Abstract

The purpose of this study was to examine the physical activity patterns of children with Down syndrome. A cross-sectional approach and accelerometry were used to measure the time children with Down syndrome (N  =  104) spent in sedentary, light, and moderate-to-vigorous physical activity. Results indicated that adolescents from ages 14 to 15 years were the most sedentary and spent the least amount of time in light and moderate-to-vigorous physical activity. A general trend of decreasing physical activity as children increase in age was found. This trend is similar to that found among typically developing youth. Participants in this study were found to spend a majority of their day engaged in sedentary activities. Results indicate that most participants were not accumulating the recommended 60 minutes of moderate or vigorous physical activity.

A primary health concern facing North America is the prevalence of individuals who are overweight and obese. Physical inactivity is a contributing risk factor to this epidemic and has also been linked to type 2 diabetes, stroke, cardiovascular disease, and some cancers (U.S. Department of Health and Human Services, 2002). Unfortunately, the rate of individuals classified as overweight and obese has increased in all segments of the U.S. population (Troiano et al., 2007). In a nationwide attempt to counter this, the U.S. Department of Health and Human Services (USDHHS) has established guidelines for physical activity in an effort to promote healthy lifestyles.

According to the Physical Activity Guidelines for Americans, the USDHHS recommends that children and adolescents engage in a minimum of 60 min of physical activity daily (USDHHS, 2008). In the document, specific guidelines are outlined for children and adolescents. These guidelines include at least 60 min of daily moderate physical activity and at least 3 days of vigorous physical activity per week. Activities that exemplify these minimum criteria include bicycle riding, brisk walking, rollerblading, yard and house work, running, jumping rope, and active sports (e.g., basketball, tennis, hockey, and swimming; USDHHS, 2008). Muscle- and bone-strengthening activities are also recommended and should occur at least 3 days per week.

The 60-min guideline has been established as a minimum threshold amount of activity to see health-related benefits. In general, additional benefits are gained with increases in the amount of physical activity. These increases include greater intensity, increased frequency, and/or longer duration. Research suggests that physical activity of more than 60 min is related to greater increases in health and a decrease in premature death (USDHHS, 2008).

Physical activity is also an important component in maintaining a healthy body weight. The Centers for Disease Control and Prevention (CDC) estimates that roughly 15% of youth are either overweight or obese (above the 85th and 95th percentile in body mass index [BMI] adjusted for age and gender, respectively; CDC, 2002). Childhood obesity puts children at an increased risk for developing diabetes, high cholesterol, and being overweight in adulthood (Foley, Bryan, & McCubbin, 2008; Goran, Ball, & Cruz, 2003). Childhood obesity also appears to be more prominent among individuals with disabilities. Healthy People 2010 indicated that obesity in persons with disabilities was 32% greater than in individuals without disabilities (USDHHS, 2000). Previous research indicates that 28%–59% of people with an intellectual disability or Down syndrome are overweight or obese (Illingworth, Moore, & McGillivray, 2003; Rimmer, Braddock, & Fujijura, 1993).

Down syndrome is a genetic disorder most commonly caused by the presence of extra genetic material or an extra copy of the 21st chromosome, resulting in gene overexpression (Roizen & Patterson, 2003). Individuals with Down syndrome generally experience significant delays in the onset of developmental milestones, including early motor milestones such as standing and walking (Jobling, 1998; Latash, Woods, & Ulrich, 2008; Ulrich, Lloyd, Tiernan, Looper, & Angulo-Barroso, 2008; Ulrich, Ulrich, Angulo-Kinzler, & Yun, 2001). Some common phenotypic characteristics account for this delayed development, including muscle hypotonia, immaturity of the central nervous system, poor postural control, and poor balance (Block, 1991; Davis & Kelso, 1982; Reid & Block, 1996). These factors are further compounded by lower aerobic capacities, lower peak heart rates, and decreased muscular strength (Balic, Mateos, Blasco, & Fernhall, 2000; Frey, Stanish, & Temple, 2008).

