Longitudinal study of physical activity and sedentary behavior in children.

Abstract

Physical activity is thought to decline during childhood, but the extent of the decline is unknown. We made objective measures of 2-year changes in physical activity and sedentary behavior in English children who participated in the Gateshead Millennium Study to explore the nature, timing, and extent of changes in physical activity and sedentary behavior before adolescence.
We conducted a longitudinal study of 405 children (207 girls), aged 7 years, in 2006/2007 and again 24 months later. Physical activity and sedentary behavior were measured with the Actigraph GT1M accelerometer. Data were analyzed in 2010. Changes in total volume of physical activity (accelerometer counts per minute [cpm]), moderate-to-vigorous-intensity physical activity (MVPA), and sedentary behavior were quantified. Factors associated with changes in physical activity and sedentary behavior were tested by using linear regression. Tracking of physical activity and sedentary behavior over the 2-year period was assessed by rank-order correlation.
Mean daily volume of physical activity declined by 83 cpm (interquartile range [IQR]: -189 to 31) over 2 years; the percentage of daily time spent in MVPA was low at baseline and declined by 0.3% (IQR: -1.4 to 0.9). The percentage of daily time in sedentary behavior was high at baseline and increased from 78.0% to 81.1% of the day (change 3.1% [IQR: -0.3 to 6.0]). The decline in MVPA and increase in sedentary behavior were significantly greater in girls and in those with higher BMI z scores at baseline. Physical activity and sedentary behavior showed moderate tracking over the 2-year period.
We report here new evidence of low and declining levels of physical activity and MVPA and increasing sedentary behavior before adolescence.

Full text

Page 1

DOI: 10.1542/peds.2010-1935
; originally published online December 20, 2010; 2011;127;e24
Pediatrics
S. Pearce, John J. Reilly and for the Gateshead Millennium Study Core Team
Laura Basterfield, Ashley J. Adamson, Jessica K. Frary, Kathryn N. Parkinson, Mark
Longitudinal Study of Physical Activity and Sedentary Behavior in Children




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Longitudinal Study of Physical Activity and Sedentary
Behavior in Children
WHAT’S KNOWN ON THIS SUBJECT: Levels of physical activity
during childhood are expected to be quite stable with age.
Physical activity is believed to decline markedly at adolescence,
particularly for girls.
WHAT THIS STUDY ADDS: Physical activity declines before
adolescence in both boys and girls. Strategies to prevent the
decline in physical activity should be considered and started for
both sexes before adolescence.
abstract
OBJECTIVE: Physical activity is thought to decline during childhood,
but the extent of the decline is unknown. We made objective measures
of2-yearchangesinphysicalactivityandsedentarybehaviorinEnglish
children who participated in the Gateshead Millennium Study to ex-
plore the nature, timing, and extent of changes in physical activity and
sedentary behavior before adolescence.
METHODS: We conducted a longitudinal study of 405 children (207
girls), aged 7 years, in 2006/2007 and again 24 months later. Physical
activity and sedentary behavior were measured with the Actigraph
GT1M accelerometer. Data were analyzed in 2010. Changes in total
volume of physical activity (accelerometer counts per minute [cpm]),
moderate-to-vigorous–intensity physical activity (MVPA), and seden-
tary behavior were quantified. Factors associated with changes in
physical activity and sedentary behavior were tested by using linear
regression. Tracking of physical activity and sedentary behavior over
the 2-year period was assessed by rank-order correlation.
RESULTS: Mean daily volume of physical activity declined by 83 cpm
(interquartile range [IQR]: ?189 to 31) over 2 years; the percentage of
dailytimespentinMVPAwaslowatbaselineanddeclinedby0.3%(IQR:
?1.4 to 0.9). The percentage of daily time in sedentary behavior was
highatbaselineandincreasedfrom78.0%to81.1%oftheday(change
3.1%[IQR:?0.3to6.0]).ThedeclineinMVPAandincreaseinsedentary
behavior were significantly greater in girls and in those with higher
BMI z scores at baseline. Physical activity and sedentary behavior
showed moderate tracking over the 2-year period.
