Systematic Review of the Health Benefits of Physical Activity and Fitness in School-Aged Children and Youth

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Janssen and LeBlanc International Journal of Behavioral Nutrition and Physical Activity
2010, 7:40
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Review
Systematic review of the health benefits of physical
activity and fitness in school-aged children and
youth
Ian Janssen*
1,2
and Allana G LeBlanc
1
Abstract
Background: The purpose was to: 1) perform a systematic review of studies examining the relation between physical
activity, fitness, and health in school-aged children and youth, and 2) make recommendations based on the findings.
Methods: The systematic review was limited to 7 health indicators: high blood cholesterol, high blood pressure, the
metabolic syndrome, obesity, low bone density, depression, and injuries. Literature searches were conducted using
predefined keywords in 6 key databases. A total of 11,088 potential papers were identified. The abstracts and full-text
articles of potentially relevant papers were screened to determine eligibility. Data was abstracted for 113 outcomes
from the 86 eligible papers. The evidence was graded for each health outcome using established criteria based on the
quantity and quality of studies and strength of effect. The volume, intensity, and type of physical activity were
considered.
Results: Physical activity was associated with numerous health benefits. The dose-response relations observed in
observational studies indicate that the more physical activity, the greater the health benefit. Results from experimental
studies indicate that even modest amounts of physical activity can have health benefits in high-risk youngsters (e.g.,
obese). To achieve substantive health benefits, the physical activity should be of at least a moderate intensity. Vigorous
intensity activities may provide even greater benefit. Aerobic-based activities had the greatest health benefit, other
than for bone health, in which case high-impact weight bearing activities were required.
Conclusion: The following recommendations were made: 1) Children and youth 5-17 years of age should accumulate
an average of at least 60 minutes per day and up to several hours of at least moderate intensity physical activity. Some
of the health benefits can be achieved through an average of 30 minutes per day. [Level 2, Grade A]. 2) More vigorous
intensity activities should be incorporated or added when possible, including activities that strengthen muscle and
bone [Level 3, Grade B]. 3) Aerobic activities should make up the majority of the physical activity. Muscle and bone
strengthening activities should be incorporated on at least 3 days of the week [Level 2, Grade A].
Background
Canada's first set of physical activity guidelines for chil-
dren and youth were introduced in 2002 [1,2]. The basic
recommendation within these guidelines was that chil-
dren and youth, independent of their current physical
activity level, should increase the time they spend on
moderate-to-vigorous intensity physical activity by 30
minutes per day, and over a 5 month period progress to
adding an additional 90 minutes of daily physical activity.
Recently, a narrative literature review was conduced to
provide an update on the evidence related to the biologi-
cal and psycho-social health benefits of physical activity
in school-aged children and youth which has accumu-
lated since the publication of Canada's guidelines [3].
This narrative review explored whether Canada's physical
activity guidelines for children and youth are appropriate,
and made recommendations as to how the guidelines
could be modified to reflect current knowledge.
Several other narrative reviews have examined the rela-
tion between physical activity and health in school aged
children, a small sample of which are referenced here [4-
* Correspondence: ian.janssen@queensu.ca
1 School of Kinesiology and Health Studies, Queen's University, Kingston,
Ontario, Canada
Full list of author information is available at the end of the article

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8]. Although informative, narrative reviews have severe
limitations. First and foremost, it is uncertain as to
whether all of the relevant scientific evidence has been
examined. The authors of a narrative review may be
exclusive with the materials they review, and these mate-
rials may have been selected and interpreted in a biased
manner. Thus, the reader is faced with uncertainty and
doubt when interpreting a narrative review. The reader
may be better served when the choices made in the
review are explicit, transparent, clearly stated, and repro-
ducible. This can be achieved through a systematic
review. Systematic reviews attempt to reduce reviewer
bias through the use of objective, reproducible criteria to
select relevant publications, to synthesize and critically
appraise the findings from these publications, and to
employ defined evidence-based criteria when formulat-
ing recommendations [9].
The purpose of this report was to: 1) perform a system-
atic review of the evidence informing the relation
between physical activity and health in school-aged chil-
dren and youth, defined here as those aged 5-17 years;
and 2) make recommendations on the appropriate vol-
ume, intensity, and type of physical activity for minimal
and optimal health benefits in school-aged children and
youth. A previously developed evaluation system was
used to set the level of evidence and grade for the recom-
mendations. This report was part of a much larger proj-
ect around Canada's physical activity guidelines, and
comparable systematic reviews for adults [10] and older
adults [11] have also been published in the journal. Addi-
tional details on the scope and purpose of the larger proj-
ect [12] and the interpretation of the recommendations
from an independent expert panel [13] can also be found
elsewhere in the journal.
Overview of existing physical activity guidelines for
children and youth
Before conducting the systematic review, this paper pro-
vides a brief overview on existing physical activity guide-
lines for school-aged children, as well as an explanation of
the scientific evidence that informed the guideline devel-
opment process.
The publication of Canada's physical activity guidelines
for children and youth in 2002 represented a joint effort
of the Canadian Society for Exercise Physiology and
Health Canada. Two sets of guidelines were published,
one for children aged 6 to 9 years [2] and a second for
youth aged 10 to14 years [1]. In addition to the physical
activity guides, which highlighted the recommended
physical activity levels for these two age groups, a number
of other promotional and educational packages were
developed, including family booklets [14,15], teacher
booklets [16,17], as well as physical activity magazines for
children [18] and youth [19].
The key recommendations within Canada's child and
youth physical activity guides are:
1) Increase the time currently spent on physical activ-
ity by 30 minutes per day, and progress over approxi-
mately 5 months to 90 minutes more per day.
2) Physical activity can be accumulated throughout
the day in periods of at least 5 to 10 minutes.
3) The 90 minute increase in physical activity should
include 60 minutes of moderate activity (e.g., brisk
walking, skating, bicycle riding) and 30 minutes of
vigorous activity (e.g., running, basketball, soccer).
4) Participate in different types of physical activities -
endurance, flexibility, and strength - to achieve the
best health results.
5) Reduce non-active time spent on watching televi-
sion and videos, playing computer games, and surfing
the Internet. Start with 30 minutes less of such activi-
ties per day and progress over the course of approxi-
mately 5 months to 90 minutes less per day.
Many other countries and organizations have devel-
oped physical activity recommendations for school-aged
children and youth, as recently summarized [3]. With few
exceptions, these countries and organizations recom-
mend that children and youth participate in at least 60
minutes of moderate-to-vigorous intensity physical activ-
ity on a daily basis. One of these recommendations was
published in 2005 as part of a systematic review that
linked physical activity to several health and behavioural
outcomes in school-aged children and youth [20]. This
systematic review was sponsored by the U.S. Centers for
Disease Control and Prevention (CDC) and was devel-
oped by a multidisciplinary expert panel. The expert
panel considered over 850 articles published in 2004 or
earlier, identified by computerized database searches and
by searching the bibliographies of the panellists' own
libraries [20]. Based on conceptual definitions and inclu-
sion and exclusion criteria developed by the panel, partic-
ipants systematically evaluated relevant articles
(primarily intervention studies) for each of the 14 health
and behavioural outcomes considered. On the basis of
their reviews, the panel provided a summary of the evi-
dence for strength (strong, >60% of studies reviewed;
moderate, 30-59% of studies reviewed; and weak, <30% of
studies reviewed) and the direction (positive, null, or neg-
ative) of the effects of physical activity on each of the
health and behavioural outcomes. The strength of evi-
dence was judged from the statistical significance of the
outcomes; it did not include other factors usually consid-
ered in systematic review, such as the effect sizes of phys-
ical activity and the quality and types of studies.
The expert panel reached the following conclusions: (i)
Evidence-based data are strong to conclude that physical
activity has beneficial effects on adiposity (within over-
weight and obese youth), musculoskeletal health and fit-
ness, and several components of cardiovascular health.

