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When it is necessary or desirable to obtain some breakdown of the pattern of daily energy expenditure or to investigate some special aspect of a work situation, measurements of energy expenditure - or at least of physical activity- will have to be made. Some indications of the most appropriate methodology are now given, but this does not always include all the detailed description of the techniques. Extra information can be found in Consolazio et al., Durnin and Passmore, and Garrow (See Bibliography).
The measurement of the energy expenditure of man depends on the following principle: All the energy used by the body in carrying out either external work or internal work (such as the movements of the heart and respiratory muscles, etc.), or in chemical synthesis (such as the manufacture of enzymes in the digestive juices or of hormones in the endocrine glands), or in maintaining the ionic gradients between the fluids inside and outside the tissue cells, is ultimately degraded into heat. A measurement of the heat ouput of the body is thus also a measure of its energy expenditure; this may be done under laboratory conditions in a specially designed box and is called "direct calorimetry".
Because the energy available in food can be liberated in the body and used for the above processes only as a result of oxidations that ultimately depend on a supply of oxygen from the air, a measurement of the oxygen uptake by the body is also a measure of energy expenditure; this is termed "indirect calorimetry." Only indirect calorimetry and some of its extensions will be considered here, as direct calorimetry is of limited practical interest in the present context of total energy output by free-living populations.
Measurement of the oxygen uptake by the body in order to calculate energy expenditure requires that the volume of expired air must be known and that the oxygen content and (sometimes) the carbon dioxide content of the expired air must also be analysed. Both of these gases need to be known if the RQ technique of calculating energy expenditure is utilized. Nevertheless, in our experience, it is perfectly satisfactory to use a formula that requires only the oxygen percentage of the expired air. (See Weir in the Bibliography). The formula needed to calculate energy expenditure by Weir's technique is as follows: Energy (kcal/min) = Vstp x Oi-Oe/20 where Vstp is the volume of air expired in litres per minutes and Oi and Oe are the percentages of oxygen in inspired and expired air, respectively.
The error involved in not estimating the carbon dioxide is about 0.5 per cent and usually, is of no significance. On the other hand, there are occasions when the RQ might provide useful information and, naturally, in these cases carbon dioxide in expired air will also need to be analysed.
The method of analysis of expired air or of atmospheric air, which has been used for many years and has a world-wide reputation for accuracy and reliability, employs either the Haldane technique or that of Scholander. With these methods oxygen and carbon dioxide are absorbed by various chemicals. A recommended model is the Lloyd Haldane apparatus (manufactured by Gallenkamp, Christopher Street, London EC2, UK), or the Scholander apparatus (supplied by Otto K. Hebel, Swarthmore, Pa., USA).
Even with the Lloyd simplified apparatus, the Haldane method needs a fair degree of manipulative skill and the number of duplicate analyses that can be done per day, even by an expert analyser, is quite limited if the work continues over an extended period of time. The Scholander has similar limitations. For these reasons, there has been a development of quick and simple methods for gas analyses. Many of these are available. The Pauling oxygen analyser (made by Beckman Instruments Inc.,
South Pasadena, California) utilizing the paramagnetic properties of oxygen, is probably the most widely-used apparatus of its kind. Various models are manufactured that compare for accuracy very well with the LloydHaldane apparatus. They can be used after the acquisition of only a modicum of skill, although they need frequent calibration. Normally, once experience is gained, oxygen analyses should not take longer than 2 to 3 minutes.
Another oxygen analyser that we have used extensively is the Servomex (Servomex Controls Ltd., Crowborough, Surrey, UK). This instrument is as reliable and accurate as the Beckman.
Newer instruments (some supplied by Beckman) make use of oxygen electrodes and have the same degree of accuracy as the paramagnetic models. They are slightly more expensive but have the advantage of being somewhat more robust.
