Welk PA in Children for Measurement Class.doc

7/26/2019 Welk PA in Children for Measurement Class.doc

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Measurement Issues in the Assessment of Physical

Activity in ChildrenKeywords: self-report, activity monitors, observation, validity, activity patterns

Gregory J. Welk, Charles B. Corbin and Darren Dale

The health benefits of physical activity for adults have been well established (U.S. Department of

Health and Human Services, !!"#. Similar lin$s with children are not as well established since

it ta$es time for unhealthy behaviors to influence chronic disease. %evertheless, there has been

tremendous interest in assessin& and promotin& physical activity amon& children. 'uch of thisinterest stems from the hi&hly publicied increases in the prevalence of pediatric obesity

()ortma$er, Diet, Sobol, * +ehler, ! Troiano, /le&al, 0ucmars$i, 1ampell, * 2ohnson,

!!3 Troiano * /le&al, !!#. Studies have documented the important role that physical activityplays in wei&ht control (4ippe * Hess, !!# and si&nificant trac$in& coefficients have been

observed for obesity (+hita$er, +ri&ht, * Diet, !!#, coronary ris$ factors ('ahoney, 5auer,

5ee, * 1lar$e, !!# and physical activity6inactivity (7ate, 8aranows$i, Dowda, * Trost, !!"7ate et al., !!!# amon& youth. To advance wor$ in these (and other# areas, and further the

promotion of physical activity in children, continued efforts are needed to improve our ability to

assess this comple9 behavior.

There are a number of different techniues that have been used to assess physical activity in avariety of populations (self-report, activity monitors, pedometers, heart rate monitors, doubly

labeled water, and indirect calorimetry# and others that have been developed specifically for

children (direct observation#. ;ach of the measures has specific advanta&es and disadvanta&esthat must be considered when selectin& an instrument. < number of e9cellent reviews of physical

activity assessments have described the relative merits of the different approaches for adults

(


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review some of the more common physical assessment tools to determine the usefulness of each

in studyin& childrenAs physical activity.

Table . 1haracteristics That Differentiate 1hildren /rom


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bout of hi&h intensity activity lon&er than minutes was recorded. The median duration

between hi&h intensity activities was seconds, but ran&ed between ? s and > min. 3 s.

7eriods of rest were clearly lon& in proportion to periods of activity, but !3G of the IrestAintervals were less than = min. and 3 s. This indicates that children do not remain inactive for

e9tended periods of time. 1ollectively, these findin&s clearly document the hi&hly transitory

nature of childrenAs physical activity. The authors su&&est that short, intermittent bouts ofvi&orous physical activity (with freuent rest periods of lon&er duration# are typical of children

and, in fact, may be necessary for normal &rowth and development (8ailey et al., !!3#.

Table >. < Summary of %


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in physical activity. The implications of these various characteristics of children for each of the

more common assessment techniues will be discussed later in this paper.

Uniqe %cti&ity Gidelines "or Children

2ust as the uniue characteristics of children should be considered when ma$in& decisions about

the method of physical assessment so too should the uniue e9pectations for children in activitybe considered. The need to assess physical activity in any population is based on the desire to

determine the current activity status of that population and to determine if that population ismeetin& activity criteria that are appropriate for optimal health and development. /or years, the

activity &uidelines for children were assumed to be similar to those recommended for adults

(#. The recent % hours# G of children

with H4 M ?! for

> consecutiveminutes

Girls: 12%

active Boys: 23%active

Girls: 53%


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G of children

with H4 M ?! for ?,

3-minute bouts

Total number

of minutes with H4M ?! (wee$day#

Boys: 70%

Girls: 32

minutes Boys: 45minutes

hours# G of children

with H4 M ?! for >

consecutive minutes

G of children

with H4 M ?! for ?,

3-minute bouts

Total number of

minutes with H4

M?! (wee$day#

Girls: 34%

active Boys: 39%

Girls: 85%

Boys: 90%

Girls: 59


hours6day over ?