CONCLUSIONS: We report here new evidence of low and declining lev-
els of physical activity and MVPA and increasing sedentary behavior
before adolescence. Pediatrics 2011;127:e24–e30
AUTHORS: Laura Basterfield, PhD,aAshley J. Adamson,
PhD,aJessica K. Frary, BSc,aKathryn N. Parkinson, PhD,a
Mark S. Pearce, PhD,band John J. Reilly, PhD,cfor the
Gateshead Millennium Study Core Team
aInstitute of Health and Society, Human Nutrition Research
Centre, andbInstitute of Health and Society, Sir James Spence
Institute, Royal Victoria Infirmary, Newcastle University,
Newcastle Upon Tyne, United Kingdom; andcDivision of
Developmental Medicine, University of Glasgow, Glasgow, United
Kingdom
KEY WORDS
childhood, physical activity, sedentary behavior
ABBREVIATIONS
MVPA—moderate-to-vigorous–intensity physical activity
SES—socioeconomic status
Each author is responsible for the reported research; each
author has participated in the concept and design, analysis and
interpretation of data, and drafting or revising of the
manuscript, and each author approved the manuscript as
submitted.
www.pediatrics.org/cgi/doi/10.1542/peds.2010-1935
doi:10.1542/peds.2010-1935
Accepted for publication Sep 20, 2010
Address correspondence to Laura Basterfield, PhD, Institute of
Health & Society, Human Nutrition Research Centre, Newcastle
University, M1.151 Leech Building Medical School, Framlington
Place, Newcastle Upon Tyne NE2 4HH, United Kingdom. E-mail:
laura.basterfield@ncl.ac.uk
PEDIATRICS (ISSN Numbers: Print, 0031-4005; Online, 1098-4275).
Copyright © 2011 by the American Academy of Pediatrics
FINANCIAL DISCLOSURE: The authors have indicated they have
no financial relationships relevant to this article to disclose.
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Levels of habitual physical activity and
sedentary behavior are now well es-
tablishedasimportanttoboththecur-
rent and future health of children and
adolescents,1–3andattemptstoreduce
the decline in physical activity in ado-
lescence have been the focus of many
public health interventions in recent
years.4,5
Moststudiesofchangesinphysicalac-
tivity during childhood and adoles-
cence have been
rather than longitudinal. In addition,
most previous studies used subjective
methods of measurement of physical
activity,whichdonotprovideaccurate
estimates of the amount and intensity
of physical activity.6In addition, longi-
tudinal studies that have used objec-
tive methods7–17have usually mea-
sured change during adolescence
ratherthanduringchildhoodandhave
usually focused on girls7–9,11,12,15,16be-
cause of concern that adolescent de-
clines in physical activity are espe-
cially marked in girls. Little is known
about the timing, nature, and magni-
tudeofchangesinphysicalactivitylev-
els in childhood, and even less is
known about longitudinal changes in
levels of objectively measured seden-
tary behavior. Moreover, results of
olderstudiesconductedbeforetheep-
idemic of pediatric obesity may not
provide evidence that is readily appli-
cable to contemporary children and
adolescents. Finally, no studies have
revealed longitudinal changes in the 3
constructs (total volume of physical
activity, moderate-to-vigorous–intensity
physical activity [MVPA], and seden-
tary behavior6), all of which have been
identified as important to current and
future health.1,2Understanding the
timing, nature, and extent of changes
in physical activity and sedentary be-
havior during childhood is crucial
forthedevelopmentofinformed,effec-
tive, and evidence-based interventions
aimed at preventing obesity and pro-
cross-sectional
moting cardiometabolic health. The
primary aim of this study, therefore,
was to quantify changes in objectively
measured habitual physical activity
and sedentary behavior over a 2-year
period in a sample of English children,
beforeadolescence,byusingalongitu-
dinal study design. Secondary aims of
this study were to identify factors as-
sociated with changes in physical ac-
tivity and sedentary behavior and to
assess the extent to which physical
activityand sedentary
“tracked” over time.
