Physical Activity, Fitness, School Readiness, and Cognition in Early Childhood: A Systematic Review

Abstract

Background:

Early childhood is an important age for brain and cognitive development. Given the support of physical activity and fitness on cognition and academic performance in older children, more research has emerged recently focusing on younger children. In this systematic review, the authors review the relations between physical activity/fitness and academic-related (ie, school readiness and cognitive) outcomes in early childhood.

Methods:

A search was conducted from PubMed, PsycINFO, Web of Science, ERIC databases, and reference lists for articles that had participants aged less than 6 years were written in English, and were in peer-reviewed journals. Articles were excluded if the design was a case study or case series report. The Grading Recommendations Assessment, Development and Evaluation framework was followed to assess the quality of evidence by study design.

Results:

Sixty-eight articles reporting on 72 studies (29 observational and 43 experimental) were included. The majority of study effects were mixed, and the quality of evidence varied from very low to low.

Conclusions:

A clear consensus about the role of physical activity and fitness on academic-related outcomes in early childhood is still lacking given the high heterogeneity in methodological approaches and overall effects. Additional high-quality studies are needed to determine what specific dosages of physical activity are impactful at this age.

Early childhood is as an important phase for brain and cognitive development. The early years of life are marked by increased neuroplasticity of the brain and enhancements in cognitive processing and abilities. This age also marks a critical period in the development of school readiness skills and cognitive functions.^1–3 School readiness encompasses domains such as attention and comprehension, and academic proficiencies such as socio-emotional and fine motor skills. Cognitive functions include domains such as perception, pattern recognition, attention, executive function, reasoning, and memory. Early childhood school readiness and cognition, referred to here as academic-related factors, are associated with long-term health and social well-being. For example, early childhood (ie, 2–6 y) school readiness influences how children perform and progress in school^4,5 and cognitive functions are positively associated with both current and future academic performance.^6,7 Importantly, emerging studies suggest that academic-related factors may be influenced by health behaviors even in early childhood.^1,2

Physical activity and fitness are 2 related health behaviors that have been implicated as potential determinants of academic-related measures in young children.⁸ Biological and behavioral pathways between physical activity and fitness with academic-related outcomes in early childhood have not been adequately explored. However, cognitive development could be influenced by physical activity behaviors and fitness levels through (1) resulting physiological adaptations such as increased neurogenesis and upregulation of growth factors and neurotrophins in the brain, (2) increased activation of brain regions due to cognitive demands and coordination requirements of complex physical activities, and (3) increased retention and transfer of skills from cognitively demanding and engaging physical activities.^9,10

The 2018 Physical Activity Guidelines for Americans Advisory Report concluded that there was moderate evidence that both acute and chronic physical activity can improve cognitive outcomes such as executive functions, processing speed, memory, and academic performance in older children and adults.¹¹ Given the increasing support of the benefits of physical activity and fitness on cognition and academic performance in older children,^12,13 more research and interest has recently emerged focusing on younger children. Although there has been some support of beneficial effects of physical activity on cognitive measures, a lack of sufficient studies resulted in the inability of the Physical Activity Guidelines for Americans Advisory Report to assign a level of evidence for children aged less than 6 years.¹¹ The Physical Activity Guidelines for Americans Advisory Report has acknowledged the general limitations of physical activity and health outcomes literature in children aged less than 6 years and identified the need for additional high-quality studies that examine the effects of physical activity on cognitive health.^8,13

