on performance, that was based on an earlier exposition
by Hill (1950~. They explained why larger people, even if lean, could not
be expected to run distances as effectively as smaller people. Their argu-
ment was based on the way the various body dimensions change as body
size changes. Table 7-4 shows how some selected dimensions change
with height if body proportions remain constant. Because areas are two-
dimensional, they are related to the square of height. Volume is three-
dimensional and thus related to height cubed. Flow rates are related to the
square of height, while frequency and acceleration are inversely related
to height. The derivations of these relationships are outside the scope of
this paper.
TABLE 7-3 Typical Body
Measurements of Marathon and
Middle Distance Runners
Height 176 cm (5'9")
Weight 63 kg (139 lbs)
Percent fat 5 percent
Lean body weight 60 kg (132 lbs)
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0
EVERETT A. HARMAN AND PETER N. FRYKMAN
TABLE 7-4 Various Dimensions
as Functions of Height (H)
Segment length
Muscle cross-sectional area
Body mass
Skin surface area
Flow rate
Frequency
Acceleration
H
H2
H3
H2
H2
1/H
1/H
Assuming constant body proportions, oxygen requirement is related to
body mass, which is in turn proportional to height cubed. Oxygen transport
depends on cardiac output, which is a flow rate proportional to height squared.
Thus as body size increases, oxygen requirement increases faster than does
the ability to transport oxygen. It is for this reason that Astrand proposed
measuring aerobic fitness in terms of ml x kg-2/3 x minute-i rather than the
conventional ml x kg-i x minute-i, which favors the smaller body. Maxi-
mal oxygen uptake in absolute terms increases with body weight but, ex-
pressed relative to body mass, decreases with body weight. As a function
of body mass raised to the two-thirds power, it remains constant over a
wide range of body weights. It must be made clear however, that oxygen
uptake expressed in the standard ml x kg- x minuted is closely related to
distance running performance. Correlation of 0.91 for men and 0.89 for
women between running performance and rate of oxygen uptake expressed
relative to body mass enabled Mello et al. (1988a) to develop equations that
effectively predict relative oxygen uptake from 2-mile run time. Thus, us-
ing Astrand and Rodahl's (1986) recommended kg2/3 for equating aerobic
fitness of people of different sizes might indicate one's fitness relative
to similar-sized individuals. It doesn't however, alter the fact that smaller
people are more likely to run faster over middle to long distances.
Law (Burfoot, 1990) developed tables, based on 5,000 10-km perfor-
mances and over 7,000 marathon performances from the 1987 Marine Corps
Marathon, to compare both men and women of differing body weight. Ta-
ble 7-5 shows the ninety-ninth, ninetieth, seventy-fifth and fiftieth percen-
tile performance times for the mens' 10-km run. It can be seen that at each
percentile, the larger runners were considerably slower. For example, the
ninety-ninth percentile 10-km run time was almost 10 minutes slower for
men over 195 pounds than for those under 155 pounds. Astrand and Rodahl's
(1986) theory is supported in that the times in the table are close to those
calculated if oxygen uptake in liters per minute increases with the two-
thirds power of body mass, and running speed is proportional to oxygen
uptake in ml x kg-i x minute-~.
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BODY SIZEICOMPOSITION AND MILITARY TASKS
TABLE 7-5 Times in Minutes for the 10-kilometer Run
Referenced by Percentile and Body Weight
Percentile Body Weight (lbs)
<155 155-174 175-194 195+
Minutes: seconds
99 29:50 33:39 36:54 39:29
90 35:10 39:24 42:49 45:37
75 39:13 42:56 45:57 48:18
50 44:06 47:03 49:44 53:14
111
Load carriage ability is not well predicted by unloaded running, because
although ~ slight body build is well adapted to unloaded running, it is not well
adapted to load carriage, particularly as loads become heavy. Larger people
tend to have greater lean body mass (LBM) which helps to support and move
the load carried. Table 7-6 shows correlations of LBM with both height and
body weight. It can be seen that, for both men and women, LBM is well
related to total body weight, at least for a young, military population.
Association of Lean Body Mass with Military Performance
Table 7-7 shows correlations of load carriage performance with LBM
and percent BE. It can be seen that fatness is associated with slower load
carriage. Higher LBM is associated with faster load carriage. The correla
TABLE 7-6 Correlations of Lean Body Mass with Height
and Weight
Study Height Weight
l
Men Women Men Women
r
Teves et al. 0.60 0.75 0.91 0.88
(1985)
Harman et al. 0.68 0.85
(1988)
Myers et al. 0.62 0.72 0.91 0.89
(1983)
Fitzgerald et al. 0.63 0.69 0.79 0.76
(1986)
r = Pearson product-moment correlation coefficient (see tables that follow).
OCR for page 112
2
EVERETT A. BARMAN AND PETER N. FRYKMAN
TABLE 7-7 Correlations of Load Carriage Performance
with Lean Body Mass and Percent Body Fat in Male
Subjects
Load LBM
Study Distance (kg) r r
Mello et al. 2 km 46 -0.54 0.00
(1988b) 4 km 46 -0.39 0.38
8 km 46 -0.45 0.48
12 km 46 -0.55 0.29
Knapik 20 km 46 -0.26 0.05
(U.S. Army Res.
