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A second approach to looking at activity level in studies of energy intake and energy requirements is to ask the question: what might be the potential role of activity level in the process wherein inadequate energy intake is translated into deficits in behavioral development? One possibility that has been suggested is that less active children are less able to elicit developmentally facilitative interactions from caregivers in their environment. For example, as hypothesized by Chavez and Martinez: "Malnutrition depresses activity which in turn isolates the individual from... necessary interaction with the mother and the family, and from all sources of stimuli that are of vital importance to the functional development of the brain." (CHAVEZ and MARTINEZ, 1984, p. 319).
Underlying this quote is the assumption that more active children will be better able to elicit developmentally facilitative interactions from their primary caregivers. However, at least within the temperament literature, this assumption has not received strong empirical support. Indeed, much of the available evidence relating children's activity levels to subsequent parent behaviors is either inconsistent (BATES, 1989b) or suggests that less active children are more likely to elicit optimal parental behaviors than are more active children (DUNN and PLOMIN, 1986; Buss, 1981).
There are several reasons for this state of affairs. First, within the framework of Bell's (BELL and CHAPMAN, 1986) control model, parents tend to act to restrain the behavior of their highly active children and to stimulate the behavior of their less active children. Since parents attempt to modulate their child's activity to an optimal level, we should not necessarily expect that more active children would receive more stimulation from their parents (BELL and CHAPMAN, 1986).
Second, as noted by BATES (1987), specific parent reactions are not automatically elicited by differences in their child's temperamental activity level. Rather, parental reactions appear to be a combined function of the child's activity level, the behaviors the child is displaying while being active (i.e., constructive versus active behaviors) and by the parents own individual tolerance for high or low activity levels. For example, data by HUBERT and WACHS (1985) indicated that up to 40% of the parents in our sample equated temperamentally-based high activity of their infant with greater perceived difficultness of the infant; nearly 20% of the sample felt that the more curious or exploratory their infant was, the more temperamentally difficult their infant was. Examination of the rationale for these ratings suggested that many parents see high mobility as necessitating greater supervisory efforts by the parents, while high levels of exploratory behavior or curiosity are viewed as an example of demanding behavior by some parents.
In addition to differential parental tolerance, differential reactivity by parents to their child's characteristic behaviors also appears to be a function of parental skill factors. For example, as noted by SUPER et al. (1981), the reaction of Colombian mothers to differences in their infant's state differed as a function of whether or not the mother had received training in facilitating infant development.
What the above suggests is that the assumption that more active children will receive more facilitative caregiver behaviors is not necessarily valid. While some evidence suggests that more active children do receive more facilitative caregiver behavior (CHAVEZ and MARTINEZ, 1984), the totality of evidence does not allow us to accept that this conclusion holds for all cases. Rather, congruent with our earlier discussion about activity level as an index of information processing, it seems clear that an adequate understanding of the relation of child activity level to caregiver behaviors necessitates more than just measuring activity level per se. Rather, the parents' characteristics, the parents' affective reaction to high or low activity level and the content of the child's activity must be assessed and integrated into our model, before we can come to a clear understanding of the relation of activity level to caregiver-child interaction patterns.
A second approach to understanding the process whereby activity level relates to decrements in behavior is to consider the possibility that activity level may act as potential mediator of the environment (BARON and KENNY, 1986). Over 25 years ago, based on clinical observations, ESCALONA (1963) suggested that inactive infants showed better development when guided by maternal interactions, whereas more active infants did best when caregivers played a less involved role. A few years later, SCHAFFER (1966) published a paper suggesting that more active children are more resistant to the detrimental effects of prolonged hospitalization than are less active children. It was unclear, however, whether the group differences reported by Schaffer were a function of differential reactivity of more and less active children to the environment or were due to differential treatment of more and less active children by hospital personnel. This line of research was not followed up very much until several years ago, when I presented data indicating that parental mediation of the environment for the child was particularly critical for the development of mastery motivation in temperamentally less active babies; in contrast, for highly active babies, confirming Escalona's original suggestion, parental mediation tended to inhibit the development of mastery motivation (WACHS, 1987b). Particularly critical in this study is the fact that there were no differences in the measured home environments of more and less active children. Thus, the results suggested differential reactivity of more and less active children.