Given the recent growth of original research studies, evidence should continue to be collectively examined to better understand the relations between physical activity and fitness measures and academic-related outcomes in early childhood. In a 2012 systematic review that was conducted to inform the Canadian 24-hour movement guidelines for children ages 0–4 years, only one article that reported on the association between physical activity and a cognitive outcome was included.¹⁴ In a similar review to update the guidelines in 2017, 13 studies focusing on the link between physical activity and cognition were identified,¹⁵ indicating a rapid growth in recent publications. Using slightly varied search methods and criteria, 3 other systematic reviews reporting on early childhood have been published in recent years. Carson et al¹⁶ and Tandon et al¹⁷ examined relationships between physical activity and cognitive development in children aged 0–5 years (including both observational and experimental designs), while Zeng et al¹⁸ explored the effects of physical activity on cognitive development from randomized controlled trials conducted specifically in preschoolers. While these previous reviews generally conclude that physical activity has beneficial effects on cognitive measures, authors noted variability in findings, measures, and quality of the evidence. Additionally, these reviews did not include fitness as an exposure of interest.

Although physical activity and fitness are closely related, fitness indicators may have independent or interactive relationships with academic-related outcomes.¹² Whereas physical activity can generally be described as any bodily movements that result in increased energy expenditure (compared with rest or sleep), fitness is considered a set of health- (eg, cardiorespiratory, muscular strength, and muscular endurance) and skill-related (eg, balance, speed, agility, coordination, reaction time, and power) attributes.¹⁹ In regard to cognition, there has been more consistent evidence of cardiorespiratory fitness as a positive correlate to cognitive outcomes than physical activity levels in preadolescent children.¹² However, previous studies and reviews in preschoolers have mainly focused on physical activity variables in relation to academic-related outcomes, which may partially explain the inconsistent associations that have previously been reported.^8,16,20 Given that previous reviews have provided recommendations to include measures of fitness in future studies,^16–18 and recent publications have begun addressing this gap,^21–23 collectively reviewing the relations between fitness and academic-related outcomes is warranted.

In addition to the paucity of previous reviews examining the associations between physical activity and fitness measures and academic-related outcomes in early childhood, interpretations may be limited due to differences in review methodologies (ie, study design and age range eligibility and search terms). For example, one review only included randomized controlled trials so that causal relationships could be explored.¹⁸ However, results from quasi-experimental and observational studies (particularly high-quality, longitudinal studies) can provide important information regarding the associations between physical activity and cognitive outcomes, as well as inform future experimental studies and translational practices. Zeng et al’s¹⁸ review also narrowed their focus to preschool age children (ie, ages 4–6 y). Given that more evidence for overall early childhood is needed, a review of studies that include those conducted in younger children (ie, infants and toddlers) may be beneficial. Although the review by Tandon et al¹⁷ included observational designs, study quality was not assessed. Furthermore, although previous reviews included some studies with academic performance measures, search terms such as “school readiness” were not used; therefore, some studies examining academic outcomes may have been excluded.

In addition to serving as an important phase for brain and cognitive development, early childhood may be a key age for interventions targeting physical activity and fitness given that health behaviors are developed during these early years, and both physical activity habits and fitness levels are maintained through childhood and even into adulthood.^24–26 The aim of the current systematic review was to examine relations between physical activity and academic-related outcomes (eg, cognition and school readiness skills) in early childhood. Here, we provide a holistic view of published studies in order to steer ongoing research agendas by identifying important gaps from current studies that should be addressed in future research. To expand on previous reviews to identify both new and potentially previously overlooked studies that could provide valuable information on these relationships, both observational and experimental studies conducted in children from birth through age 6 were included.

Methods

Protocol and Registration

This systematic review was preregistered with the International Prospective Register of Systematic Reviews (registration number: CRD42020144600) and followed the Preferred Reporting Items for Systematic Reviews and Meta-Analysis guidelines.²⁷

Eligibility Criteria

To be included in the review, original research articles needed to be published in English in a peer-reviewed journal, and the protocol had to follow an observational (eg, cross-sectional, cohort, case control) or experimental (eg, acute or experimental randomized or quasi trials) study design. Our original search included articles published between January 1, 1980 and July 24, 2019. An updated search was conducted to include articles published between July 2019 and December 31, 2020. Case studies, case series reports, reviews, and protocol papers were excluded. Additional eligibility criteria were established by using Population, Intervention, Comparator, and Outcome study criteria.²⁸

Population.

