Can we modulate physical activity in children?

Abstract

Intuition tells us that physical activity is central to weight reduction in obese children. Evidence, on the other hand, suggests that increases in physical activity are difficult to achieve in the short term, and may not be possible in the long term. One explanation could be an 'activitystat', a feedback loop in the child's brain that controls physical activity according to a set point. This brief article, which argues that it may not be possible to modulate the activity of children, reviews the principles of feedback control as they apply to physical activity, discusses evidence for its central control, and demonstrates how a physical activity control loop might operate to defend the set point. Studies restricted to objective measurement suggest that the physical activity of children varies in a systematic, rather than random manner. It varies little from environment to environment, from year to year or from place to place. Where children undertake more activity at one time of day, they appear to compensate at another. Systematic variation of this kind implies control, and the control of physical activity appears to lie with the child, not with his environment. Perturbation (temporary change in response to disturbance) during short-term physical activity interventions may be mistaken for modulation (permanent change in set point), a fundamentally different response. Perturbation lasts no longer than the disturbance that causes it, and there is little evidence that interventions raise activity long term, if at all.

Does a Classroom Standing Desk Intervention Modify Standing and Sitting Behaviour and Musculoskeletal Symptoms during School Time and Physical Activity during Waking Time?

“…For example, some studies have found that an increase in physical activity at one part of the day tends to be followed by a reduction in physical activity at another part of the day in children [47,48]. Conversely, some studies have shown no compensatory behaviour with children staying active after school, even if they were more active at school [31,32,49].…”

Doubly labeled water validation of a computerized use-of-time recall in active young people

“…In New Zealand, more than one third of young people aged 5-24 years are overweight or obese [6]. Because of its potential to increase daily energy expenditure, regular physical activity may be an important modifiable lifestyle behavior for both the prevention and treatment of childhood obesity [7,8], though the impact of physical activity on overall energy balance remains a topic of debate [9,10]. Furthermore, decreasing time spent being sedentary (engaging in sitting or lying activities associated with low levels of energy expenditure) has emerged as another potential target to promote energy balance and maintain optimal body composition.…”

The ActivityStat Hypothesis

“…There has been an increasing interest in the activitystat concept of late and recent publications demonstrate that the issue is hotly contested in the physical activity research forum [4,5] . The number of published papers alone purporting to investigate the activitystat hypothesis is indicative of a growing trend in the literature.…”