Inst. Environ.
Med., unpublished)
Dziados et al.
( 1 987)
10 miles 18 ~.30 0.15
Percent Fat
*
r = Pearson product-moment correlation coefficient; correlations mean:
higher lean body mass ~ faster times; higher percent body fat ~ slower
times.
lions are stronger for LBM than for percent BF. It thus may be more
important to screen potential recruits for LBM than for percent BF.
Added evidence as to the importance of LBM for performance of mili-
tary tasks is the positive relationship between LBM and lifting ability.
Table 7-8 shows correlations of lifting performance with LBM and percent
BF. It is clear that LBM is an important factor in lifting, much more so
than percent BF. The low but positive correlations of percent BF with
lifting ability suggest a weak trend for fatter people to lift more effectively,
probably because individuals with more fat tend to have greater LBM.
Table 7-9 shows the weak but positive association among men between
LBM and fatness. However, the Myers et al. (1983) data suggest that the
trend declines or even disappears with training, probably as the fatter men
lose weight. Figure 7-1, from the work of K. E. Friedl (unpublished) shows
that men above the BF standard lose body weight, while those below the BF
standard gain body weight during basic training. Overall, men gain about
2.5 kg of LBM during basic training, while losing 1 to 2 percent fat. Wom-
en also gain about 2.5 kg of LBM in basic training, but there is disagree-
ment as to whether they gain or lose in percent body fat (K. E. Friedl,
unpublished; Myers at al., 1983; Teves et al., 1985~.
The weaker correlations for women than for men between lean body
weight and lifting ability might be related to lack of experience among
women with lifting, which results in greater variability in technique. It
should also be noted that the correlations listed for the Myers et al. (1983)
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BODY SIZEICOMPOSIT1ON AND MILITARY TASKS
113
TABLE 7-X Correlations of Lifting Performance with Lean Body Mass
(LBM) and Percent Body Fat
Men Women
LBM Percent Fat LBM Percent Fat
Study
Lift
Type r* r r r
Teves et al. Maximal 0.45 0.06 0.26 0.10
(1985)
Sharp et al. Repetitivet 0.68 0.25
(unpublished) Maximal 0.48 0.15
Myers et al. Maximal 0.64 0.26 0.45 -0.03
(1983)
*r = Pearson product-moment correlation coefficient; positive correlations mean: higher
lean body mass ~ better lifting; higher percent body fat ~ better lifting.
"Maximal number of lifts with 90 pounds in 10 minutes.
study are before basic training. Yet the correlations between LBM and
lifting ability stayed quite constant through both basic training and ad-
vanced individual training. The relationship between LBM and lifting abil-
ity for women actually strengthened after training, probably due to practice
with lifting, which lessened variability in technique. In contrast, correla-
tions of lifting ability with percent BF dropped to about zero after basic
training for both men and women, and remained there through advanced
individual training. Thus, percent BE of the working soldier appears to be
unrelated to lifting ability.
In addition to being positively associated with load carriage and lifting,
LBM is related to other military task performances. Table 7-10 shows that
LBM tended to be positively associated with the ability to push, carry and
TABLE 7-9 Correlations of Percent Body
Fat with Lean Body Mass
Study
Men Women
*
r
Teves et al. (1985) .42 .15
Myers et al. (1983)
before basic training .36 .11
after basic training .1 1 .09
after AITt .09 .06
*r = Pearson product-moment correlation coefficient
tAIT = advanced individual training
OCR for page 114
4
12
8
4
o
-4
-8
-12
-16 L 111 1 11
-20- . 1 1 1 1 1 1 1 1 1 1
26
PERCENT BODY FAT AT EAD
FIGURE 7-l Change in body weight of military men from entry to active duty
(EAD) to the end of basic training (BT) and assignment to first unit.
_ EAD TO END OF BT
EVERETT A. HARMAN AND PETER N. FRYKMAN
CHANGE IN WEIGHT (POUNDS)
~,11.
. . . . . . . . . . .
~ EAD TO FIRST UNIT
exert torque. As observed for lifting, lean body mass was a better indicator
of performance ability than was percent BF. 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 (Myers et al., 19831.
Discussion and Conclusions
Where does all this lead? Fat weight clearly impairs distance running
ability, but distance running is rarely required of soldiers. The performan-
ces of common physically demanding military tasks, including load car-
riage, lifting, pushing, and exerting torque, are more closely related to LBM
than to percent BF. There is even a weak trend for body fatness to improve
performance in lifting, pushing, and torque exertion.
The evidence presented suggests that minimum LBM standards may be
more important to military performance than are maximum percentage BF
standards. Perhaps recruits should be required to meet standards for both
minimum LBM and maximum percent BF.
Another alternative is to eliminate BF standards completely in favor of
performance tests. Despite the consistent trend for LBM to be associated
OCR for page 115
BODY SlZElCOMPOSlTION AND MILITARY TASKS
115
with lifting and load carriage ability, the correlation coefficients are fair at
best. Thus, depending on their stringency, body composition standards
could exclude many potential recruits capable of effectively performing
military jobs well and grant entry to many individuals physically incapable
of satisfactorily performing their military jobs.