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(ii) Evidence-based data are adequate to conclude that
physical activity has beneficial effects on adiposity levels
in those with a normal body weight, on blood pressure in
normotensive youth, on plasma lipid and lipoproteins
levels, on non-traditional cardiovascular risk factors
(inflammatory markers, endothelial function and heart
rate variability), and on several components of mental
health (self-concept, anxiety and depression) [20]. A sum-
mary of evidence concerning the health outcomes exam-
ined by the expert panel is shown in Table 1 [Additional
file 1]. The amount, intensity, and type of physical activity
required to achieve the result, when clear, is also shown
in the table.
In 2008 a second systematic review of literature exam-
ining the relation between physical activity and key fit-
ness and health outcomes within school-aged children
and youth was published. This systematic review was part
of the "Physical Activity Guidelines for Americans" proj-
ect that was undertaken by the Unites States Department
of Health and Human Services [21]. Unlike the 2005 CDC
sponsored systematic review that focused on intervention
studies, the 2008 review considered both observational
and experimental studies. The 2008 systematic review
concluded that few studies have provided data on the
dose-response relation between physical activity and var-
ious health and fitness outcomes in children and youth.
However, substantial data indicate that health and fitness
benefits will occur in most children and youth who par-
ticipate in 60 or more minutes of moderate-to-vigorous
physical activity on a daily basis. For children and youth
to gain comprehensive health benefits they need to par-
ticipate in the following types of physical activity on 3 or
more days per week: vigorous aerobic exercise, resistance
exercise, and weight-loading activities.
Although informative, the recommendations made
within the 2005 and 2008 systematic reviews did not
include a level of evidence or grade, which are now
becoming a routine part of evidence based reviews. The
level of evidence helps inform the reader about the
strength of evidence that informed the recommendation.
The grade considers the harms and benefits of imple-
menting the intervention, and informs the reader about
whether an intervention should be implemented.
Questions addressed in systematic review
The following questions were addressed in this system-
atic review:
1) How much (volume) physical activity is needed for
minimal and optimal health benefits in school-aged chil-
dren and youth? To address this question careful consid-
eration was given to whether dose-response relations
existed between physical activity and fitness with the var-
ious health outcomes, and if so, the pattern of these rela-
tions (e.g., linear, or curvilinear relations with large
improvements in health occurring with limited increases
in physical activity at the low end of the physical activity
scale, or curvilinear relations with small improvements in
health occurring with increases in physical activity at the
low end of the physical activity scale).
2) What types of activity are needed to produce health
benefits? Specific consideration was given to what types
of activity (aerobic, resistance, etc.) influenced the differ-
ent health outcomes, and whether more than one type of
activity would be needed for overall health and well-
being.
3) What is the appropriate physical activity intensity?
Attention was given to the intensity of physical activity
measured (observational studies) or prescribed (experi-
mental studies). An underlying assumption was that chil-
dren and youth would prefer lower intensity activities
over higher intensity activities. Therefore, for higher
intensity activities to be recommended over lower inten-
sity activities there would need to be either: i) no evi-
dence that low intensity activities were beneficial for
health and evidence that higher intensity activities
impacted health in a favorable manner, or ii) clear evi-
dence that higher intensity activities impacted the health
outcomes to a greater extent than lower intensity activi-
ties.
4) Do the effects of physical activity on health in school-
aged children and youth vary by sex and/or age? Results
were examined to see if: i) the moderating effects of sex
and/or age on the relations between physical activity and
health were explored, and if not, iii) whether there were
consistent patterns across studies (either statistically or in
order of magnitude) that were suggestive of sex or age dif-
ferences.
Methods
Eligibility criteria
This systematic review was limited to key indicators of
different health outcomes known to be related to physical
activity in school-aged children and youth. Decisions on
what health outcomes to include in the systematic review
were made by examining what outcomes were studied in
previously conducted reviews of this nature [20,21] and
in consultation with the Steering Committee for the
Canadian Physical Activity Guidelines project. These key
indicators consisted of:
1) High blood cholesterol, high blood pressure, and
markers of the metabolic syndrome as a measure of
cardiometabolic risk
2) Overweight/obesity as a measure of adiposity
3) Low bone density as a measure of skeletal health
4) Depression as a measure of mental health
5) Injuries as a negative health outcome of physical
activity