days#

G of children

with H4 M ?! for >

consecutive minutes

G of children

with H4 M ?! for ?,

3-minute bouts

G of children

with H4 M 3! for ?,3-minute bouts

Girls: 37%

Boys: 39.5%

Girls: 88%

Boys: 92%

Girls: 70% Boys

79%

)illiam

(!>#

&irls and >> boys

a&es "-

1ontinuous heart rate

monitorin& (> hours# Total number of

minutes with H4 M"

Total number of

minutes with H4 M

=

Girls: 9 minutes

Boys: 21 minutes

Girls: 30


2an (!!># " &irls and boys

a&es "-

1ontinuous heart rate

monitorin& (-

hours#

G of children

with H4 M "G of a&e

predicted ma9 for >minutes

Total number of

minutes with H4 M"G of a&e predictedma9 N 33 bpm

Total: 7% active

Total: 15

minutes

Direct bser&ation +tdies

Baranos!i"1987#

14 $irls an 10&oys a$es 8'12

(irect o&servationon to ays "12)ours#1

% o* c)ilren

active *or 20consecutive

8'13% o*

c)ilren

58'63% o*


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minutes

% o* c)ilren

active *or 14minutes it) only 1sto+ or &rea!

Total num&er o*minutes o* activity(reported for thosewho were "active")

c)ilren

61'71 total

minutes o* activity

,lea+"1992#

27 $irls an 29&oys

(irect o&servation2 % o* c)ilren

active *or 20consecutiveminutes

% o* c)ilren

active *or 10consecutiveminutes

Total minutes

o* activity

14% o* c)ilren

active

46% o* c)ilren

active

88.5 minutes

+el"-)eport Instrments

-rai$"1996#

49 $irls a$es 8'11 ,el*'re+ort o*+revious year

vera$e

minutes +er ay inmoerate activity /4 Ts

96.7 minutes

Gortma!eret al."1999#

336 5t)$raec)ilren

To activityassessments 1. 24)r recall 2. 16'itemsurvey

um&er o*

minutes o*moerate +)ysicalactivity / 6 Tscom+ute it) tomeasures

inutes +er

ay *or treatmentan control $rou+s1. 72'82 minutes2. 89'99 minutes

curray"1998#

45 c)ilren "25$irls an 20 &oys#in $raes 6'8

-om+uterieactivity recall

um&er o*

minutes o* +)ysicalactivity "nos+ecication o*intensity#

Girls: 85


yers"1996#

995 &oys an $irlsa$es 9'15

,el*'e+ort o*+revious ay",-#

um&er o*

minutes o* +)ysicalactivity

Total: 168

minutes

oss "1985# ational sam+le o*

5t)

an 6t)

$rae

arent re+ort o*

c)ils activity3

% o* c)ilren

+er*ormin$ re$ularactivity

um&er o*

minutes o* +)ysicalactivity

Girls: 49%

Boys: 56% Total:102'120 minutes

,imons'orton

2410 3r$raec)ilren

ctivity ntervieit) a lo$

um&er o*

minutes o*

Girls: 83

minutes Boys: 97


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"1997# moerate tovi$orous activity aay

minutes

ey *or a&&reviations: ; )eart rate< ; +)ysical activity= ,- ; ,el*'ministere )ysicalctivity ecall

1ctivity ene as continuous slo or *ast trun! movements2ctivity ene as &ein$ commensurate it) a )eart rate o* 140 &+m

3ctivity ene as >e?ercise involvin$ lar$e muscle $rou+s in ynamic movement *or +erios o* 20minutes or lon$er 3 or more times a ee!.>

Characteriing %cti&ity 'e&els in Children

@f the assessment of physical activity patterns of children is the &oal, the standard used to define

Ebein& activeF becomes hi&hly relevant. /ailure to use appropriate standards can lead tosi&nificant misinterpretations of both individual and &roup assessments of physical activity.

