Body Composition and Physical Performance Applications for the Military Services (1990) / Chapter Skim
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12 Body Composition and Performance in Relation to Environment
12 Body Composition and Performance in Relation to Environment
Pages 195-206
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From page 195... ...
have expressed the mortality from a variety of chronic conditions and diseases as a percentage of the "standard" mortality values observed in subjects of the same age and sex who had an "ideal" body mass relative to their height. Notice that a substantial increase of vulnerability develops only when there is a major excess of body mass (and by inference a major excess of body fat)
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From page 196... ...
One study of military recruits arbitrarily set the upper limit of ideal values at 14 percent body fat in men (Amor, 1978) , although the same author's data apparently suggested that 16.8 percent fat would correspond with the upper limit of the actuarial ideal body mass.
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From page 197... ...
However, if the military threshold of obesity were to be set at the ideal body mass, TABLE 12-3 Relation of Job Intensity to Prevalence of Obesity among Military Personnel in the British Army Percentage Obese Job Intensity (n)
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From page 198... ...
PERFORMANCE IN COMFORTABLE CLIMATES Physical Performance Physical performance may be classified simply into endurance activities, well exemplified by prolonged marching with a backpack, and lifting tasks that are commonly the limiting factor in the front-line employment of military personnel (for example, the ability to lift a mass of 36 kg from the ground to a height of 1 10 cm; Nottrodt and Celentano, 1984~. The metabolic load imposed by any given task reflects the sum of resting metabolism plus the energy cost of the required activity (Shepherd, 19741.
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From page 199... ...
However, if the extra body mass is fat, there is certainly no compensatory development of maximal oxygen intake; indeed, oxygen transport is often poorer than in a lighter person, so that endurance performance is at least correspondingly limited. In moderate obesity, there is no change of mechanical efficiency, so that the oxygen cost of walking per kg of body mass is unchanged.
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From page 200... ...
and C are constants, M is body mass, and n is an exponent varying from 0.1 to 0.2 in very light arm work to near 1.0 in heavy physical tasks involving displacement of much of the body mass. The second term in this last equation distinguishes the influence of body mass on resting metabolism, a particular advantage in situations where a heavy, muscular Person is performing relatively light industrial work.
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From page 201... ...
is needed for an appreciable increase of morbidity from back problems and of deaths from such diseases as coronary atherosclerosis and diabetes (Society of Actuaries, 19591. Moreover, the economic impact of obesity-related morbidity and mortality would be greatest in older members of the labor force, after the normal time of retirement TABLE 12-5 Estimated Monetary Costs Incurred by the Canadian Forces in 1973 (1973 Canadian dollars)
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From page 202... ...
By selecting personnel who meet specified standards of body composition and physical fitness, a unit may be enriched by the recruitment of premium personnel. HOT AND COLD ENVIRONMENTS Because heat exchange is proportional to body surface area, tolerance of hot and cold environments may be influenced somewhat by the differences of body surface area between a tall, thin ectomorph and a short, fat endomorph.
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From page 203... ...
and a uniform pattern of heat loss, a woman who had accumulated 5 kg of body fat, with a resultant 2.5 mm increase of the subcutaneous fat layer, would have a subcutaneous temperature some 3.8°C higher than a person of ideal body composition. It might be thought that a thick layer of subcutaneous fat would be an advantage when adapting to a very cold climate.
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From page 204... ...
One recent calculation suggested that with an initial thermal gradient of 7°C from the body core to the environment, the core temperature would rise by an additional 0.8 to 2.0°C if a person with an additional 2 mm of subcutaneous fat undertook industrial work (Shepherd, 1987; Table 12-61; conversely, if the rise of core temperature were to be avoided by a slower rate of working, it would be necessary to reduce the work-rate by 1 1 to 28 percent. CONCLUSIONS AND RECOMMENDATIONS In young adults who make up the bulk of military personnel, the main argument for controlling the burden of body fat is a deterioration of physi
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From page 205... ...
It is thus recommended that the target body fat percentage set for military personnel correspond to their actuarial ideal of body mass. The adverse effect of body fat upon performance is exacerbated when personnel must operate in a hot climate, but a modest excess of fat may contribute to buoyancy and insulation when working in cold water.
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From page 206... ...
1978. Loss of body fat during an arctic winter expedition.
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