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3. Methodological procedures for analysing energy expenditure

Introduction
Survey of habitual activities
Determination of critical activities
Determination of key participants
Measuring energy expenditure rates
Time-motion analysis
Estimation of energy expenditure rates from time-allocation data
Assessment of endurance capacity
Summary
References

JUDITH NYDON and R. BROOKE THOMAS
Department of Anthropology, University of Massachusetts' Amherst, Massachusetts, USA

Introduction

It is the purpose of this paper to review the relative merits of approaches used in collecting and analysing human energy expenditure data from an anthropological and population perspective. As shown diagramatically in figure 1, expenditure patterns of population segments result from (a) the nature of local energy acquisition, including relevant environmental, technological, and exchange factors, and (b) the quantity and patterns of energy consumption. Total energy expenditure, in turn, consists of energy spent carrying out any number of functions, including those necessary to ensure the continued well-being of a population. Such functions involve individual biological as well as group economic maintenance and reproduction.

In reference to figure 1, it should be noted that expenditure is not simply a dependent variable. It can assume a determinant role in limiting and channelling a population's energy acquisition, principally through its potential influence on group work capacity. In this way, the three components of generalized energy flow - energy acquisition, consumption, and expenditure - together comprise the elements of a complex feedback system.

In this chapter we are concerned with methods for estimating the overall time and energy flows from which a human system can be described and adaptive behavioural patterns assessed. These considerations can suggest to researchers locally relevant, nutrition-related problems of particular population segments, or particular types of activities that warrant more detailed examination and possible intervention.

Procedures for collecting and analysing data pertaining to all three components of a flow study are outlined in table 1. In the sections that follow, those procedures related to energy expenditure will be considered in detail, with major emphasis placed specifically on the measurement of economically related activities and labour patterns. Because of the difficulty of obtaining accurate measures under field conditions, less attention will be given to a consideration of biological factors that influence individual variations in expenditure (e.g. the energy costs associated with physiological maintenance, pregnancy, growth and development. The reader is referred to the following for a summary of these data: Brody (1945), Durnin and Passmore (1967), Consolazio (1971), Garrow (1974, 1978), FAO/WHO/UNU (1985), and Durnin (1987).

Fig. 1. Factors affecting human energy flow

Table 1. Methods and procedures used in measuring and analysing energy flow

1. Energy acquisition

Collection of data

Regional survey of production
Questionnaires and conversations concerning production techniques
Direct measurement

• of production per land unit or animal, per time unit
• of food stores
• of wastage and loss preceding consumption
• in experimentation with productive techniques

Conversion to caloric values
Evaluation of the measurement period
Representativeness of annual production
Annual variability in production

2. Energy consumption

Collection of data
Weighing of food consumed
Questionnaires concerning food use
Daily recording of food items consumed
Conversion to caloric values
Establishment of consumption by sex-age group
Evaluation of the adequacy of energy consumption
Comparison with international standards
Presence of deficiency-related symptoms
Anthropometric indicators of caloric balance

3. Energy expenditure

Survey of habitual activity
Determination of critical activities
Importance in subsistence pattern
Extent to which activity is relied on
Performance effort necessary
Determination of participants in activities
Measuring energy expenditure
In field measurements
Under standardized testing conditions
Estimation of the energy cost of activities not examined
Time-motion studies
Assessment of endurance capacity in performing activities

We are assuming that a general methodological review oriented toward individuals who have not previously worked with human energetic analytical techniques would be most useful. Furthermore, it is assumed that field technicians or investigators just becoming acquainted with time-energy expenditure analysis will not have the advantage of a large research team or expensive equipment. Recommendations are, therefore, made with these points in mind.

In order to maintain continuity, many of the examples used will be drawn from research carried out by Brooke Thomas (1973a) on a Quechua Indian population. Despite its atypical setting in the high Andes of southern Peru, the Nuñoa population shares a number of characteristics with other third-world rural groups. It is reliant on both plant (hardy tubers and cereals) and animal resources (alpaca, llama, sheep) which provide marginal caloric intake. Labour is carried out by most family members without the use of machines. Finally, the group is only loosely tied to the national economy, hence many productive and distributive activities have no monetary consequences. Since labour is not sold nor is a cash value ascribed to many items exchanged, utilizing a standard economic analysis based on cash flow is largely precluded.

Beginning with an overview, figure 2 presents a schematic representation of factors influencing both individual and group work-performance requirements. Determinants of an individual's biological work potential, indicated on the left-hand side of the figure, and reviewed in comprehensive texts on work physiology (Durnin and Passmore, 1967; Edholm, 1967; LangeAnderson et al., 1971; Shephard, 1978; Astrand and Rodahl, 1986), and human environmental physiology (Folk, 1974; Damon, 1975; Frisancho, 1979; Edholm and Weiner, 1981). Individual variations in performance become meaningful in the context of their combined effects in meeting group performance requirements (right side of figure 2). Depending upon behavioural, demographic, and environmental conditions, essential tasks vary in terms of their frequency of occurrence, duration, and intensity of work (Thomas, 1973b). From an energetic point of view, power requirements or rates of expenditure per unit time and total energy input are most relevant. Energy expenditure measures, however, need to be accompanied by some assessment of an individual's ability to complete a task. This item will be discussed under "endurance capacity" in a later section.

