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R E S E A R C H Open Access
Systematic review of the relationships
between physical activity and health
indicators in the early years (0-4 years)
Valerie Carson
1*
, Eun-Young Lee
1
, Lyndel Hewitt
2
, Cally Jennings
1
, Stephen Hunter
1
, Nicholas Kuzik
1
,
Jodie A. Stearns
1
, Stephanie Powley Unrau
1
, Veronica J. Poitras
3
, Casey Gray
3
, Kristi B. Adamo
4
, Ian Janssen
5
,
Anthony D. Okely
2
, John C. Spence
1
, Brian W. Timmons
6
, Margaret Sampson
3,7
and Mark S. Tremblay
3
Abstract
Background: Given the rapid development during the early years (0-4 years), an understanding of the health implications
of physical activity is needed. The purpose of this systematic review was to examine the relationships between objectively
and subjectively measured physical activity and health indicators in the early years.
Methods: Electronic databases were originally searched in April, 2016. Included studies needed to be peer-reviewed,
written in English or French, and meet a priori study criteria. The population was apparently healthy children aged
1 month to 59.99 months/4.99 years. The intervention/exposure was objectively and subjectively measured physical
activity. The comparator was various volumes, durations, frequencies, patterns, types, and intensities of physical activity.
The outcomes were health indicators ranked as critical (adiposity, motor development, psychosocial health, cognitive
development, fitness) and important (bone and skeletal health, cardiometabolic health, and risks/harm). The Grading of
Recommendations Assessment, Development, and Evaluation (GRADE) framework was used to assess the quality of
evidence for each health indicator by each study design.
Results: Ninety-six studies representing 71,291 unique participants from 36 countries were included. Physical activity
interventions were consistently (>60% of studies) associated with improved motor and cognitive development, and
psychosocial and cardiometabolic health. Across observational studies, physical activity was consistently associated
with favourable motor development, fitness, and bone and skeletal health. For intensity, light- and moderate-intensity
physical activity were not consistently associated with any health indicators, whereas moderate- to vigorous-intensity,
vigorous-intensity, and total physical activity were consistently favourably associated with multiple health indicators.
Across study designs, consistent favourable associations with health indicators were observed for a variety of types of
physical activity, including active play, aerobic, dance, prone position (infants; ≤1 year), and structured/organized. Apart
from ≥30 min/day of the prone position for infants, the most favourable frequency and duration of physical activity
was unclear. However, more physical activity appeared better for health. Evidence ranged from “very low”to “high”
quality.
Conclusions: Specific types of physical activity, total physical activity, and physical activity of at least moderate- to
vigorous-intensity were consistently favourably associated with multiple health indicators. The majority of evidence was
in preschool-aged children (3-4 years). Findings will inform evidence-based guidelines.
Keywords: Physical activity, Prone position, Adiposity, Motor development, Psychosocial health, Cognitive development,
Fitness, Skeletal health, Cardiometabolic health, Injury, Early years, Infants, Toddlers, Preschoolers
* Correspondence: vlcarson@ualberta.ca
1
Faculty of Physical Education and Recreation, University of Alberta,
Edmonton, AB T6G 2H9, Canada
Full list of author information is available at the end of the article
© The Author(s). 2017 Open Access This article is distributed under the terms of the Creative Commons Attribution 4.0
International License (http://creativecommons.org/licenses/by/4.0/), which permits unrestricted use, distribution, and
reproduction in any medium, provided you give appropriate credit to the original author(s) and the source, provide a link to
the Creative Commons license, and indicate if changes were made. The Creative Commons Public Domain Dedication waiver
(http://creativecommons.org/publicdomain/zero/1.0/) applies to the data made available in this article, unless otherwise stated.
The Author(s) BMC Public Health 2017, 17(Suppl 5):854
DOI 10.1186/s12889-017-4860-0
Content courtesy of Springer Nature, terms of use apply. Rights reserved.
Background
The health benefits of physical activity, in particular mod-
erate- to vigorous-intensity physical activity (MVPA), have
been frequently studied in school-aged children and youth
(5-17 years) as well as adults (≥18 years) [1–4]. Accord-
ingly, global recommendations on the amount of MVPA
recommended for health benefits in these age groups ex-
ists [5]. In contrast, less research has focused on the health
benefits of physical activity in the early years (0-4 years).
Given that the early years are a critical and rapid
period of physical, cognitive, social, and emotional devel-
opment [6], determining the dose (e.g., frequency, inten-
sity, time/duration, type) of physical activity needed for
healthy growth and development is of great importance.
To better understand the dose of physical activity
needed in the early years, in 2012 Timmons and col-
leagues conducted a systematic review that examined the
relationship between physical activity and multiple health
indicators in this age group [7]. Favourable associations
between physical activity and some aspects of health,
including adiposity, bone and skeletal health, motor skill
development, psychosocial health, cognitive development,
and cardiometabolic health, were reported [7]. However,
within this review, cross-sectional studies were excluded a
priori; consequently, only 22 studies were identified and
limited information on the dose of physical activity re-
quired for health benefits was found [7].
The previous systematic review by Timmons and col-
leagues helped inform the first Canadian Physical Activity
Guidelines for the Early Years [8]. Given the limited infor-
mation on the dose of physical activity required for good
health, guideline formation was influenced by expert opin-
ion, international harmonization, and stakeholder input
[8]. The guidelines state that for healthy growth and devel-
opment, infants (<1 year) should be physically active sev-
eral times daily, and toddlers (1-2 years) and preschoolers
(3-4 years) should accumulate at least 180 min per day of
physical activity at any intensity spread throughout the
day and progress to 60 min per day of energetic play by
5 years of age [8]. These recommendations align with
physical activity recommendations in Australia [9] and the
United Kingdom [10].
Since the dissemination of physical activity guidelines
for children of the early years in Australia, Canada, and
the United Kingdom [8–10], a number of new studies
have examined physical activity in this age group, pri-
marily in preschool-aged children [11]. However, due to
several gaps and limitations in the literature, it remains
unclear whether children in the early years are suffi-
ciently active for good health [11, 12]. For example, no
clear benchmark exists for the appropriate dose of
physical activity in infants; limited research has been con-
ducted with toddlers [13–15]; and estimates of the propor-
tion of preschool-aged children meeting the physical
activity guidelines vary considerably (27%-100%) [11]. This
variation is partly due to different methodologies used
across studies, and in particular different cut-points for
light-intensity physical activity (LPA) [11]. Despite differ-
ences in cut-points used, most of the physical activity in
preschool-aged children appears to be of low-intensity
[11, 16, 17]. Currently, the specific frequency, intensity,
duration, and type of physical activity required for good
health in the early years remains unclear.
To ensure physical activity guidelines are reflective of
the most up-to-date scientific knowledge, it is important
to revisit and update the available evidence [18]. As
studies with cross-sectional designs were excluded in the
2012 review [7] that informed the current Canadian
guidelines, all available evidence was not originally
captured. Causality cannot be determined with cross-
sectional studies. However, given the limited evidence,
cross-sectional studies may help to expand the current un-
derstanding of the relationships between physical activity
and health in the early years. Since the 2012 review, other
systematic reviews have been completed but they have
focused on specific types of physical activity (e.g., outdoor
play, structured physical activity) or specific health indica-
tors (e.g., motor development, cognitive development, psy-
chosocial health) [19–23], and three of the five reviews
only included preschool-aged children [20, 22, 23]. To our
knowledge, no systematic review has been conducted that
comprehensively examined the relationships between sub-
jectively and objectively measured physical activity and a
broad range of health indicators in infants, toddlers, and
preschoolers across study designs. Therefore, the purpose
of this systematic review was to examine the associations
between objectively and subjectively measured physical ac-
tivity and health indicators in the early years across all
study designs. To help inform guideline updates or devel-
opment, an additional purpose was to determine what dose
of physical activity is associated with health indicators in
children of the early years.
Methods
Protocol and registration
This systematic review was registered with the International
Prospective Register of Systematic Reviews (PROSPERO;
Registration no. CRD42016035937; available from: https://
www.crd.york.ac.uk/PROSPERO/display_record.php?ID=
CRD42016035937). It was conducted and reported follow-
ing the Preferred Reporting Items for Systematic Reviews
and Meta-Analyses (PRISMA) statement for reporting sys-
tematic reviews and meta-analyses [24].
Eligibility criteria
For a study to be included in this review, it had to be
peer-reviewed, published, written in English or French,
and meet a priori (i.e., before database searches and
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screening) determined Population, Intervention, Compari-
son, and Outcome (PICO) study criteria [25]. Conference
abstracts and grey literature were not eligible because they
may not be subject to the same peer-review rigour.
However, preliminary results from registered clinical
trials were eligible.
Population
The population was apparently healthy (i.e., general popu-
lation, including samples of overweight/obese children but
not samples of children exclusively with a diagnosed
medical condition) young children (mean age: 1 month-
59.99 months/4.99 years). Where an age range was re-
ported instead of a mean, samples with a lower limit of
1 month-59.99 months/4.99 years and an upper limit
of <6 years were eligible for inclusion. If a mean age or
age range was not reported, samples described as infants,
toddlers, and/or preschoolers were included. For longitu-
dinal or experimental study designs, the age criterion ap-
plied to at least one measurement time point of the
exposure. For feasibility (i.e., staff and funding restrictions
and overall project timelines) and to maximize the
generalizability of findings, experimental studies were re-
quired to have a minimum sample size of 15 participants
in at least one intervention group and observational stud-
ies were required to have a minimum sample size of 100
participants. Setting minimum sample size inclusion cri-
teria a priori is consistent with a similar systematic review
in school-aged children and youth [2]; however, more
lenient cut-offs were chosen a priori in the present review
because it was anticipated the volume of research was
lower in the early years age group. Age subgroups were
defined as 1.0-12.99 months (≤1.0 year) for infants, 13.0-
35.99 months (1.1-2.99 years) for toddlers, and 36.0-
59.99 months (3.0-4.99 years) for preschoolers.
Intervention (exposure)
The interventions were volumes, durations, frequencies,
patterns, types, and intensities of physical activity. For
this review, physical activity was defined as any bodily
movement generated by skeletal muscles that results in
energy expenditure above resting levels [26]. “Prone pos-
ition”or “tummy time”in infants, and “outdoor time”in
any age group, were considered eligible physical activity
exposures. Total energy expenditure measured by doubly
labelled water or direct/indirect calorimetry was not
considered an eligible exposure because it includes rest-
ing metabolic rate and the thermic effect of food in
addition to activity energy expenditure [27]; however, ac-
tivity energy expenditure measured by these methods was
eligible. Physical activity could be measured objectively
(e.g., accelerometer, direct observation) or subjectively
(e.g., proxy-report). For experimental studies, interven-
tions had to target physical activity exclusively with no
other health behaviours (e.g., physical activity and diet or
physical activity and sedentary behaviour), but were not
required to have reported a measured change in physical
activity.
Comparison
The comparators were volumes, durations, frequencies,
patterns, types, and intensities of physical activity. A com-
parator or control group was not required.
Outcomes (health indicators)
The outcomes were eight health indicators chosen by the
review team and collaborators based on the scientific lit-
erature to reflect physical, social, and cognitive health. The
review team and collaborators ranked the eight health indi-
cators as “critical”or “important”in line with the Grading
of Recommendations Assessment, Development, and
Evaluation (GRADE) framework [28, 29]. Critical health
indicators included: adiposity (e.g., overweight, obesity,
body mass index [BMI], skinfold thickness, body fat),
motor development (e.g., gross motor skills, fine motor
skills, locomotor and object control skills), psychosocial
health (e.g., self-efficacy, self-esteem, prosocial behaviour,
aggression, social functioning, depressive symptoms, anx-
iety symptoms, quality of life), cognitive development (e.g.,
language development, attention, executive functioning),
and fitness (e.g., cardiovascular fitness, musculoskeletal
fitness). Important health indicators included: bone and
skeletal health (e.g., bone mineral density, bone mineral
content, skeletal area, Vitamin D), cardiometabolic health
(e.g., blood pressure, insulin resistance, blood lipids), and
risks/harm (e.g., injury, plagiocephaly).
Information sources and search strategy
The search strategies for this review were developed and
peer-reviewed by two librarians with expertise in system-
atic reviews. The following databases were searched be-
tween April 14 and 28, 2016 (the full MEDLINE search
was run at this time and again in July to ensure currency):
SPORTDiscus (dates of coverage not stated), MEDLINE
In-Process & Other Non-Indexed Citations and Ovid
MEDLINE (1946-July 29, 2016), EMBASE (1974 to 2016
April Week 4), PsycINFO (1806 to April Week 4 2016),
and Cochrane Central Register of Controlled Trials
(CENTRAL) (February 2016 issue). No date or study de-
sign limits were included (see Additional file 1 for the
complete search strategies). As more than 6 months had
passed since the initial full search, a partial search update
was conducted in all databases on November 1, 2016, to
capture any randomized controlled trials (RCTs) or clus-
tered RCTs that included “critical”health indicators. A
partial search update rather than a full update was con-
ducted because of logistical reasons (i.e., staff and funding
restrictions and overall project timelines). Furthermore, a
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large volume of observational studies had already been
captured, so it was a priority to focus on studies with
designs that have the potential to provide the highest qual-
ity of evidence to inform review findings and guideline
formation.
All records retrieved from the database searches were
imported into Reference Manager Software (Version 11;
Thompson Reuters, San Francisco, CA, USA), and dupli-
caterecordswereremovedbyemployingatwo-step
strategy. Specifically, duplicates were first identified auto-
matically in Reference Manager; one member of the review
team then manually checked and removed additional dupli-
cates where appropriate. After de-duplication, records were
imported into Distiller SR Software (Evidence Partners,
Ottawa, ON, Canada) for screening. First, titles and ab-
stracts were screened by two independent reviewers; if a
record was included by at least one reviewer, the record
was obtained for further screening. Second, full-text articles
were obtained and screened by two independent reviewers.