Motor delays in early childhood act as one barrier to physical activity participation for individuals with Down syndrome. Motor delays may persist in older children with Down syndrome and can be compounded by intellectual disabilities to impact the ability to learn new skills, activities, and games, adding another barrier to older children's participation in physical activity. Other known barriers include facility and transportation restrictions, a lack of integrated program options, and low motivation for physical activity (Menear, 2007). In one sibling study, children with Down syndrome were found to spend less time in and engage in shorter bouts of vigorous physical activity compared with their typically developing siblings (Whitt-Glover, O'Neill, & Stettler, 2006). In general, the literature is limited on the physical activity of children with disabilities, including children with Down syndrome (Fernhall & Unnithan, 2002; Foley et al., 2008). The aim of this study was to examine the physical activity patterns of children with Down syndrome. With a better understanding of patterns and trends in physical activity, we can improve current physical activity guidelines and future interventions for children with Down syndrome.

Method

Participants

Approval for this study was obtained from the institutional review board. Prior to participating in the study, parents provided signed informed written consent. Once consent was obtained from the parents, the children were asked whether they would like to participate. At that time, the children gave written assent. Both consent and assent were required for participation in the study. One hundred and four participants with Down syndrome (57 males, 47 females) between 8 and 16 years of age were recruited from Down syndrome parent support groups and organizations throughout the state of Michigan to participate in a physical activity intervention. There was no attempt to include or exclude individuals based on the distinction of mosaicism, translocation, or trisomy 21. Diagnosis was based on parent report from a physician. None of the participants had a physical disability or medical condition that would limit physical activity participation.

Measurement

Physical activity was measured with the Actical accelerometer (Mini Mitter/Respironics, Bend, Oregon) over a 7-day period. The data provided was time-stamped and included information on the bout length and intensity of physical activity. The Actical accelerometer is one of the smallest accelerometers available (28 mm × 27 mm × 10 mm and 17 g) and uses an omni-directional sensor with a 0.5- to 3-Hz range capable of detecting movements in all planes to create a composite measure of movement. The voltage generated by the sensor is amplified and filtered via analog circuitry and then passed into an analog to a digital converter, and the process is repeated 32 times each second (32 Hz). The resulting 1 s value is divided by four and then added to an accumulated activity value for the duration of the specified 15 s epoch (Pfeiffer, McIver, Dowda, Almeida, & Pate, 2006). For this study, a 15 s epoch was selected on the basis of literature related to the erratic and sudden bursts of activity common to youth (Pfeiffer et al., 2006; Rowlands, 2007).

Participants wore the monitor on an elastic belt on the right hip just above the iliac crest for all waking hours of the day (Figure 1). The monitor was to be worn for all activities except swimming, showering or bathing, and sleeping. Parents or guardians of the participants were provided with a log to record any times when the monitor was not worn (i.e., swimming, bathing, forgetting to put it on in the morning, taking it off for comfort, or any other reasons for which it may have been removed). Monitors were returned after a 7-day period via priority mail, and data were downloaded via an Actical Reader interface unit and associated software.

Figure 1

Two participants wearing accelerometers.

Figure 1

Two participants wearing accelerometers.

Data Reduction

For inclusion in this study, the monitor had to be worn for a minimum of 10 hr per day, for at least 4 days out of the 7-day monitoring period, including one weekend day. These criteria have been previously established in the literature as suggested guidelines for obtaining valid and reliable accelerometry data (Masse et al., 2005; Puyau, Adolph, Vohra, Zakeri, & Butte, 2004; Trost, McIver, & Pate, 2005). Based on a 15 s epoch, the data were then reduced and assigned to one of the following categories: sedentary activity (counts of <25), light physical activity (counts of 25–375), moderate physical activity (counts of 376–1,625), or vigorous activity (counts >1,626). Data counts assigned to physical activity categories are related to energy expenditure validated in typically developing children (Puyau, Adolph, Vohra, & Butte, 2002). Table 1 lists common activities of children and their associated data counts.