In contrast to the Army, many police and fire departments only accept
applicants who pass physically demanding performance tests that closely
simulate job tasks. Advantages of this approach include
· actual performance is tested, rather than performance by inference.
· recruits who pass physically demanding performance tests might be
less likely to be injured after enlistment, saving the Army medical and lost
workforce costs.
· attrition might be reduced because potential applicants not physically
or psychologically prepared for the demands of military duty are less likely
to be able to train themselves to pass physically demanding performance
tests.
· such testing would not necessarily lower the rate of recruit accep-
tance. It might help to select applicants more suited to their jobs and less
likely to prematurely leave the military.
In addition, it does not appear that the existing Army physical fitness
(PT) test would be effective for entry screening. Table 7-11 shows some of
the minimal existing data relating physical fitness test scores to lifting and
load carriage, the two most common physically demanding Army tasks. Of
the three studies listed, the correlations from Myers et al. (1983) are based
on the largest number of subjects and indicate only a weak positive associa-
tion between number of push-ups and maximal lifting ability. The correla
TABLE 7-10 Correlations of Performance with Percent
Body Fat and Lean Body Mass (LBM) after Advanced
Individual Training
Percent Fat
Lean Body Mass
Task Men Women Men Women
r
Weight pushed .20 .17 .52 .37
Torque .18 .14 .35 .30
Push work .09 .10 .23 .26
Carry work -.03 .17 .27 .02
r = correlation coefficient; positive correlations mean: higher percent
body fat ~ better performance; higher lean body mass ~ better performance.
OCR for page 116
6
EVERETT A. HARMAN AND PETER N. FRYKMAN
TABLE 7-11 Correlations of Army Physical Fitness Test (PT)
Scores with Lifting and Load Carriage Performance
Lifting Load Carriage
Study Men Women Men Women
r
J. Knapik (U.S. Army Res. Inst.
Med., unpublished)
(n = 89 males)
push-ups
sit-ups
2-mile run
Myers et al. (1983)
(n = 751 males, 450 females)
push-ups
sit-ups
2-mile run
Harman et al. (1988)
(n = 32 males)
2-mile run
. *
_ 0.09
0.19
0.16
0.24
0.06
-0.06
-0.37
0.32
0.24
-0.14
*r = correlation coefficient; positive correlations mean: better PT score ~ better
lifting or load carriage
lions of 2-mile run performance with lifting show no association in the
Myers et al. (1983) data and weak association in the Harman et al. (1988)
report, where the negative correlation indicates some tendency for the
better runners to lift less effectively. This is not surprising given the ten-
dency for greater LBM to be detrimental to running ability but salutary to
lifting ability. The J. Knapik data (unpublished) also show little relation-
ship between the physical fitness test scores and load carriage ability.
There are obvious reasons, in addition to the differences between load-
ed and unloaded running abilities already discussed, why the PT tests do
not effectively predict military task performance. The first relates to As-
trand and Rodahl's (1986) discussion of body size. Assuming constant
body shape, body weight increases with the cube of height, while strength,
which reflects muscle cross sectional area (Ikai and Fukanaga, 1968; Ryushi
and Fukanaga, 1986), is proportional to the square of height. Because muscle
strength does not keep pace with increasing body mass, larger individuals are
at a disadvantage in manipulating their own bodies. Thus, smaller people
can more easily perform push-ups and sit-ups but cannot lift as much be-
cause the greater absolute strength of larger muscles can be effectively
applied to the manipulation of objects external to the body, as in lifting.
An additional reason why push-up, sit-up, and 2-mile run scores are not
strongly associated with military task performance relates to the concept of
OCR for page 117
BODY SIZEICOMPOSITION AND MILITARY TASKS
117
strength specificity, which holds that the more dissimilar two exercises are,
the less their performances can be expected to be associated. The move-
ments involved in push-ups and sit-ups are quite dissimilar to those in-
volved in lifting and load carriage. The development of new physical fit-
ness tests more specifically related to military tasks would require careful
analysis and experimentation.
There are many different jobs in the U.S. Army, yet all soldiers must
meet the same age- and gender-specific standards for BE and physical fit-
ness. Because the Army is already dealing with great diversity and com-
plexity in other areas, perhaps it can also deal with a limited number of
different physical standards for different jobs. Tough standards could be
applied to combat units and physically demanding occupational specialties.
More lenient standards for non-physically demanding jobs could help avoid
excluding fatter or weaker individuals who might have skills and abilities of
potential benefit to the Army.
The U.S. Army should clearly define its reasons for having body com-
position standards. This report has shown that the existing standards are
not well related to military task performance. If performance is the main
reason for having standards, then new standards should be developed. If
appearance is an important consideration, then psychological studies should
be undertaken to determine how the appearance of fatness affects military
morale and interpersonal relations. If health is the critical factor, then
epidemiologic studies should be given priority. Identification of the prob-
lem is the most important step in finding its solution.
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Representative terms from entire chapter:
running performance