Carbon Dioxide Analysis
There are many different analysers for measuring CO2 by physical methods, mainly depending on the infrared properties of carbon dioxide. Most of these analysers are expensive. While the analysis of carbon dioxide is not essential for the calculation of energy metabolism it may provide useful ancillary information; a CO2 analyser is thus often a valuable piece of equipment. Again. CO2 analysers ought to be calibrated (by standard gas mixtures and also by the use of the Lloyd-Haldane or Scholander techniques) if results are to be of real scientific value. One competent technician can carry out very large numbers of CO2 and oxygen analyses after a fair degree of expertise has been accumulated.
In difficult field situations - especially in hot, humid environments in developing countries - it may be necessary to fall back upon the manual techniques of gas analysis and this will limit the number of measurements that can be made.
Instruments for Indirect Calorimetry
There are several methods by which the expired air of a subject can be measured. The technique that has been in most common use for many years uses the Max-Planck respirometer (manufactured by Zentralwerkstatt Gottingen GmbH, Gottingen, Federal Republic of Germany). This is a simple instrument, based on the same principle as the domestic gas meter. It is a small portable meter weighing about 3 kg and can be carried on the back by means of canvas straps. The meter contains a counter that records in litres the volume of the expired air. There is also a by-pass by which a small fraction of the expired air is diverted into a small rubber bag fitted on to the side of the meter. This sample of expired air is subsequently analysed for its oxygen and, if necessary, carbon dioxide contents. Many laboratories throughout the world have made extensive use of the Max-Planck respirometer over several years and its practicability for field use has been thoroughly tested.
Nonetheless, it has several disadvantages. It is somewhat cumbersome and is not the most desirable instrument to use on small adults or on children. It also has an appreciable resistance to air flow at high levels and is therefore not suitable if very severe physical activity is being undertaken by the subject (where pulmonary ventilations of upwards of 60 litres per minute are encountered). Naturally, this is not often likely to present a problem. For most types of activity, from rest up to moderately severe exercise, it is usually adequate.
Various other indirect calorimetry meters- such as the "MISER" or the "Oxylog" have been or are being manufactured. None that we have tested is reliable and available in quantity; there is a serious need for a modern, light-weight, accurate instrument of this type.
Valves, Mouthpieces, and Masks
Most mouthpieces that contain inspiratory and expiratory valves are now made of some light-weight plastic material; a variety of these are on the market. Few are ideal because they are nearly always based on a Tshaped structure that induces resistance to air flow if the expired air is being breathed out at high volumes. They should always be checked to make sure that there are no leakages at either the inlet or the outlet, as small movements of the disc can cause leakages and introduce an error. These valves must be used in conjunction with a nose clip that can be easily purchased. In our experience it is often necessary to ensure that the nose clip does not irritate the skin of the nose, particularly if it is being used in a hot environment. With some facial types it may be very difficult to find a nose clip that fits well and stays in position. It may then be necessary to use a mask. Masks are not simple things to fit, and meticulous care must be taken to see that there is no leak around the cheek and chin. Many subjects prefer masks to mouthpieces, and the investigator must decide his own preference. In the case of children, masks are almost always impracticable; leakages are common and can be considerable.
The main problem in trying to assess physical activity is to use a technique that causes a minimum of interference with the normal daily life of the person and that is not too complicated to allow the provision of accurate and fairly detailed information. While it is important to know the exact occupation of the individual, and to find out precisely what physical effort occurs during his work period, it is also desirable to obtain a clear picture of his normal activity during his leisure time. Ideally, the duration of such an assessment ought to cover several days, although a minimum period of 24 hours may sometimes be sufficient. The period measured should also represent a fairly average pattern of normal life for the subject; for example, in some occupations seasonal factors may be of significance (agricultural jobs, forestry, even some types of office work). The weekend should, if possible, always be included because this may give a better indication of whether the subject is an active person or is mainly of a sedentary disposition.
Children, especially school-age ones, pose special problems in this regard. Attendance or non-attendance at school, the influence of holidays, whether or not the children assist in work in the home, in agriculture, or elsewhere, will have to be taken into account.