Articles which reported on participants in early childhood (birth through 6 y at baseline) were included. Articles were excluded if age of the participants was not defined or if all or majority of participants were beyond kindergarten grade level (by US definitions) without age stratification.

Intervention (Exposure).

For observational studies, exposures included physical activity (ie, any bodily movement that resulted in energy expenditure) or fitness levels (eg, cardiorespiratory or muscular fitness). For experimental studies exposures included acute bouts (ie, a single session) of physical activity or a physical activity or fitness intervention. Studies were included if they used objective (eg, accelerometry) or subjective (eg, parent- or teacher-reported questionnaire) measurements.

Comparison.

For observational studies, the comparator was the nonexposed group (eg, less physically active compared with more physically active). For experimental studies, the control groups were defined as standard care, alternative condition, or intervention groups.

Outcomes.

Outcome variables were objective or subjective measures relating to school readiness (eg, academic achievement score, academic skill assessment, or classroom behavior) or cognition (eg, executive control or memory measures). Studies that reported only gross motor or fundamental movement skills as the exposure or outcome were not included.

Information Sources and Search Strategy

A systematic literature search was conducted using Boolean strategies with a predefined list of keywords (ie, various terms for physical activity, cognition, school readiness skills, and youth) in PubMed, PsycINFO, Web of Science, ERIC, and by manual review of reference lists of eligible studies and review articles. Our list of search terms was developed from compiling lists of key terms used in similar review papers and relevant original research papers and through refinement after preliminary searches (eg, search terms were assessed for comparability across databases). Specific search terms for physical activity or fitness included physical activity, exercise, sedentary, LPA, MPA, VPA, MVPA, sport, movement, accelerometry, accelerometer, fitness, and motor skills. Search terms for academic-related variables included academic, achievement, attention, cognition, cognitive, executive function, executive control, school readiness, memory, learning, inhibitory control, inhibition, neurocognition, engagement, literacy, on-task, off-task, self-regulation, language, decision making, planning, and classroom behavior. Finally, our age-related search terms included early childhood, infants, toddlers, preschool, preschool, preschooler, early years, child, children, childcare, and head start. Articles known to authors were also screened for eligibility. The search filters can be viewed in Supplementary Table 1 (available online). Database results were imported into the Rayyan program.²⁹ After duplicates were removed, 2 authors (C.W.S. and S.B.) independently searched and screened the titles and abstracts of eligible articles to determine inclusion. Exclusion by both authors was necessary for a study to be excluded at the first level. A full-text copy of each article that met the initial screening criteria was obtained, and the same 2 authors independently examined all full text manuscripts. Discrepancies were resolved with a discussion to reach consensus and, when necessary, a third author (R.M.C.S.) was consulted for a final decision.

Data Extraction

Study characteristics were extracted from full-text articles that met inclusion criteria following the Population, Intervention, Comparator, and Outcomes framework by 1 author (C.A.) and reviewed and cross-referenced for accuracy by the 2 other authors (C.W.S.L. and S.B.) in a prepiloted Excel document. Extracted information for observational studies included participants (ie, age, sex, setting, and location), parent study (if applicable), exposure(s) (ie, variable, measurement method, measurement timing), outcome(s) (ie, variable, measurement method, measurement timing), covariates, analysis method, and results. Observational study designs were categorized as cross-sectional or longitudinal. Experimental studies were categorized as acute or chronic experimental. Acute studies were those which examined the effects of single bouts of physical activity on school readiness or cognition outcomes (eg, the effects of 1 physical activity session on cognitive performance). Chronic experimental studies were those which examined effects after repeated exposure to the intervention (eg, the effects of a physical activity intervention delivered over several weeks on changes in cognitive performance from baseline to postintervention). Extracted information for experimental studies included participants (ie, age, sex, setting, and location), intervention(s) (ie, description, delivery method, dosage/length, timing, implementation measures), outcome(s) (ie, variable, measurement method, measurement timing), study design, covariates, analysis method, and results.

