|Research Methods in Nutritional Anthropology (UNU, 1989, 201 pages)|
|3. Methodological procedures for analysing energy expenditure|
Up to this point we have been concerned solely with determining the energy costs of activities, without consideration of the actual physiological strain imposed on the individual. This factor becomes important in evaluating how long an activity can be maintained and may be particularly critical for analysis involving strenuous, high-endurance tasks. Long-distance load-carrying serves as an example. While a 12-year-old boy could carry a 25 kg load at an energyexpenditure rate considerably below that of a young man, the former's endurance capacity is expected to be substantially less.
Christensen (1953) has considered various indicators for grading physical effort. Categories of light, moderate, heavy, and very heavy have been proposed based on caloric expenditure, heart rate, body temperature, and sweating rate during work. Ability to predict an individual's endurance capacity depends not so much on the absolute values of these measures, but the degree to which they approach a maximal limit.
This is particularly so for oxygen consumption and heart rate. Thus, in Nuñoa where maximal working capacity or oxygen consumption rate for men is equivalent to approximately 10.6 kcal/min., the cost of planting guiñoa seed is 5.2 kcal/min or approximately 50 per cent of the maximal value (see table 3) (Thomas, 1973a). Had we measured instead a young man who had had tuberculosis, such that his maximal working capacity was reduced by 12 per cent (Rode and Shepard, 1971), he would then be working at 56 per cent of maximal instead of 50 per cent. In the case of planting quiñoa, normal well-conditioned young men could perform this activity for considerably longer than those who had had tuberculosis. Measures of physiological strain can, therefore, provide a basis for deciding which individuals or segments of a population are best suited for strenuous-endurance activities.
Determination of maximal working capacity values is described in most texts on work physiology (see Weiner and Lourie, 1969; Lange-Anderson et al., 1971; Shephard, 1978, 1985; Astrand and Rodahl, 1986). Two types of tests are recommended for the field: the bicycle ergometer and the step test. Because of problems in transporting the bike ergometer, high cost, and lack of familiarity of many subjects with riding a bicycle, we would recommend an adjustable step test. This can be con
structed in the field and made in a manner that allows it to be broken down for transporting. Step height is set at 40 per cent of leg length and the subject steps at a rate of 30 steps per minute carrying a pack of 25 per cent of body weight. A high-flow respiratory valve, several 200-litre Douglas bags and accompanying three-way valves, and a gas meter are the basic equipment needed to collect expired air. Otherwise, equipment and analytical procedures are the same as those referred to under "indirect calorimetry. "