The assessment of physical activity may not be easily ascertainable from the measurement of total energy expenditure alone. For example, it is quite possible that the total energy output of individuals may be similar and yet the pattern of expenditure may be very different: some may have a fairly uniform expenditure throughout the day, whereas others may have very low levels for part of the day, and high levels at other times. Sometimes it may be useful to discover this pattern, and it may require a detailed assessment of how the day is spent by the subject. This applies equally to adults or children.
Calculation of Energy Expenditures
When measurements of total energy expenditure are needed there are two requirements: first, an accurate account of all of the time spent on each and every activity of the day by the subject. Second, it is necessary to assess the metabolic cost of each activity. The energy expenditure is then calculated by energy expenditure = time spent in each activity (min) x (multiplied by) metabolic cost of activity (kcal or KJ/min)
Tables 8.1 and 8.2 (see TABLE 8.2. Mean Duration (per cent of total) of Various Types of Activities and Their Contribution to Total Mean Daily Energy Expenditure (ee) of 2 New Guinean Populations ) show contrasting examples of the use of this method. The first sets out the energy expended by a sedentary office worker of middle age, and the second shows how this form of calculation allows the formation of a picture of the duration and of the proportion of energy contributed by the different activities of daily life in New Guinean populations. The measurement of the metabolic cost of the activities is done by indirect calorimetry using one of the described techniques. In practice, it is almost impossible to measure the cost of every activity of a subject. To measure directly, on each individual, anything like the range of activities shown in table 8.2, is quite impracticable.
TABLE 8.1. Mean Daily Energy Expenditure of a Middle-aged Male Office Worker (ht. 175 cm; wt. 85 kg)
|Washing, dressing, etc.||
|Moving around in office||
TABLE 8.2. Mean Duration (per cent of total) of Various Types of Activities and Their Contribution to Total Mean Daily Energy Expenditure (ee) of 2 New Guinean Populations
|% time||% e.e.||% time||% e.e.||% time||% e.e.||% time||% e.e.|
|Walking around (strolling)||2.2||3.3||2.1||2.9|
|All other walking||7.7||19.4||6.5||17.1||10.9||27.3||9.8||25.4|
|Hunting and gathering||1.5||2.3||-||-||0.4||0.7||-||-|
|Sitting and standing activities||1.5||2.3||2.4||3.7||2.4||3.4||2.8||4.5|
The primary aim must be to obtain an assessment of the average energy expenditure of each of the important activities of each individual. "Important" activities are those that contribute significantly to total daily energy metabolism. "Sleeping" is one of these, but values of basal metabolic rate can be used adequately for this and they can be extracted from published tables. "Sitting," because usually several hours of each day are spent in this way, "walking," some work tasks, etc., are others. It is more important to try and measure these activities several times on each individual, than to diversify the measurements too widely. The only way to be fairly sure that the true average normal situations have really been measured is by careful observation of the individual over, preferably, several days.
In the case of relatively unimportant activities that last only short periods of time, or occur only sporadically and infrequently, appropriate values may be taken either from published tables or from results obtained on other individuals from the same population.
Indeed, a rough indication of energy expenditure could be attempted in this situation without having made any measurement of oxygen consumption at all, if such measurement is impossible to obtain, as is sometimes the case for groups of women because of difficulties due to religion or custom. The error, however, is likely to be quite large.
Where values other than those actually measured are applied to an individual's specific activities, an allowance will often have to be made for differing body sizes. The adjustment is only sensible on a direct proportionality basis; i.e., if a published value refers to a 60 kg man and the individual studied weighs 50 kg, the published value should be taken at 5/6 of its level. More precise refinements are unjustified in this context because of the large inter-individual variability.
Such tables appear in Durnin and Passmores. Energy, Work and Leisure. Considerable experience and judgement are necessary in deciding which measurements to make and when a value can be extracted from the literature. It is probable that little direct guidance can be given on this, and it has to be left to the common sense, knowledge, and experience of the investigator.