behavior
METHODS
Participants, Recruitment, and
Consent
The Gateshead Millennium Study is a
birth cohort study of 1029 infants
(born in Gateshead, northeast En-
gland) and their families recruited in
1999–2000.Thedetailsoftheaims,de-
sign, and sampling of this birth cohort
were recently published.18In brief, the
sample population resided in Gates-
head and was predominantly (98%)
from the white ethnic majority group
and socioeconomically representative
of northeast England. For the present
study, all families who had not previ-
ouslyoptedoutofthecohortweresent
aletterandinformationleafletinviting
them to take part. Baseline measures
were collected between October 2006
andDecember2007,whenthechildren
were aged 6 to 8 years (hereafter de-
scribedasaged7years),andfollow-up
data were collected 24 months later
(October 2008 to September 2009),
when the children were aged 8 to 10
years (hereafter described as aged 9
years).Afavorableethicalopinionwas
given by the Gateshead and South
Tyneside Local National Health Service
Research Ethics Committee for base-
line data collection at 7 years of age
and by the Newcastle University Fac-
ulty of Medical Sciences Ethics Com-
mittee for follow-up data collection
at 9 years of age. Informed written
consent was obtained from the par-
ent/main guardian of each child, and
children provided their assent to
participation.
Objective Measurement of Physical
Activity and Sedentary Behavior
Habitual physical activity and seden-
tarybehaviorweremeasuredbyusing
Actigraph GT1M accelerometers (Acti-
graph, Pensacola, FL). The Actigraph is
a small, unobtrusive, and lightweight
monitor worn on the right hip on an
elastic waistband. The Actigraph has
high validity (relative to reference
measures of physical activity, direct
observation, and energy expenditure),
high reliability, and low reactivity in
children19and has been used success-
fully in pediatric physical activity stud-
ies over the past 10 years.6
Childrenwereaskedtoweartheaccel-
erometer during waking hours for 7
days and remove them only for bed
and water-based activities such as
showering, bathing, or swimming.
Families were also given a log sheet to
note when the monitor had been worn
andremovedeachday.Theaccelerom-
eters were set to record data in 15-
second sampling intervals (epochs)
throughout the period in which the ac-
celerometer was worn. Before analy-
sis, the data were collapsed to 60-
second epochs. Data were reduced
manually by using accelerometry out-
putandlogsheets,asdescribedprevi-
ously,20to delete occasional periods of
nonweartime(correspondingtotimes
noted by the parent as unworn).
Three constructs were calculated
from the physical activity recorded
with the accelerometer: total volume
ofphysicalactivity,expressedasmean
countsperminute(cpm);MVPA,equiv-
alent to an energy expenditure in ex-
cess of ?3 times the energy expended
atrest(expressedasminutes/dayand
the percentage of daily time spent in
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MVPA); and sedentary behavior, equiv-
alent to no translocation of the trunk
(percentage of daily time spent in sed-
entary behavior).
ToquantifyMVPAandsedentarybehav-
ior,evidence-basedcutoffpointsfrom
a body of pediatric calibration and val-
idation studies were applied to accel-
erometry output.6A cut point of 3200
cpm21and above was used to quantify
MVPA, and a cut point of 1100 cpm and
below was used to quantify sedentary
behavior.22The sedentary behavior ac-
tually measured in this study can be
defined best as no movement of the
trunk.6,22Sedentarybehaviorisamore
complex construct than this and one
that is still evolving,23and other as-
pectsofsedentarybehaviorareimpor-
tant to health outcomes (notably
television-viewing23)butwerenotmea-
sured in this study. Because the Acti-
graph cut points used in this study
were derived from studies using Acti-
graph model 7164, and the more re-
cent Actigraph GT1M model has been
shown to have a consistent bias of 9%
relative to model 7164,24a ?9% cor-
rection was applied to the raw accel-
erometry data before applying cut
points.