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We recognized that although cardiorespiratory and
musculoskeletal fitness are partially genetic in origin,
they are in large measure a reflection of physical activity
participation in recent weeks and months [22]. Therefore,
the systematic review also included studies that examined
the relation between fitness and health. For our purposes,
fitness was assumed to be a proxy measure of physical
activity. Any studies evaluating the relationship between
physical activity or fitness and one or more of the key
health outcomes listed above within school-aged children
and youth were eligible for inclusion.
In consultation with the Steering Committee of the
Canadian Physical Activity Guidelines and Measurement
Project and the authors who were completing the adult
and older adult systematic reviews, a decision was made
to limit the pediatric systematic review to: 1) studies
examining the key health indicators above, and 2) for
observational studies, the outcomes must have been mea-
sured in a dichotomous (yes or no) manner and presented
as prevalences or ratio scores (odds ratio, relative risk,
hazard ratio). This decision was made for three reasons:
(i) to help ensure that the systematic review would be
manageable in size and scope for a single research team
to complete in a timely manner, (ii) to eliminate many of
the observational studies with small sample sizes, and (iii)
to ensure that the health outcomes, at least for the obser-
vational studies, were presented in a reasonably consis-
tent pattern from study to study. This helped us to make
comparisons between studies and to characterize the
magnitude of effect for physical activity.
To further illustrate why the aforementioned limita-
tions were put in place, consider the following. Within
children and youth physical activity has been related to
over two dozen different health outcomes. For adiposity
alone, several adiposity measures have been considered
including body weight, BMI, several skinfold and circum-
ference measures, total body fat, and several specific
body fat depots. Preliminary literature searches on adi-
posity - as measured using both continuous (e.g., body
weight, BMI, visceral fat, skinfolds) and categorical (over-
weight/obese vs. normal weight) outcomes to capture the
measures indicated above, revealed over 15,000 pub-
lished papers. The results from these papers were pre-
sented in several formats including comparison of group
means for continuous adiposity measures according to
physical activity level, relations between continuous adi-
posity and physical activity measures which were pre-
sented in a variety of ways (e.g., r values, regression
coefficients); comparison of group means for physical
activity according to adiposity status; ratio scores (odds
ratios, relative risks, hazard ratios) for the prediction of
obesity status according to physical activity level; com-
parison of the prevalence of obesity according to physical
activity level; etc. Without employing some criteria to
limit the types of measures and outcomes, it would have
been virtually impossible to synthesize the results from
these studies.
Cross-sectional studies, case-control studies, cohort
studies (prospective and retrospective) and intervention
studies (including randomized and quasi experimental
designs) were eligible for inclusion in the systematic
review. Only published, English language studies includ-
ing human participants were included. To be included
studies had to be limited to school-aged children and
youth between 5-17 years of age, or present data specifi-
cally for a subgroup of participants within this age range.
For the observational studies, there were no limitations
placed on the form of physical activity (e.g., question-
naire, activity diary, pedometer, accelerometer) or fitness
(cardiorespiratory or musculoskeletal fitness) measure-
ments. For intervention studies, all cardiorespriatory
and/or musculoskeletal based interventions were eligible
for inclusion. Intervention studies were excluded if they
included a dietary (e.g., caloric restriction) or other
behavioral risk factor component (e.g., smoking cessa-
tion) that may have independently affected the health
outcomes and subsequently made it impossible to distin-
guish the independent effect of the physical activity por-
tion of the intervention.
Search strategy
Literature searches were conducted in MEDLINE (1950-
January 2008, OVID Interface), EMBASE (1980-January
2008, OVID Interface), CINAHL (1982-January 2008,
OVID Interface), PsycINFO (1967-January 2008, OVID
Interface), all Evidence-Based Medicine Reviews (1991-
January 2008, OVID Interface), and SPORTDiscus (up to
January 2008, EBSCO Interface).
The electronic search strategies were executed by a sin-
gle researcher (AB) under direction of the primary author
(IJ). They were not restricted by publication type or study
design; however, they were limited to human participants
and English language. The following string of search
terms were used for each of the study outcomes to iden-
tify physical activity related papers conducted within the
age group of interest: ('physical activity' OR 'fitness' OR
'exercise' OR 'energy expenditure') AND ('child' OR 'ado-
lescent' OR 'youth' OR 'juvenile'). The following search
terms were added (e.g., AND) for the cholesterol search:
('high cholesterol' OR 'hypercholesterolemia' OR 'hyper-
lipidemia' OR 'dyslipidemia'). For hypertension the fol-
lowing search terms were added: ('high blood pressure'
OR 'hypertension'). For metabolic syndrome the follow-
ing search terms added: ('metabolic syndrome' OR 'syn-
drome X' OR 'deadly quartet' OR 'plurimetabolic
syndrome' OR 'insulin resistance' OR 'insulin resistant').
For obesity the following search terms were added:
('obese' OR 'obesity' OR 'overweight'). For low bone min-
eral density the following search terms were added:
('bone density' OR 'bone strength' OR 'bone mass' OR

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'bone mineral density'). For depression the following
search terms were added: ('depression' OR 'mood disor-
der'). For injuries the following search terms were added:
('injury' OR 'injuries').
A total of 42 electronic searches were performed (7
health outcomes × 6 search engines) and the information
from each search was saved as a text file that included all
of the retrieved citations. Using SAS software version 9
(SAS Institute, Carry, NC), the text files were separated
back into individual citations and exported into a Micro-
soft Access database. The database included the follow-
ing information for each citation: unique identifier for
the database, paper title, authors, journal name, volume
and issue number, page numbers, and the abstract. See
Figure 1 for an illustration of the Microsoft Access data-
base form. Within the Microsoft Access database, dupli-
cate citations - those citations that were identified in
more than one of the search engines and/or for more
than one of the health outcomes - were identified by a
match of the title and were removed using automated
procedures.
Screening of citations
After duplicate citations were removed from the Access
database, the abstract of each citation was reviewed by a
single reviewer to determine if it should be included
within the systematic review. The full-text articles of all
potentially relevant citations were obtained, and saved as
Adobe-PDF files that were linked to the Access database.
Whenever it was uncertain as to whether a citation was
appropriate, the full-text copy was obtained. After the
first reviewer screened the database, the citations that
were deemed ineligible were reviewed by a second
reviewer to determine if any potentially relevant citations
were missed, and full-text copies of these citations were
also obtained. Copies of all of the full-text articles were
then reviewed by the two reviewers for inclusion criteria;
if uncertain as whether or not to include an article, the
article in question was reviewed again until a final deci-
sion was made.
Data abstraction
A single reviewer (AL) abstracted data from all eligible
full-text citations using an electronic data abstraction
form. Refer to Figure 2 for an illustration of electronic
data abstraction form. The data abstraction was com-
pleted in a second Microsoft Access Database, which was
linked to the first Microsoft Access Database using a
unique identifier. The abstracted data included informa-
tion on the study design, participants, details of the phys-
Figure 1 Copy of electronic abstract review form.

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ical activity (or fitness) measures or interventions, and
key findings. After data abstraction was completed, the
information was checked by a second reviewer (IJ) and
corrected when necessary.
Assigning levels of evidence and formulation of
recommendations
The goal was to use a rigorous, evidence-based approach
to develop levels of evidence on the relation between
physical activity and health in school-aged children that
could be used to formulate recommendations for the spe-
Figure 2 Copy of electronic database abstraction form.

