|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|
The position adopted in this paper is that the reciprocal interaction that exists between motor maturation and organized physical activity suggests a way of addressing such an issue. We propose that, in a population at risk of chronic energy deficiency, the study of the relationships between motor milestones in early life - obviously dependent on the availability of energy - and later functioning is a test of the functional significance of reduced physical activity. To test this hypothesis we have taken advantage of a longitudinal study in rural Guatemala that allows for correlational analyses of motor maturation during the first 15 months of life and performance on a series of functional tests in adolescence.
We first assume that physical activity contributes to motor maturation which, in turn, is a codeterminant of organized action. Physical activity mobilizes and strengthens the skeletal and neuromuscular systems and allows for the onset (i.e., milestones) and development of increasingly complex movements. Motor maturation, in turn, is a prerequisite of activity involving directionality, as organization is dependent on selective movements. For example, before a child creeps for the first time it must have reached a stage of maturation of the skeletal and neuromuscular system that makes the action mechanically possible. Conjointly, creeping Implies that the infant has reached a developmental stage that allows for the onset of that particular directed action. Once a child has incorporated creeping into its repertoire, its view of the physical environment changes as it is then exposed to visual and tactile stimuli which were previously beyond reach or unavailable.
The onset of a developmentally significant action (e.g., creeping, sitting, standing), dependent on the reciprocal interactions of physical activity and motor maturation, is not necessarily the result of a directive from a central control at a particular instant. From a systems view of growth and development (KUGLER, SCOTT KELSO and DURVEY, 1982; THELEN, 1987; THELEN and FOGEL, 1989) the action is viewed as a result of the simultaneous presence and relationship of various elements in different developmental domains. The convergence of the availability of energy, the presence of necessary antecedent movements, the maturity of the skeletomuscular system, drive, and the appropriate environmental circumstances may all be needed.
It follows that data on motor maturation, particularly derived from the assessment of motor milestones, should provide useful information for the study of developmentally meaningful actions. Based on the arguments already formulated, we propose that if physical activity is reduced under conditions of chronic energy deficiency, then the onset of developmentally meaningful actions will be delayed. It is already known that the motor maturation of malnourished children is delayed (MALINA, 1984) and that nutrition supplementation has beneficial effects on the performance of nutritionally at risk infants on motor developmental scales (Jogs and POLLITT, 1987). What is not known is whether motor maturation predicts functional performance in adolescence and adulthood.
If the propositions in the previous paragraphs are correct, then the maturation of motor actions (i.e., milestones) that lead to developmentally meaningful behaviors should be correlated with cognitive test scores in later life in populations with chronic energy deficiency in early childhood.
The attractiveness of this proposal is enhanced by the solid evidence already available that in well-nourished populations the scores on scales of motor and mental development in the first 24 months of life maintain a zero correlation with later cognitive test scores (McCALL, 1979, 1981; LEWIS, JASKIR and ENRIGHT, 1986). Thus, the search for a statistically significant correlation, even in a population which is nutritionally at risk, goes against common wisdom in developmental psychology. Evidence that motor test scores in infancy and cognitive test scores in childhood and adolescence covary in such a population would strengthen the theoretical argument presented previously. The argument would be even stronger if the correlations in the same nutritionally at risk population between mental development test scores and childhood and adolescent scores were, as in the case of the well-nourished populations, not different from zero.
In particular, we hypothesize that energy deficiency in infancy affects the timetable of motor maturation and delays the onset of behaviors which are instrumental in the reciprocal interaction between the infant and its environment. The acquisition of behaviors such as sitting alone, rolling, creeping, standing alone, taking steps, or walking alone, broadens the infant's view of the world and allows for engagement in more diverse motor activities than before the onset of such behaviors (BAYLEY, 1936). We also conjecture that the delay in the acquisition of such behaviors and the consequent interference with the interaction between the infant and its environment has long-term developmental consequences. By this we mean that delayed motor maturation due to chronic energy deficits interferes with the acquisition of basic abilities and skills that are necessary to function in society. School-related behaviors are examples of such abilities.