Results were classified into one of 4 overall effect categories (ie, null, positive, mixed, or negative). Null findings indicated that there was no statistical significance in the association or effect. Findings were classified as positive if the association or effect was beneficial (eg, more time spent active was associated with superior cognitive performance) and statistically significant. Findings were classified as negative if the findings were statistically significant in the opposite direction of what was predicted (eg, more time spent active was associated with lower cognitive performance). Finally, findings were classified as mixed if there was more than one association or effect examined and a combination of null, positive, and/or negative results were reported.

Quality Assessment

The overall quality of studies by study design was determined following the Grading Recommendations Assessment, Development and Evaluation Working Group’s framework by 3 authors (C.W.S.L., S.B., and C.A.).³⁰ Within the Grading Recommendations Assessment, Development and Evaluation framework, the quality of evidence is categorized as high, moderate, low, and very low. Randomized controlled studies start with their quality rating as high, while all other studies start with a quality rating of low. The quality of the study can be downgraded depending on various study factors, such as limitations of study design (ie, observational studies typically start at a low quality of evidence level), inconsistency in results across studies, indirectness (ie, factors that impact confidence in the effects related to differences in exposures, outcomes, and populations) imprecision (ie, confidence in the actual estimates of effect), and risk of bias (ie, concerns related to study execution). Discrepancies in ratings were discussed and resolved between the authors, with consultation of the fourth author if needed (R.M.C.S.).

Analysis

The synthesized summary tables that included study details, results, and quality factors of included studies were coded and analyzed for descriptive statistics in Stata (Release 16.0; StataCorp LLC, College Station, TX). For observational studies, results are presented by exposure category (ie, physical activity and fitness). There is potential for physical activity to be overestimated with subjective measures (eg, parent- or self-report tools) compared with objective measures.³¹ Therefore, to explore if studies with objective measures of physical activity differ in overall effects, observational studies with physical activity as an exposure are first presented overall, followed by only those with objective measures of physical activity. Experimental study findings were not stratified by exposure category given that all interventions could be described as physical activity interventions (ie, even if fitness was a targeted factor).

Results

Description of Studies

The number of articles reviewed and excluded at each stage is presented in a Preferred Reporting Items for Systematic Reviews and Meta-Analysis flow diagram (Figure 1). A total of 14,828 articles were identified through searches and 785 articles were identified as duplicates and initially removed. After full title and abstract screening, 13,910 were removed (mainly due to the exposure, outcome, study design, or age not meeting eligibility criteria). One hundred and thirty-three full-text articles were obtained to review further. After 65 articles were excluded for failing to meet eligibility criteria, 68 articles (describing 72 studies) were included in the final review.

Figure 1 —

Flow diagram of the search screening and identification process for article inclusion.

The included studies are summarized in Supplementary Table 2 (available online). Studies were conducted in 19 countries and were predominantly conducted in preschool/kindergarten age samples (n = 69). Only 2 studies included infants or toddlers. The articles were published between 1996 and 2020, with 62.3% published within the last 5 years (2016+). Studies applied both observational (n = 29) and experimental (n = 43) designs. Outcome variables included a range of measures such as overall cognitive function, executive function, language and literacy development or abilities, numeracy development or mathematics abilities, memory, general school readiness, and attention and behaviors (eg, academic on and off-task behaviors, hyperactivity, and other psychosocial health measures such as emotional and social skills). As expected, due to heterogeneity in methodologies and measures, a meta-analysis was not possible.

Data Synthesis

Cross-Sectional Studies.