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cific volume, intensity, and type of physical activity
needed. At present there is no universally accepted
method for formulating evidence-based recommenda-
tions. In consultation with the Steering Committee for
this project and the authors performing the systematic
reviews in adults and older adults, we chose to use the
process that was recently employed for the development
of Canada's obesity prevention and management guide-
lines [23]. Within this system, the level of evidence for a
recommendation is based on an objective appraisal of the
literature according to a pre-specified scale as reflected
by the study designs and quality. As shown in Table 2
[Additional file 2], the level of evidence can range from 1
(highest) to 4 (lowest). The grade for a recommendation
reflects the level of evidence and several additional fea-
tures, including: benefits and risks of physical activity
participation, magnitude of the effects, cost of the inter-
vention, and value of an intervention to an individual or
population. As indicated in Table 3 [Additional file 3], the
grade for the recommendation may be an A, B, or C. Note
that while the level of evidence assigned is not necessarily
linked to the corresponding grade, a high grade is less
likely in the setting of low-quality of evidence.
Note that the level of evidence in the aforementioned
grading system is based in part on the quality of the stud-
ies. This grading was particularly relevant for experimen-
tal studies wherein the level of evidence would change
from Level 1 to Level 2 based on whether or not the ran-
domized controlled trials (RCTs) have important limita-
tions. A single investigator (IJ) assessed the quality of the
RCTs included in this systematic review using the vali-
dated checklist developed by Downs and Black [24]. This
27-item checklist assess the quality of reporting (e.g., are
the interventions of interest clearly described, have all the
adverse events that may be a consequence of the inter-
vention been reported), external validity (e.g., were the
subjects representative of the population), internal valid-
ity (e.g., was an attempt made to blind those measuring
the outcome, were the outcome measures accurate),
selection bias (e.g., were the study subjects randomized,
was randomization assignment concealed until recruit-
ment was complete), and statistical power.
To evaluate the magnitude of effect of physical activity
on the various health outcomes examined, in addition to
statistical significance, the following criteria were applied
to evaluate the strength of the ratio scores (odds ratio, rel-
ative risk, hazard ratio) for the observational studies. For
positive associations 1.01-1.50 = weak association, 1.51-
3.00 = moderate association, and 3.01 or higher = strong
association. For negative associations: 0.71-0.99 = weak
association, 0.41-0.70 = moderate association, 0.00-0.40 =
strong association [25]. For the experimental studies,
measures of effect were calculated based on Cohen's d,
which was calculated as the difference between the pre-
and post-treatment mean within a given treatment group
divided by the average of the standard deviation of the
pre- and post-treatment means [26]. Cohen's d effect
measures ≥ 0.49 were considered to be weak, values rang-
ing from 0.50-0.79 were considered to be moderate, and
values ≥ 0.80 were considered to be strong [26]. Note that
several experimental studies did not report the informa-
tion required to calculate Cohen's d, and for these studies
effect measures have not been presented.
When possible (e.g., at least 4 studies) we performed
meta-analyses to calculate summary odds ratio and
Cohen's d effect size measures for the observational and
experimental studies, respectively [27]. These summary
estimates represent a weighted average of the estimates
provided in the various studies included in the meta-anal-
ysis. These meta-analyses were performed separately for
each health outcomes, separately for observational and
experimental studies, and separately based on type of
physical activity measurement or exercise modality pre-
scribed.
Results
Literature review
The flow of citations through the systematic review pro-
cess is shown in Figure 3. For each of the 7 health out-
comes, several citations were retrieved in more than one
Figure 3 Flow of articles through the systematic review.

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of the 6 search engines. After removing duplicates, a total
of 437 citations were identified for cholesterol, 1151 for
depression, 2505 for injury, 1181 for bone density, 1677
for blood pressure, 5824 for obesity, and 1677 for the
metabolic syndrome. Thus, the grand total was 13174.
Many of these 13174 citations were retrieved for 2 or
more health outcomes, and after removing these dupli-
cates there was a total of 11,088 unique citations. After
the titles and abstracts of these 11,088 citations were
reviewed, full-text copies of 454 potentially relevant cita-
tions were obtained and reviewed. Of these 454 citations,
86 unique citations passed the eligibility criteria and were
included in the systematic review. Several of these 86
citations included results for 2 or more of the 7 relevant
health outcomes.
Cholesterol and blood lipids
A total of 9 articles examining blood lipids and lipopro-
teins met the inclusion criteria. Only one of these studies
was observational in nature [28]. This cross-sectional
study was conducted on a representative sample (n =
3110) of 12-19 year old American adolescents and mea-
sured cardiorespiratory fitness using a submaximal tread-
mill test. The results indicated that unfit girls, defined as
the lowest 20% fit, were 1.89 (95% confidence interval:
1.12-3.17) times more likely to have hypercholesterolemia
and 1.03 (0.74-1.43) times more likely to have a low HDL-
cholesterol by comparison to moderately and high fit
girls. Unfit boys were 3.68 (2.55-5.31) times more likely to
have hypercholesterolemia and 1.25 (0.79-1.95) times
more likely to have a low HDL-cholesterol by comparison
to moderately and high fit boys.
A total of 8 experimental studies (6 RCT, 2 non-ran-
domized) examined the effect of exercise interventions
on changes in blood lipids and lipoproteins, as summa-
rized in Table 4 [Additional file 4] [29-36]. For the most
part, these studies were limited to children and youth
with high cholesterol levels [30] or obesity [29,32,34,36]
at baseline. The sample sizes were quite small and only 2
of these interventions included more than 37 participants
[32,36]. The interventions ranged from 6 to 24 weeks in
duration and included anywhere from 1 to 4 hours per
week (9-34 minutes per day on average) of prescribed
exercise. Six of the 8 exercise programs included various
forms of moderate-to-vigorous physical activity as
explained in the methods sections of the papers.
The results from these intervention studies were mixed.
The 5 studies that were based on aerobic exercise alone
observed significant improvements in at least one lipid/
lipoprotein variable. The summary effects size measures
(95% confidence interval) for the aerobic exercise inter-
ventions were -3.03 (-3.22, -2.84) for triglycerides and
0.26 (0.03, 0.49) for HDL-cholesterol. The interventions
that were based on resistance training [33] and circuit
training [34] reported small and/or insignificant changes
for all of the lipid/lipoprotein variables examined, and the
effect sizes within these studies tended to be quite small
(eg, <0.5). Not surprisingly, the interventions that pro-
duced significant changes were also based on the studies
that employed the largest sample sizes. This suggests that
many of the studies were underpowered.
Due to the design of these interventions (eg, only one
dose of exercise prescribed in a given study), the nature of
the dose-response relation between exercise and blood
lipids in children and youth remains unclear. Further-
more, the interventions that produced favorable effects
on blood lipids did not tend to prescribe higher volumes
or intensities of exercise by comparison to the interven-
tions that did not produce significant changes. The favor-
able interventions were, however, based on 'high risk'
participants, implying that low volumes of moderate-to-
vigorous exercise may be beneficial for youngsters at the
greatest risk.
The effects of age and sex have not been adequately
addressed in the existing literature. Thus, conclusions
cannot be made on the moderating effects of these demo-
graphic characteristics on the relation between physical
activity and blood lipids in school-aged children and
youth.
High blood pressure
A total of 11 articles examining high blood pressure met
the systematic review inclusion criteria. Three of these
studies were observational in nature (2 cross-sectional,
one prospective cohort) (Table 5) [Additional file 5]
[28,37,38]. Of these 3 studies, one relied on self-reported
measures of physical activity [37] and the remaining two
measured cardiorespiratory fitness [28,38]. Within all 3
observational studies the relations between physical
activity or fitness with hypertension were weak in magni-
tude (e.g., odds ratios <1.5), and in one case [28] was
insignificant. Only one study examined more than 2 lev-
els of physical activity or fitness (e.g., compared risk esti-
mates across at least 3 groups), and thus was able to
provide some insight into the dose-response relation.
Within that study only participants within the least fit
quartile were more likely to have hypertension relative to
participants in the most fit quartile, a finding that was
consistent in boys and girls [38].
Eight experimental studies, 4 of which were RCTs,
examined the influence of exercise interventions on
changes in blood pressure (Table 6) [Additional file 6]
[29,33,34,39-43]. Most of these studies were limited to
children and youth with high blood pressure [39-42] or
obesity [29,34]. The sample sizes were quite small; only
one of these studies included more than 37 participants
[42]. The interventions ranged from 4 to 25 weeks in
duration. With one exception [43], the interventions