Previous analyses of accelerometry
data have shown that 3 days of accel-
erometry with a minimum of 6 hours
recordingperdayprovidedacceptable
reliability.25,26Analyses on the current
data set confirmed that reliability was
high over any 3 days for each of the 3
constructs that were measured, and
there were no differences when week-
end days were included/excluded.27As
aresult,measureswereeligibleforin-
clusioninourstudyifatleast3daysof
accelerometryofatleast6hours/day26
were obtained at both baseline and
follow-upmeasures.Forchildrenfrom
the United Kingdom, there are small
but significant seasonal variations in
objectively measured habitual physi-
cal activity28,29; therefore, follow-up
measurements were made as close to
the baseline time of year as practica-
ble to match baseline and follow-up
measures for season.
Anthropometrics and Descriptive
Characteristics of Study
Participants
Height was measured to 0.1 cm with a
Leicester portable height measure
(Chasmors, London, United Kingdom),
and weight was measured to 0.1 kg in
light indoor clothing and percentage
body fat was estimated with a Tanita
TBF300MA (Chasmors). Waist circum-
ferencewasmeasuredto0.1cmatthe
minimum circumference between the
lowest rib and the iliac crest. BMI (kg/
m2) was calculated for each child, and
z scores were estimated to UK popula-
tion reference data.30Socioeconomic
statuswas reported
Townsend scores at birth,18an area-
based measure derived from the UK
census in 1991. The child’s postal code
(zipcode)atbirthwaslinkedtocensus
data for the enumeration district to
provide a Townsend score, a well-
validated measure of socioeconomic
deprivation.31The Townsend score is
based on the percentage of unem-
ployed economically active 16- to 65-
year-olds, household overcrowding,
and not owning a car. The distribution
of these scores in the northern region
is known, so the scores could be di-
vided into 5 ordered centiles (each
comprising20%ofthepopulation)that
corresponded to the quintiles for the
general population.
by using
Statistical Analysis
Thesamplesizeforourstudywasfixed
by the size of the recruited cohort and
the extent of sample attrition over the
2-year period. However, the sample
size was similar to or larger than that
of most previously reported longitudi-
nal studies (eg, Janz et al10and Met-
calfe et al32). In addition, the accuracy
of both the reported levels of physical
activity and sedentary behavior and
the changes in levels over the 2-year
period are increased by the use of ac-
celerometry and the longitudinal de-
sign of the study.
Data were checked for normality, and
physical activity data were found to
be skewed. Therefore, longitudinal
changes in all 3 constructs over the
2-year period (calculated by subtract-
ing7-yeardatafrom9-yeardata)were
tested for significance by using
Wilcoxon signed-rank tests. Mann-
Whitney U tests were used to assess
the significance of differences be-
tween boys and girls in levels of phys-
ical activity and sedentary behavior.
Linearregressionanalysiswasusedto
detectfactorsatbaseline(age7years)
that were associated with changes in
total volume of physical activity, MVPA,
and sedentary behavior. The proposed
candidateexplanatory
agreed on in the analysis plan were
sex, physical activity at baseline (cpm
and percentage of time spent in
MVPA), baseline sedentary behavior
(percentage of time spent sedentary),
socioeconomic status (SES) (Town-
send score quintiles), and child BMI z
score at 7 years of age as an index of
weightstatus.Spearmanrankcorrela-
tions between baseline and follow-up
measures were used to assess the ex-
tent to which tracking occurred over
the 2-year period for all 3 constructs.