@nterpretations of studies on activity levels in children also can vary widely dependin& on what

type of assessment is used. Some e9amples illustratin& the importance of these issues for

characteriin& activity levels in children are provided below.7rior to the development of specific physical activity standards for children, many studies were

conducted to evaluate the habitual activity levels of children. To provide obOective information

about activity patterns, a number of studies used heart rate monitors (. @ntensity of 7 isolated days of measurement.

The intensity of physical activity is often used to cate&orie physical activity but is notcommonly used as an outcome measure. Several studies have reported mean heart rates or mean

activity counts durin& the day or portion of the day (2an et al., !!> 2an, !!=#. +hile this

may be useful for statistical comparisons, the values themselves are difficult to interpret. 8ecausethe maOority of a childAs day is spent in restin& or li&ht activities, mean values would be low and

would not provide meanin&ful information about their true activity level. @f mean levels were

reported for a &roup, the lar&e intra-individual variability in activity patterns in children would

ma$e interpretations of the data even more difficult.The duration of activity is &enerally reported in minutes or percenta&e of time spent bein& active.

#.

Lbtainin& ener&y e9penditure estimates from physical activity reuires information about themetabolic costs of the activities that are performed. /or indirect calorimetry and doubly labeled

water techniues, these measures are made directly accordin& to established metabolic

calculations. /or observation and self-report measures, estimates are typically made usin&multiples of restin& metabolic rate (';TS#. 8ecause the ';T values for various activities are

not well established for children (


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@t is apparent from Table = that a number of different approaches can be used to obtain a similar

outcome measure. The ease and accuracy of assessin& these different components varies amon&

each of the instruments. The advanta&es, disadvanta&es, and specific measurement issues forassessin& childrenAs activity behaviors will be described below.

Self-Report Instruments

Self-report instruments provide a convenient way to assess activity patterns on lar&e populations.

+hile they have been commonly used for a variety of research purposes, there is widespreadconcern about the accuracy of self-report data from children. 'ost validation studies with

children have reported only moderate correlations between various self-report forms and other

obOective criteria (Sallis, !!#. The lac$ of stron& correspondence and the described tendencyfor overestimation have led to the consensus that children can not provide accurate self-report

information about their activity patterns. ;fforts have been made to describe the co&nitive and

methodolo&ical issues pla&uin& self-report instruments (8aranows$i et al., !=#, but little is$nown about the specific co&nitive s$ills reuired for children (or adults# to accurately complete

self-reports (8aranows$i, !3 8aranows$i, ! Du4ant *


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have recently been published to facilitate their use by both researchers and teachers (+el$ *

+ood, >#.

Heart Rate Monitors

Heart rate monitors provide an obOective indicator of the physiolo&ical effect of physical activity.They have been found to provide a valid measure of heart rate in children (Du4ant et al., !!?

Treiber et al., !!#, and heart rate has been shown to be linearly related to PL>and ener&y

e9penditure durin& physical activity. However, the numerous other factors that influence heartrate under restin& conditions contribute considerable error when heart rate monitors are used for

e9tended periods of monitorin&. @n a recent study (+el$, 1orbin, * 0ampert, !!#, we found

that heart rate indicators were hi&hly correlated with a direct observation measure under activeconditions in physical education (r .!#, but wea$ly correlated under inactive conditions in the

classroom (r .=!#. +hile this type of error would bias measures of mean heart rate, they would

not affect estimates of total minutes of activity (e.&., minutes M = bpm#. Still, there are a

number of difficulties inherent in usin& heart rate monitors for field-based research (4iddoch *

8oreham, !!3#. 7roblems with "-cycle interference and lost data from si&nal interruptionsma$e data collection and data processin& challen&in&. Delayed heart rate responses and the

influence of other factors can add considerable error to heart rate recordin&s. Discomfort fromwearin& a transmitter device can also reduce participant compliance.