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included between 60 to 180 minutes/week of prescribed
exercise. This equates to 9 to 30 minutes/day when aver-
aged over a week.
Despite the small sample sizes, the results from these
intervention studies were positive with reports of signifi-
cant reductions in systolic blood pressure in response to
aerobic exercise training, with effect sizes that all tended
to be large (>0.80) [29,39,41-43]. Two of the aerobic based
interventions also reported significant reductions (~6%
to 11%) in diastolic blood pressure [34,39]. The summary
effect size measures for the aerobic exercise interventions
were -1.39 (-2.53, -0.24) for systolic blood pressure and -
0.39 (-1.72, 0.93) for diastolic blood pressure. Unlike the
aerobic-based exercise programs, only two of the four
studies that employed other training modalities, such as
resistance exercise, reported a significant effect on blood
pressure [33,40], with small to modest effect sizes being
observed. The summary effect size measures for the non-
aerobic exercise interventions were -0.61 (-2.27, 1.05) for
systolic blood pressure and -0.51 (-2.18, 1.06) for diastolic
blood pressure.
Because the aerobic exercise intervention studies pre-
scribed similar volumes and intensities of exercise, and
because they found comparable reductions in blood pres-
sure, the effects of the volume and intensity (moderate vs.
vigorous) of exercise on blood pressure remain unclear.
Due to limited variations in the age of the participants in
these studies, the effects of age on the relation between
exercise and blood pressure remains unclear. Most of the
studies included both males and females, suggesting that
aerobic exercise is effective at controlling blood pressure
within box sexes.
Metabolic syndrome
The metabolic syndrome has received considerable
research attention in recent years in both adults and
youngsters. Sixteen articles examining the metabolic syn-
drome met the inclusion criteria. The metabolic syn-
drome components (e.g., abdominal obesity,
triglycerides, insulin, HDL-cholesterol, inflammatory
markers, etc.) and criteria (e.g., cut-points used to define
high-risk values) employed in these studies varied consid-
erably. Eight of the 17 identified studies were observa-
tional in nature (7 cross-sectional, 1 prospective), as
summarized in Table 7 [Additional file 7] [28,44-51].
Many of these observational studies examined large and
heterogeneous samples of participants, suggesting that
the findings are quite generalizable to the general popula-
tion. Of the 3 cross-sectional studies that employed self-
reported measures of physical activity, the reported rela-
tions with the metabolic syndrome were either weak or
modest in strength, and all were non-significant
[45,48,49]. The summary odds ratio for the least active
group relative to the most active group in these 3 studies
was 1.68 (95% confidence interval: 1.22, 2.31). By compar-
ison, the study that used accelerometers to measure phys-
ical activity in an objective manner [51] and the 4 studies
that used direct measures of cardiorespiratory fitness
[28,46,47,50] all reported strong and significant relations
with the metabolic syndrome. The summary odds ratio
for the least fit group relative to the most fit group in the
4 studies that measured fitness was 6.79 (95% confidence
interval: 5.11, 9.03). Further examination of these later
studies revealed clear dose-response relations; however,
the nature (e.g., linear or curvilinear) of the dose-
response relation is unclear. In addition, comparison of
the risk estimates in males and females suggests that the
relation between physical activity and fitness with the
metabolic syndrome is stronger in males. The influence
of age on these relations remains uncertain.
Eight experimental studies, 5 of which were RCTs,
examined the effect of exercise interventions on changes
in markers of the metabolic syndrome, primarily in the
form of fasting insulin and insulin resistance (Table 8)
[Additional file 8] [32-34,36,52-55]. All but one of these
studies was conducted in an overweight/obese sample
[33]. The number of participants included in these stud-
ies was modest, with all but a single study being limited to
52 participants or less [36]. The exercise interventions
ranged from 6 to 40 weeks in duration and included any-
where from 80 to 200 minutes per week (10-30 minutes
per average day) of prescribed exercise. About half of the
exercise programs were aerobic in nature.
The results from these 8 studies were mixed (Table 8).
All of the 4 interventions that focused on aerobic exercise
observed significant improvements in at least one of the
insulin variables examined. Conversely, only one of the
four interventions that employed resistance or circuit
training observed any meaningful improvements [54].
The summary effect size measures (95% confidence inter-
val) for fasting insulin in the aerobic and resistance exer-
cise interventions were -0.60 (-1.71, 0.50) and -0.31 (-
0.82, 0.19), respectively. No intervention studies system-
atically considered the influence of the dose or intensity
of exercise, or sex and age effects, on markers of the met-
abolic syndrome. More research is needed to address
these issues.
Overweight and obesity
The relation between physical activity and fitness with
obesity in school-aged children and youth has been
extensively studied. A total of 31 observational studies (24
cross-sectional, 3 prospective cohort, 2 case-control, 1
mixed) were retrieved that met the appropriate inclusion
criteria, as summarized in Table 9 [Additional file 9] [56-
86]. Overweight and obesity were classified using age-
and gender-specific body mass index (BMI) criteria (e.g.,
BMI z-scores) in the majority of these observational stud-