SPSS 17 (SPSS Inc, Chicago, IL) and
Stata 10 (Stata Corp, College Station,
TX) were used for statistical analyses.
Significance was set at P ? .05.
variables
RESULTS
Characteristics of Study Sample
and Dropout, Including Age and
Accelerometry Variables
Characteristics of study participants
are listed in Table 1. For practical rea-
sons, only children still living in the re-
gion at the time of follow-up measures
were recruited, and only children who
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had both baseline (age 7 years) and
follow-up(age9years)measurements
were included in our analysis (n ?
405). A total of 105 children studied at
baseline were lost to follow-up because
theydidnothaveconsenttotakepartor
wereunabletobetraced(n?55),were
missing accelerometry log sheets (n ?
9), were not wearing the accelerometer
(n?6),didnotreachtheminimumwear
criteria (n ? 8), lost their accelerome-
ters(n?14),orhadmalfunctioningac-
celerometers(n?13).
Participants followed up to 9 years of
age were not significantly different to
those lost to follow-up with respect to
initial levels of physical activity and
sedentary behavior, BMI, or SES. At
baseline, when children were aged 7
years, mean duration of accelerom-
etry was 6.4 days and 11.1 hours/day;
at follow-up when children were aged
9 years, mean duration of accelerom-
etry was 6.1 days and 11.3 hours/day.
Overall physical activity levels were
low (median: 26 minutes of MVPA daily
at 7 years of age and 24 minutes at 9
years of age [both sexes combined]).
Only26of405(6.4%)childrenachieved
ameanof60minutesofMVPAdailyat7
years of age and only 23 of 405 (5.7%)
at 9 years of age. Nine children (2.2%)
achieved an average of 60 minutes of
MVPA at both time points.
Longitudinal Changes in Physical
Activity and Sedentary Behavior
Changesintotalvolumeofphysicalac-
tivity, MVPA, and sedentary behavior
overthe2-yearperiodaresummarized
in Table 2. In summary, over the 2-year
period the total volume of physical ac-
tivity declined significantly, MVPA de-
clined significantly, and sedentary be-
havior increased significantly (Table
1). There were significant differences
between boys and girls for change in
the 3 constructs of physical activity
(mean cpm, P ? .020; MVPA minutes/
day,P?.012;percentageofMVPA,P?
.006) but no difference in the percent-
ageoftimespentsedentary(P?.274)
(Table 2).
Factors Associated With
Longitudinal Changes in Physical
Activity and Sedentary Behavior
The regression analysis of factors as-
sociatedwithchangeintotalvolumeof
physical activity, MVPA, and sedentary
behavior is shown in Table 3. In sum-
mary, after adjustment for baseline
levels of physical activity and seden-
tary behavior (which had significant
influences on changes in these vari-
ables), longitudinal declines in total
TABLE 1 Participant Characteristics
Anthropometry, Mean (SD)
All Children (N ? 401–405)Boys (n ? 195–198)Girls (n ? 205–207)
Baseline Follow-upBaseline Follow-upBaselineFollow-up
Age (range), y
Height, cm
Weight, kg
Waist, cm
BMI
BMI z score
Physical activity/sedentary behavior
data, median(IQR)
Total physical activity, mean cpm
MVPA, min
Time spent in sedentary behavior, %
Time spent in MVPA, %
7.4(6.4–8.4)
124.8(0.3)
26.2(0.3)
56.4(0.3)
16.7(0.1)
0.37(0.05)
9.3(8.4–10.2)
135.5(0.3)
33.1(0.4)
60.7(0.3)
17.9(0.1)
0.53(0.05)
7.4(6.4–8.4)
125.0(0.4)
26.1(0.4)
56.8(0.4)
16.6(0.2)
0.39(0.08)
9.3(8.4–10.2)
135.5(0.5)
32.7(0.5)
60.9(0.5)
17.7(0.2)
0.53(0.08)
7.4(6.5–8.4)
124.6(0.4)
26.2(0.4)
56.0(0.4)
16.8(0.2)
0.36(0.07)
9.3(8.4–10.2)
135.4(0.4)
33.5(0.5)
60.4(0.4)
18.1(0.2)
0.52(0.07)
721(601–864)
26(18–37)
78.0(73.9–81.9)
3.8(2.6–5.7)
643(523–785)a
24(15–37)a
81.1(76.8–84.4)a
3.6(2.4–5.2)a
731(623–876)
28(19–43)
77.2(72.6–80.9)
4.1(2.8–6.3)
688(569–831)a
28(20–43)
79.5(75.5–83.2)a
4.3(2.9–6.2)
710(588–848)
24(17–34)b
78.6(74.6–82.9)b
3.7(2.5–5.4)b
612(496–728)a,b
21(13–30)a,b
82.3(78.4–85.3)a,b
3.0(2.1–4.5)a,b
aPaired longitudinal data: 9 years significantly different from 7 years.