Agreement between reviewers was required for a study to
be included or excluded. Discrepancies that could not be
resolved by the two independent reviewers were resolved
by discussions with a third reviewer or with the review
team if needed.
The reference lists of relevant reviews identified during
screening were also checked to see if any additional rele-
vant studies could be identified. To capture registered
clinical trials, two trial registries (https://clinicaltrials.gov
and http://www.who.int/ictrp/en/) were searched on
February 1, 2017, using search terms for physical activity
and the early years age group. This final search was to
detect any large studies that were in progress and could
potentially overturn findings. If found, this pending new
evidence would have been included in the discussion.
Data extraction
Descriptive study characteristics as well as information
regarding the exposure, outcome, and results were ex-
tracted in Microsoft Excel for each included study. For
the results, where applicable, information was extracted
from both unadjusted models and the most fully ad-
justed model. Furthermore, a finding was deemed to be
statistically significant when p< 0.05 was reported, even
if statistical significance was defined differently in a
study. One reviewer completed data extraction for each
study and a second reviewer checked the extracted data.
A third reviewer then checked all extracted results.
Quality assessment
The quality of evidence assessment for each included study
design within each health indicator was guided by the
GRADE framework [30]. Quality of evidence reflects the
level of confidence in the estimated effects. Detailed infor-
mation on GRADE methodology can be found elsewhere
[30]. Briefly, five assessment criteria (risk of bias, inconsist-
ency, indirectness, imprecision, other [e.g., dose-response
evidence]) were used to rate quality of evidence as “high”,
“moderate”,“low”,or“very low”. Quality of evidence rat-
ings started at “high”for RCTs and “low”forallotherex-
perimental and observational studies. The quality of
evidence could be downgraded for any study design due to
limitations associated with the five assessment criteria. The
review team decided a priori that if the only identified
sources of bias were selection bias due to the use of a con-
venience sample or performance bias due to lack of inter-
vention/control group blinding, the quality of evidence
would not be downgraded because of the risk of bias. If no
limitations were identified, the quality of evidence from
non-randomized and observational study designs could be
upgraded if large effect sizes or evidence of a dose-
response gradient were reported. Since dose-response evi-
dence could not be determined for cross-sectional studies,
observations of a gradient of higher exposure with higher/
lower outcome were considered a reason to upgrade the
quality of evidence associated with this study design [29].
Risk of bias was the only criterion out of the five assess-
ment criteria that was first assessed at the individual study
level. The Cochrane risk of bias assessment was used for
experimental studies [31]. For observational studies, the
risk of selection bias, performance bias, selective reporting
bias, detection bias, attrition bias, and other biases (e.g.,
inadequate control for key confounders) was assessed
[32]. For all studies, risk of bias was assessed by one re-
viewer and checked by two other reviewers. Overall qual-
ity of evidence was evaluated by one reviewer and verified
by the larger review team, including two members with
expertise in systematic review methodology.
Data analysis
Two members of the review team with experience in
conducting meta-analyses assessed the data for each
health indicator to determine if any of the data was suffi-
ciently homogenous with regard to statistical, clinical,
and methodological characteristics for meta-analyses.
Due to high levels of heterogeneity in study design
and measured outcomes, only one meta-analysis was
possible for four studies that included adiposity as a
health indicator [33–36]. Change (post-intervention minus
baseline) values from studies were entered into Review
Manager Software 5.3 (The Cochrane Collaboration,
Copenhagen, Denmark). When necessary, standard devia-
tions of change were calculated based on other available
statistics in accordance with the Cochrane Handbook for
Systematic Reviews of Interventions [31]. Additionally,
one study [37] only presented results by sex-specific sub-
groups, and thus had to be entered into the meta-analysis
accordingly. Based on the subjectively assessed heterogen-
eity of the interventions, random-effects models were used
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to calculate the weighted mean difference according to the
DerSimonian and Laird method [38, 39]. Due to the small
number of studies included in the meta-analysis, sensitiv-
ity analyses and/or sub-group analyses were not possible.
A narrative synthesis was also conducted for all included
studies. Results were first synthesized by health indicator
and study design then further synthesized by intensity or
type of physical activity. For fitness and cardiometabolic
health, results were also synthesized by different dimen-
sions of the indicator (i.e., cardiorespiratory fitness and
other fitness measures; blood pressure, cholesterol, and tri-
glycerides). Finally, a sub-group analysis was conducted to
examine frequency and duration of physical activity. Since
not all studies reported on frequency and duration, data
were synthesized across health indicators but examined
separately for experimental and observational study de-
signs. For observational study designs, frequency and dur-
ation data were also synthesized for intensity and type of
physical activity. When multiple associations were exam-
ined (e.g., physical activity and BMI and physical activity
and waist circumference or sex-stratified analyses between
physical activity and BMI), a study was classified in one of
four mutually exclusive groups: 1) “favourable”if at least
one favourable but no unfavourable associations were ob-
served, 2) “unfavourable”if at least one unfavourable but
no favourable associations were observed, 3) “null”if no
favourable or unfavourable associations were observed, and
4) “mixed”if both favourable and unfavourable or
favourable, unfavourable and null associations were all
observed. Within the narrative analysis, all studies
were weighted equally. Finally, unless otherwise stated,
findings are based on samples classified as preschool-aged
children.
Results
Description of studies
After de-duplication, 20,848 titles and abstracts and 915
full-text articles were screened (see Fig. 1). It was deter-
mined that 96 studies (87 unique samples) met the inclu-
sion criteria. Of the 96 studies, 4 were identified through
the MEDLINE update of the full search. No additional
studies were identified in the partial update search or the
trial registry searches. Reasons for excluding full-text arti-
cles included: not original research (e.g., review; n= 116),
non-English language or non-French language (n= 4), in-
eligible age (n= 321), special population (n=19),no
measure of physical activity (n= 155), no measure of a
health indicator of interest/did not assess the association
between physical activity and health indicator of interest
(n=98),samplesize(n= 48), intervention did not exclu-
sively target physical activity (n= 45), and other (e.g.,
physical activity was a covariate, not human participants;
n= 13). Some full-text articles were excluded for multiple
reasons. Additionally, nine full-text articles could not be
located so these records were excluded.
The 96 studies involved 86,040 participants (71,291
from unique samples) from 36 different countries. An
experimental study design was used in 24 studies, in-
cluding RCTs (n= 8), clustered RCTs (n= 4), non-
randomized intervention (n= 9), and cross-over trial
(n= 3) designs. An observational study design was used
in the remaining 72 studies, including longitudinal
(n= 7), longitudinal with additional cross-sectional ana-
lyses (n= 5), case-control (n= 4), case cross-over
(n= 1), and cross-sectional (n= 55) designs. Out of the
96 studies, 80 were classified as preschool samples, two
as toddler samples, 13 as infant samples, and one as
both infant and toddler samples (i.e., 0.1-2.9 years).
Physical activity was measured objectively in 38 stud-
ies, primarily by accelerometers; 10 studies used direct
observation, heart rate monitors, pedometers, and/or
doubly labelled water (i.e., activity energy expenditure).
Physical activity was measured subjectively in 48 studies
by proxy-report questionnaire, log, or interview. Five stud-
ies used both objective and subjective measures of physical
activity. For 15 studies that included physical activity inter-
ventions, physical activity was not measured but these
studies were included in the review because the interven-
tion targeted physical activity exclusively. The types of
physical activity included in both observational and experi-
mental studies were: active play, active transportation, aer-
obic, biking, dance, home-based, exercise play, indoor,
leisure, outdoor, passive cycling, prone position, rough-
and-tumble play, sport, structured/organized, walking, and
weight bearing. Further information on the study design,
sample, exposure, outcome, and main findings for all
individual studies are summarized in Tables S1 to S8 in
Additional file 2. It should be noted that the number of
studies summed across study designs and across health
indicators is more than 96 because 20 studies included
more than one health indicator of interest, and five
studies presented both longitudinal and cross-sectional
findings.
Data synthesis
Adiposity
The association between physical activity and adiposity
was examined in 57 studies (49 unique samples; see Table 1
and Table S1 in Additional file 2). Meta-analyses of four
studies, including three clustered RCTs [33–35] and one
non-randomized intervention [36], involving a total of
1100 participants, found no significant differences between
intervention and control groups for BMI (weighted mean
difference = −0.04 kg/m
2
; 95% confidence interval = −0.12,
0.03; I
2
= 43%; n= 1971; see Fig. 2).
In the RCT, the mean sum of four skinfolds was sig-
nificantly lower in the intervention group whose parents
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received physical activity recommendations from a nurse
when their child was an infant, compared to the control
group, who did not receive recommendations [40]. How-
ever, no significant group differences were observed for
percentage overweight, waist or hip circumference, or
body fat percentage. Furthermore, physical activity did
not significantly differ between the intervention and the
control group [40]. The quality of evidence was down-
graded from “high”to “low”because of very serious in-
directness (see Table 1).
For the four clustered RCTs, a significant decrease in BMI
was observed in the intervention group (structured/orga-
nized physical activity plus cognitive-behavioural training
and resources) compared to the control group (structured/
organized physical activity) in one study [34]. However, no
significant differences in adiposity were observed between
the intervention (structured/organized physical activity or
aerobic physical activity or government-led physical activity
program) and the control groups (standard care) in the
other three studies [33, 35, 41]. Furthermore, physical activ-
ity did not significantly differ between the intervention and
the control groups in one study [41]. The quality of evidence
was downgraded from “high”to “low”because of a serious
risk of bias and serious indirectness (see Table 1).
For the two non-randomized interventions, there were
no significant differences in adiposity between intervention
(structured/organized physical activity) and control (stand-
ard care) groups in one study [36] or from baseline to
follow-up in another study (structured/organized physical
activity) [42]. The quality of evidence was downgraded
from “low”to “very low”because of a serious risk of bias
(see Table 1).
Among the seven longitudinal studies, physical activity
was favourably associated with adiposity for at least one
associationinthreestudies[43–45] and not associated with
adiposity in three studies [46–48]; mixed findings were
observed in one study [49]. For two of the studies that found
some favourable associations, a number of null associations
were also observed [44, 50]. One study with favourable find-
ings had an infant sample [45]. In regard to intensity or type
of physical activity, at least one favourable association was
observed between each of the following physical activity ex-
posures and adiposity: total physical activity (TPA; 2/4 stud-
ies), MVPA (1/1 study), and aerobic physical activity (1/1
study). However, primarily null or mixed associations were
observed between each of the following physical activity ex-
posures and adiposity: vigorous-intensity physical activity
(VPA), activity energy expenditure, home-based physical ac-
tivity, leisure physical activity, and structured/organized
physical activity (see Table 1). The quality of evidence was
downgraded from “low”to “very low”because of a serious
risk of bias (see Table 1).
Fig. 1 Flow diagram for the identification, screening, eligibility, and inclusion of studies [24]
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Table 1 The relationship between physical activity and adiposity
#of
studies
Design Quality assessment # of
participants
Absolute effect Quality
Risk of bias Inconsistency Indirectness Imprecision Other
Mean baseline age ranged from 41 weeks-59.6 months; where mean age was not reported, baseline age ranged from 2 weeks- <6 years. Data were collected by RCT, clustered RCT, non-randomized
intervention, longitudinal with up to 4-year follow-up, case-control, and cross-sectional study designs. Adiposity was assessed objectively by BMI, weight-for-height z-score, BMI z-score (CDC, WHO,
other country-specific reference data), weight/height
3
, weight percentiles, weight status (CDC, WHO, IOTF, Kaup index, country-specific reference data, BMI > 18, BMI percentile ≥95, ≥85th and ≥95th
percentiles), waist circumference (absolute, percentile), hip circumference, waist-to-hip ratio, waist circumference z-score (Netherlands reference data), waist circumference-for-age z-score, sum of
skinfolds, triceps skinfold thickness, body fat % (bioelectrical impedance, dual-energy X-ray absorptiometry), fat mass index (dual energy X-ray absorptiometry, air-displacement plethysmography), fat
free mass index (dual energy X-ray absorptiometry, air-displacement plethysmography), fat mass (dual energy X-ray absorptiometry, air-displacement plethysmography), fat free mass (dual energy
X-ray absorptiometry), % fat mass, trunk fat mass index, lean mass index (dual-energy X-ray absorptiometry), and subjectively by weight status (CDC ≥85th percentile). In 2 studies, it was unclear
whether weight status (CDC ≥85th percentile) or BMI was measured objectively or subjectively.
1 RCT
a
No serious
risk of bias
No serious
inconsistency
Very serious
indirectness
b
No serious
imprecision
None 161 The PA intervention (PA recommendations from nurse)
was favourably associated with improved adiposity (sum of
4 skinfolds but not % overweight, waist circumference, hip
circumference, or body fat %)in1 study [40].
LOW
c
4 Clustered RCT
d
Serious risk
of bias
e
No serious
inconsistency
Serious
indirectness
f
No serious
imprecision
None 3028 The PA interventions (structured/organized PA) were
favourably associated with adiposity in 1 study [34].
The PA interventions (structured/organized PA,
aerobic PA, or government-led PA program) were
not associated with adiposity in 3 studies [33,35,41].
LOW
g
2 Non-randomized
intervention
h
Serious risk
of bias
i
No serious
inconsistency
No serious
indirectness
No serious
imprecision
None 640 The PA interventions (structured/organized PA) were
not associated with adiposity in 2 studies [36,42].
VERY
LOW
j
7 Longitudinal
k
Serious risk
of bias
l
No serious
inconsistency
No serious
indirectness
No serious
imprecision
Dose-response
gradient
m
2441 TPA was favourably associated with adiposity (change in
weight-for-height z-score but not waist circumference-for-age
z-score in 1 study)in2 studies [43,45] and
not associated with adiposity in 2 studies [46,49].