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ies. The majority of these studies assessed physical activ-
ity or sport participation using self- or parental-reported
tools. These studies tended to report weak to modest
relationships between physical activity and overweight/
obesity, with many risk estimates being non-significant.
Of the 25 available data points, the median odds ratio for
overweight/obesity in the least active group relative to
the most active group was 1.33. It is noteworthy that the
studies that assessed moderate-to-vigorous intensity
physical activities alone were more consistently and
strongly related to obesity than the studies that included
low intensity activities within the physical activity mea-
sure.
Four studies were identified that employed objective
measures of physical activity, including one study that
used pedometers [73] and 3 studies that used accelerome-
ters [59,67,83]. These studies tended to report significant
relations between physical activity with overweight/obe-
sity that were strong in magnitude. Of the 8 available data
points for cross-sectional findings, the median odds ratio
was 3.79. An additional 4 studies measured the relation
between cardiorespiratory fitness and obesity [75,76,82].
All of these studies reported significant relations between
physical activity and fitness with overweight/obesity that
were modest to strong in magnitude.
Several of the observational studies examining over-
weight and obesity presented analyses that were stratified
by sex [56-58,60,64,67,71,73-75,77,79,81]. Although sex
differences were rarely tested for using the appropriate
statistical techniques, visual inspection of the risk esti-
mates provided suggests that in 12 of the 14 studies the
associations between physical activity and fitness with
obesity were stronger in males than in females.
Many of the observational studies presented their
results in a manner that permitted the dose-response
relations with obesity to be examined
[57,59,61,62,64,65,69,71,73,74,79,80,82,84]. From these
studies it is apparent that a dose-response relation
between physical activity and obesity exists. However, the
pattern of this dose-response relation is unclear as some
studies observed linear patterns and others observed cur-
vilinear patterns.
In addition to the observational studies discussed
above, 24 intervention studies, 17 of which were RCTs,
examining changes in obesity measures were included in
the systematic review (Table 10) [Additional file 10]
[29,32,34-36,39,42,43,52-55,87-98]. It is important to
note that in many of these studies the primary aim of the
intervention was to improve other health measures (e.g.,
blood lipids, insulin resistance, and bone density) and not
obesity measures per se. These studies examined several
different measures of total (% fat, BMI, weight) and
abdominal (waist circumference, trunk fat, visceral fat)
adiposity. The studies ranged in length from 4 weeks to 2
years, with most being 4 to 6 months in duration. The
amounts of exercise prescribed typically ranged from 2 to
3.5 hours per week, which averages out to 17 to 30 min-
utes per day. Half of the studies were limited to over-
weight and obese participants.
About 50% of the exercise interventions that were aero-
bic in nature observed significant changes in measures of
BMI, total fat, and/or abdominal fat in response to train-
ing. Only 3 of the 17 studies that employed other training
modalities (resistance training, circuit training, pilates,
jumping exercises) observed significant improvements in
measures of total fat, abdominal fat, or BMI in response
to training. The effect sizes, even for the studies that
found significant improvements, tended to be small
(<0.50). For the interventions that were based on aerobic
exercise, the summary effect size measures were -0.40 (-
1.10, 0.31) for % body fat and -0.07 (-0.89, 0.75) for BMI.
For the resistance exercise intervention, the summary
effect size calculation for % body fat was -0.19 (-1.55,
1.18).
Variations in the effects of age, sex, and exercise dose
on changes in obesity measures in response to exercise
training have not been systematically addressed in the lit-
erature. Thus, no conclusions can be drawn on the poten-
tial moderating effects of these variables.
Bone mineral density
Many observational studies have examined the relation
between physical activity and continuous measures of
bone mineral density such as bone mineral content values
in grams, bone density values in g/cm2, and cortical bone
area measures in cm2 (see review [99]). However, no
observational studies in the literature search met the sys-
tematic review criteria of predicting a low bone mineral
density as a dichotomous outcome.
As summarized in Table 11 [Additional file 11], a total
of 11 experimental studies examining changes in bone
mineral density in response to exercise training were
retrieved in the systematic review [55,88-94,100-103].
Two of these studies presented identical data on the same
group of participants, and were therefore presented as a
single study in the table [101,102]. The physical activity
programs employed in these interventions typically con-
sisted of moderate-to-high strain anaerobic activities
such as impact resistance training, high impact weight
bearing, and jumping. These programs were performed
anywhere from 3 to 60 minutes in length on at least 2 or 3
days of the week, and lasted from a few months to 2 years
in duration.
The results from these studies, although not undis-
puted, indicate that as little as 10 minutes of moderate-
to-high impact activities performed on as little as 2 or 3
days of the week can have a modest effect on bone min-
eral density when combined with more general weight