All studies:

Study quality and effects are presented by study design in Table 1. Among the 29 observational studies, 19 utilized cross-sectional designs (n = 8919 participants). Physical activity related independent variable measures included overall physical activity levels (n = 10), meeting physical activity recommendations (n = 3), fitness levels (n = 3), sports participation (n = 1), outdoor play (n = 2), active play (n = 1), and active commuting (n = 1). Categories of outcome measures included general cognitive function (n = 3), executive function (n = 9), attention and behavior (n = 8), language and literacy development or abilities (n = 6), numeracy development or mathematics abilities (n = 4), and overall school readiness (n = 5). The overall quality of evidence for cross-sectional studies was categorized as “very low” due to concerns of potential bias and inconsistency in the findings.

Table 1.

Overall Effects and Quality by Study Design

		Quality assessment
No. of studies	Design	Risk of bias	Inconsistency	Indirectness	Imprecision	Other	No. of participantsa	Overall effectb	Quality
19	Cross-sectional	Serious risk of biasc	Serious inconsistencyc	No serious indirectness	No serious imprecision	None	8919	3 null, 15 mixed, and 1 negatived	Very low
10	Longitudinal	Serious risk of biase	Some inconsistencye	No serious indirectness	Some imprecisione	None	8045	2 null and 8 mixedf	Very low
6	Acute experimental	Some risk of biasg	Some inconsistencyg	No serious indirectness	Serious imprecisiong	None	267	6 mixedh	Low
37	Chronic experimental	Serious risk of biasi	Some inconsistencyi	Some indirectnessi	No serious imprecision	None	4510	8 null, 14 positive, and 15 mixedj	Moderate to low

^aThe number of participants may not represent unique participants.

^bOverall effect key: null = no statistically significant association/effect; positive = statistically significant beneficial association/effect; mixed = at least one statistically significant association/effect if more than one association/effect examined; negative = statistically significant nonbeneficial association/effect

^cDowngraded to very low quality of evidence due to serious risk of bias (primarily from missing eligibility criteria and subjective measurement methods) and serious inconsistency of effects.

^dStudy effects were null,^34,64,65 mixed,^{22,32,33,35,37,40–42,45,63,66–69} and negative.⁴⁴

^eDowngraded to very low quality of evidence due to serious risk of bias (primarily from missing eligibility criteria and subjective measurement methods), some inconsistency of effects, and some imprecision (low number of studies).

^fStudy effects were null^49,50 and mixed.^{23,42,45–48,51,52}

^gDowngraded to low quality of evidence due to some risk of bias (concerns regarding concealment and blinding), some inconsistency of effects, and serious imprecision (low number of studies).

^hStudy effects were all mixed.^53–58

ⁱDowngraded to low quality of evidence due to serious risk of bias (many unrandomized designs and some concerns regarding concealment and blinding), some inconsistency of effects, and some indirectness (intervention types and dosages varied).

^jStudy effects were null,^{34,62,70–75} positive,^75–89 and mixed.^62,90–103

All physical activity studies:

The majority of cross-sectional study results with physical activity measures as predictors were mixed (n = 12). While none of the studies reported only positive associations between physical activity measures and academic-related measures, 3 studies observed null findings, and one study reported an inverse association between higher levels of physical activity and executive functioning. Meeting the early childhood physical activity recommendations of the Canadian and Australian 24-hour movement behavior guidelines was not associated with behavioral and emotional problems³² or emotional and theory of mind understanding.³³

Objectively measured physical activity studies:

Eleven of the 16 physical activity cross-sectional studies measured physical activity objectively via accelerometry. Among those, one report indicated null results,³⁴ 9 studies reported mixed findings,^35–43 and one reported a negative association.⁴⁴ The majority of these studies with objectively measured physical activity examined executive function outcomes, and the overall study quality among this subset was categorized “low” overall quality of evidence.

Fitness studies:

Only 3 cross-sectional studies included fitness measures as predictors. Among these, outcomes consisted of executive functions and attention. Specifically, cardiorespiratory fitness was positively associated with attention,⁴⁵ inhibition,²² and future academic performance.²³ Among multiple fitness measures, only agility was positively associated with working memory.^22,45

Longitudinal Studies.