Following up this line of research, a student of mine, Mary Jane Gandour, in her dissertation utilized a different measure of the environment (parental attention focusing behavior) and a different outcome measure (toddler exploratory behavior). Her results essentially replicated my earlier findings. Specifically, for temperamentally more active toddlers, greater amounts of parental attention focusing tended to inhibit exploratory behavior, whereas for less active toddlers, parental attention focusing tended to facilitate the development of exploratory behavior (GANDOUR, 1989). Analysis indicated no differences in the measured environments of more and less active toddlers, again suggesting differential reactivity. What this line of research suggests is that the child's temperamental activity level may be a critical mediator of the child's interaction with its environment.
What are the implications of the above findings for energy intake and energy requirement studies? First, I would remind you that imbalances between energy requirements and energy expenditure do not occur randomly. Rather, these imbalances covary with a variety of other factors, including adequacy of the child's rearing environment GRANTHAM-McGREGOR 1984; POLLITT, 1988; RUSH, 1984). Thus, I would suggest that we cannot understand how variability in energy intake and energy requirements translates into variability in behavioral development, unless we know something about the nature of the psychosocial rearing environment the child encounters. I would also suggest that we cannot fully understand the relation of psychosocial rearing factors to behavioral development, unless we know something about the role of child characteristics, such as activity level, which may mediate environmental influences (WACHS and GRUEN, 1982).
Viewing this within a synergistic framework (LESTER, 1979), let me suggest the following process model. Children who are low in activity due to reduced energy intake may be more in need of increased stimulation from their parents or caregivers than highly active children. However, if these caregivers also have a low energy intake, then they may be less able to provide the extra stimulation their children need (CRAVIOTO and DELICARDIE, 1972; POWELL and GRANTHAM-McGREGOR 1985). Under these conditions, the impact upon development of low energy intake of the child may by synergistic. First, to the extent that imbalances between energy requirements and energy expenditure adversely influence central nervous system development (CRNIC, 1983), these children are at risk. Second, to the extent that the low energy intake level of these children means that they have lower activity levels, these children will also have a greater need for active intervention from their caregivers, which means that they are at double risk. To the extent that the low energy intake of the caregivers prevents them from providing the extra stimulation that these children need (over and above normal levels of stimulation) means that these children are at even greater risk. 4
To the extent that low energy intake covaries with morbidity, which in turn may influence activity level, suggests that these children may be at an even greater level of risk (POLLITT, 1983).4
However, the above model, while congruent with available data may, in fact, be oversimplistic. As presented here, the proposed model seems to suggest that all aspects of development may be equally influenced by the risk factors described above. However, it is becoming increasingly apparent from studies of environmental influences upon development that the environment does not act in a global, all or none fashion, but rather in a highly specific manner. That is, specific aspects of the environment influence specific aspects of development (WACHS and GRUEN, 1982).
The fact that specific predictors
appear to be uniquely related to certain specific outcome dimensions is not a new finding,
even in the nutritional literature. Prior research from the Bogota intervention project
(WABER et al., 1981) suggests that nutritional supplementation primarily affects
motor development, as compared to educational intervention which appears to uniquely
affect early learning. Supporting this hypothesis, in data from the Egyptian project
(WACHS et al., 1988), we reported a complex interaction suggesting that, for less
adequately nourished children, the impact of caregiver interactions was primarily upon the
child's emotionality and state control, whereas for more adequately nourished children
caregiver influences were reflected in the child's interaction with the environment. The
implication of these data for studies relating energy intake and energy requirements to
activity, is that, to understand the contribution of activity, we need to look beyond
activity level and the quality of the child's psychosocial transactions with the
environment. In these studies, we also need to measure multiple aspects of the child's
development and cannot rely upon a single outcome measure.