bResults for the girls were significantly different from those of the boys.
TABLE 2 Longitudinal Changes in Total Physical Activity, MVPA, and Sedentary Behavior From 7 to 9 Years of Age
All Children (N ? 405) Boys (n ? 198) Girls (n ? 207)
Median (IQR)
P
Median (IQR)
P
Median (IQR)
P
Change in total physical activity,
mean cpm
Change in MVPA, min/d
Change in time spent in MVPA, %
Change in time spent sedentary, %
?83(?189to31)a
?.001
?55(?153to52)a
?.001
?100(?227to22)a,b
?.001
?2(?10to7)a
?0.3(?1.4to0.9)a
3.1(?0.29to6.0)a
.012
.003
?1(?8to8)
0.03(?1.1to1.1)
2.9(?0.6to5.6)a
.970
.878
?4(?11to5)a,b
?0.62(?1.7to0.6)a,b
3.6(?0.2to7.1)a
?.001
?.001
?.001
?.001
?.001
aNine-year measurement significantly different from 7-year measurement.
bResults for the girls were significantly different from those of the boys.
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volumeofphysicalactivity(accelerom-
etry cpm) were greater in girls than
boys but were not related to BMI z
scoresorSES.Longitudinaldeclinesin
MVPA were significantly greater in
girls than boys and in those with
higher initial BMI z score but were not
related to SES. Longitudinal increases
in sedentary behavior were signifi-
cantly greater in girls but not related
to BMI z score or SES. There was no
interaction between sex and any base-
line variable.
Tracking of Physical Activity and
Sedentary Behavior Over a 2-Year
Period
Rank-order
baselineandfollow-upmeasuresofto-
tal volume of physical activity, MVPA
minutes/day,percentageoftimespent
in MVPA, and percentage of time spent
in sedentary behavior were r ? 0.54,
0.57, 0.58, and 0.57, respectively (all
P ? .001).
correlations between
DISCUSSION
Main Findings, Implications, and
Comparisons With Other Evidence
We found low levels of habitual physi-
calactivityandhighlevelsofsedentary
behavior in participating children at 7
years of age, with declines in physical
activity and increases in sedentary
behavior by 9 years of age. Recent
evidence, based on contemporary
samples of children and adolescents
that have used accelerometry with
evidence-based cut points,6suggests
that levels of physical activity are typi-
cally very low and levels of sedentary
behavior very high. In addition, small
numbers of longitudinal studies of
children with objective measures10,17
and 1 recent cross-sectional study
with objective measures33suggested
that declines in physical activity may
typically occur well before adoles-
cence. Our results, therefore, add to
the body of evidence that low levels of
physical activity are established early
in childhood and decline further dur-
ingchildhoodandbeforeadolescence.