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bearing aerobic activities that are also beneficial for car-
diovascular risk factors and obesity prevention (e.g., jog-
ging, play, etc.).
Depression
Only 6 studies on depression and related symptoms met
the inclusion criteria. Table 12 [Additional file 12] out-
lines the 3 observational studies [104-106]. These were all
cross-sectional in design, used self-reported measures of
physical activity, and reported small and insignificant
[104,106] or modest [105] relations between physical
activity and depression. Interestingly, within the later
study the relation between physical activity and depres-
sion were more evident at a moderate intensity of physi-
cal activity than at a vigorous intensity of physical activity
[105].
The 3 experimental studies that examined changes in
depression [107-109], all of which were RCTs based on
aerobic exercise, are outlined in Table 13 [Additional file
13]. The volume of exercise prescribed in these studies
was very modest (60 to 90 minutes per week). All three of
these studies observed significant improvements in at
least one depressive symptom measure in response to 8
to 12 week exercise programs. The effect sizes were small
to modest in these studies, with very broad 95% confi-
dence intervals. One of the studies included both high
intensity and moderate intensity exercise programs, and
only the high intensity program resulted in significant
improvements in depression scores in comparison to the
control group, which performed flexibility exercises
[108].
Injuries
Injuries are a leading cause of disability and mortality in
young people. It has been reported that approximately
50% of medically treated injuries within 6th to 10th grade
Canadian youth occur during physical activity [110].
Thus, it is not surprising that there is an extensive litera-
ture on physical activity and injuries in the pediatric pop-
ulation (see review [111]). However, most of the
published information is limited to groups of participants
that have all been injured or groups of participants com-
prised entirely of athletes (eg, football players, ballet
dancers).
Only 3 articles examining injury met the inclusion cri-
teria for this systematic review [112-114]. These studies
were all cross-sectional in nature and relied on self- or
parental-reported measures of physical activity and
sports participation (Table 14) [Additional file 14]. These
studies examined medically treated injuries; however,
limited or no information on the severity of and long-
term recovery from these injuries was presented. All 3 of
the studies reported higher rates of injury in physically
active children and youth compared with inactive chil-
dren and youth. Furthermore, within all 3 of the papers
there was clear evidence of a dose-response relation
between physical activity participation and the likelihood
of injury. That is, as the physical activity level increased,
the likelihood of injury increased in a graded fashion.
One study assessed vigorous sports, and within that study
the risk estimates for injury within the most active group
would be considered high [114]. Conversely the risk esti-
mates for injury were modest within the 2 studies that
measured moderate-to-vigorous intensity activities
[112,113]. The quality of the evidence for the injury out-
come, which is based on cross-sectional studies, is lim-
ited as cross-sectional research only provides a low level
of evidence. Follow-up (incidence) studies that also take
into consideration the volume of sports participation
would provide a more powerful level of evidence.
Quality assessment of RCTs
The RCTs that are listed within the summary tables con-
tained several significant limitations. The study samples
were small, and non-representative. Although few of the
studies addressed the issue of statistical power, the lack of
power was clearly an issue. Specifically, for a number of
the health outcomes, the RCTs in which significant find-
ings were observed were also the RCTs with the largest
sample sizes. Almost without exception, the RCTs
included in the systematic review did not report adverse
events for the physical activity interventions (e.g., inju-
ries), provided little or no detail on the drop-outs, and did
not perform intent-to-treat analyses. Given the consis-
tency of these limitations across studies, Level 2 was the
highest level that could be assigned to any of the recom-
mendations.
Discussion
Recommendations based on systematic review
Recommendation #1
Children and youth 5-17 years of age should accu-
mulate an average of at least 60 minutes per day and
up to several hours of at least moderate intensity phys-
ical activity. Some of the health benefits can be
achieved through an average of 30 minutes per day.
[Level 2, Grade A]
There is strong and consistent evidence based on
experimental studies for several health outcomes that
participating in as little as 2 or 3 hours of moderate-to-
vigorously intense physical activity per week is associated
with health benefits. Evidence from observational studies
also demonstrates dose-response relations between phys-
ical activity and health, with differences in health risk
between the least active (or fit) and the second least
active (of fit) groups. Thus, it would seem appropriate to
set minimal physical activity targets that reflect a low
level of physical activity (see Recommendation #1). Fur-

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thermore, the current recommendation of 90 minutes
more per day (Canadian) or 60 minutes per day (US, UK,
Australian) may be quite intimidating, particularly for
children and youth who are very inactive. From a behav-
iour modification perspective, having a target that seems
out of reach may actually undermine physical activity
participation [115].
That being said, with the exception of injuries, the
dose-response evidence from observational studies for
several health outcomes suggests that more physical
activity will be better, and that additional health benefits
can still be achieved at the higher end of the physical
activity spectrum. Therefore, it would also seem appro-
priate to set higher physical activity targets (60 minutes
and up to several hours) that would elicit more pro-
nounced health benefits for those children and youth
who are already somewhat active (see Recommendation
#1). This approach is consistent with recommendations
made by the U.S. National Association for Sports and
Physical Education[116] and the Australia Department of
Health and Ageing [117], both of whom have recom-
mended that children and youth participate in at least 60
minutes, and up to several hours, of moderate to vigorous
intensity physical activity every day.
This type of dual message provided in Recommenda-
tion #1 will hopefully encourage children and youth who
are very inactive to engage in at least a modest amount of
physical activity, while at the same time encourage mod-
erately active children and youth to achieve even greater
benefits by becoming more active. The minimal and opti-
mal doses of physical activity required for good health in
children and youth remain unclear, and more carefully
conducted dose-responses studies are warranted in the
pediatric age range.
Previous physical activity recommendations and guide-
lines for school-aged children and youth indicate that a
high volume of physical activity needs to be performed
everyday. The need for children and youth to engage in
physical activity on a daily basis to maintain good health
was not supported by the evidence reviewed here. In
other words, it is unknown as to whether a child who
accumulates 7 hours of activity over the week, with one
hour being performed on each day, would have any
greater health benefits than a child who accumulates 7
hours of activity over the week, with different amounts of
activity being performed each day (including some days
with no activity). Thus, the recommendation made in this
systematic review calls for an "average" of at least 60 min-
utes per day instead of at least 60 minutes everyday.
Future studies need to address whether a "days per week"
recommendation is warranted. In addition, future studies
within children and youth should consider whether the
daily physical activity needs to be accumulated in bouts
of at least a few minutes in duration (eg, 5 or 10 minutes).
Most children accumulate the majority of their physical
activity in a very sporadic manner (eg, a couple of min-
utes here and there), and new evidence suggests that this
sporadic pattern of activity may not be as beneficial as
bouts of activity that last at least 5 minutes in length
[118].
Given the positive effect of physical activity on 6 of the
7 health outcomes examined, including observations
from several large and diverse samples, this Recommen-
dation was assigned a Grade A.
Recommendation #2
More vigorous intensity activities should be incorpo-
rated or added when possible, including activities that
strengthen muscle and bone. [Level 3, Grade B].
Moderate intensity activity in children and youth has
been defined in a variety of ways, depending on the
method chosen to measure physical activity. The lower
threshold of moderate intensity activity is usually defined
as 4 METS (4 × resting metabolic rate), although it is not
uncommon for investigators to use 3 METS. In general,
the lower threshold of vigorous intensity activity is usu-
ally defined as 7 METS (7 × resting metabolic rate) in
children.
The majority of observational studies have focused on
measuring moderate-to-vigorous intensity physical activ-
ity. Furthermore, the relations between overall physical
activity (including low intensity activities) and obesity do
not appear to be as strong or consistent as the relations
between moderate-to-vigorous intensity activity and obe-
sity. In addition, the intervention studies included within
this systematic review almost exclusively prescribed
physical activity of at least a moderate intensity. Thus,
while it is clear that moderate and vigorous intensity
activities are associated with many health benefits, the
same is not true for low intensity activity. Therefore, Rec-
ommendation #1 indicates that the physical activity
should be of at least a moderate intensity. More consider-
ation on the impact of low intensity activities on health
should be given in future studies.
The next question to address is whether vigorous inten-
sity activities provide benefits above and beyond that of
moderate intensity activities. Regrettably, few studies
have systematically addressed this question. The available
information suggests that vigorous intensity activities
provide additional health benefits beyond modest inten-
sity activities. Furthermore, many of the experimental
studies that observed significant changes in the health
variables examined prescribed exercise that would fall
within the vigorous intensity or upper-end of the moder-
ate intensity range. Recommendation #2, therefore, sug-
gests that vigorous intensity activities should be included
when possible. This recommendation was assigned a
lower level of evidence (Level 3) because of the limited
amount of evidence and the inconsistency in the evidence