Recording Activities: Questionnaires
Probably more important than taking a very large number of measurements by indirect calorimetry is the accurate recording of the time spent in each activity of the subject. This can be done in various ways. One way is by a detailed questionnaire. In our experience, this may be unreliable and should be employed only with great care and analysed with appropriate scepticism. Most people grossly exaggerate, possibly quite unconsciously, the amount of time they spend in physical activity. In carefully controlled studies that we have carried out, we have found that this exaggeration is so large and variable that a questionnaire type of study, even used on highly intelligent people, may be of little value.
Nonetheless, questionnaires are widely used in the assessment of physical activity. Many of these have been designed, but they will almost certainly need to be adapted to local conditions. Some can be obtained from the World Heath Organization. When used in the proper fashion, questionnaires may be reasonably repeatable and they give information that can be used to categorize activity, at least in a rather gross fashion.
Recording Activities-Diary Techniques
This technique requires either the subject or an observer to fill a diary that records, usually minute-by-minute or sometimes in five-minute periods, the various activities throughout the 24 hours. Simple code letters are employed to stand for the various activities of the day; for instance "lying in bed" could be designated by the letter B, "sitting" by the letter S, "standing" by St, "walking" by W, standing "activities" which involve all the many small movements that are often done either in the house or in many sedentary occupations, but that last only perhaps a few seconds at a time - by STA, and so on. More complex activities can be covered by an appropriate symbol.
By this technique it may be practicable to have an individual keep a very precise record of how he spends his day. One advantage of such a method is that it is carried out continuously so that there should be no need for the individual to make guesses to cover gaps of memory. It does not require much intelligence, but mainly needs literacy and good motivation. Sometimes it may be necessary to record the activities of the person by an observer. It is desirable to check the subject's own recordings fairly frequently, usually at least once a day, and with experience, questioning will clear up most problems of possible inaccuracy or that need further explanation. For field studies, any reasonably intelligent person with a modicum of common sense can act as a competent observer, after adequate training. A good sense of humour is useful, but little scientific training is necessary and the experience can soon be gained. If these qualities can be obtained in local assistants, so much the better.
Heart- rate Measurement
Indirect assessment of energy expenditure, or simply of general physical activity, may also be attempted by heart-rate recording. In any individual, there is a relationship between heart rate and oxygen consumption, and this relationship is the basis for the monitoring of physical activity by recording heart rate over lengthy periods of time. However, it is also well known that the relationship between heart rate and energy expenditure will vary within the individual, depending upon the type of physical activity being undertaken. For example, using the whole body or a large part of it, as in walking or running, will show a different relationship than exercise that uses only one arm or other small muscle groups, and the relationship can also vary depending upon the degree of physical fitness of the individual and by disturbing influences, such as emotion, environmental conditions, body temperature, meals, smoking, drinking and so on.
Variations among individuals are considerable. For these reasons we have carried out carefully controlled studies, both in our laboratories and with normal field conditions, where we have attempted to relate heart rate and oxygen consumption. We have found that the range of variation is large and this method may be useful only for separating groups of people into wide subdivisions; for instance, in separating the top 20 per cent and the bottom 20 per cent of a typical sedentary population for their physical activity.
The difficulty of using continuous heart rate can be easily assessed by a simple calculation. For example, an average rate covering a large part of a sedentary day might be around 90 to 95 beats per minute. If the length of the waking day comprises 16 hours, this would give a total of heart beats in this time of 90 x 60 x 16, which is equal to 86,400. If, during the lunch hour, such an individual spent half an hour doing very hard exercise with an average heart rate of 170, this would mean a difference of 30 x (170 - 90), which is equal to 30 x 80 or 2,400 beats. Half an hour's brisk walking in the evening, with heart rate at 1 20/min, would add a further 900 to the total.