Fig. 2. Factors influencing individual work performance and group performance requirements (after Thomas, 1973b, p. 65).

Two pieces of information are required to determine total energy expended for a given task: the rate of energy expenditure, usually expressed as kilocalories per minute (kcal/min), and the amount of time spent performing the task. Thus,

Total energy expenditure = Energy cost of activity (kcal/min) x time spent in activity (min)

A number of techniques, which vary in accuracy and practicality under field conditions, are available for estimating these two variables. The sections that follow briefly review (a) survey techniques used for determining "critical activities," defined as those activities for which actual measurement of expenditure rates is desirable; (b) methods of indirect calorimetry and derived techniques for measuring expenditure rates of activities deemed critical; and (c) time-allocation methods and alternative methods of estimating energy expenditure rates of activities not measured.

Survey of habitual activities

Before considering appropriate techniques of measurement, decisions must be made regarding choice of those specific activities for which relatively precise information is required. In addition, data are needed on population characteristics in order to assure representative sampling. Therefore, in selecting appropriate activities and segments of the population for examination, it is first necessary to obtain a general impression of local conditions that influence their working effectiveness and efficiency.

The primary objective of this initial stage of investigation is to describe daily, weekly, seasonal, and annual rounds of habitual behaviour and the key participants in these behaviours. To accomplish this objective, qualitative assessment is required of (a) regular daily activities performed by the entire population (e.g. eating, sleeping, resting, and leisure activities); (b) daily activities performed by particular segments of the population (e.g. herding, food preparation, child care, and office work); and (c) seasonal activities performed by diverse population segments, especially for agrarian and hunting populations. In the Andes these seasonal activities include planting, harvesting, wool-shearing, slaughtering, and gathering. Unlike later stages of research involving more intensive observation by the investigator or diary-keeping by subjects, this initial phase combines more casual observation, employing questionnaires and conversations with informants (consult Pelto and Pelto, 1978).

Observation of weekday and weekend activity patterns of different population segments can be supplemented by questionnaries designed to elicit detailed comparative information on resource utilization, production techniques, sources of income, and associated activities. Questionnaires are indispensable, especially for providing data on low visibility phenomena, or events that are temporally and spatially dispersed in a manner that makes observation difficult.

Table 2 summarizes a questionnaire administered to the Nuñoa population. Questions emphasize information on types of productive tasks performed, such as food production, spinning, and weaving, and who is engaged in these tasks. Following the administration of questionnaires, conversations with informants were conducted to clarify details of observation and questionnnaire data, and to raise new questions. From these techniques, one is able to establish modal habitual activity patterns and to determine associations among these patterns, as well as interpersonal or inter-household variation.

Table 2. Summary of production questionnaires administered to Nuñoa indigenous household heads

Source: Thomas, 1973a, p. 60

Determination of critical activities

With data on habitual activity patterns, it is possible to define activities that demand more precise methods for determining energy expenditure ("critical activities"), as opposed to those for which less precision is required ("non-critical activities"). The distinction between critical and non-critical activities is important because it is virtually impossible to measure accurately the energy costs of all activities performed by members of a population. Furthermore, greater precision in estimating energy expenditure tends to be more costly in terms of required time and personnel.

Determinations of critical versus non-critical activities naturally depend on the specific research goals of a project. Nevertheless, some general criteria can be suggested for identifying those of relevance: (a) the importance of an activity to a population's or family's subsistence; (b) the extent to which an activity is relied upon; and (c) the performance effort necessary to accomplish a task or activity. In reference to the latter, it is often desirable to include activities representing a broad range of energy expenditure levels. Combining these parameters, critical activities can be delimited with respect to frequency of occurrence, economic importance, and required effort. Under research conditions involving severe time and personnel constraints, priority for actual measurement of energy expenditure should be given to tasks determined to have both high economic importance and high energy demands, as it is these activities that are likely to present potential stress points in the pattern of overall population adaptation.

Table 3 presents a list of activities for which measurements were obtained in the Nuñoa study cited above. Decisions as to which activities to measure were made primarily on the basis of responses to the questionnaire outlined in table 2. The activities selected ranged from those with a high frequency of occurrence and low work-intensity (e.g. sleeping and herding) to those with low or seasonal occurrence and high work-intensity (e.g. planting potatoes and foot ploughing). Such activities also included economically important production-related tasks such as planting, picking, threshing, and grinding of most major crops. Taken together with generalized activities such as sitting, standing, lying, and walking, these comprise a large portion of the average daily energy expenditure of population members. The measurement of generalized activities is also particularly valuable in providing a basis for extrapolation of expenditure rates for many tasks and activities not directly measured. Spinning, for example, is a low work-level task for which sitting or standing measures can be used with reasonable accuracy.

Table 3. Energy-expenditure rates and percentage of maximal values for measured activities as performed by Nuñoa men and women^a

a. Conversion factors of 4.85 and 5 kcal/litre of oxygen consumed has been used for computing submaximal and maximal values. Based on anthropometric data (Frisancho, 1979), a typical man and woman of 20 years and above weigh 54 and 52 kgs respectively.
b. From Mazess et al., 1969.
Source Thomas 1973a, p. 75.

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