All studies:

Ten of the 19 observational studies used longitudinal designs (n = 8045 participants). These studies examined overall physical activity levels (n = 4), meeting physical activity guidelines (n = 3), fitness levels (n = 2), and sports participation (n = 1) as independent variables and executive function (n = 5), attention and behavior (n = 6), language and literacy development or abilities (n = 2), numeracy development or mathematics abilities (n = 2), and overall school readiness (n = 4) as outcomes. The overall quality of evidence for longitudinal studies was categorized as “very low” due to concerns of potential bias, inconsistency, and imprecision.

All physical activity studies:

The majority of the longitudinal studies (n = 6) with physical activity predictors reported mixed results. Two studies examined the predictive nature of physical activity and reported that greater parent-reported leisure-time physical activity at age 6 years was positively associated with some academic indicators later in childhood,⁴⁶ and low physical activity levels at age 6 were associated with lower working memory performance at age 14 years.⁴⁷ Although Howard et al⁴⁸ observed that sport participants had greater self-regulation than children that did not participate in early childhood sports, participation was not predictive of change in self-regulation over time. On the other hand, 2 studies examining total physical activity⁴⁹ and compliance with physical activity guidelines⁵⁰ in the preschool years were not associated with prospective measures of psychosocial health. Additional mixed results were reported by 3 recent longitudinal studies for prospective relations between physical activity and behavior measures (eg, problem behaviors and social/emotional skills) and executive function measures.^42,51,52

Objectively measured physical activity studies:

Over half of the longitudinal studies that evaluated physical activity measured it objectively (n = 5). As described above, the 2 studies examining prospective associations between physical activity (parameterized as total activity and meeting guidelines) with later social and emotional skills were null.^49,50 The remaining 3 studies reported a mix of associations. Meeting physical activity guidelines alone or in combination with another 24-hour movement behavior was associated with some indicators of executive function performance.⁴² Moderate to vigorous physical activity and physical activity guideline compliance were associated with some changes in school year measures of problem behaviors and school readiness.^51,52 However, these findings were drawn from a physical activity intervention study, so observational results could possibly be confounded by the experimental condition. Overall, the quality of evidence for longitudinal studies with device-measured physical activity was “low.”

Fitness studies:

Only 2 longitudinal studies explored relations between fitness measures and academic-related outcomes. Both studies examined the influence of baseline fitness on cognitive performance after one school year and reported that some fitness components were associated with improvements in attention and working memory,⁴⁵ and that cardiorespiratory fitness was indirectly associated with academic achievement (ie, via executive functions).²³

Acute Experimental Studies.

Among the 43 experimental studies, 6 studies (n = 267 participants) examined the effects of an acute bout of physical activity on overall cognitive function (n = 1), executive function (n = 3), attention (n = 1), and behaviors (n = 2). All acute experimental studies reported mixed results. Five studies were conducted in school settings and one was completed in a lab setting. Oriel et al,⁵³ Palmer et al,⁵⁴ Tandon et al,⁵⁵ Webster et al,⁵⁶ and Zhang et al,⁵⁷ all examined the acute effects of structured physical activity in the classroom compared with standard sedentary classroom practices and reported greater improvements postexercise in some cognitive outcomes, but not in all measures or subgroups. Mireau et al⁵⁸ compared 45 minutes of movement breaks with seated rest. Although there was no effect on cognitive performance, the authors noted some changes in electroencephalography activity between the exercise and resting conditions. Due to risks of bias, inconsistency of findings, and imprecision in acute experimental studies, the overall quality of evidence was categorized as “low.”

Chronic Experimental Studies.

