|Activity, Energy Expenditure and Energy Requirements of Infants and Children (International Dietary Energy Consultative Group - IDECG, 1989, 412 pages)|
|Long-term developmental implications of motor maturation and physical activity in infancy in a nutritionally at risk population|
A basic premise of the analyses presented in this paper was that data on motor maturation among infants who were nutritionally at risk have the potential of providing insightful information on long-term effects of chronic energy deficiency. The correlational analyses presented were rooted in the proposition that if the maturation of motor actions (e.g., creeping) that lead to developmentally meaningful behaviors (e.g., environmental exploration) are delayed by chronic energy deficiency, then motor maturation test scores of infants who are nutritionally at risk should be correlated with their cognitive test scores in later childhood and adolescence. The analyses were done in the context of a large body of developmental data which conclusively show that, among well-nourished subjects, the scores on developmental scales of motor and mental development in the first 24 months of life maintain a zero correlation with later cognitive test scores.
In this study, intrauterine growth as reflected by birth weight neither predicted anthropometric data nor mental and motor test scores at 15 months. On the other hand, at 15 months of age, weight and height predicted both mental and motor developmental test scores. However, both measurements of body growth were more closely associated with the motor than with the mental scores. This finding is consistent with the available evidence which suggests that, in infancy, motor maturation is more sensitive to nutritional insult than those behaviors that are generally interpreted as reflecting mental function (Jogs and POLLITT, 1984).
The third set of analyses showed that, in comparison to the mental scores, the motor scores were better predictors of the factor scores that emerged from the preschool cognitive test battery at 36 and 48 months. However, linear growth measures at 15 months were as good predictors as motor test scores of performance in the preschool period. Thus, these analyses provided only weak support for our theoretical formulations.
On the other hand, the fourth set of correlational analyses between motor scores at 15 months and the functional performance measures in adolescence were in full agreement with our formulations. Motor test scores at 15 months predicted at a statistically significant level (p < .05) literacy, reading and vocabulary scores, and maximum grade attained in school. On the other hand, as is the case of many other studies among well-nourished children, the present analyses showed that neither the mental test scores nor anthropometry in infancy predicted cognitive performance in adolescence. It must be underscored that, despite our familiarity with the literature, we do not know of any other longitudinal study in the world among well-nourished subjects that has conducted analyses similar to those reported in this paper and obtained similar results. Similar analyses with chronically energy-deficient populations are not available.
An explanation which could be an alternative to the thesis presented in this paper is that both motor maturation and cognitive test performance in this sample were dependent on a third variable. Social and economic variables are obvious candidates for such an explanation. However, this alternative is seriously weakened by the fact that there is no obvious reason why social and economic variables would affect motor and not mental test scores. If the underlying mechanisms were social environmental factors then the mental development scores should have been as strong predictors of the adolescent test scores as the motor score. This was not the case.
Figure 9 depicts in diagrammatic form the pattern of relationships that we propose exist between energy intake, motor maturation, physical activity and developmental test scores in two populations adapted to two different levels of energy intake. In one, the supply of energy meets the needs of the population which is well-nourished, and motor maturation and physical activity are independent of energy intake. Exceptions to these zero relationships between intake, maturation and activity are likely to be found in cases of obesity. Obese children mature faster (DIETZ, 1987) and are less active (DURNIN, 1984) than children whose weight falls within the normal range. Further, for most of the population, functional performance in adolescence is also independent of motor maturation and activity. Exceptions to these cases may be found in the presence of neurodevelopmental pathology and gross motor maturational delay in infancy and early childhood. These have been associated with poor cognitive test and educational achievement performance in the school-age period (SILVA, 1980).
In contrast, in a population where the supply of energy fails to meet the physical needs (Figure 1) and accommodations must be made to reach energy balance (i.e., in a chronically energy-deficient population), the relationships between the variables in question would be significantly different from zero. As the results from the analyses that have been presented suggest, low intake (inferred from retarded growth) is related to motor maturation (i.e., motor test scores) which, in turn, is related to developmental test scores in adolescence. The associations between physical activity and maturation are only inferred from the theoretical formulations in the introduction.
It cannot be overemphasized that the results from this study must be interpreted with caution. However, they do suggest that one practical way of looking at the possible long-term effects of chronic energy deficiency is by assessing its impact on motor milestones which are important determinants of cognitive and socioemotional development.