The 2-year changes in physical activity
and sedentary behavior observed in
this study were significant and, al-
though relatively modest in magni-
tude,areagreatcauseforconcernbe-
cause of the low level of baseline
physicalactivityandhighlevelofbase-
line sedentary behavior. In this study,
unfavorable changes in physical activ-
ityandsedentarybehavioroccurredin
both sexes, but these changes were
generally more severe in girls than
boys and in those with higher baseline
weightstatus.Identifyingfactorsasso-
ciated with declines in objectively
measured physical activity and with
increasesinobjectivelymeasuredsed-
entary behavior would be useful to in-
form the development of future public
health interventions aimed at modify-
ing these behaviors.9Our results sug-
gest that public health interventions
aimedatpreventingdeclinesinphysical
activity should be targeting elementary
school–aged children, because unfavor-
able trends in health behaviors seem to
bealreadyestablishedbeforepuberty.In
Scotland, for example, as in some other
countries, public health policy is based
on the assumption that physical activity
is high during childhood but declines
markedly only during adolescence. Pre-
vention of declines in physical activity in
adolescent girls is a Scottish public
healthpriority,34butaccordingtoourre-
sults, we would question the assump-
tionsonwhichthispolicywasbased.
Tracking of physical activity and sed-
entarybehavior
strong in this study, which is broadly
consistent with other recent stud-
ies14,35of tracking of physical activity
and sedentary behavior measured ob-
jectively during childhood. However,
evenforthemostphysicallyactivechil-
dren, levels of objectively measured
physical activity at both time points
were low (Table 2).
was moderately
Study Strengths and Weaknesses
There
strengthstothisstudy:Thestudysam-
ple was relatively large and represen-
tative of children recruited from the
Gateshead Millennium Study longitudi-
nal birth cohort study; measurements
were made during a period of relative
social and educational stability; physi-
cal activity and sedentary behavior
were objectively and accurately mea-
sured; the longitudinal design allowed
the measures to be repeated after a
2-yearperiod;and,intermsofSES,the
sample was representative of families
living in northeast England.18
are severalmethodologic
Potential weaknesses include the is-
sueofgeneralizabilitytoothersettings
and samples, and there was some
sample attrition from baseline to the
TABLE 3 Factors Associated With Change in Total Volume of Physical Activity, MVPA, and Sedentary Behavior From 7 to 9 Years of Age (N ? 404)
Change in total Physical Activity,
Mean cpm
Change in MVPA, % Change in Sedentary Behavior, %
? (95% CI)
P
? (95% CI)
P
? (95% CI)
P
Baseline BMI z score
Sexa
Baseline test variable
Constant
?14.7(?31.0to1.7)
?50.4(?85.3to?15.6)
?0.6(?0.6to?0.5)
422.2(338.4–506.0)
.078
.005
?0.2(?0.4to?0.1)
?0.8(?1.2to?0.4)
?0.4(?0.5to?0.4)
3.0(2.2–3.7)
.011 0.3(?0.1to0.7)
1.6(0.7–2.5)
?0.5(?0.6to?0.5)
41.1(35.5–46.6)
.148
?.001
?.001
?.001
?.001
?.001
?.001
?.001
?.001
aNote on coding for sex: boys 1 and girls 2. CI indicates confidence interval.
e28
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2-year follow-up. However, there was
no difference in SES, BMI, BMI z score,
or physical activity/sedentary behav-
ior levels between those who partici-
pated in the follow-up and those who
did not.