MVPA was favourably associated with adiposity (fat free
mass but not BMI, fat mass, or % fat mass in 1 study)in
1 study [49].
VPA was not associated with adiposity in 1 study [48].
Activity energy expenditure was favourably (fat free
mass), unfavourably (BMI, fat mass), and not (% fat mass)
associated with adiposity in 1 study [49].
Aerobic PA was favourably associated with adiposity
(baseline PA only not change in PA)in1 study [44].
Home-based PA was not associated with adiposity in
1 study [47].
Leisure PA was not associated with adiposity in
1 study [44].
Structured/organized PA was not associated with
adiposity in 2 studies [44,47].
VERY
LOW
n
3 Case-contol
o
Serious risk
of bias
p
No serious
inconsistency
No serious
indirectness
No serious
imprecision
None 2271 TPA was not associated with adiposity in 1 study [51].
MPA was not associated with adiposity in 1 study [52].
VPA was not associated with adiposity in 1 study [52].
Outdoor PA was favourably associated with adiposity
in 1 study [51] and not associated with adiposity in
1 study [53].
VERY
LOW
q
40 Cross-sectional
r
Serious risk
of bias
s
Serious
inconsistency
t
No serious
indirectness
No serious
imprecision
37,813 TPA was favourably associated with adiposity (age 6 months
but not 1, 2, 3, and 4 years in 1 study; boys only in 1 study;
VERY
LOW
v
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Table 1 The relationship between physical activity and adiposity (Continued)
#of
studies
Design Quality assessment # of
participants
Absolute effect Quality
Risk of bias Inconsistency Indirectness Imprecision Other
Exposure/
outcome
gradient
u
95th percentile of vector magnitude and fat free mass index
but not BMI, fat mass, or waist circumference and 90th
percentile of vector magnitude and % fat mass and fat
free mass index but not BMI, fat mass index, or waist
circumference in 1 study)in6 studies [55,56,60,61,
63,64], unfavourably associated with adiposity (BMI
z-score but not waist circumference z-score in 1 study
and hip circumference but not relative weights, skinfold
thicknesses, and waist circumference in 1 study)in3
studies [50,66,69], and not associated with adiposity in
11 studies [45,46,49,54,65,72,73,75,81,82,86].
LPA was favourably associated with adiposity (waist
circumference z-score but not BMI z-score)in1 study [50],
unfavourably associated with adiposity (% body fat and
fat mass index but not trunk fat mass index and lean mass
index)in1 study [89], and not associated with adiposity
in 6 studies [55,67,76,84,86,87].
LPA 5-min bouts were not associated with adiposity in
1 study [86].
MPA was unfavourably associated with adiposity in 1 study
[50] and not associated with adiposity in 2 studies [55,89].
MVPA was favourably associated with adiposity (% fat mass
but not BMI, fat free mass, fat mass in 1 study; boys only in
1 study; % body fat and fat mass index but not trunk fat mass
index or lean mass index in 1 study; % fat mass and fat free
mass index but not BMI, fat mass index, or waist circumference
in 1 study; girls only and waist circumference at the 90th
percentile but not the 10th, 25th, 75th percentiles or BMI z-score
or waist circumference in 1 study)in6 studies [49,54,55,
60,88,89], unfavourably associated with adiposity (boys
only and BMI z-score but not waist circumference in 1 study)
in 3 studies [67,69,88], and not associated with adiposity
in 8 studies [65,76,77,82,84–87].
MVPA 5-min bouts were not associated with adiposity in
1 study [86].
VPA was favourably associated with adiposity (boys only in
1 study; % body fat, fat mass index, trunk fat mass index but
not lean mass index in 1 study; fat free mass index but not
BMI, fat mass, fat mass index, and waist circumference in
1 study)in4 studies [54,55,60,89], unfavourably associated
with adiposity in 1 study [50], and not associated with
adiposity in 3 studies [67,74,82].
Activity energy expenditure was favourably (fat free
mass), unfavourably (BMI), and not (fat mass, % fat mass)
associated with adiposity in 1 study [49].
Indoor PA was not associated with adiposity in 1 study [81].
Leisure PA was favourably associated with adiposity
(intermediate vs. none but not high vs. none)in1 study [59].
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Table 1 The relationship between physical activity and adiposity (Continued)
#of
studies
Design Quality assessment # of
participants
Absolute effect Quality
Risk of bias Inconsistency Indirectness Imprecision Other
Outdoor PA was favourably associated with adiposity in
1 study [58] and not associated with adiposity in 8 studies
[61,73,75,78–81,83]
Organized Sport was unfavourably associated with adiposity
(girls only)in1 study [68].
Structured/organized PA was favourably associated with
adiposity in 1 study [57].
Active play was favourably associated with adiposity
(weekdays only in 1 study)in2 studies [62,65] and not
associated with adiposity in 1 study [71].
Active transportation was not associated with adiposity
in 1 study [70].
BMI: body mass index; CDC: Centers for Disease Control and Prevention; IOTF: International Obesity Task Force; LPA: light-intensity physical activity MPA: moderate-intensity physical activity; MVPA: moderate- to
vigorous-intensity physical activity; PA: physical activity; RCT: randomized controlled trial; TPA: total physical activity; VPA: vigorous-intensity physical activity; WHO: World Health Organization
a
Includes 1 RCT [40]
b
The intervention did not result in a significant change in physical activity [40]
c
Quality of evidence was downgraded from “high”to “low”because of very serious indirectness
d
Includes 4 clustered RCTs [33–35,41]
e
Unclear whether outcome assessors were blinded to group allocation and unclear if the outcome was objectively measured in 1 study [34]. Large amount of missing data primarily because mean attendance at child
care was 48% and it is unknown if the reason for poor attendance was related to adiposity in 1 study [41]. Physical activity was not measured so it is unknown if the intervention resulted in a significant change in
physical activity in 1 study [35]
f
The intervention did not result in a significant change in physical activity in 1 study [41]
g
Quality of evidence was downgraded from “high”to “low”because of serious risk of bias and serious indirectness
h
Includes 2 non-randomized interventions [36,42]
i
No control group in 1 study [42]. Physical activity was not measured so it is unknown if the intervention resulted in a significant change in physical activity in 2 studies [36,42]
j
Quality of evidence was downgraded from “low”to “very low”because of serious risk of bias
k
Includes 7 longitudinal studies [43–49]
l
Convenience sample was used in 1 study [44]. Psychometric properties unknown for the subjective physical activity measures in 3 studies [44,45,47]. Large unexplained loss to follow-up and incomplete data in 1
study [45]. No potential confounders were adjusted for in 2 studies [43,45]. Potentially inappropriate statistical analysis: one study mutually adjusted for other movement behaviours in the fully adjusted models [49]
m
A dose-response gradient of higher aerobic PA and MVPA with better adiposity was observed in 2 studies [44,49]. A dose-response gradient of higher activity energy expenditure was associated with both better
and worse adiposity depending on the adiposity measure in 1 study [49]
n
Quality of evidence was downgraded from “low”to “very low”because of serious risk of bias; because of this limitation, was not upgraded for a dose-response gradient
o
Includes 3 case-control studies [51–53]
p
Psychometric properties unknown for the subjective physical activity measures in 3 studies [51–53]
q
Quality of evidence was downgraded from “low”to “very low”because of serious risk of bias
r
Includes 40 cross-sectional studies [45,46,49,50,54–89]
s
Convenience sample was used in 11 studies [54,56,62,63,67,69,76,77,85,86,88]. Low participation rate in 3 studies [54,68,84]. Psychometric properties unknown for the subjective physical activity measure in 15
studies [45,57,59,61–65,68,70,71,75,79,80,84]. No potential confounders were adjusted for in 19 studies [45,50,56,61,64–67,69,71,72,76,77,80,81,83,85–87]. Large amount of unexplained missing data or it
was unclear if the large amount of missing data was related to adiposity in 9 studies [50,57,62,65,67,68,80,82,89]. Physical activity was measured only during child care in 3 studies [58,60,82]. Potentially
inappropriate statistical analysis: other movement behaviours were mutually adjusted for in the fully adjusted models in 3 studies [49,55,89]
t
Favourable and unfavourable associations between physical activity and adiposity observed across studies
u
A gradient for higher TPA, MVPA, VPA activity energy expenditure, outdoor PA, and physical education with better adiposity was observed in 6 studies [49,55,57,58,88,89]. A gradient for higher activity energy
expenditure and LPA, MVPA with worse adiposity was observed in 3 studies [49,88,89]
v
Quality of evidence was downgraded from “low”to “very low”because of serious risk of bias and serious inconsistency; because of this limitation, was not upgraded for an exposure/outcome gradient
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For the three case-control studies, physical activity
was favourably associated with adiposity in one study
[51] and not associated with adiposity in two studies
[52, 53]. One study with null findings had an infant
and toddler sample [53]. In terms of the intensity or
type of physical activity, at least one favourable asso-
ciation was observed between outdoor physical activ-
ity and adiposity (1/2 studies). However, primarily
null associations were observed between each of the
following physical activity exposures and adiposity:
TPA, moderate-intensity physical activity (MPA), and
VPA (see Table 1). The quality of evidence was down-
graded from “low”to “very low”because of a serious
risk of bias (see Table 1).
For the 40 cross-sectional studies, physical activity was
favourably associated with adiposity for at least one as-
sociation in 12 studies [54–65], unfavourably associated
with adiposity for at least one association in four studies
[66–69], and not associated with adiposity in 20 studies
[45, 46, 70–87]; mixed findings were observed in four
studies [49, 50, 88, 89]. In two of the studies that
observed some favourable associations, primarily null
associations were observed [55, 64]. One study with
favourable findings [64] and one study with null findings
[45] had infant samples. Similarly, one study with null
findings had a toddler sample [86]. In regard to intensity
or type of physical activity, at least one favourable asso-
ciation was observed between each of the following and
adiposity: active play (2/3 studies), leisure physical activ-
ity (1/1 study), and structured/organized physical activity
(1/1 study); and at least one unfavourable association
was observed between organized sport and adiposity (1/
1 study). However, primarily null or mixed findings were
observed between each of the following physical activity
exposures and adiposity: TPA, LPA, LPA bouts, MPA,
MVPA, MVPA bouts, VPA, activity energy expend-
iture, active transportation, indoor physical activity,
and outdoor physical activity (see Table 1). The qual-
ity of evidence was downgraded from “low”to “very
low”because of a serious risk of bias and serious in-
consistency (see Table 1).
Motor development
The association between physical activity and motor de-
velopment was examined in 23 studies (21 unique sam-
ples; see Table 2 and Table S2 in Additional file 2).
Among the four RCTs, significant increases in motor de-
velopment were observed in the intervention groups
(planned passive cycling or structured/organized phys-
ical activity) compared to the control groups (standard
care) in three studies [90–92]. One intervention involved
an infant sample [91]. In the fourth study, no significant
differences in motor development were observed be-
tween the intervention (parents received physical activity
recommendations from a nurse when their child was an
infant) and control (no recommendations) groups [40];
however, physical activity was not significantly different
between groups [40]. The quality of evidence was down-
graded from “high”to “low”because of a serious risk of
bias and serious indirectness (see Table 2).
In the two clustered RCTs, greater increases in total
motor development and jumping were observed in the
intervention group (structured/organized physical activity)
compared to the control group (standard care) in one
study; however, no such increases were seen in running,
hopping, catching, or kicking [33]. In the second study, no
significant difference was observed in motor skills be-
tween the intervention (government-led physical activity
program) and control (standard care) groups [41]. How-
ever, physical activity was also not significantly different
between groups [41]. The quality of evidence was down-
graded from “high”to “low”because of a serious risk of
bias and serious indirectness (see Table 2).
Among the six non-randomized interventions, signifi-
cant increases in at least one measure of motor develop-
ment were observed in the intervention group (free play
and structured activities, structured/organized physical
activity, dance program, or swimming) compared to the
control group (usual care) in five studies [36, 93–96],
and significant increases from baseline to follow-up in
the 12-m run and standing long jump were observed in
one study (structured/organized physical activity) [42].
However, for two of the interventions, more null than
Fig. 2 Meta-analysis of the effect of physical activity interventions on body mass index
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Table 2 The relationship between physical activity and motor development
#of
studies
Design Quality assessment # of
participants
Absolute effect Quality
Risk of bias Inconsistency Indirectness Imprecision Other
Mean baseline age ranged from 18.3 weeks-59.79 months; where mean age was not reported, baseline age ranged from 0 months-5 years. Data were collected by RCT, clustered RCT, non-
randomized intervention, longitudinal with up to 20-month follow-up, and cross-sectional study designs. Motor development was assessed by fundamental movement skills/motor ability/motor
performance/motor development/motor skills/gross-motor development/psychomotor skills (objectively measured; Test of Gross Motor Development –2, movement assessment battery, Movement
Assessment Battery for Children –2, APM-Inventory, Dutch Second Edition of the Bayley Scales of Infant and Toddler –3, Motoriktestfürvier-bissechsjährige Kinder 4-6; 12-m run, standing long jump,
Motor Test Battery 3-7, Alberta Infant Motor Scales, neurological examination technique for toddler-age, Children’s Activity and Movement in Preschool Study Motor Skill Protocol, Comprehensive
Developmental Inventory for Infants and Toddlers, Gessel Development Schedules –Development Quotient, adapted measures from the Zurich Neuromotor Assessment test), achievement of
developmental milestones (proxy-report questionnaire), coordination (proxy-report questionnaire), and fine motor coordination/fine motor development (proxy-report interview; Comprehensive
Developmental Inventory for Infants and Toddlers).