Thirty-seven of the 43 experimental studies examined the chronic effects of physical activity on academic-related outcomes (n = 4510 participants). Interventions that were examined can be generally categorized into general structured physical activity programs (n = 15), structured physical activity programs with academic integration (n = 16), game-based programs with physical activity opportunities (n = 3), and multicomponent health behavior programs (ie, physical activity was included as one of 2 or more targeted health behaviors) (n = 3). Outcome categories varied considerably including overall cognitive function (n = 6), executive function (n = 7), language and literacy development and abilities (n = 14), numeracy development or mathematics abilities (n = 3), attention (n = 4), memory (n = 5), and behaviors (n = 10).

Overall effects varied with the studies reporting null, positive, or mixed effects (n = 8, 14, and 21, respectively). The proportion of effects did not appear to vary considerably by the type of intervention implemented in the studies or by the type of outcome measured. Due to concerns with bias risk, inconsistency, and indirectness, the quality of evidence of chronic experimental studies was categorized as “low to moderate.”

Discussion

Although previous research findings regarding the association between physical activity and cognitive brain health was categorized as insufficient in early childhood to determine a level of evidence, recent reviews have demonstrated an uptick in studies examining such relationships. Therefore, the purpose of this systematic review was to comprehensively evaluate existing and recently published studies in order to update the evidence on the relationships between physical activity and academic-related outcomes in early childhood. This review was comprised of 72 studies from 68 articles meeting the inclusion criteria, an increase of approximately 5- to 6-fold from previous reviews. However, although our findings support a growth of research in recent years, there was high heterogeneity in research and methodological approaches and overall effects of the included studies, which led to generally low levels for quality of the evidence across study designs.

Similar to other reviews, we found preliminary evidence that some academic and cognitive outcomes (ie, executive function and behavioral measures) benefit from physical activity in young children, although there was not complete consistency across studies.^17,18,59 However, the overall positive effects of studies in previous reviews appear to be more consistent than that of the current review. This may partially be due to the high variability in the exposure/outcome combinations that were measured in an increased number of studies, as well as the method of categorized effect (ie, using both mixed and positive to label effects). Also, in alignment with other reviews, physical activity did not appear to adversely impact cognitive outcomes (with the exception of one cross-sectional study). Among previous reviews that evaluated study quality, overall the quality of evidence was described as low or varied.^18,59 There was also heterogeneity in the study quality assessment of the current review between study designs ranging from low to moderate, with stronger evidence stemming from the experimental studies.

Although our findings are line with previous reviews, there is still not a clear consensus of the evidence regarding the effects of physical activity on cognitive and academic outcomes in young children.^14–18 Thus, the present review added to our understanding of such relationships by further highlighting some promising behaviors and interventions. For example, many chronic experimental studies examined interventions that integrated physical activity into academic components of the preschool programs, the majority of which reported positive or mixed results. Therefore, as in preadolescent children, this may be a viable option to promote cognition and academic performance while also providing young children with physical activity opportunities.¹² Some of the recent studies included in this review have also used larger and more representative samples than earlier studies, which was a recommendation from previous reviews. While this assists with improving the generalizability of findings, researchers should continue to emphasize the inclusion of representative samples in future studies.

Although early childhood is particularly unique as it presents a phase of significant brain and cognitive development,^1,2 mechanistic pathways between physical activity, fitness, and academic-related factors are not yet fully understood in this age group. However, studies conducted in animals and humans (ie, older children and adults) have identified potential pathways between physical activity and cognitive-related outcomes. Such pathways include (1) physiological adaptations (structural and functional) induced by acute and chronic physical activity that may alter cognitive functions, which in turn may mediate academic performance and (2) greater activation of certain brain areas and cognitive functions due to cognitively demanding gross locomotor skills used in some physical activities or physically active games or modalities that are cognitively challenging (eg, games that required greater activation of executive functions).⁶⁰ Future studies examining biological and behavior pathways in early childhood are needed to more clearly identify potential causal mechanisms of these relationships.

This comprehensive review also highlights some research opportunities to contribute to the evidence of early childhood relationships between physical activity and cognitive health.