/i&ure . Hypothetical dia&ram illustratin& the potential variability in activity patterns within a minute for a child.

8ecause childrenJs activity is hi&hly sporadic and intermittent, short bouts of activity would be avera&ed with rest

brea$s to represent the activity level for the minute. @f activity cutpoints based on steady-state activity are used, theminute may be scored as inactive despite the presence of some vi&orous activity.


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< promisin& application of heart rate monitorin& techniues is for estimations of ener&y

e9penditure and for studies on obesity and wei&ht control (5ivin&stone, !!#. Usin&

individualied H4: PL>re&ression euations and techniues that control for errors caused byvariability in restin& heart rate, a number of studies have demonstrated stron& predictions for

ener&y e9penditure in children (5ivin&stone et al., !!> Spady, ! Treuth,


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direct observation techniues usin& momentary time samplin& procedures may provide the best

criterion measure since they can address chan&es in activity levels within a minute.


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wee$ periods, and does not interfere with normal activity patterns. The limitations are the cost

and the difficulty in obtainin& the stable isotopes of water. @t is also not useful for e9aminin&

patterns of activity or for partitionin& ener&y e9penditure associated with physical activity.@nterested readers are referred to more detailed descriptions of these techniues and their

applicability for research on children ()oran, !!3 Hill, 2ohnson, 'elby, * 7eters, !!3

+esterterp * )oran, !!#.

+mmary

This paper reviewed the nature of childrenAs physical activity patterns and how the uniue nature

of children can impact the assessment of physical activity. To accurately assess childrenAs activity

patterns, an instrument must be sensitive enou&h to detect, code, or record sporadic andintermittent activity. 1are also must be used to select criterion measures that reflect appropriate

physical activity &uidelines for children.

< number of different measurement approaches have been described for assessin& childrenAs

activity, but no specific method can be identified as the best option for all studies. Selection of anappropriate instrument depends on the specific research uestion bein& addressed as well as the

relative importance of accuracy and practicality (8aranows$i * Simons-'orton, !!#. /or

e9ample, accurate measures of ener&y e9penditure usin& doubly-labeled water, indirect

calorimetry, or heart rate calibration euations may be needed for certain clinical studies, but thecost and inconvenience would ma$e them impractical for field-based assessments on lar&er

samples.

The Eaccuracy-practicalityF trade-off presents a more challen&in& predicament with children thanfor adults. @n adults, a number of self-report instruments have been found useful for lar&e

epidemiolo&ical studies or interventions where less precision is needed. 8ecause of

developmental differences, especially in ability to thin$ abstractly and perform detailed recall()oin& et al., !!! Sallis, !!#, children are less li$ely to ma$e accurate self-report assessmentthan adults. Thou&h self-report methods are still li$ely to be a principal source of information for

many studies, other approaches (or the use of combined measures# may be needed to better

characterie childrenAs activity levels.

+hile obOective instruments (e.&., direct observation or activity monitorin reuire more timeand resources than self-report, there are options available to simplify data collection. Lne

approach may be to focus assessments on $ey times or places that allow children to be active.

The time after school, for e9ample, appears to be a critical period that defines their propensity forphysical activity (Ha&er, !!!#. 'onitorin& of entire &roups for discrete periods of time (e.&.,

recess or physical education# may also be useful to understand variability in activity patterns

since children would all be e9posed to the same stimulus or opportunity to be active.

7ro9y measures may also be useful in studyin& activity in children. /or e9ample, several studies(8aranows$i, Thompson, Du4ant, 8aranows$i, * 7uhl, !!? Sallis et al., !!?# have

demonstrated that time spent outside is stron&ly predictive of activity in children. @nvolvement in

community sports pro&rams may also be a useful pro9y measure as sports pro&rams have been


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found to account for appro9imately 33-"3G of childrenAs moderate to vi&orous activity

(0atmary$ * 'alina, !!!#.


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>-=>?.

?->3.

".

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