4 RCT
a
Serious risk
of bias
b
No serious
inconsistency
Serious
indirectness
c
No serious
imprecision
None 705 The PA interventions (planned passive cycling or structured/
organized PA) were favourably associated with improved motor
development in 3 studies [90–92].
The PA intervention (PA recommendations from nurse) was
not associated with improved motor development in 1 study [40].
LOW
d
2 Clustered RCT
e
Serious risk
of bias
f
No serious
inconsistency
Serious
indirectness
g
No serious
imprecision
None 1564 The PA intervention (structured/organized PA) was favourably
associated with improved motor development (total score and
jumping individual score but not for running, hopping, catching,
and kicking)in1 study [33].
The PA intervention (government-led PA program) was not
associated with motor development in 1 study [41].
LOW
h
6 Non-randomized
intervention
i
Serious risk
of bias
j
No serious
inconsistency
No serious
indirectness
No serious
imprecision
None 946 The PA interventions (free play and structured activities,
structured/organized PA, dance, or swimming) were favourably
associated with improved motor development (boys only and
running speed between time 2 and 3 only in 1 study; one-leg balance
only in 1 study)in6 studies [36,42,93–96].
VERY
LOW
k
1 Longitudinal
l
Serious risk
of bias
m
No serious
inconsistency
No serious
indirectness
No serious
imprecision
None 197 Prone position was favourably associated with motor development
(higher prone duration and gross motor development only at age 6
mo but not at age 24 mo and prone-specific milestones only)[97].
VERY
LOW
n
10 Cross-sectional
o
Serious risk
of bias
p
No serious
inconsistency
No serious
indirectness
No serious
imprecision
Exposure/
outcome
gradient
q
1833 TPA was favourably associated with motor development
(correlations but not when comparing quartiles of fundamental
movement skills in 1 study)in3 studies [56,69,100], unfavourably
associated with motor development (running speed only in 1 study)
in 2 studies [81,101], and not associated with motor development
in 1 study [86].
LPA was not associated with motor development in 3 studies
[67,86,100].
LPA 5-min bouts were not associated with motor development
in 1 study [86].
MVPA was favourably associated with motor development (total
and locomotor [high vs. low only] but not for object control skills in
1 study)in3 studies [67,69,100] and not associated with motor
development in 1 study [86].
MVPA 5-min bouts were not associated with motor development
in 1 study [86].
VPA was favourably associated with motor development (total and
locomotor [high vs. low only] but not for object control skills) in
1 study [67].
VERY
LOW
r
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Table 2 The relationship between physical activity and motor development (Continued)
#of
studies
Design Quality assessment # of
participants
Absolute effect Quality
Risk of bias Inconsistency Indirectness Imprecision Other
Indoor PA was favourably associated with motor development
(throwing at target only)in1 study [81].
Outdoor PA was not associated with motor development in
1 study [81].
Prone position was favourably associated with motor development
(gross motor development but not fine motor development in 1 study)
in 3 studies [97–99].
LPA: light-intensity physical activity; MVPA: moderate- to vigorous-intensity physical activity; PA: physical activity; RCT: randomized controlled trial; TPA: total physical activity; VPA: vigorous-intensity physical activity
a
Includes 4 RCTs [40,90–92]
b
No intention-to-treat analysis; parent-child dyads were excluded if they did not carry out the management plan or if they became sick during the study; and the physical activity program was interrupted in 1 study
[90]. Physical activity was not measured, so it is unknown if the intervention resulted in a significant change in physical activity in 3 studies [90–92]
c
The intervention did not result in a significant change in physical activity in 1 study [40]
d
Quality of evidence was downgraded from “high”to “low”because of serious risk of bias and serious indirectness
e
Includes 2 clustered RCTs [33,41]
f
Large amount of missing data primarily because mean attendance at child care was 48%, and it is unknown if the reason for poor attendance was related to the motor development in 1 study [41]
g
The intervention did not result in a significant change in physical activity in 1 study [41]
h
Quality of evidence was downgraded from “high”to “low”because of serious risk of bias and serious indirectness
i
Includes 6 non-randomized interventions [36,42,93–96]
j
The outcome was measured post-intervention only in 2 studies [93,96]. No control group in 1 study [42]. Physical activity was not measured so it is unknown if the intervention resulted in a significant change in
physical activity in 6 studies [36,42,93–96]
k
Quality of evidence was downgraded from “low”to “very low”because of serious risk of bias
l
Includes 1 longitudinal study [97]
m
Psychometric properties unknown for the subjective physical activity measures
n
Quality of evidence was downgraded from “low”to “very low”because of serious risk of bias
o
Includes 10 cross-sectional studies [56,67,69,81,86,97–101]
p
Convenience sample was used in 6 studies [56,67,69,86,99,101]. Psychometric properties unknown for the subjective physical activity measure in 5 studies [56,97–99,101], and the outcome measure in 2 studies
[69,101]. Potential confounders were not adjusted for in 7 studies [67,69,81,86,98,100,101]. Large amount of missing motor development data in 1 study [67]
q
A gradient for higher MVPA and VPA with better motor development was observed in 2 studies [67,100]
r
Quality of evidence was downgraded from “low”to “very low”because of serious risk of bias; because of this limitation, was not upgraded for an exposure/outcome gradient
The Author(s) BMC Public Health 2017, 17(Suppl 5):854 Page 44 of 215
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favourable effects were observed with the different
motor development measures [94, 96]. One intervention
had an infant sample at baseline [96]. The quality of evi-
dence was downgraded from “low”to “very low”because
of a serious risk of bias (see Table 2).
In the longitudinal study, higher duration of prone po-
sitioning at 4 months of age was favourably associated
with the earlier achievement of several developmental
milestones and gross motor development at 6 months but
not at 24 months of age [97]. However, no significant dif-
ferences were observed in fine motor development [97].
In separate analyses, no significant differences in motor
development at 6 and 24 months of age were observed be-
tween infants who had, versus had not, experienced prone
position at 4 months of age [97]. Apart from “crawled on
abdomen”, significant differences for achievement of de-
velopmental milestones were also not observed between
groups [97]. In further analyses comparing infants that
preferred prone position at 6 months of age to those that
did not, no significant differences were observed in gross
and fine motor development at 24 months of age; how-
ever, the prone-preference group achieved several devel-
opmental milestones significantly earlier [97]. The quality
of evidence was downgraded from “low”to “very low”be-
cause of a serious risk of bias (see Table 2).
Among the 10 cross-sectional studies, physical activity
was favourably associated with at least one measure of
motor development in seven studies [56, 67, 69, 97–100],
unfavourably associated with motor development in one
study [101], and not associated with motor development
in one study [86]; mixed findings were observed in one
study [81]. Three of the studies with favourable associa-
tions [97–99] and one study with unfavourable associa-
tions had infant samples [101]. One study with null
findings had a toddler sample [86]. For the intensity or
type of physical activity, at least one favourable association
was observed between each of the following physical activ-
ity exposures and motor development: MVPA (3/4 stud-
ies), VPA (1/1 study), indoor physical activity (1/1 study),
and prone position (3/3 studies). However, primarily null
or mixed findings were observed between each of the fol-
lowing physical activity exposures and motor develop-
ment: TPA, LPA, LPA bouts, MVPA bouts, and outdoor
physical activity (see Table 1). The quality of evidence was
downgraded from “low”to “very low”because of a serious
risk of bias (see Table 2).
Psychosocial health
The association between physical activity and psycho-
social health was examined in 11 studies (9 unique sam-
ples; see Table 3 and Table S3 in Additional file 2).
Among the two RCTs, greater increases in psychosocial
health were observed in the intervention groups (planned
passive cycling or dance program) compared to the
control groups (standard care) [90, 102]. One of the inter-
ventions had an infant sample [90]. The quality of
evidence was downgraded from “high”to “moderate”be-
cause of a serious risk of bias (see Table 3).
In the clustered RCT, no significant differences in
quality of life were observed between the intervention
(government-led physical activity program) and control
(standard care) groups [41]. Physical activity was also
not significantly different between groups [41]. The
quality of evidence was downgraded from “high”to “very
low”because of a serious risk of bias and very serious
indirectness (see Table 3).
Among the two longitudinal studies, sport participa-
tion was favourably associated with psychosocial health
in one study [103], and TPA was favourably associated
with psychosocial health in one study [104] but not the
other [103]. The quality of evidence was downgraded
from “low”to “very low”because of a serious risk of bias
(see Table 3).
Among the six cross-sectional studies, physical activity
was favourably associated with at least one measure of
psychosocial health in one study [105], unfavourably as-
sociated with at least one measure of psychosocial health
in three studies [101, 106, 107], and not associated with
psychosocial health in two studies [108, 109]. However,
primarily null associations were observed in all studies.
One study with unfavourable associations had an infant
sample [101]. In regard to intensity or type of physical
activity, at least one favourable association was observed
between MVPA and psychosocial health (1/2 studies),
and at least one unfavourable association was observed
between bike riding and psychosocial health (2/2
studies). However, primarily null or mixed findings were
observed between each of the following physical activity
exposures and psychosocial health: TPA, exercise play,
rough-and-tumble play, and walking (see Table 3). The
quality of evidence was downgraded from “low”to “very
low”because of a serious risk of bias and serious incon-
sistency (see Table 3).
Cognitive development
The association between physical activity and cognitive
development was examined in 13 studies (13 unique
samples; see Table 4 and Table S4 in Additional file 2).
Among the two RCTs, significant increases in cognitive
development were observed in the intervention groups
(planned passive cycling or structured/organized physical
activity) compared to the control groups (standard care)
[90, 91]. One intervention involved an infant sample [90].
The quality of evidence was downgraded from “high”to
“moderate”because of a serious risk of bias (Table 4).
For the clustered RCT, significant increases in free
and/or cued recalls of previously learned Italian words
were observed in the physical activity intervention
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Table 3 The relationship between physical activity and psychosocial health
#of
studies
Design Quality assessment # of
participants
Absolute effect Quality
Risk of bias Inconsistency Indirectness Imprecision Other
Mean baseline age ranged from 18.3 weeks-57.61 months; where mean age was not reported, baseline age ranged from 12 months-5 years. Data were collected by RCT, clustered RCT longitudinal with up to 8-
to 10-year follow-up, and cross-sectional study designs. Psychosocial health was assessed by social competence (proxy-report; Social Competence Behavior Evaluation: Preschool Education Questionnaire);
internalizing behaviour problems (proxy-report; Social Competence Behavior Evaluation: Preschool Education Questionnaire); externalizing behaviour problems (proxy-report; Social Competence Behavior Evaluation: Pre-
school Education Questionnaire); quality of life (self-reported; Dartmouth Primary Care Cooperative Project charts); health-related quality of life (proxy-report; PedsQL 4.0); temper frequency (proxy-report interview); sociabil-
ity, emotionality, and soothability (proxy-report; Child Temperament Questionnaire); conduct problems (proxy-report; Strengths and Difficulties Questionnaire); anxiety
symptoms (proxy-report; Preschool Anxiety Scale –Revised); classroom peer acceptance (proxy-report; sociometric interviews); and personal-social behaviour (objectively measured; Gessell Development Schedules –De-
velopment Quotient).
2 RCT
a
Serious risk
of bias
b
No serious
inconsistency
No serious
indirectness
No serious
imprecision
None 170 The PA interventions (planned passive cycling or dance) were favourably
associated with improved psychosocial health in 2studies[90,102].
MODERATE
c
1 Clustered
RCT
d
Serious risk
of bias
e
No serious
inconsistency
Very serious
indirectness
f
No serious
imprecision
None 1467 The PA intervention (government-led PA program) was not
associated with psychosocial health [41].
VERY LOW
g
2 Longitudinal
h
Serious risk
of bias
i
No serious
inconsistency
No serious
indirectness
No serious
imprecision
Dose-response
gradient
j
9989 TPA was favourably associated with psychosocial health (active vs. less
active but not active vs. average)in1 study [104] and not associated
with psychosocial health in 1 study [103].
Sport participation was favourably associated with psychosocial health (high
risk and recovery trajectories but not the rebound trajectory)in1study[103].
VERY LOW
k
6 Cross-
sectional
l
Serious risk
of bias
m
Serious
inconsistency
n
No serious
indirectness
No serious
imprecision
None 5517 TPA was unfavourably associated with psychosocial health in 1 study
[101] and not associated with psychosocial health in 1 study [109].
MVPA was unfavourably associated with psychosocial health in 1 study
[107] and not associated with psychosocial health in 1 study [109].
Bike riding was unfavourably associated with psychosocial health (for
boys only on weekdays only in 1 study)in2 studies [106,107].
Exercise play was favourably associated with psychosocial health (mixed
gender [not non-mediated] and same gender but not other gender groups)
in 1 study [105], unfavourably associated with psychosocial health (boys
only, weekend only, and only for > 2 and ≤24 h group) in 1 study [106],
and not associated with psychosocial health in 1 study [107].
Routh-and-tumble play was not associated with psychosocial health in
2 studies [105,108].
Walking was not associated with psychosocial health in 2studies[106,107].
VERY LOW
o
MVPA: moderate- to vigorous-intensity physical activity; PA: physical activity; RCT: randomized controlled trial; TPA: total physical activity
a
Includes 2 RCTs [90,102]
b
No intention-to-treat analysis; parent-child dyads were excluded if they did not carry out the management plan or if they became sick during the study and the physical activity program was interrupted
in 1 study [90]. Physical activity was not measured, so it is unknown if the intervention significantly changed physical activity in 2 studies [90,102]
c
Quality of evidence was downgraded from “high”to “moderate”because of serious risk of bias
d
Includes 1 clustered RCT [41]
e
Large amount of missing data primarily because mean attendance at child care was 48%, and it is unknown if hte reason for poor attendance was related to psychosocial health
f
The intervention did not result in a significant change in physical activity
g
Quality of evidence was downgraded from “high”to “very low”because of serious risk of bias and very serious indirectness
h
Includes 2 longitudinal studies [103,104]
i
No psychometric properties reported for the subjective physical activity measures in 2 studies [103,104]
j
A significant trend was observed for poor quality of life when moving from the active to less active groups in 1 study [104]
k
Quality of evidence was downgraded from “low”to “very low”because of serious risk of bias; because of this limitation, was not upgraded for a dose-response gradient
l
Includes 6 cross-sectional studies [101,105–109]
m
Convenience sample was used in 5 studies [101,105–108]. Physical activity was measured only during child care in 1 study [109]. Potential confounders were not adjusted for in 3 adjusted studies [101,107,109].