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that is available. This recommendation was given a lower
grade (Grade C) because of the potential increase in
injury risk associated with more vigorous intensity activi-
ties and sports. However, the injury data is weak and
future studies, particularly intervention studies, should
examine and report on injuries associated with physical
activity in children.
Recommendation #3
Aerobic activities should make up the majority of the
physical activity. Muscle and bone strengthening activ-
ities should be incorporated on at least 3 days of the
week. [Level 2, Grade A].
Many of the health outcomes examined, particularly
obesity and the cardiometabolic health measures,
responded almost exclusively to aerobic exercise inter-
ventions. It is also likely that most of the activity that was
captured in the observational studies was aerobic in
nature. Recommendation #3 therefore suggests that phys-
ical activity should focus on aerobic activities. However,
bone health was more favorably affected by modest
amounts of resistance training and other high-impact
activities (jumping) that were performed on at least 2 or 3
days of the week. Thus, this recommendation indicates
that a small amount of bone strengthening activities
should be incorporated.
Limitations
This systematic review has several limitations, many of
which related to practical issues around conducting the
study (e.g., budgetary, human resource, and time con-
straints). First, because we did not include unpublished
studies and studies that were published in a language
other than English, and because we did not perform an
extensive cross-referencing of the references lists from
the papers that were retrieved in the electronic databases,
several relevant papers may be been excluded. Second,
the review was limited to 7 health outcomes and did not
include several other outcomes that may be relevant for
children and youth such as academic performance,
emerging cardiometabolic risk factors (e.g., endothelial
function, inflammatory markers), risky and aggressive
behaviours (e.g., substance use and abuse, bullying and
fighting), and measures of mental health and well-being
outside of depression. Third, a large percentage of obser-
vational studies in the area were excluded because they
did not report their findings in a dichotomous manner.
Together, these limitations may have biased the Results
and Recommendations that were made. Nonetheless,
despite these limitations and the differences in methodol-
ogy employed, the recommendations made here are
remarkably comparable to the recommendations for chil-
dren and youth that were part of the recently completed
"Physical Activity Guidelines for Americans" project [21].
The reader is referred to the Expert Panel report for a
more comprehensive discussion of the limitations of this
systematic review [13].
Conclusion
In summary, the findings of this systematic review con-
firm that physical activity is associated with numerous
health benefits in school-aged children and youth. The
dose-response relations between physical activity and
health that were observed in several observational studies
suggest that the more physical activity, the greater the
health benefit. However, the results from several experi-
mental studies suggested that even modest amounts of
physical activity can have tremendous health benefits in
high-risk youngsters (e.g., obese, high blood pressure). To
achieve substantive health benefits, the physical activity
should be of at least a moderate intensity, and it should be
recognized that vigorous intensity activities may provide
an even greater benefit. Aerobic-based activities that
stress the cardiovascular and respiratory systems have the
greatest health benefit, other than for bone health, in
which case high-impact weight bearing activities are
required.
Additional material
Additional file 1 Table 1. Association between physical activity and
health and behavioural outcomes in children and youth.
Additional file 2 Table 2. Criteria for assigning a level of evidence to rec-
ommendations.
Additional file 3 Table 3. Criteria for assigning a grade to recommenda-
tions.
Additional file 4 Table 4. Experimental studies examining the influence of
exercise on changes in traditional blood lipids and lipoproteins in school-
aged children and youth.
Additional file 5 Table 5. Observational studies examining the relation
between physical activity and fitness with hypertension in school-aged
children and youth.
Additional file 6 Table 6. Experimental studies examining the influence of
exercise on changes in blood pressure in school-aged children and youth.
Additional file 7 Table 7. Observational studies examining the relation
between physical activity and fitness with the metabolic syndrome in
school-aged children and youth.
Additional file 8 Table 8. Experimental studies examining the influence of
exercise on changes in markers of the metabolic syndrome (insulin resis-
tance) in school-aged children and youth.
Additional file 9 Table 9. Observational studies examining the relation
between physical activity and fitness with obesity in school-aged children
and youth.
Additional file 10 Table 10. Experimental studies examining the influ-
ence of exercise on changes in obesity measures in school-aged children
and youth.
Additional file 11 Table 11. Experimental studies examining the influ-
ence of exercise on changes in bone mineral density in school-aged chil-
dren and youth.
Additional file 12 Table 12. Observational studies examining the relation
between physical activity and fitness with depression in school-aged chil-
dren and youth.
Additional file 13 Table 13. Experimental studies examining the influ-
ence of exercise on changes in measures of depression in school-aged chil-
dren and youth.

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Competing interests
Production of this paper has been made possible through a financial contribu-
tion from the Public Health Agency of Canada. The views expressed herein do
not necessarily represent the views of the Public Health Agency of Canada. I
Janssen has received honoraria, speaker fees, and consulting fees from several
non-profit organizations, including the Public Health Agency of Canada, that
have an interest in physical activity and health.
Authors' contributions
IJ designed the methods, assisted with the completion of the systematic
review, and drafted the manuscript. AB lead most of the components of the
systematic review and helped drafts some of the methodology sections of the
paper.
All authors have read and approved the final manuscript.
Acknowledgements
Production of this paper has been made possible through a financial contribu-
tion from the Public Health Agency of Canada. The views expressed herein do
not necessarily represent the views of the Public Health Agency of Canada. The
leadership and administrative assistance was provided by the Canadian Soci-
ety for Exercise Physiology.
Author Details
1School of Kinesiology and Health Studies, Queen's University, Kingston,
Ontario, Canada and 2Department of Community Health and Epidemiology,
Queen's University, Kingston, Ontario, Canada
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Additional file 14 Table 14. Observational studies examining the relation
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and youth.
Received: 20 July 2009 Accepted: 11 May 2010
Published: 11 May 2010
This article is available from: http://www.ijbnpa.org/content/7/1/40© 2010 Janssen and LeBlanc; licensee BioMed Central Ltd. This is an Open Access article distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/2.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.International Journal of Behavioral Nutrition and Physical Activity 2010, 7:40

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doi: 10.1186/1479-5868-7-40
Cite this article as: Janssen and LeBlanc, Systematic review of the health
benefits of physical activity and fitness in school-aged children and youth
International Journal of Behavioral Nutrition and Physical Activity 2010, 7:40