In regard to the use of activity level in studies of energy expenditure and energy requirements, the following facts seem well established:
1. Activity level can be influenced by inadequate energy intake.
2. At a behavioral level, activity level can also be viewed as a dimension of children's temperament.
3. Energy-based differences in activity level can be viewed as reflecting part of the constitutional contribution to temperament.
4. There are a variety of valid approaches to assessing temperamental activity at a behavioral level.
Given these facts, if the goal of the researcher is to study the influence of energy expenditure and energy requirements upon activity level per se, with no attempt to generalize beyond activity level or to discuss the implication of reduced activity levels for developmental outcomes, then he can safely ignore most of what is discussed in this paper and concentrate only on the section involving measurement. However, if the goal of the researcher is to generalize beyond activity level per se, and attempt to draw conclusions about what are the developmental implications of reduced activity level, then a new set of facts become salient:
1. The use of activity level as a proxy for other processes such as exploration or information processing is simply not sufficient. To understand the developmental processes involved in reduced activity level, the researcher must also look at what the child is doing while being active. In addition, and perhaps more critically, in understanding the developmental implications of variability in activity level, it is imperative for the researcher to determine whether or not the activity level displayed by the child is appropriate for the context the child is functioning in, and whether the child can modulate activity level across contexts.
2. Just as one cannot assume that high activity level means more information intake by the child, the researcher also cannot assume that active children are more likely to elicit developmentally facilitative stimulation from their caregivers. To understand the role of children's activity upon caregiver-child transactions, it is also critical to investigate the way in which the caregiver views the child's activity level along a positive-negative dimension, as well as studying the strategies the caregiver has available to deal with differences in children's activity levels.
3. Theoretically, children whose activity is reduced due to inadequate energy intake should be at greater risk for developmental problems, since these children also have a greater need for adult involvement and adult mediation of the environment. However, without direct measurement of the nature of caregiver-child transactions we can say little about whether the actual risk encountered by the child is equivalent to the expected risk.
To the extent that the researcher wishes to draw developmental implications from studies of activity level, one major conclusion thus can be drawn: The interrelation of energy intake, energy requirements and activity level must be looked at within a multidimensional framework, emphasizing the process wherein energy intake, energy expenditure, activity, contextual factors, and the child's environment relate to different outcome variables, rather than assuming a linear or unidimensional relation. Many of the issues I have raised here have also appeared in the nutrition literature. For example, in the current debate on the "small but healthy" hypothesis, SCRIMSHAW and YOUNG (1989) invoke the concepts of physiological and behavioral adaptation and accommodation. In my reading of this paper, it seems clear that neither behavioral adaptation nor behavioral accommodation can be understood without taking into account contextual factors, specifically what the culture or the environment requires of the individual. Clearly, there seems to be a parallel here with my comments on the necessity for taking context into account when discussing activity level. Similarly, BEATON (1989), when discussing the relevance of anthropometric variables for the small but healthy controversy, makes the point that a complete understanding of the relation of protein-calorie intake to function means that we must go beyond height and weight markers and utilize a process approach. Again, there is a parallel between what Beaton suggests and the points I have raised about the necessity of going beyond activity markers and looking at process. The use of marker variables like activity level or height and weight may indeed be parsimonious, but there are different ways of interpreting parsimony.
Let me close with a quote from an
earlier paper of mine, concerning the adequacy of existing environmental action models for
explaining variability in behavioral development. I believe this quote is also relevant
when we look at studies relating energy intake and energy requirements to behavior and
development: "In terms of theory, we have for the most part reified the law of
parsimony... However, properly interpreted, the law of parsimony does not refer to the
simplest explanation per se, but rather the simplest explanation given the nature of the
phenomena. As McCALL and McGHEE (1977) have noted, there is no a priori reason to
assume that nature is necessarily parsimonious when it comes to human development"
(WACHS, 1986, p. 274).
I wish to thank Jack Bates and
Avanelle Kirksey for their reading and commenting on a preliminary draft of this
manuscript.
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