No psychometric properties reported for the subjective physical activity measures in 1 study [101]. No psychometric properties reported for the outcome measure in 2 studies [101,105]. Large amount of missing
data in 1 study [106]
n
Favourable and unfavourable associations between physical activity and psychosocial health observed across studies
o
Quality of evidence was downgraded from “low”to “very low”because of serious risk of bias and serious inconsistency
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Table 4 The relationship between physical activity and cognitive development
#of
studies
Design Quality assessment # of
participants
Absolute effect Quality
Risk of
bias
Inconsistency Indirectness Imprecision Other
Mean baseline age ranged from 18.3 weeks-4.94 years; where mean age was not reported, baseline age ranged from 12 months-5 years. Data were collected by RCT, clustered RCT, non-randomized
intervention, cross-over trial, and cross-sectional study designs. Cognitive development was assessed by psychomotor skills (objectively measured), time on task (direct observation), early literacy and
language skills (objectively measured), creativity (direct observation; Thinking Creatively in Action and Movement test), attention (direct observation), attention span (proxy-report interview; proxy-report Child
Temperament Questionnaire), literacy skills (self-report; Woodcock Johnson, Peabody Picture Vocabulary Test), math skills (self-report; Woodcock Johnson Applied Problems subscale), language development
(objectively measured; Gessell Developmental Schedules –Development Quotient), free and cued word recall (objectively measured), cognitive function (objectively measured; Herbst Test), and sustained
attention and response inhibition (objectively measured; Picture Deletion Task for Preschoolers).
2 RCT
a
Serious
risk of
bias
b
No serious
inconsistency
No serious
indirectness
No serious
imprecision
None 454 The PA interventions (planned passive cycling or structured/organized PA) were
favourably associated with improved cognitive development in 2 studies [90,91].
MODERATE
c
1 Clustered
RCT
d
No
serious
risk of
bias
No serious
inconsistency
No serious
indirectness
No serious
imprecision
None 125 The PA intervention (physical exercises to enact meanings of words) was
favourably associated with improved cognitive development [110].
The PA intervention (physical exercises unrelated to words) was favourably
associated with improved cognitive development (cued recall of words but not free
recall of words)[110].
HIGH
4 Non-
randomized
intervention
e
Serious
risk of
bias
f
No serious
inconsistency
No serious
indirectness
No serious
imprecision
None 460 The PA interventions (structured/organized PA, free play and structured PA, or
academic MVPA lessons) were favourably associated with improved cognitive
development (only in intervention sites that actively participated in the intervention in 1
study; for alliteration in 2/2 studies; and for rhyming and picture naming in 1/2 studies)in
4 studies [93,111–113].
VERY LOW
g
3 Cross-over
trial
h
Serious
risk of
bias
i
No serious
inconsistency
No serious
indirectness
No serious
imprecision
None 182 The PA condition (structured/organized PA or MVPA breaks) was favourably
associated with improved cognitive development (sustained attention but not response
inhibition in 1 study)in2 studies [114,115].
Recess conditions were favourably associated with cognitive development in 1 study
[116].
VERY LOW
j
3 Cross-
sectional
k
Serious
risk of
bias
l
No serious
inconsistency
No serious
indirectness
No serious
imprecision
None 3138 TPA was unfavourably associated with cognitive development in 1 study [101]andnot
associated with cognitive development in 1 study [109].
MVPA was not associated with cognitive development in 1 study [109].
Outdoor PA (at child care)wasnot associated with cognitive development in 1study[58].
VERY LOW
m
MVPA: moderate- to vigorous-intensity physical activity; PA: physical activity; RCT: randomized controlled trial; TPA: total physical activity
a
Includes 2 RCTs [90,91]
b
No intention-to-treat analysis; parent-child dyads were excluded if they did not carry out the management plan or if they became sick during the study and the physical activity program was interrupted in 1 study
[90]. Physical activity was not measured, so it is unknown if the intervention significantly changed physical activity in 2 studies [90,91]
c
Quality of evidence was downgraded from “high”to “moderate”because of serious risk of bias
d
Includes 1 clustered RCT [110]
e
Includes 4 non-randomized interventions [93,111–113]
f
Physical activity was not measured, so it is unknown if the intervention significantly changed physical activity in in 2 studies [93,113]
g
Quality of evidence was downgraded from “low”to “very low”because of serious risk of bias
h
Includes 3 cross-over trials [114–116]
i
Condition was not randomly assigned in 1 study [116]. Physical activity was not measured, so it is unknown if there were significant differences in physical activity between conditions in 2 studies [114,116]. Unclear
what conditions had significant differences in the outcome measure in 1 study [116]
j
Quality of evidence was downgraded from “low”to “very low”because of serious risk of bias
k
Includes 3 cross-sectional studies [58,101,109]
l
Convenience sample was used in 1 study [101]. Physical activity was measured only during child care in 2 studies [58,109]. No potential confounders were adjusted for in 2 adjusted studies [101,109]. No
psychometric properties reported for the subjective physical activity measure or the outcome measure in 1 study [101]
m
Quality of evidence was downgraded from “low”to “very low”because of serious risk of bias
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groups (physical activity to enact meaning of words and
physical activity unrelated to words) compared to the
control groups (no physical activity) [110]. The quality
of evidence remained at “high”(Table 4).
Among the four non-randomized interventions, a
significant increase in at least one measure of cognitive
development was observed in the intervention groups that
participated in the intervention (academic lessons, free
play, and structured activities) compared to the control
groups (standard care) in three studies [93, 111, 112], and
significant increases in children’screativityatfollow-up
compared to baseline were reported in one study [113].
The quality of evidence was downgraded from “low”to
“very low”because of a serious risk of bias (Table 4).
Among the three cross-over trials, at least one meas-
ure of cognitive development was significantly higher in
the physical activity condition (MVPA breaks, struc-
tured/organized physical activity) compared to the con-
trol condition (typical instruction, sedentary session) in
two studies [114, 115], and attention was significantly
higher after 10-, 20-, and 30-min outdoor recess condi-
tions in one study [116]. The quality of evidence was
downgraded from “low”to “very low”because of a ser-
ious risk of bias (Table 4).
Among the three cross-sectional studies, physical ac-
tivity was unfavourably associated with cognitive devel-
opment in one study [101] and not associated with
cognitive development in two studies [58, 109]. The
study with unfavourable associations had a sample of in-
fants [101]. In regard to intensity or type of physical ac-
tivity, at least one favourable association was observed
between TPA and cognitive development (1/2 studies).
However, MVPA and outdoor physical activity were not
associated with cognitive development (see Table 4). The
quality of evidence was downgraded from “low”to “very
low”because of a serious risk of bias (see Table 4).
Fitness
The association between physical activity and fitness was
examined in three studies (three unique samples; see
Table 5 and Table S5 in Additional file 2). In the longitu-
dinal study, TPA was favourably associated with cardio-
respiratory fitness [43]. The quality of evidence was
downgraded from “low”to “very low”because of a ser-
ious risk of bias (see Table 5).
Among the two cross-sectional studies, physical activ-
ity was favourably associated with at least one measure
of fitness in both studies [55, 117]. As for physical activ-
ity intensity or type, at least one favourable association
was observed between each of the following physical ac-
tivity exposures and cardiorespiratory fitness: TPA (2/2
studies), MVPA (1/1 study), and VPA (1/1 study). Simi-
larly, at least one favourable association was observed
between each of the following physical activity exposures
and muscular fitness and speed-agility: TPA (1/1 study),
MVPA (1/1 study), and VPA (1/1 study). However, null
LPA and MPA were not associated with cardiorespiratory
fitness, muscular fitness or speed-agility (See Table 5). The
quality of evidence was downgraded from “low”to “very
low”because of a serious risk of bias (see Table 5).
Bone and skeletal health
The association between physical activity and bone and
skeletal health was examined in seven studies (seven unique
samples; see Table 6 and Table S6 in Additional file 2). For
the RCT, total bone mineral content in a baseline sample of
infants was not significantly different between the interven-
tion (structured/organized physical activity) and control
(fine motor activity) groups [118]. However, physical activ-
ity was also not significantly different between groups. The
quality of evidence was downgraded from “high”to “low”
because of very serious indirectness (see Table 6).
Among the six cross-sectional studies, favourable associ-
ations were reported between physical activity and at least
one measure of bone and skeletal health in five studies
[119–123], and null associations were reported in one
study [124]. One study with favourable associations had a
sample of infants [119]. In regard to intensity or type of
physical activity, at least one favourable association was
observed between each of the following physical activity
exposures and bone and skeletal health: TPA (2/3 studies),
MPA (1/2 studies), MVPA (2/3 studies), VPA (2/2 studies),
leisure time physical activity (1/1 study), outdoor physical
activity (3/3 studies), and weight-bearing physical activity
(1/1 study). Conversely, LPA was not associated with bone
and skeletal health (see Table 6). The quality of evidence
was downgraded from “low”to “very low”because of a
serious risk of bias (see Table 6).
Cardiometabolic health
The association between physical activity and cardiomet-
abolic health was examined in nine studies (eight unique
samples; see Table 7 and Table S7 in Additional file 2). In
the non-randomized intervention, children in the inter-
vention group (structured/organized physical activity) had
significantly lower diastolic blood pressure than the con-
trols (standard care) [125]. The quality of evidence was
downgraded from “low”to “very low”because of a serious
risk of bias (see Table 7).
Among the two longitudinal studies, physical activity
was not associated with any measure of blood pressure,
cholesterol, or triglycerides in one study [43], and mixed
findings with blood pressure were observed in the other
study, though primarily null associations were observed
[126]. In regard to intensity or type of physical activity,
at least one favourable association was observed between
aerobic physical activity and blood pressure (1/1 study),
and at least one unfavourable association was observed
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Table 5 The relationship between physical activity and fitness
#of
studies
Design Quality assessment # of
participants
Absolute effect Quality
Risk of bias Inconsistency Indirectness Imprecision Other
Mean baseline age ranged from 4.04-4.48 years. One study reported the sample was of preschool age but did not provide a mean or range. Data were collected by longitudinal with 1-year follow-up
and cross-sectional study designs. Fitness was assessed as cardiorespiratory fitness (treadmill test, 20-m shuttle run from the PREFIT fitness test battery), muscular fitness including handgrip strength
and standing long jump (PREFIT fitness test battery), speed-agility (4 × 10 shuttle run from the PREFIT fitness test battery), and physical working capacity (Ruffier’s test using Ruffier–Dickson index). All
outcomes were objectively measured.
1 Longitudinal
a
Serious risk
of bias
b
No serious
inconsistency
No serious
indirectness
No serious
imprecision
None 123 TPA was favourably associated with cardiorespiratory fitness [43]. VERY
LOW
c
2 Cross-
sectional
d
Serious risk
of bias
e
No serious
inconsistency
No serious
indirectness
No serious
imprecision
Exposure/outcome
gradient
f
594 Cardiorespiratory fitness
TPA was favourably associated with fitness (only for 95th, 90th, 75th
but not 50th and 25th percentiles of vector magnitude in 1 study)in
2 studies [55,117].
LPA was not associated with fitness in 1 study [55].
MPA was not associated with fitness in 1 study [55].
MVPA was favourably associated with fitness in 1 study [55].
VPA was favourably associated with fitness in 1 study [55].
Other fitness measures
TPA was favourably associated with muscular fitness and speed-agility
(only for 95th, 90th, 75th but not 50th and 25th percentiles of vector
magnitude and not for standing long jump at the 75th percentile)
in 1 study [55].
LPA was not associated with muscular fitness and speed-agility
in 1 study [55].
MPA was not associated with muscular fitness and speed-agility
in 1 study [55].
MVPA was favourably associated with muscular fitness (standing
long jump but not handgrip strength) and speed-agility in
1 study [55].
VPA was favourably associated with muscular fitness and
speed-agility in 1 study [55].
VERY
LOW
g
LPA: light-intensity physical activity; MPA: moderate-intensity physical activity; MVPA: moderate- to vigorous-intensity physical activity; TPA: total physical activity; VPA: vigorous-intensity physical activity
a
Includes 1 longitudinal study [43]
b
The findings that were reported did not adjust for any potential confounders
c
Quality of evidence was downgraded from “low”to “very low”because of serious risk of bias
d
Includes 2 cross-sectional studies [55,117]
e
No potential confounders were adjusted for; a convenience sample was used and it is unclear if the fitness measure is suitable for this age group in 1 study [117]. Potentially inappropriate statistical analysis: other
movement behaviours were mutually adjusted for in the fully adjusted models in 1 study [55]
f
A gradient for higher TPA, MVPA, VPA with higher fitness was observed in 1 study [55]
g
Quality of evidence was downgraded from “low”to “very low”because of serious risk of bias; because of this limitation, was not upgraded for an exposure/outcome gradient
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Table 6 The relationship between physical activity and bone and skeletal health
#of
studies
Design Quality assessment # of
participants
Absolute effect Quality
Risk of bias Inconsistency Indirectness Imprecision Other
Meanbaselineagerangedfrom9.27-57.12months.Onestudyreportedthebaselineageas6monthsbutameanwasnotgiven.DatawerecollectedbyRCTandcross-sectional study designs. Several
bone and skeletal health measures were assessed by X-ray absorptiometry including: total bone mineral content, bone mineral density of the lumbar spine (L2-L4), total body bone area, periosteal circumference
of tibia, endosteal circumference of tibia, cortical bone area of tibia, hip bone area, hip bone mineral content, areal bone mineral density, and estimated volumetric bone mineral density. Bone and skeletal health
was also assessed by vitamin D (25-(OH)- vitamin D3 measured in serum), vitamin D (25-(OH)- vitamin D3 parathyroid hormone in non-fasting
venous blood samples), and bone stiffness (quantitative ultrasound). All outcomes were objectively measured.
