LITERATURE
FBWM 76-2, FBWM 76-2, Bonn
2. SOURCES OF ANTHROPOMETRIC DIFFERENTIATION
Many different factors contribute to anthropometric variability.
Some of the more important of these are biological in nature and in- trinsic to the individual, while others are primarily environmental and can thus be considered as extrinsic. Still other factors relate to the procedures used in obtaining and processing the data. Each of these variables contribute to a greater or lesser extent to the an- thropometric characteristics of the individual, and ultimately to the anthropometric distinctiveness of different populations.
Of the biological variables affecting human physical
PRESENT AND FUTURE NEEDS 47
characteristics, some of the more important are genetic in nature.
These include sex, always a factor influencing physical differentia- tion. Taking the United States as an example, we find that on the average men are about 13 cm taller and 13 kg heavier than women (Stoudt et al., 1965; Abraham et al., 1979). Other body dimensions tend to vary correspondingly, with men almost always having the larger absolute measurements. Exceptions are hip breadths and cir- cumferences, and thigh circumferences, where women have the larger average measurements. Body proportions also vary by sex. Men have arms and legs not only absolutely longer than women, but also longer relative to stature and sitting height (Damon et al., 1966).
Anthropometric distinctiveness can also result from the common genetic backgrounds possessed by members of the same race, ethnic group, national population, or geographic region or subregion. World- wide, the variability of anthropometrically distinct groups is great
indeed. Looking at international differences, when "large" popula- tions i.e., North Americans or Northwest Europeans are compared with
"small" populations, Le., Southeast Asians, average stature and weight differences can be the order of 14 cm and 27 kg. If 95th per-
centile Americans were compared with 5th percentile Southeast Asians, the differences become much more extreme, or very roughly double the above values. (Churchill et al., 1971; White, 1964). Other ethnic or geographic differences are less extreme but still often of consid- erable practical significance.
Age is also one of the more obvious factors that differentiates people in terms of body size. The year-to-year changes that take place as part of the growth and development process are reasonably well documented, at least as far as a few basic anthropometric indi- cators and other selected dimensions are concerned. See, for example, Snyder et al., (1975) and Hamill et al., (1977). Where children must be accommodated by a given design as well as adults, anthropometric variability can easily result in a two-fold difference-or more. Age changes less well known are those that take place in adults during the normal aging process, more especially the sometimes rather marked changes in body size and capabilities that occur during senescence (Friedlander et al., 1977; Damon and Stoudt, 1963).
Another basic biological variable, though also clearly influenced in part by environmental factors, is the health of the individual, as affected by diet, physical activity and medical care. Malnutrition, undernutrition, and overnutrion change body size in obvious ways.
Dieting or "weight-watching", and oVereating can produce significant anthropometric changes in short time periods. Physical activity and eXercise, or the lack of it, produce changes in weight and measure- ments involving muscle tissue and fat. The presence or'absence, type and quality, of medical care during infectious and chronic disease is also reflected in human morphology. Again, the physically handicapped present distinct anthropometric subgroups.
48 H.W.STOUDT Environmental variables affecting human body size and capabili- ties can be classified as either primarily physical or socio-cultural.
The former includes climate and altitude, and the effects of gravity and weightlessness. As an example, stature typically increases by a full 5 cm in the weightlessness of space flight, almost all of the change taking place in the trunk and neck caused by a lengthening of the spinal column (Thornton, 1978). As for the socio-cultural en- vironment, various aspects have repeatedly been shown to be associated with anthropometric differentiation. Occupation is one of the more obvious; civilians differ from the military, and within each of these major groups, specific occupations may differ from each other. Other factors include social status, economic status, and educational level, though clearly, complex interrelationships exist between many of these socio-cultural variables. For a more detailed overview of the biolog- ical and environmental factors affecting human body size, see Annis
(1978).
In terms of future, as opposed to present, needs for an anthro- pometric data base, special attention must be paid to the secular in- creases in body size that have been documented on a world-wide basis in recent years. Most current estimates for stature increases in the United States range from about 0.8 to 1.3 cm per decade (Stoudt, 1979), though some estimates based on military populations are lower.
As stature increases, so do most other body dimensions. Although there is some indication that this increase may be ending, at least among more socio-economically favored groups, this does mean that pre- sent day anthropometric data may not necessarily accurately describe future generations, thus necessitating remeasurement of the same popu- lation over different time periods.
A final area to be considered in assessing anthropometric differ- entiation between populations relates to the procedures and techniques used to obtain this information. An initial question concerns samp- ling and subject selection, i.e., who gets included in, or excluded from, whether by intent or chance, any measured population. Truly random samples are difficult to obtain. All subjects must, after all, be volunteers. However, attention to the proper stratification of subjects based on consideration of the variables described above can produce reasonably representative samples. Where this is not done, random variation among small groups, or bias in subject selection, can result in anthropometrically distinct subgroups drawn from the same parent population.
Finally, the measuring techniques employed, the measuring instru- ments, the body position of the subjects, and the presence or absence of clothing or personal equipment can result in very significant an- thropometric differences between groups. As but one example, while subjects have traditionally been measured unclothed for purposes of biological research and comparability between studies, special re-
quirements for workspace design may necessitate the measurement of
PRESENT AND FUTURE NEEDS 49 fully clothed and equipped subjects. As an alternative, specially determined increments or decrements for clothing and equipment can be added to, or subtracted from, nude body dimensions. Such issues raise the question of comparability of data between studies, and will some- times restrict the applicability of given sets of data to only those special conditions under which they were taken. While there is rea- sonable standardization between most static anthropometric surveys, sources of potential differences must always be carefully examined.
For other, more specialized studies, especially of dynamic or func- tional anthropometry, the possibilities of study uniqueness or lack of comparability are considerably greater.
In summary, the number and complexity of the factors described above, as well as their potential interactions, all contribute in dif- ferent ways and in different magnitudes to anthropometric variability between populations. As a result, each of these distinct populations may require anthropometric description for human factors engineering purposes.