There would thus be a total difference in the heart rate between a 1 6-hour day when almost no exercise was taken (total 86,400 beats) and a day with a significant amount of severe exercise (89,300 beats) of such a small amount that normal variability would more than obscure it. While this may be an oversimplification, with the limited amount of information that one can obtain from heart rates, it seems that, unless very careful relationships between heart rate and energy expenditure are obtained for each individual, under possibly different sets of circumstances, the amount of final knowledge about the level of physical activity of the subjects may be somewhat small.
With more sophisticated instrumentation. a breakdown of heart rates during the waking day is feasible. However, apart from the general confounding influences mentioned above, the practical problems of using these instruments in the field, the difficulty in maintaining them in an acceptably accurate state, their expense, and the problems in interpreting the results, all contribute to the conclusion that they are probably not suitable to use at the present time.
The older models of pedometers are notoriously inaccurate and quite unsuitable for use in measuring energy expenditure. However, prototypes of improved models have recently been described and it is possible that these, or other instruments, might be of reasonable practical use.
Further comments on these and other aspects of methods for measuring physical activity are given in the WHO publication "Habitual Physical Activity and Health" (see Bibliography).
It is important to have a clear objective when undertaking measurements of energy expenditure in man. Certain types of physical activity or inactivity (e.g., sitting) may be of significance because they occupy a large amount of time, or (e.g., short-term severe work) because they require considerable physical effort and high levels of fitness, or (e.g., long-duration moderate work) because they expend large amounts of energy. The approach to the measurement may be different in these various circumstances: a moderate error in measurement of a longer-duration activity (e.g., of the order of 0.5 kcal/min (2 KJ)) will make a difference of 200 (·84 MJ) over a seven-hour period, whereas a relatively large error (2 kcal/min (8 KJ)) in a short-term strenuous activity may make a difference of much less than 100 kcal (·42 MJ) in the day.
Therefore, key activities, and the reason why they are key activities, should be carefuly assessed either before measurements are started or at an early stage of the investigation.
No one should be deterred from attempting to measure energy expenditure when this will provide useful information. We have carried out measurements of total daily energy expenditure, usually over seven consecutive days, on more than 1,000 individuals ranging in age from 11 to 80 years, and from pre-adolescent school children through office clerks, housewives, farmers, industrial workers, New Guinean villagers, Ghanaian soldiers, Ethiopian labourers, and many more. The technique is laborious, but quite practicable and it can be reasonably accurate.
Particularly in the evaluation of food aid, or in assessing deterioration in nutritional state, changes in physical activity and energy expenditure may occur earlier than changes in body weight, and are thus of much importance.
Assessment of the degree of physical fitness of an individual is fraught with problems. The first problem concerns the meaning of physical fitness: "Fitness for what?. " Many tests attempt to evaluate skill, strength, flexibility, etc. These have usually little relevance to nutritional influences and little bearing as health indicators, are complex to carry out, and will not be described here.
The only relevant tests are those that allow some appraisal of overall physiological function as it reflects the ability to undertake physical exercise. Testing this will usually involve making measurements of cardiovascular and respiratory functions, because these best indicate the degree of physical stress on the body. What is measured is the ability of the body to maintain the various internal equilibria reasonably near the resting state during muscular exertion. and to return these equilibria to the resting level as soon as possible after exercise has ceased; that is, to perform efficiently any large muscular activity and to recover rapidly thereafter.
Physical fitness at reasonable levels cannot exist unless nutrition is adequate. The ability to undertake strenuous physical activity without undue stress is an important facet of a healthy state; it enables one to do necessary physical work easily and to enjoy strenuous leisure activities. Physical fitness can therefore be considered as one critical area of health that may be affected by nutritional factors, and the measurement and evaluation of physical fitness may well be important references in the nutritional comparison of population groups or in judging the results of intervention programmes.
Tests of Physical Fitness
The stress that is imposed on the human body by strenuous physical effort varies with the level of the maximal capacity of the body to perform exercise. If an individual has a physical working capacity of a certain amount and does exercise at a level of 50 per cent of his capacity, he is under much less stress than another person doing the same activity using 70 per cent of his capacity. The larger the level of the physical working capacity of an individual, the more strenuous exercise he will be able to take and the less stress he will have imposed on him by any particular exercise level relative to someone of a lower exercise capacity.
