Variation in physical activity lies with the child, not his environment: evidence for an ‘activitystat’ in young children (EarlyBird 16)

Abstract

The correlations within groups and the similarities between them suggest that physical activity in children is under central biological regulation. There are implications both for public health planners and for the potentially novel signalling pathways involved.

Body composition is associated with physical activity in daily life as measured using a triaxial accelerometer in both men and women

“…Therefore, the effect of seasonality was taken into account using the number of relevant daylight hours for the 2 weeks monitored. 26 The association between %BF and the proportion of time spent on physical activity of low, moderate and high intensity was determined using multiple linear regression. The association between %BF and physical activity was determined for each gender separately, taking body mass and height into account.…”

Can we modulate physical activity in children?

“…11 The hypothesis of an Activitystat advanced by Wilkin et al 2 implies that the 'set point' for habitual physical activity is set 'low', and attempts to increase habitual physical activity via interventions are likely to be counteracted by compensatory declines in physical activity. It is worth noting that there are several distinct concepts here; the existence of an Activitystat; the nature of any Activitystat; whether any set point for habitual physical activity (or presumably physical activity energy expenditure or total energy expenditure) is set 'low' or 'high'; the issue of whether any compensation for physical activity in children would lie largely on the energy intake side of the energy balance equation rather than on the energy expenditure side of energy balance.…”

“…Although acknowledging limitations in the evidence, these are not 'empty reviews' and are not consistent with the 'Activitystat hypothesis' in its current form. 2 Moreover, there is no need to invoke a complex explanationFsuch as a regulatory mechanism for physical activityFfor the apparent 'failure' of some previous interventions, as plausible and more parsimonious explanations exist. These include lack of statistical power in some studies; inadequate implementation of the intervention; limitations in current 'intervention science' can mean that the behaviours targeted by the intervention may not have been altered meaningfully by the intervention.…”

“…1 One recent challenge to use physical activity interventions to prevent obesity is the view that these will be counteracted by an internal compensatory mechanism exerting an effect to maintain current level of physical activity. 2 If it is established that such a mechanism exists, it could bring about a paradigm shift in the design of public health strategies aimed at obesity prevention by reducing the emphasis on physical activity. The present short critique therefore aims to consider the evidence that interventions to promote physical activity during childhood and adolescence might be counteracted by tightly controlled internal regulation of habitual physical activity or physical activity energy expenditure.…”

Reply to Wardle J et al. School-based physical activity and changes in adiposity

“…Because there is a mainstream literature, unfortunately not cited in the article, with evidence to the contrary. 3 Science is about testing null hypotheses and, where this has been done using objective measures, no significant differences in physical activity have been found among school children despite 5-fold differences in PE time offered. 4 The most telling question was left unanswered by the present study because physical activity was not measured: 'How much of the variation in physical activity among children can be accounted for by the PE time offered in school?'…”