There has been no consensus on the
appropriate accelerometer cut points
touseforchildrentoquantifyintensity
of physical activity. The value of 3200
cpm21used in our study was based on
apreviouspediatricstudyinwhichac-
celerometer output was calibrated
againstenergyexpenditureandissim-
ilar to the cut point suggested by a
number of other pediatric calibration
studies.6Other studies have used both
higher and lower cut points (eg, 2000
cpm36), but these cut points have not
usually been based on calibration
studies that aimed to identify the most
appropriate cut point for MVPA.6The
1100-cpm cut point used to quantify
sedentary behavior in our study is
higher than that used by some other
pediatric studies (some have used 100
cpmtodefinesedentarybehavior)and
was based on a calibration study on
younger children,22but empirical evi-
dence suggests that it is appropriate
forolderchildren.6Theuseofdifferent
cut points has a moderately large im-
pact on objective measurement of
MVPAandalessmarkedeffectonmea-
surement of sedentary behavior in
children.6
We used individualized manual accel-
erometerdata reduction
present study, as in previous studies6:
we chose not to exclude strings of ze-
ros unless they corresponded with re-
ported nonwear time, despite parents
not being with their children during
inthe
the entire monitoring period. This de-
cision was made on the basis of trying
to include as much data as possible,
although it may reduce the proportion
oftimespentinMVPAandincreasethe
proportion of time spent in sedentary
behavior. The absolute time spent in
MVPA should not be so greatly
affected.
However, taking into account these
limitations,thereportedfindingswere
consistent with several other recent
studies that also used objective meth-
odstomeasurephysicalactivity.Inad-
dition,thelevelsoftotalphysicalactiv-
ity and MVPA observed in the present
study were similar to those observed
in recent studies of both slightly
younger and slightly older samples
within the United Kingdom.14,17,28,32,37,38
These findings also question the hy-
pothesis that physical activity levels
only decline markedly during adoles-
cence, especially taken alongside the
recent studies reporting the levels of
objectively measured physical activity
during adolescence in the United King-
dom.39Longer-term follow-up will be
required to investigate the extent to
which the patterns observed in the
present study are generalizable to
othergroupsofchildrenandtoassess
whethermostofthedeclineinphysical
activity that occurs before adulthood
occurs before, rather than during,
adolescence.
CONCLUSIONS
The low levels of childhood MVPA and
high levels of sedentary behavior re-
ported here present a major public
health concern. These findings, if rep-
licated in other groups of preadoles-
cents, suggest that efforts to prevent
declines in physical activity should
be directed at children not just at
adolescents.
ACKNOWLEDGMENTS
This work was supported by grants
from the Scottish Government Chief
Scientist Office (grant CZH/4/484), the
UKNationalPreventionResearchInitia-
tive (incorporating funding from Brit-
ish Heart Foundation, Cancer Re-
search UK, Diabetes UK, English
Department of Health, Economic and
Social Research Council, Food Stan-
dardsAgency,MedicalResearchCoun-
cil, Research and Development Office
fortheNorthernIrelandHealthandSo-
cial Services, Chief Scientist Office of
the Scottish Government Health Direc-
torate, Welsh Assembly Government,
andWorldCancerResearchFund),and
GatesheadPCT.Thefundingbodieshad
noroleinthedecisiontopublishorthe
content of the article. The cohort was
first set up with funding from the
Henry Smith Charity and Sport Aiding
Medical Research for Kids.
MembersoftheGatesheadMillennium
Study Core Team are Ashley Adamson,
AnneDale,RobertDrewett,AnnLeCou-
teur, Paul McArdlev, Kathryn Parkin-
son, Mark Pearce, John Reilly, and
Charlotte Wright.
We acknowledge the support of an ex-
ternal reference group in conducting
the present study. We appreciate the
support of Gateshead Health National
HealthServiceFoundation
GatesheadEducationAuthority,andlo-
cal schools. We thank members of the
research team for their effort. We es-
pecially thank the families and chil-
dren who participated in the Gates-
head Millennium Study.
Trust,
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DOI: 10.1542/peds.2010-1935
; originally published online December 20, 2010; 2011;127;e24
Pediatrics
S. Pearce, John J. Reilly and for the Gateshead Millennium Study Core Team
Laura Basterfield, Ashley J. Adamson, Jessica K. Frary, Kathryn N. Parkinson, Mark
Longitudinal Study of Physical Activity and Sedentary Behavior in Children


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