1 RCT
a
No risk of
bias
No serious
inconsistency
Very serious
indirectness
b
No serious
imprecision
None 422 The PA intervention (structured/organized PA) was not associated with
improved bone mineral content [118].
LOW
c
6 Cross-
sectional
d
Serious risk
of bias
e
No serious
inconsistency
No serious
indirectness
No serious
imprecision
Exposure/
outcome
gradient
f
14,774 TPA was favourably associated with bone and skeletal health in 2 studies
[119,123] and not associated with bone and skeletal health in 1 study [124].
LPA was not associated with bone and skeletal health in 1 study [123].
MPA was favourably associated with bone and skeletal health in 1 study [123]
and not associated with bone and skeletal health in 1 study [124].
MVPA was favourably associated with bone and skeletal health in 2 studies
[122,123] and not associated with bone and skeletal health in 1 study [124].
VPA was not associated with bone and skeletal health in 2 studies [123,124].
Leisure time physical activity was favourably associated with bone and
skeletal health in 1 study [123].
Outdoor activity was favourably associated with bone and skeletal health in
3 studies [119–121].
Weight-bearing activity was favourably associated with bone and skeletal
health in 1 study [123].
VERY
LOW
g
LPA: light-intensity physical activity; MPA: moderate-intensity physical activity; MVPA: moderate- to vigorous-intensity activity; PA: physical activity; RCT: randomized
controlled trial; TPA: total physical activity; VPA: vigorous-intensity physical activity
a
Includes 1 RCT [118]
b
The intervention did not significantly change physical activity
c
Quality of evidence was downgraded from “high”to “low”because of very serious indirectness
d
Includes 6 cross-sectional studies [119–124]
e
Potential confounders were not adjusted for in 2 studies [120,121]. Potentially inappropriate statistical analysis: other movement behaviours were mutually adjusted for in the fully adjusted models in 1 study [123]. No
psychometric properties were reported for the subjective physical activity measure in 4 studies [119–121,123]. A convenience sample was used in 2 studies [120,124]
f
A gradient for higher TPA, MPA, MVPA, leisure time physical activity, outdoor activity, and weight-bearing physical activity with better bone and skeletal health was observed in 2 studies [119,123]
g
Quality of evidence was downgraded from “low”to “very low”because of serious risk of bias; because of this limitation, was not upgraded for an exposure/outcome gradient
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Table 7 The relationship between physical activity and cardiometabolic health
#of
studies
Design Quality assessment # of
participants
Absolute effect Quality
Risk of
bias
Inconsistency Indirectness Imprecision Other
Mean baseline age ranged from 3-4.9 years. One study reported only that the children were preschool age. Data were collected by non-randomized intervention, longitudinal with up to 2 years
follow-up, and cross-sectional study designs. Cardiometabolic health was assessed by mean arterial pressure, DBP, SBP, total cholesterol, total serum cholesterol, HDL, triglycerides, HDL
2
, LDL,
LDL/HDL, total serum cholesterol/HDL, HDL/total triglycerides, and clustered cardiovascular risk score (SBP, triglycerides, total cholesterol/HDL, HOMA-IR, sum of two skinfolds). All outcomes were
objectively measured.
1 Non-randomized
intervention
a
Serious risk
of bias
b
No serious
inconsistency
No serious
indirectness
No serious
imprecision
None 264 BP
The PA intervention (structured/organized PA) was favourably
associated with DBP during rest and activity [125].
VERY
LOW
c
2 Longitudinal
d
Serious risk
of bias
e
No serious
inconsistency
No serious
indirectness
No serious
imprecision
None 291 BP
Aerobic PA was favourably associated with BP (SBP but not DBP,
boys only, 2-year follow-up but not 1-year follow-up)in1 study [126].
Leisure PA was unfavourably associated with BP (DBP but not SBP,
boys only, 1-year follow-up but not 2-year follow-up)in1 study [126].
Structured PA was not associated with BP (SBP or DBP)in
1 study [126].
Cholesterol
TPA was not associated with cholesterol (total serum cholesterol, HDL,
HDL
2
, LDL, LDL/HDL, or total serum cholesterol/HDL)in1 study [43].
Triglycerides
TPA was not associated with triglycerides in 1 study [43].
VERY
LOW
f
6 Cross-sectional
g
Serious risk
of bias
h
Serious
inconsistency
i
No serious
indirectness
No serious
imprecision
Exposure/
outcome
gradient
j
1882 Clustered risk score
TPA was favourably associated with clustered risk score (boys only,
Quartile 1 vs. Quartile 5 only)in1 study [127].
MPA was not associated with clustered risk score in 1 study [127].
MVPA was not associated with clustered risk score in 1 study [127].
VPA was favourably associated with clustered risk score (boys only,
Quartile 2 vs. Quartile 5 only)in1 study [127].
BP
TPA was unfavourably associated with BP (SBP and DBP)in
1 study [117] and not associated with BP (SBP, DBP, or mean
arterial pressure)in3 studies [66,72,81].
Aerobic PA was not associated with BP (SBP or DBP)in
1 study [126].
Indoor PA was not associated with BP (SBP or DBP)in
1 study [81].
Leisure PA was not associated with BP (SBP or DBP)in
1 study [126].
Outdoor PA was not associated with BP (SBP or DBP)in
1 study [81].
Structured PA was not associated with BP (SBP or DBP)in
1 study [126].
Cholesterol
TPA was favourably associated with cholesterol (total cholesterol but
not HDL)in1 study [81] and not associated with cholesterol (total
cholesterol, HDL, or HDL/total cholesterol) in 1 study [72].
Indoor PA was not associated with cholesterol (total cholesterol or HDL)
in 1 study [81].
VERY
LOW
k
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Table 7 The relationship between physical activity and cardiometabolic health (Continued)
#of
studies
Design Quality assessment # of
participants
Absolute effect Quality
Risk of
bias
Inconsistency Indirectness Imprecision Other
Outdoor PA was unfavourably associated with cholesterol (HDL but
not total cholesterol)in1 study [81].
Triglycerides
TPA was not associated with cholesterol (total cholesterol, HDL, or
HDL/total cholesterol)in1 study [72].
BP: blood pressure; DBP: diastolic blood pressure; HDL: high-density lipoprotein cholesterol; HOMA-IR: homeostatic model assessment –insulin resistance; LDL: low-density lipoprotein cholesterol; MPA: moderate-
intensity physical activity; MVPA: moderate- to vigorous-intensity physical activity; PA: physical activity; SBP: systolic blood pressure; TPA: total physical activity; VPA: vigorous intensity physical activity
a
Includes 1 non-randomized intervention [125]
b
No intention-to-treat analysis; results are based on children who were measured at all 3 time points. Physical activity was not measured, so it is unknown if the intervention significantly changed physical activity
c
Quality of evidence was downgraded from “low”to “very low”because of serious risk of bias
d
Includes 2 longitudinal studies [43,126]
e
Potential confounders were not adjusted for in 1 study [43]. No psychometric properties were reported for the subjective physical activity measure in 1 study [126]
f
Quality of evidence was downgraded from “low”to “very low”because of serious risk of bias
g
Includes 6 cross-sectional studies [66,72,81,117,126,127]
h
No potential confounders were adjusted for in 5 studies [66,72,81,117,127]. Convenience sample in 1 study [117]. No psychometric properties were reported for the subjective physical activity measure in 1
study [126]
i
Favourable and unfavourable associations between physical activity and cardiometabolic health observed across studies
j
A gradient for higher TPA with worse total cholesterol was observed in 1 study [81]
k
Quality of evidence was downgraded from “low”to “very low”because of serious risk of bias and serious inconsistency; because of this limitation, was not upgraded for an exposure/outcome gradient
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Table 8 The relationship between physical activity and risks/harm
#of
studies
Design Quality assessment # of
participants
Absolute effect Quality
Risk of
bias
Inconsistency Indirectness Imprecision Other
Mean baseline age ranged from 7.4 weeks-24 months; where mean age was not reported, baseline age ranged from 2 months-4.5 years. Data were collected by case cross-over and longitudinal with
4.5-6.5 years follow-up, case control, and cross-sectional study designs. Risks/harm was assessed as injury risk (proxy-report; Participant Event Monitoring method), injury severity (proxy-report; minor
injury severity scale), fracture incidence (proxy-report), and plagiocephaly (objectively measured).
1 Case cross-
over
a
Serious risk
of bias
b
No serious
inconsistency
No serious
indirectness
No serious
imprecision
None 170 TPA was unfavourably associated with injury risk but was not associated with
injury severity [128].
LOW
c
1 Longitudinal
d
Serious risk
of bias
e
No serious
inconsistency
Serious
indirectness
f
No serious
imprecision
Dose-response
evidence
g
2692 Outdoor time was favourably associated with fracture incidence in the
winter but unfavourably associated with fracture incidence in the summer
[129].
VERY
LOW
h
1 Case-control
i
Serious risk
of bias
j
No serious
inconsistency
No serious
indirectness
No serious
imprecision
None 194 TPA was favourably associated with plagiocephaly (at present but not at
6 weeks of age)[130].
Prone position was favourably associated with plagiocephaly (for ≥5 min/day
but not whether it was provided or not) at 6 weeks of age [130].
VERY
LOW
k
1 Cross-
sectional
l
Serious risk
of bias
m
No serious
inconsistency
No serious
indirectness
No serious
imprecision
None 380 Prone position was not associated with plagiocephaly [131]. VERY
LOW
n
min: minutes; TPA: total physical activity
a
Includes 1 case cross-over study [128]
b
Convenience sample
c
Quality of evidence remained at “low”
d
Includes 1 longitudinal study [129]
e
No psychometric properties were reported for outdoor time and fracture incidence, and there was a large unexplained loss to follow-up
f
Outdoor time was the measure of physical activity
g
Dose-response evidence was observed for higher outdoor time with lower fracture incidence
h
Quality of evidence was downgraded from “low”to “very low”because of serious risk of bias and serious indirectness; because of these limitations, was not upgraded for dose-response evidence
i
Includes 1 case-control study [130]
j
No psychometric properties were reported for the subjective physical activity measures
k
Quality of evidence was downgraded from “low”to “very low”because of serious risk of bias
l
Includes 1 cross-sectional study [131]
m
Convenience sample and no psychometric properties were reported for the subjective physical activity measure
n
Quality of evidence was downgraded from “low”to “very low”because of serious risk of bias
The Author(s) BMC Public Health 2017, 17(Suppl 5):854 Page 53 of 215
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between leisure physical activity and blood pressure (1/1
study). Structured physical activity was not associated
with blood pressure [126]. Similarly, TPA was not associ-
ated with cholesterol or triglycerides (See Table 7). The
quality of evidence was downgraded from “low”to “very
low”because of a serious risk of bias (see Table 7).
Among the six cross-sectional studies, physical activity
was favourably associated with at least one measure of
cardiometabolic health in one study [127] and unfavour-
ably associated with cardiometabolic health in one study
[117]; null associations were found in three studies [66,
72, 126], and mixed findings were found in one study
[81]. In the study where some favourable associations
were observed, primarily null associations were observed
[127]. In regard to intensity or type of physical activity,
at least one favourable association was observed between
each of the following physical activity exposures and a
clustered risk score: TPA (1/1 study) and VPA (1/1
study). However, MPA and MVPA were not associated
with a clustered risk score. The following types of phys-
ical activity were not associated with blood pressure:
TPA, aerobic physical activity, indoor physical activity,
outdoor physical activity, leisure physical activity, and
structured physical activity. At least one favourable asso-
ciation was observed between TPA and cholesterol (1/2
studies), and at least one unfavourable association was
observed between outdoor physical activity and choles-
terol (1/1 study). However, indoor physical activity was
not associated with cholesterol. Similarly, TPA was not
associated with triglycerides (see Table 7). The quality of
evidence for the cross-sectional studies was downgraded
from “low”to “very low”because of a serious risk of bias
and serious inconsistency (see Table 7).
Risks/harm
The association between physical activity and risks/harm
was examined in four studies (four unique samples; see
Table 8 and Table S8 in Additional file 2). In the case
cross-over study, a high activity level, compared to a low
activity level, was unfavourably associated with injury risk
among toddlers, but activity level was not associated with
injury severity [128]. The quality of evidence remained at
“low”(see Table 8).
In the longitudinal study, findings differed based on
the season, with more outdoor time in the summer asso-
ciated with an increased likelihood of reporting a frac-
ture, and more outdoor time in the winter associated
with a decreased likelihood of reporting a fracture [129].
The quality of evidence was downgraded from “low”to
“very low”because of a serious risk of bias and serious
indirectness (see Table 8).
In the case-control study, cases (those with plagioce-
phaly) had an increased likelihood of being in the very in-
active/inactive/average group compared to the active/very
active group [130]. Cases were also more likely to partici-
pate in a lower duration of prone position per day. The
quality of evidence was downgraded from “low”to “very
low”because of a serious risk of bias (see Table 8).
In the cross-sectional study, no associations were
observed between first age of tummy time or tummy
time duration and plagiocephaly [131]. Infants with a
lower frequency of tummy time were more likely to
have plagiocephaly in unadjusted models but not in
adjusted models. The quality of evidence was down-
graded from “low”to “very low”because of a serious
risk of bias (see Table 8).
