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Physical fitness may influence the type of activities performed by children and the time allocated to those that demand most energy. Only a few studies have been done on the overall physical fitness of undernourished children or on its modification with changes in nutritional conditions. These have been based on aerobic capacity as a function of heart rate, on submaximal aerobic tests and on maximal oxygen consumption.
Physical fitness is reduced in children with severe protein-energy malnutrition. When adequate treatment is given, physical fitness increases with improvement of nutrition conditions, as shown by TORUN et al. (1976, 1979) in children between 2 and 4 years old. Figure 8 shows that, as nutritional rehabilitation progressed, there was a gradual weekly increment in the regression coefficients of oxygen consumption on heart rate, which indicates an increase in aerobic capacity.
Submaximal exercise tests have been done using a treadmill or bicycle ergometer in 6-year-old Colombian children (SPURR et al., 1978) and in children of school-age in Ethiopia (ARESKOG et al., 1969), Tanzania (DAVIES, 1973a, b), India (SATYANARAYANA et al., 1979), and Brazil (DESAI et al., 1983). Maximal oxygen consumption while walking on a treadmill, has been measured in Colombian boys and girls between 6 and 16 years old (SPURR and REINA, 1989b; other studies summarized by Spurr, 1983, 1987). The results obtained in most of those studies indicate that undernourished children had lower maximal oxygen consumption values, compared to children with better nutritional status or background from their own country, or from the United States and Europe. This is illustrated in Figure 9. However, the effect of nutritional status disappears when aerobic capacity is expressed per unit of body weight or lean body mass. Thus, it seems that the physiological potential to perform physical work is maintained in children with mild or moderate malnutrition, but their smaller size limits the maximal effort that they are capable of. This is consistent with the observations and conclusions of VITERI (1971) and SPURR (1983, 1987) in undernourished adults with reduced maximal oxygen consumption, largely due to their decreased muscle mass.
The decrease in maximal aerobic
capacity may have a negative impact on the children's ability to do physical work that
demands high energy expenditure. In rural areas of the developing world, culture and
economics often demand that children of school age and adolescents engage in heavy
physical work from an early age. Even in societies where child labor is not customary, the
small size of undernourished children may have important consequences on physical activity
in the long term. It is conceivable that these undernourished children will become small
adults with depressed physical work capacity and reduced productivity in heavy work (DESAI
et al., 1984; IMMINK et al., 1984; SATYANARAYANA et al., 1979; SPURR,
1983; VITERI, 1971).
Low or restricted energy intakes reduce the physical activity of infants and children, even at a very early age. When this is transient, it will be reversed rapidly with nutritional improvement, and it may have no important morphologic, functional, or behavioral consequences. However, a prolonged reduction in physical activity due to sustained low energy intake, may limit or reduce the child's social interactions and exploration of its environment. This is more evident under circumstances where children are encouraged or forced to participate in very energy-demanding activities. These include games, sport competitions and the need to work in rural areas.
Such limitations may contribute to a slower cognitive development, suboptimal social performance, smaller body size and reduced productivity in physical work. All this, in turn, will hinder the child's development to its full biological potential, reduce its quality of life in a broad sense, and limit its contributions to family welfare, either in childhood and adolescence, or in later adult life. Therefore, interventions to improve nutrition and function at an early age, and maintaining them through childhood, will have important biological, social and economic implications.
It is thus inappropriate to refer to
the reduction of physical activity as an adaptation to low or restricted energy intake, as
this term has the connotation of a desirable, positive adjustment. Under the best
circumstances, it should only be considered as an adequate but short-term compensatory
response.
Most of the work done by the author
in this field was in collaboration with or through the inspiration and encouragement of
Dr. Fernando E. Viteri. The guidance and support of Dr. Robert B. Bradfield and the late
Dr. C. Frank Consolazio are gratefully acknowledged. Some of the INCAP studies quoted were
partially supported by the World Health Organization and the United Nations University.
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The first questions were asked to clarify some methodological aspects of the studies on which Torun had reported.
In Guatemala, during recovery from PEM, more active children showed greater linear growth than less active children on the same diet. In a new study, which is currently underway, weight-for-height is increasing more in the more active children. The individual calibration of heart rate against oxygen consumption is possible even in relatively small children. In Guatemala, a treadmill and a pediatric face-mask were used for this purpose.
There is some controversy about the usefulness of VO2 max measurements. For most work situations at a submaximal oxygen consumption level, the measured VO2 max does not allow prediction of work performance. The counterargument is that heavy physical work is quite frequent, and that individuals who can do such heavy work at 60% of their VO2 max can sustain this activity longer. Adjusting VO2 for body weight downplays the fact that a larger person can perform more work in absolute terms.
The study undertaken by Rutishauser and Whitehead in Uganda was criticized because of the small sample sizes and because the two groups of children came from different cultural backgrounds, which could explain, at least partially, their different behavior pattern. Others emphasize the pioneering nature of the study which was among the first to show that different activity patterns could be observed under such circumstances.
Durnin presents a graph on relationships between sample size, number of measurements required, and the power of a study to detect predetermined differences in energy intakes in longitudinal and cross-sectional studies. The required sample sizes appear very large; 200 subjects, for instance, are needed to detect a 200 kcal difference in intake as statistically significant (p < .05). By implication, this means that many of the studies involving nutritional supplementation could not be expected to yield statistically significant results, simply because of small sample sizes.