Background
Prevalence estimates internationally suggest that substantial proportions of preschool-aged children (3–5 years) are insufficiently physically active and engage in high levels of screen-based entertainment [
1‐
5]. For example, one Australian study indicated that only 5 and 20% of 3- to 5-year-olds met national guidelines for physical activity and electronic screen-based entertainment, respectively [
2]. Understanding the impact of these prevalence rates should be a high priority, however early childhood is the developmental period for which we know the least about the independent effects of physical activity and screen behaviours on development and health [
6‐
9]. Rapid technological advancements in mobile electronic media have made screen-based forms of entertainment for young children ubiquitous, and research demonstrating the influence on cognition, socialisation, behaviour, and health has lagged behind the rate of adoption [
10]. Evidence indicates that physical activity is likely to improve young children’s weight status, bone health and motor development [
6], however evidence for other health outcomes such as cardiometabolic health is less clear. Likewise, although the early years are characterised by rapid and formative changes in cognition, socialisation, and behaviour [
11], the independent influences of habitual physical activity and screen-based entertainment on cognitive and psychosocial development among preschool children are not well understood [
7‐
9].
Emerging evidence suggests that physical activity may affect school-aged children’s higher-order cognitive processes, such as executive functions, that in turn affect self-regulation [
12‐
14]. Self-regulation is a construct composed of multiple inter-related high-level cognitive skills responsible for formulating goals, planning how to achieve them, and carrying out these plans effectively [
15]. These executive functions develop throughout childhood and include inhibition, cognitive flexibility, and working memory [
15]. Self-regulation and executive functions are strong indicators of school readiness and later academic achievement [
16], and are intimately linked to children’s psychosocial development and behaviour [
17]. In a seminal experimental study, Davis and colleagues [
12] found that regular physical activity improved executive functions and altered brain activity in inactive overweight 7- to 11-year-olds. Remarkably, children’s ability in mathematics improved despite the fact they received no direct instruction in this area. Nevertheless, the influence of physical activity on cognition and executive function in young children is not well established [
8]. Consequently, it remains unclear if physical activity aids cognitive development in early childhood, and if so, how much physical activity, of what intensity, and which types might be required for optimal development.
Psychosocial development encompasses children’s emotional, behavioural and social functioning. In Australia, approximately 50% of 2–3 year-olds exhibit externalising (e.g., aggression) and internalising (e.g., anxiety) behavioural problems “sometimes” or more often, and 10% of 4–5 year-olds display consistent behavioural problems in these areas [
18]. These behavioural problems can be persistent and can place children at risk of problematic developmental pathways [
19]. A recent systematic review indicated that there are too few studies to draw conclusions about associations between electronic media use or physical activity and psychosocial development in young children [
7]. Studies in this area have investigated a narrow range of screen-based behaviours, with only one of seven studies in 3–5 year-olds examining multiple screen behaviours beyond TV viewing [
20]. Likewise, studies have typically not controlled for the potentially beneficial effects of physical activity, as only two studies concurrently assessed electronic media behaviours and physical activity [
20,
21]. Of the studies that have examined associations between physical activity and psychosocial development, only one study used an objective measure of physical activity [
21], which raises concerns about measurement accuracy, and all but one study [
22] used a cross-sectional design, from which it is difficult to determine if physical activity is the cause or consequence of psychosocial outcomes. Furthermore, there is little research on relations between physical activity and media use, on the one hand, and children’s social cognition, on the other hand. Social cognition, which includes children’s empathy and understanding of mind and emotion, has been shown to be an important predictor of early social behaviour and integration [
23‐
25] that is highly sensitive to the child’s social and communicative environment [
26]. Physical activity, which often involves group based participation, and media use, which removes young children from interpersonal communications, might both exert indirect effects on children’s social behaviour (e.g., behaviour problems, social skills, prosocial behaviour, etc.) through their potential influences on the development of social cognitive capacities, which have been shown to change rapidly in the preschool period [
27] and rely heavily on executive functions [
28]. In keeping with this interpretation, there is limited cross-sectional research which suggests that high levels of television viewing may be detrimentally associated with young children’s social cognition [
29]. Finally, to our knowledge, objective psychophysiological assessments of emotional and social development, such as heart-rate variability, have not been collected in population samples of young children with concurrent assessments of lifestyle behaviours such as electronic media use or physical activity. Understanding if physical activity or electronic media use are associated with psychophysiological biomarkers would assist in explaining potential pathways through which these lifestyle behaviours might influence young children’s psychosocial development.
Investigating associations of lifestyle behaviours with cardiovascular and diabetes-related health outcomes in young children is difficult, because invasive clinical measures such as blood tests are not appropriate for population samples. However, non-invasive measures such as
retinal micro-vasculature assessments could provide important insights into the early development of cardiovascular structure. The blood vessels of the retina can be assessed non-invasively in the field using portable retinal imaging and this measure has been used as a marker of systemic micro-vasculature. In adults, changes in retinal vascular caliber (narrower retinal arteriolar caliber and wider venular caliber) predict higher risks of hypertension and diabetes [
30], higher risk for stroke [
31], coronary heart disease [
31], and coronary heart disease mortality [
32]. Retinal micro-vascular changes, at least in adults, appear to be structural markers of subclinical cardiovascular disease and predict future vascular events [
33,
34]. Furthermore, in adulthood, retinal micro-vasculature assessments provide clinically meaningful information on risk of cardiovascular disease, beyond conventional risk factors such as blood pressure [
31]. Notably, deleterious retinal vascular changes are likely to be present before the manifestation of other cardiovascular disease risk factors such as elevated blood pressure in young children [
35]. Paediatric studies demonstrate that: i) higher blood pressure and body mass index (BMI) at 3–5 years of age [
35], and ii) higher levels of television use and lower levels of participation in parent-reported outdoor sporting activity as early as 6 years of age [
36], were associated with adverse retinal micro-vasculature development. However, the nature of the associations between objectively measured physical activity and electronic media use with retinal micro-vasculature in preschool-aged children remain unknown.
In recognition of the potential health and developmental benefits for young children of increasing physical activity and reducing screen-based entertainment, several countries including Australia [
37], Canada [
38], and the United Kingdom (UK) [
39], have released guidelines for physical activity and sedentary behaviours. Consistent with the guidelines released in other countries, the Australian
National Physical Activity Recommendations for Children 0‐
5 years specify that 3–5 year-olds should be physically active for ≥3 h/day, and that their screen-based entertainment should be limited to <1 h/day [
37]. There is, however, ongoing discussion surrounding these recommendations [
40] because the amount and intensity of physical activity [e.g., light- (LPA), moderate- (MPA), or vigorous-intensity physical activity (VPA)], and the amount and types of screen behaviours that might influence development and health in 3–5 year-olds remain unclear [
6‐
9]. Scholars have highlighted the need for further evidence to understand the impact of physical activity and screen-based behaviours on development and health among young children [
6‐
9,
40].
The aim of the Preschool Activity, Technology, Health, Adiposity, Behaviour, and Cognition (PATH-ABC) study is to contribute to addressing this knowledge deficit by investigating the following research questions among 3–5 year-old children, both cross-sectionally and longitudinally:
Are physical activity and use of screen-based entertainment independently associated with cognitive and psychosocial development and health outcomes?
-
Do the associations differ by the intensity (e.g., LPA or moderate-to-vigorous-intensity physical activity (MVPA)), amount, or type of physical activity?
-
Do the associations differ by the type (e.g., TV/DVDs or computer/portable electronic devices) and amount of screen-based entertainment or the total amount of sedentary behaviour?
-
Do the associations differ by sex, age or socioeconomic position?