Frequency and duration
The impact of different frequencies or durations of phys-
ical activity on health indicators could be compared only
across studies (i.e., within-study comparisons were not
possible), as most studies dichotomized physical activity
frequency and duration or had only a single- or two-arm
physical activity intervention.
In 19 experimental studies, times per day of intervention
delivery were reported [34, 35, 42, 90–95, 102, 111–116,
118, 125]. Regardless of frequency, the intervention had
favourable impacts on at least one health indicator in the
majority of studies (1 time/day, 14/15 studies; 2 times/day,
2/3 studies; 4 times/day, 1/1 studies). In 19 experimental
studies, times per week of intervention delivery were re-
ported or could be calculated [33, 35, 36, 42, 90–95, 102,
111–116, 118, 125]. Regardless of frequency, favourable
impacts on at least one health indicator were observed in
the majority of studies (1 time/week, 3/3 studies; 2 times/
week, 6/6 studies; 3-4 times/week, 6/6 studies; 5 times/
week, 0/1 study; 6 times/week, 0/1 study; 10 times/week,
2/2 studies; 24 times/week, 1/1 study).
Only five observational studies examined the association
between frequency of physical activity and a health indica-
tor [56, 71, 120, 121, 131]. In one study, participants who
engaged in TPA <5 times per week were significantly
more likely to have a motor difficulty compared to partici-
pants who engaged in TPA >5 times per week [56]. It is
important to note that this study measured TPA with a
questionnaire; therefore, LPA was likely underestimated
or not captured [11]. In one bone and skeletal health
study, vitamin D levels were significantly lower in children
who participated in 0, 1-5, 6-10, 11-15, or 16-20 times per
month, compared to children who participated in outdoor
physical activity 26-31 times per month [120]. However, in
a second study, only children with no outdoor physical ac-
tivity were significantly more likely to have lower vitamin
D status compared to children who participated in out-
door physical activity 26-31 times per month [121]. In an-
other study, infants who participated in the prone position
<3 times per day were significantly more likely to have
plagiocephaly in the unadjusted but not in the adjusted
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models [131]. Similarly, the proportion of girls or boys
participating in active play <7 times per week was not sig-
nificantly different between non-obese and obese groups
in one study [71].
In 17 experimental studies, duration of intervention
delivery per day was reported [34–36, 42, 90, 91, 93–95,
111–116, 118, 125]. Regardless of duration, favourable
impacts on at least one health indicator were observed
in the majority of studies (10-15 min/day, 3/3 studies;
15-20 min/day, 0/1 study; 20-40 min/day, 7/8 studies;
45-60 min/day, 8/8 studies; note one study included
three different durations that all had favourable impacts
but statistical comparisons between groups were not made
[116]). In 18 experimental studies, total duration of inter-
vention delivery per week was reported or could be calcu-
lated [35, 36, 42, 90, 91, 93–96,102,111–116, 118, 125].
Regardless of duration, favourable impacts on at least one
health indicator were observed in the majority of studies
(10-30 min/week, 5/5 studies; 45 min/week, 2/2 studies;
70-100 min/week, 5/6 studies; 105-240 min/week, 5/7 stud-
ies; 300 min/week, 1/1 study; note one study included three
different durations that all had favourable impacts but stat-
istical comparisons between groups were not made [116]).
As for duration, 17 observational studies examined the
association between duration of physical activity and a
health indicator [45, 47, 53, 56, 58, 63, 73, 74, 78, 79, 98,
99, 106, 120, 129–131]. In infants, ≥5 h per day of unre-
stricted moving time was associated with favourable
changes in one measure of adiposity in one study [45].
Additionally, ≥30 min of prone position per day in one
study [98] and ≥60 min of prone position per day in an-
other study [99] were associated with more favourable
motor development scores or an increased likelihood of
achieving motor development milestones at an earlier age.
While ≥5 min of prone position per day was favourably
associated with plagiocephaly in one study [130], >5 min
of prone position per day was not associated with plagio-
cephaly in another study [131]. For toddlers and/or pre-
schoolers, one study found that those who participated in
TPA for ≥7 h per week were significantly less likely to be
overweight or obese [63], and a second study found that
those who participated in TPA for <840 min per week
(<14 h per week) were significantly more likely to have a
motor difficulty [56]. In one study, unfavourable associa-
tions between ≥2 h of exercise per day and psychosocial
health were observed in boys but not in girls [106].
Six studies examined the association between dur-
ation of outdoor physical activity and a health indicator
[53, 58, 78, 79, 120, 129]; the findings were mixed. Spe-
cifically, >30 min of outdoor physical activity per day
was favourably associated with adiposity [58]; ≥1hper
day was favourably associated with bone and skeletal
health [120]; and ≥28 h per week were unfavourably as-
sociated with risks/harm [129]. Null associations were
observed between outdoor physical activity and adipos-
ity in three studies [53, 78, 79], using a > 1 h per day,
≥2hperday,and≥7 h per week cut-points. Null asso-
ciations were also observed in the remaining three
studies that examined duration of physical activity [47,
73, 74]. For instance, the following durations were not
associated with adiposity: ≥2 h of active play per week-
day and ≥4 h per weekend day in one study [73],
<60 min of VPA per day outside of kindergarten in one
study [74], and ≤51.43 min per day of physical activity
at home and ≤34.59 min per day of structured physical
activity in one study [47].
Discussion
In this systematic review, evidence from 96 studies and
71,291 unique participants was synthesized to examine
the relationships between objectively and subjectively
measured physical activity and health indicators in the
early years. For experimental studies, physical activity was
consistently (>60% of studies) associated with improved
motor development, cognitive development, psychosocial
health, and cardiometabolic health. For observational
studies, physical activity was consistently associated with
favourable motor development, fitness, and bone and skel-
etal health. However, physical activity was not consistently
associated with adiposity or risks/harm across study de-
signs, and significant differences between intervention and
control groups in BMI were not observed in the meta-
analysis. Although some high-quality evidence was in-
cluded, the vast majority of evidence was of “low”to “very
low”quality. A high-level summary is provided in Table 9.
Where possible, evidence on the association between
the dose (i.e., frequency, intensity, duration, and type) of
physical activity and health indicators was also synthe-
sized. Various frequencies of physical activity were asso-
ciated with health indicators, but the most favourable
frequency of physical activity to obtain health benefits
was unclear. In regard to intensity of physical activity,
LPA and MPA were not consistently associated with any
health indicators; whereas TPA, MVPA, and VPA were
consistently associated with multiple health indicators.
In terms of duration of physical activity, the evidence in-
dicated that for infants, ≥30 min per day in the prone
position accumulated throughout waking hours was as-
sociated with health benefits. However, for toddlers and
preschoolers, the duration of physical activity needed to
obtain health benefits was unclear. In regard to type of
physical activity, consistent favourable associations with
at least one health indicator were observed across mul-
tiple studies for a variety of different types of physical
activity, including active play, aerobic, dance, prone pos-
ition (infants), and structured/organized. Finally, some
evidence existed to indicate that more physical activity
was associated with greater health benefits.
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This review builds on a previous systematic review con-
ducted in 2012 that synthesized the evidence from 22
studies on the association between physical activity and
health indicators among infants, toddlers, and pre-
schoolers [7]. In contrast to the previous review (where
cross-sectional study designs were excluded a priori), the
present review included all study designs, thereby greatly
increasing the evidence base; specifically, 55 cross-
sectional studies were included. Not surprisingly, the evi-
dence base also increased with time: a total of 45 of the
studies included in the present study were published in
2012 or later (27 of those were cross-sectional). Due to a
more comprehensive search strategy compared to the pre-
vious review, 17 additional studies, published in 2011 or
earlier were also included. However, 12 studies included
in the previous review were excluded in the present review
Table 9 High-level summary of findings by health indicator across all, experimental and observational study designs
Health indicator # of
studies
Quality of evidence Summary of findings
a
Experimental study designs Observational study designs All designs
Critical
Adiposity 57 Very low to low Favourable: 2 studies Favourable: 16 studies Favourable: 18 studies
Null: 5 studies Null: 25 studies Null: 30 studies
Unfavourable: 0 studies Unfavourable: 4 studies Unfavourable: 4 studies
Mixed: 0 studies Mixed: 5 studies Mixed: 5 studies
Motor development 23 Very low to low Favourable: 10 studies Favourable: 8 studies Favourable: 18 studies
Null: 2 studies Null: 1 study Null: 3 studies
Unfavourable: 0 studies Unfavourable: 1 study Unfavourable: 1 study
Mixed: 0 studies Mixed: 1 study Mixed: 1 study
Psychosocial health 11 Very low to moderate Favourable: 2 studies Favourable: 3 studies Favourable: 5 studies
Null: 1 study Null: 2 studies Null: 3 studies
Unfavourable: 0 studies Unfavourable: 3 studies Unfavourable: 3 studies
Mixed: 0 studies Mixed: 0 studies Mixed: 0 studies
Cognitive development 13 Very low to high Favourable: 10 studies Favourable: 0 studies Favourable: 10 studies
Null: 0 studies Null: 2 studies Null: 2 studies
Unfavourable: 0 studies Unfavourable: 1 study Unfavourable: 1 study
Mixed: 0 studies Mixed: 0 studies Mixed: 0 studies
Fitness 3 Very low Favourable: 0 studies Favourable: 3 studies Favourable: 3 studies
Null: 0 studies Null: 0 studies Null: 0 studies
Unfavourable: 0 studies Unfavourable: 0 studies Unfavourable: 0 studies
Mixed: 0 studies Mixed: 0 studies Mixed: 0 studies
Important
Bone and skeletal health 7 Very low to low Favourable: 0 studies Favourable: 5 studies Favourable: 5 studies
Null: 1 study Null: 1 study Null: 2 studies
Unfavourable: 0 studies Unfavourable: 0 studies Unfavourable: 0 studies
Mixed: 0 studies Mixed: 0 studies Mixed: 0 studies
Cardiometabolic health 9 Very low Favourable: 1 study Favourable: 1 study Favourable: 2 studies
Null: 0 studies Null: 4 studies Null: 4 studies
Unfavourable: 0 studies Unfavourable: 1 study Unfavourable: 1 study
Mixed: 0 studies Mixed: 2 studies Mixed: 2 studies
Risks/harm 4 Very low to low Favourable: 0 studies Favourable: 1 study Favourable: 1 study
Null: 0 studies Null: 1 study Null: 1 study
Unfavourable: 0 studies Unfavourable: 1 study Unfavourable: 1 study
Mixed: 0 studies Mixed: 1 study Mixed: 1 study
a
Favourable: at least one favourable but no unfavourable associations were observed; Unfavourable: at least one unfavourable but no favourable associations
were observed; Null: no favourable or unfavourable associations were observed; Mixed: both favourable and unfavourable or favourable, unfavourab le, and null
associations were all observed. Bold font indicates ≥60% of studies were in the favourable or unfavourable direction
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because of changes in inclusion criteria (e.g., sample size)
[132–143].
Despite the differences in the studies considered, the
present review gathered similar results as the previous re-
view [7]: both found that physical activity was favourably
associated with motor development, cognitive develop-
ment, psychosocial health, bone and skeletal health, and
cardiometabolic health. This is in line with other reviews
that have been published since 2012 on physical activity
and single health indicators, including cognitive develop-
ment in early childhood (aged 0-6 years) [19], psychosocial
health in early childhood [21], and motor development in
preschoolers [22]. However, it was acknowledged in both
the psychosocial health and cognitive development re-
views that the evidence was limited [19, 21].
In contrast to the review published by Timmons and
colleagues in 2012 [7], favourable associations were not
consistently observed between physical activity and adi-
posity in the present review. Although some favourable
associations were observed, a large number of null asso-
ciations were also observed, as well as some unfavour-
able and mixed associations (Table 9). Furthermore, no
significant differences in BMI between intervention and
control groups were observed in the meta-analysis of
four studies. It is important to note that the bulk of studies
used surrogate adiposity measures, such as BMI, whereas
bioelectrical impedance [40], air-displacement plethysmog-
raphyviathepediatricoptionfortheBodPod[55],ordual
energy X-ray absorptiometry [46, 49, 89] were used to
measure adiposity in only five out of the 57 studies. Fur-
thermore, the use of subjective physical activity measures
that had unknown psychometric properties and neglecting
to account for potential confounders (e.g., diet) within ana-
lyses were commonly identified risks of bias that may have
affected the findings (Table 1). Alternatively, it could be that
physical activity is not strongly associated with adiposity in
the early years, and other factors such as diet and sleep are
more important predictors in this age group [144, 145].
This conclusion is partly supported by the clearer evidence
for the impact of physical activity on more rapidly develop-
ing health indicators such as motor development, psycho-
social health, and cognitive development in the present
review, where similar risk of bias limitations existed.
To better understand the commonly examined rela-
tionship between physical activity and adiposity in the
early years, there is no need for more low-quality evi-
dence; rather, what is needed is higher-quality evidence
from strong study designs that address current limita-
tions, including the use of objective measures of physical
activity, direct measures of adiposity, and study designs
or analyses that account for potential confounding fac-
tors. Given that adiposity was by far the most commonly
studied health indicator, the focus of future high-quality
physical activity and adiposity research should be
balanced with the need for high-quality research that in-
cludes other health indicators in this age group.