Because exercise shows its effect most obviously-and is most easily measured-on the cardiovascular and respiratory systems, the measurement of exercise capacity involves these systems. The most useful measurement is that of the maximal oxygen uptake (Vo2 max) by the body, because this indicates the maximal capabilities of the respiratory and cardiovascular systems to supply oxygen (and therefore release energy) to the working muscles. As an example, two men of the same body size may have a VO: max 3 l/min in the one case and 2 I/min in the other. If they each have to do work that requires an oxygen consumption 1.5 l/min (approx. 7-8 kcal/min (29-33 KJ)), this work level is 50 per cent of the maximal capability of the first man but 75 per cent that of the second. In the second case this would involve a considerable physical stress with perhaps marked fatigue if it continued for some time. Because body size has almost a direct relationship with oxygen consumption during exercise (an 80 kg man will require roughly 8/5 or 1.6 times as much oxygen as a 50 kg man at the same exercise level), Vo2 max is often expressed, not as l/min but as ml/kg of body mass/mint Very approximate levels for people of varying degrees of fitness might be 3545 ml/kg/min for an average young man and 50 ml or more for a young man of higher levels of fitness. Extremely fit men may have values of 70-80 ml/kg/min or even higher, but these are exceptional values. With ageing there is a decrease in physical working capacity of roughly 5 per cent per decade after age 20 to 25 years; there is obviously a very large variability in this decrement. There is also a difference between the sexes, with women having about 15-20 per cent lower values.
When VO2 max is being measured on an individual, it can be measured either directly by having the person do exercise up to the extremes of his or her capability, or else by sub-maximal tests where the results are extrapolated to supposedly maximal values. Both approaches have their drawbacks. The direct measurement, to be a valid reflection of the real maximal working capacity of the individual, requires considerable motivation: it is a somewhat unpleasant experience for those not accustomed to it to exercise to complete exhaustion. Unless repeated measurements are made on each individual, it is unlikely that a real VO: max will have been obtained. Also, particularly in older people, there may be slight dangers in doing really maximal exercise.
The drawback to the sub-maximal approach concerns the accuracy of the extrapolation. As the exercise is submaximal. motivation becomes less relevant. The extrapolation requires heart-rate to be measured (sometimes in conjunction with oxygen uptake) during three or four different levels of standardized exercise, up to a moderately strenuous degree. Heart-rates should range from 100 up to about 170/min. A regression line is then constructed and extrapolated to a maximal heart-rate of a value equal to 220-age since this represents 220 minus age in years (e.g., for a 10 year old child, this value is 220-10, i.e., 210 beats/mint The work level or the oxygen uptake at this extrapolated rate is then assumed to represent the maximal.
However, two sources of error arise. First, submaximal heart-rates can vary within the individual independently of the exercise, because of such influences as emotion, time of day, effects of eating or drinking, smoking, temperature, etc. And second, a direct extrapolation from sub-maximal heart-rates to maximal will not represent the normal situation, because at near maximal values the relationship of heart-rate to oxygen uptake is different from that at lower levels of exercise. However, the error is seldom large, and a sub-maximal test, especially in a nutritional context, is probably the method of choice. With experience and especially under laboratory conditions, the direct maximal text may sometimes also be done.
Conditions for Tests
On the subject of submaximal tests, Astrand suggested certain conditions for a test of physical work capacity. As these have achieved a degree of acceptance, they are listed below.
The work level must not be too low, otherwise psychological factors will be able to influence the various physiological functions measured.
Actual Test Procedure
The submaximal test chosen does not need exact replication in all conceivable circumstances because it basically involves measurements made at four different submaximal exercise levels, chosen to result in heartrates of between 100 beats/min and 170/min in the individual being studied. Obviously these levels will vary for different people, depending upon factors such as level of fitness, sex, age, etc. The critical result is the final extrapolation to the estimated V0: max.
