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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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Astrand, P.O. and K. Rodahl, Textbook of Work Physiology (McGraw-Hill, New York, 1977).
Christensen, E.H., "Physiological Valuation of Work in the Nykroppa Iron Works," in W.F. Floyd and A.T. Welford, eds, Ergonomics Society Symposium on Fatigue (Lewis, London, 1953), pp. 93-108.
Consolazio, C.F., "The Energy Requirements of Men Living Under Extreme Environmental Conditions," in G.H. Bourne, ed. World Review of Nutrition and Dietetics, Vol. 4 (Pitman Medical, London, 1963), pp. 55-77.
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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Durnin, J.V.G.A., "Body Weight, Body Far and the Activity Factor in Energy Balance," in Energy Balance in Man, (Masson et Cie., Paris, 1973) pp. 141-150
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Garrow, J.S., Energy Balance and Obesity in Man. (North Holland Publishing Company, Amsterdam, 1978).
Godfrey, S., Exercise Testing in Children. (W.B. Saunders, London, 1974)
Lange Andersen, K., R. Basironi, J. Rutenfranz and V Selinger, Habitual Physical Activity and Health. WHO Regional Publications European Series No. 6 (WHO Regional Office for Europe, Copenhagen, 1978).
Norgan, N.G., A. Ferro-Luzzi and J.V.G.A. Durnin, "The Energy and Nutrient Intake and the Energy Expenditure of 204 New Guinean Adults," Phil. Trans. R. Soc. Lond. 268: 309-348 (1 974).
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Ernesto Pollitt
This chapter is divided into two parts. The first includes a brief description of behavioural assessment methods that have been used in published field studies on the functional consequences of energy protein malnutrition and iron deficiency. The second part includes a more detailed description of an information processing paradigm, and the methods derived thereof, that has been used in studies in Cambridge, Massachusetts, and Guatemala.