Among the cross-sectional reports, only 3 studies examined fitness measures as exposures. Given that cardiorespiratory fitness appears to be a fairly consistent determinant of cognition in older children,¹² this exposure may warrant more attention in young children. Also, many observational studies used proxies or only subcomponents of habitual physical activity (eg, participation in sports programs or active commuting). Although there were a number of observational studies that measured physical activity with accelerometers, many only reported on total physical activity or compliance with physical activity guidelines. A breakdown of physical activity intensity variables (both light and moderate to vigorous), and even timing of activity bouts in future research may help to better elucidate the relations between activity and academic-related measures. Therefore, future studies, particularly prospective designs, may want to utilize objective measurement tools with standardized methods to explore various parameters of physical activity. In addition, most studies did not account for other important factors that relate to both physical activity and cognition, such as sleep and nutrition, and future analyses may try to control for these health behaviors. Moreover, a limited number of included studies explored measures of memory, neural activity, perception, and global cognition, so greater focus on these outcomes may be warranted.

Additional randomized controlled studies will help examine the effects of different doses (eg, modality, timing, and duration) of physical activity, particularly concerning acute bout studies. Interestingly, in older children, many of the original acute bout studies were conducted in laboratory settings, whereas most of the acute studies described in this review were conducted in preschool classrooms. It may be useful to initially examine the acute effects of structured physical activity in laboratory settings, where the environment is more controlled, to identify the types of structured physical activity most effective and feasible to translate to educational and home environments. Many of the chronic intervention studies included in this review did not report on levels of implementation, so it was not always evident if the planned dosage was received. It would be important for authors of future intervention research to report implementation data (eg, process evaluation information including fidelity and acceptability measures) to understand the actual dosage, acceptability, and feasibility of such programs. Additionally, it is recommended that authors of experimental studies follow standardized reporting guidelines such as the Consolidated Standards of Reporting Trials,⁶¹ therefore, the quality of the evidence can be more accurately assessed and future meta-analyses would be possible.

Although there may be methodological challenges to consider, such as selecting the most ideal and age-appropriate physical activity interventions and cognitive measures, there is a paucity of research in children younger than preschool age (ie, typically 3–5 y). Indeed, in the current review, only 2 studies included infants (children less than 1 y) and toddlers (children aged 1–2 y) and did not stratify findings by age group (ie, both studies included a range of early childhood ages).^62,63 Given that infancy and toddlerhood are often a focus in developmental cognitive research and that more research is emerging on physical activity behaviors in toddlers, researchers may want to explore relationships between physical activity and cognition in these youngest age groups. However, it may be important to study these ages separately from preschool age children given the differences in physical activity behaviors (eg, infants progress from nonlocomotor to locomotor movements), physical activity assessment (eg, parent reports of tummy time in infants or ankle-worn accelerometers in toddlers), and cognitive assessments and domains.

While this systematic review comprehensively examined the quality of evidence of relationships between physical activity and academic-related outcomes in early childhood with a standardized approach, some limitations should be noted. It is possible that the search terms and database filters that were used could have missed some articles. Other articles that may have reported on this topic may not have been included due to our eligibility criteria (ie, published in English in a peer-reviewed journal) or publication bias. Also, it is possible that our categories to classify the overall effects of the studies may have oversimplified some of the findings, particularly when studies were exploratory in nature and did not define hypotheses.

Conclusions

This systematic review expanded on what is known from previous reports by including both observational and experimental study designs, engaging a wide range of search terms to include academic or school readiness measures, and using a standardized quality of evidence assessment tool. The present collective evaluation of physical activity and fitness studies conducted in children aged less than 6 years provides some increased support of the potential benefits on academic-related outcomes. Although the evidence is still not conclusive in these early years, the recent publication of many studies has contributed to the recommendation to promote physical activity as a tool to promote cognitive health. However, additional high-quality studies are needed to formulate conclusions regarding what specific dosages of physical activity are impactful on specific cognitive and academic outcomes.