Given that the current review included substantially
more evidence than previous reviews, sub-analyses on the
dose of physical activity, including frequency, intensity,
duration, and type were possible. Intensity of physical
activity was commonly examined in observational studies
and in three experimental studies [111, 112, 115]. Previous
research has shown that most of the physical activity that
preschool-aged children participate in is of light intensity
[11, 16, 17]. For instance, it was reported in a systematic
review examining objectively measured physical activity
and sedentary time that preschoolers spent an average of
2.2 h per day in LPA compared to 47 min per day in
MVPA [11]. Interestingly, in the present review, the higher
intensities of physical activity (MVPA and VPA), but not
the lower intensities of physical activity (MPA and LPA),
were consistently associated with multiple health indica-
tors. However, it is important to note that most TPA con-
sists of LPA, and several favourable relationships between
TPA and health indicators were observed. Moreover, the
majority of this evidence was in preschool-age samples.
Overall, these findings suggest that some developmentally
appropriate MVPA may be needed for health benefits at
least for preschool-aged children, while acknowledging
the inherent limitations of accelerometer cut-points to
distinguish different intensities of physical activity [146].
In terms of LPA, there is some evidence in youth [147]
and in adults [148] that physical activity at the higher end
of the LPA spectrum compared to the lower end of the
spectrum may be more beneficial for health but this is
masked when looking only at total LPA. Future research
should examine whether this is also the case for the early
years, including infants, toddlers, and preschoolers.
Such knowledge will help to determine whether activ-
ities at the upper end of the LPA spectrum should be
targeted and promoted over lower intensities for
health benefits in the early years.
Across both observational and experimental studies in
the present review, a wide variety of types of physical activ-
ity were examined. The finding that structured/organized
physical activity was favourably associated with health
indicators in the present review is consistent with a recent
systematic review on organized physical activity and health
in preschool children [23]. In contrast to another recent
systematic review, which reported favourable associations
between risky outdoor play (i.e., play where children can
disappear/get lost, great heights, rough-and-tumble play)
and health [20], primarily null associations were observed
between rough-and-tumble play or outdoor play and
health indicators in the present study. However, it is im-
portant to note that the age groups differed between the
two reviews, with the risky outdoor play review including
children aged 3-12 years. Furthermore, the outdoor
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physical activity studies in the present review were
not focused on “risky”outdoor play per se. Neverthe-
less, the favourable associations between a number of
different types of physical activity and health indica-
tors suggest that children in the early years should
participate in a variety of physical activities for the
most health benefits.
It was difficult to draw conclusions about the specific
frequency or duration of physical activity that is needed
for health benefits because only a small proportion of
the included studies examined these dose parameters.
Furthermore, most observational studies dichotomized
physical activity frequency or duration, and no clear pat-
tern was observed across studies for toddlers and pre-
schoolers. For experimental studies, most involved a
single- or two-arm intervention. Additionally, it was not
possible to quantify total daily frequency or duration of
physical activity because physical activity outside of the
intervention was not usually taken into account or even
measured. Despite these limitations, sparse but consist-
ent evidence in infants indicates that at least 30 min of
prone position or tummy time per day accumulated dur-
ing waking hours appears beneficial, in particular for
motor development. This aligns with the recommendation
from the Canadian Paediatric Society, which suggests at
least 10-15 min of tummy time, three times per day [149].
Unfortunately, it is not possible to draw specific conclu-
sions on frequency and duration of physical activity for
health benefits in toddlers and preschoolers. Current
physical activity guidelines in Canada, Australia, and the
United Kingdom recommend accumulating 180 min per
day of any intensity in these age groups. According to the
previously mentioned review by Hnatiuk and colleagues
[11], this daily recommendation does align with average
prevalence estimates in preschool-aged children (2.2 h or
132 min of LPA + 47 min of MVPA).
Despite not being able to make specific conclusions re-
garding frequency and duration of physical activity
needed for health benefits in toddlers and preschoolers,
some evidence existed across age groups that more
physical activity is better for health. Specifically, this was
supported in 13 studies by dose-response evidence or an
exposure/outcome gradient for cross-sectional studies,
primarily through continuous data [44, 49, 55, 57, 58,
67, 88, 89, 100, 104, 119, 123, 129]. Furthermore, 20 out
of the 24 included experimental studies observed
favourable associations with at least one health indicator.
Although some behaviour compensation could have oc-
curred, it is likely that the majority of the physical activity
accumulated as part of the intervention was in addition to
children’s baseline physical activity. Therefore, this experi-
mental evidence also supports the overall conclusion that
more physical activity is better for health. However, to
understand the specific frequency and duration of physical
activity needed for health benefits across the early years,
further dose-response evidence is needed. Specifically, this
should include observational studies that compare mul-
tiple categories of physical activity frequency and duration
in relation to health indicators, and experimental studies
that compare multiple intervention arms with different
frequency and duration of physical activity in relation to
health indicators. Experimental studies should also take
into account baseline physical activity levels.
This discussion has already highlighted a number of
research gaps and limitations that need to be ad-
dressed by future research; however, there are additional
gaps and limitations that also warrant attention. For in-
stance, most of the evidence included in this review was
based on preschool-aged children. Given the vast develop-
mental differences in early years age groups [6], the find-
ings observed in preschool-aged children may not be
generalizable to infants and toddlers. Therefore, future
research should examine the relationships between phys-
ical activity and health indicators specifically in infants and
toddlers to ensure developmentally appropriate doses of
physical activity are being identified, recommended, and
promoted. Part of this work may involve determining how
to most accurately measure physical activity in infants and
toddlers. In fact, objective measures of physical activity
were used in only two studies with samples classified as in-
fants or toddlers [86, 118], although the measurement of
physical activity was a limitation observed across all age
groups in the present review. Specifically, as noted in the
risk of bias assessments, subjective measures of physical
activity with unknown psychometric properties were com-
monly used. It is known that the sporadic and intermittent
nature of physical activity in the early years makes it diffi-
cult to accurately capture physical activity with subjective
measures [146]. Furthermore, although objective measures
of physical activity were used in 35 studies, primarily
with accelerometers, heterogeneity in data collection
(e.g., monitor placement, epoch length) and reduction
(non-wear time definitions, removal of naps, cut-points)
procedures across studies may have contributed to the in-
consistency of some findings. This may explain why simi-
lar conclusions were found across health indicators in the
present review when comparing studies that used
objective versus subjective measures of TPA as the ex-
posure. Therefore, identifying the most appropriate
accelerometer data collection and reduction procedures
for early years children should be explored in future re-
search so that these procedures can be standardized
across studies. Furthermore, among the 24 experimen-
tal studies, 15 did not measure physical activity, so it
was unclear if the intervention was in fact successful in
changing physical activity levels. Therefore, baseline
and follow-up measures of physical activity should be
included in future interventions.
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Along with the evidence gaps and limitations associ-
ated with age groups studied and physical activity meas-
urement, limited studies were available for a number of
the health indicators. For example, there were 10 or
fewer included studies for each of the following health
indicators: psychosocial health, fitness, bone and skeletal
health, cardiometabolic health, and risks/harm. Future
high-quality research that increases the evidence base
for these health indicators is needed. Additionally, while
only three studies were included for fitness, some over-
lap existed between fitness and motor development cat-
egories (e.g., standing long jump versus standing broad
jump; 12-m run versus 20-m shuttle run). Consensus is
needed on what measures constitute fitness versus
motor development in this age group.
One strength of the present systematic review was the
use of a comprehensive search strategy that was both de-
veloped and peer-reviewed by librarians with expertise
in systematic reviews. Another strength was the broad
scope of the review through the inclusion of all study
designs, both subjective and objective measures of phys-
ical activity, multiple health indicators, and multiple age
groups (i.e. infants, toddlers, and preschoolers). Further-
more, the conduct of sub-analyses on dose of physical
activity was a notable strength of the review, as was the
meta-analysis of four adiposity interventions. Finally, the
use of the established GRADE framework to guide the
review and assess the quality of evidence was an add-
itional strength [28].
The present review also had several limitations, in-
cluding English and French language limits for feasibil-
ity, as well as sample size restrictions for both feasibility
and generalizability. It is possible that studies published
in other languages or with smaller sample sizes might
have provided additional insight, especially for health indi-
cators where evidence was limited. Furthermore, while a
meta-analysis was conducted on four included studies,
due to the large heterogeneity of the study designs and
measured outcomes, the majority of findings were based
on a narrative synthesis that weighted all studies equally.
For some health indicators, conclusions from the narrative
synthesis had to be drawn from a small number of studies.
Furthermore, it was not possible to do sensitivity analyses
between higher- and lower-quality evidence because the
vast majority of evidence was “low”to “very low”quality.
Conclusions
This review synthesized evidence from 96 studies on the
health implications of physical activity in the early years.
Physical activity was consistently found to be favourably
associated with a broad range of health indicators. Sev-
eral types of physical activity, especially prone position
for infants, TPA, and physical activity of at least moder-
ate to vigorous intensity, particularly for preschool-aged
children, were consistently found to be favourable with a
number of health indicators. Although it was not pos-
sible to identify the specific frequency and duration of
physical activity needed for health benefits in all age
groups, it was consistently observed that more physical
activity (in terms of frequency or duration) was better
for health. Therefore, it can be concluded that it is im-
portant to promote physical activity in the early years.
The findings of this review will help to inform evidence-
based guidelines to facilitate physical activity promotion
aimed at optimizing the overall health of our youngest
children. Given that the study of physical activity in the
early years is still a relatively new area of inquiry, future
research should focus on addressing a number of gaps
and limitations mentioned in this review, in order to
strengthen the evidence base and accurately inform fu-
ture health promotion efforts.
Additional files
Additional file 1: Search strategies for the systematic review. (DOCX 37 kb)
Additional file 2: Supplementary Tables S1-S8. Summary of studies
included in the systematic review for each health indicator sorted by
(whenever possible) study design, age group, and physical activity
measurement. (DOCX 177 kb)
Abbreviations
BMI: Body mass index; GRADE: Grading of recommendations assessment,
development, and evaluation; LPA: Light-intensity physical activity;
MPA: Moderate-intensity physical activity; MVPA: Moderate- to vigorous-
intensity physical activity; PICO: Population, intervention, comparison, and
outcome; PRISMA: Preferred reporting items for systematic reviews and
meta-analyses; PROSPERO: International prospective register of systematic
reviews; RCT: Randomized controlled trial; TPA: Total physical activity;
VPA: Vigorous-intensity physical activity
Acknowledgements
The authors would like to thank Alejandra Jaramillo Garcia and Véronique Dorais
for methods consultation, Helena Lee for assisting with table organization, Linda
Slater for developing the electronic search strategies, and Chantelle Blair for her
help with locating full-text articles.
Funding
This study was funded by the Canadian Institutes of Health Research (CIHR),
Faculty of Physical Education and Recreation at the University of Alberta,
Canadian Society for Exercise Physiology, Healthy Active Living and Obesity
Research Group at the Children’s Hospital of Eastern Ontario Research Institute,
and the Public Health Agency of Canada. VC and KBA are supported by a CIHR
New Investigator Salary Award. SPU was supported by a Women & Children’s
Health Research Institute (WCHRI) Summer Studentship. LH was supported by
an Australian Government Research Training Program Scholarship. ADO is
supported by a National Heart Foundation of Australia Career Development
Fellowship. BWT is supported by a Canada Research Chair in Child Health &
Exercise Medicine. The funding bodies had no role in the design of the study;
in the collection, analysis, and interpretation of data; or in the writing of the
manuscript. Publication charges for this article have been funded through a
grant from the CIHR (FRN 147990).
Availability of data and materials
Not applicable.
About this supplement
This article has been published as part of BMC Public Health Volume 17
Supplement 5, 2017: 24-Hour Movement Guidelines for the Early Years: An
The Author(s) BMC Public Health 2017, 17(Suppl 5):854 Page 59 of 215
Content courtesy of Springer Nature, terms of use apply. Rights reserved.
Integration of Physical Activity, Sedentary Behaviour, and Sleep. The full
contents of the supplement are available online at https://bmcpublichealth.
biomedcentral.com/articles/supplements/volume-17-supplement-5.
Authors’contributions
VC led the design and coordination of the review. VJP, KBA, IJ, ADO, JCS,
BWT, CG, and MST helped with the design of the review, and EL helped with
the coordination of the review. MS peer reviewed the search strategies for
the review. EL conducted the literature searches, imported records, and
removed duplicates. EL, LH, CJ, SH, NK, JAS, and SPU conducted the screening
of the records, extracted the data, and appraised the quality of evidence. SPU
led the collection of full text-articles. VC led the analysis and interpretation of
data. JAS helped with the analysis and interpretation of frequency and duration
data and GRADE table summaries. EL and JCS assessed the data for meta-analysis.
NK conducted the meta-analysis and the trial registry search and screening. VC
led the writing of the paper and EL assisted with the writing of the background.
All authors were responsible for revising the manuscript critically for important
intellectual content. All authors read and approved the final manuscript.
Ethics approval and consent to participate
Not applicable.
Consent for publication
Not applicable.
Competing interests
The authors declare that they have no competing interests.
Publisher’sNote
Springer Nature remains neutral with regard to jurisdictional claims in
published maps and institutional affiliations.
Author details
1
Faculty of Physical Education and Recreation, University of Alberta,
Edmonton, AB T6G 2H9, Canada.
2
Early Start Research Institute, Faculty of
Social Sciences, University of Wollongong, Wollongong, NSW 2522, Australia.
3
Healthy Active Living and Obesity Research Group, Children’s Hospital of
Eastern Ontario Research Institute, Ottawa, ON K1H 8L1, Canada.
4
School of
Human Kinetics, Faculty of Health Sciences, University of Ottawa, Ottawa, ON
K1N 1A2, Canada.
5
School of Kinesiology and Health Studies, and
Department of Public Health Sciences, Queen’s University, Kingston, ON K7L
3N6, Canada.
6
Child Health & Exercise Medicine Program, Department of
Pediatrics, McMaster University, Hamilton, ON L8S 4K1, Canada.
7
Library and
Media Services, Children’s Hospital of Eastern Ontario, Ottawa, ON K1H 8L1,
Canada.
Published: 20 November 2017
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