Also, the particular exercise has limited importance. In a laboratory the method of choice would be to have the individuals being studied walk on a treadmill at varying speeds, or else exercise at varying levels on a bicycle ergometer. In field situations, a bicycle ergometer can also frequently be used, or else a simple step test can be devised-for example, having a 12 inch (30 cm) and a 15 inch (38 cm) block of wood as steps and making the subject step on and off these perhaps 1) 10 times/min, 2) 18 times/min, and 3) 25 times/min on the 12 inch (30 cm) step, and 4) 25 times/min on the 15" (38 cm) step.
However, all of the tests require heart-rate to be measured and it is preferable also to measure oxygen uptake. With experience, heart-rate, can be counted by feeling the pulse, either at the wrist or over the carotid area in the neck. This is not easy to do accurately, especially in a step-test where the only practicable procedure is to make the subject stop exercising for a few seconds at the end of each separate level. For example, this would mean that after stepping on and off the 12" (30 cm) block at 10 times/min for the required time, the subject would stand still for perhaps 10-12 sec. until the pulse rate is counted; he would then continue the test at 18 times/min for the appropriate time, stop again for 10-12 sec., and so on. Similarly with the bicycle test. After some experience it is possible to pick up the pulse rate almost immediately by palpating the radial pulse at the wrist and a reasonably accurate count over 10 sec. will give the heart-rate per min. by simple multiplication. These brief stoppages during the exercise test, while not ideal, are probably too short to have a significant effect on the end result, except in very fit individuals.
If no instrumentation is available, by simply counting heart-rate in the above manner and using one of the standard nomograms (e.g., 16) the VO2 max can be predicted. The error for an individual using this simplified technique is probably considerable, but it may be acceptable for assessing groups of people.
More precise techniques need the heart-rate to be measured by instrumentation. An ordinary ECG instrument is quite suitable and these are usually readily obtained and are reasonably inexpensive.
Oxygen uptake, which should also be measured if possible at each level of exercise, can be done by the Douglas Bag technique.
The exact method would therefore involve the following: for either the treadmill or bicycle ergometer, four levels of exercise need to be chosen where the heart-rates will vary from approximately 100/min at lightest level to 170/min at the heaviest (in the case of people who are unfit or over the age of 40 years, a smaller range-should be chosen-e.g., from 100/min to 155/min). The whole test is continuous with each exercise level being done for 5 min., i.e. 20 min. in all. Heart-rate is measured for about 10-20 sec. twice during the last min. of each exercise, and from 3.5 min. to the 4.5 min. is usually convenient.
Therefore, at the end of the measurements, four pairs of results have been obtained, i.e., heart-rate and oxygen uptake at four different levels. These are simply plotted on a graph, with heart rate (beats/min) being one axis and oxygen uptake (litres/min) the other. A line is drawn fitting these four points together and extended so that oxygen uptake at a theoretical heart-rate of 190/min can be estimated. This value represents the V0; max of the individual and can be expressed as ml/kg/min by dividing by the body weight of the person.
Testing physical fitness is something that could usefully be incorporated into many nutritional investigations. It is not always a simple procedure. On the other hand, it should be a practicable part of an investigation carried out by efficient, trained personnel with a modicum of equipment. A reasonable amount of basic knowledge is required of the investigator; some of this is provided here, other aspects are dealt with in the WHO booklet on exercise testing by Lange Andersen et al. and Godfrey's monograph specifically written on exercise testing in children (see Bibliography). It is highly desirable that someone in the evaluation team should have had first-hand training in a laboratory with extensive experience in exercise testing.
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Durnin, J.V.G.A., E.C Blake, M.K Allan, E.J. Shaw, E.A. Wilson, S. Blair and S. A. Yuill, "The Food Intake and Energy Expenditure of Some Elderly Men Working in Heavy and Light Engineering," Brit. J. Nutr,. 15: 587-591 (1961).
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