Table 1

Sample Physical Activity Counts for Common Activities for Children

Sample Physical Activity Counts for Common Activities for Children
Sample Physical Activity Counts for Common Activities for Children

Anthropometric Measures

Height was measured in centimeters to the nearest tenth of a millimeter with a portable stadiometer (SECA S-214 portable stadiometer). Two measurement trials were administered, and the average of the trials was recorded. Weight was measured in kilograms to the nearest gram (Health O Meter H-349KL digital scale). Two measurement trials were administered, and the average of the trials was recorded. BMI was calculated via the standard formula: body mass (kg) divided by height (m2). Percentage of body fat was calculated with a gender-specific regression equation for children with triceps and calf skinfolds (Slaughter et al., 1988). Using Lange skinfold calipers, a physician experienced in measuring skinfolds took two skinfold thicknesses at each site (triceps and calf) on the right side of the participant's body. Measurements were taken twice at each site and rounded to the nearest tenth of a millimeter. The average at each site was used in the analysis.

Statistical Methods

All analyses were conducted in SPSS Version 17.0. Participants were divided into four age groups for the purpose of approximating grade level (i.e., Grades 3, 5, 7, and 9). The age groups were as follows: 8–9 years (n  =  25), 10–11 years (n  =  38), 12–13 years (n  =  27), and 14–15 years (n  =  14). Physical activity patterns were examined for each group and each level of physical activity intensity. Relationships among percentage body fat, body mass index, body mass index percentile, physical activity levels, and age were also examined. Preliminary data analysis found no significant differences between female and male participants. As a result, all participants were combined for analysis. On the basis of physical activity recommendations, we combined moderate and vigorous physical activity to create an additional category for data analysis (USDHHS, 2008).

Results

Descriptive statistics and demographic information for the participants are displayed in Tables 2 and 3, respectively. Results of physical activity for each age group are presented in Figures 26. Analysis of covariance (ANCOVA) was used to examine physical activity patterns across each age group while controlling for the average time spent wearing the accelerometer (14.23 hr). Post hoc Bonferroni corrections were used to look at pairwise comparisons across age groups.

Figure 2

Daily time spent in sedentary activity by age.

Figure 2

Daily time spent in sedentary activity by age.

Figure 3

Daily time spent in light activity by age.

Figure 3

Daily time spent in light activity by age.

Figure 4

Daily time spent in moderate activity by age.

Figure 4

Daily time spent in moderate activity by age.

Figure 5

Daily time spent in vigorous activity by age.

Figure 5

Daily time spent in vigorous activity by age.

Figure 6

Daily time spent in moderate-to-vigorous activity by age.

Figure 6

Daily time spent in moderate-to-vigorous activity by age.

Table 2

Descriptive Statistics for Participants

Descriptive Statistics for Participants
Descriptive Statistics for Participants
Table 3

Composition of the Sample Population, by Race/Ethnicity

Composition of the Sample Population, by Race/Ethnicity
Composition of the Sample Population, by Race/Ethnicity

The general trend in physical activity demonstrated a marked decrease as children increase in age. The 14- to 15-year age group engaged in significantly more sedentary activity compared with their peers in the 12- to 13-year age group (p < .05) and both the 8- to 9-year and 10- to 11-year age groups (p < .001). The 14- to 15-year age group spent significantly less time in light physical activity compared with the 8- to 9-year age group (p < .01) and the 10- to 11-year age group (p < .001). In the area of moderate physical activity, the 14- to 15-year age group was significantly less active than the 8- to 9-year and 10- to 11-year age groups (p < .01). No group differences were found in the area of vigorous physical activity. When aggregated into moderate-to-vigorous physical activity, the 14- to 15-year age group was significantly less active than the 10- to 11-year age group (p < .01).

The 12- to 13-year age group spent significantly more time in sedentary activity compared with the 10- to 11-year age group (p < .01) and significantly less time in moderate-to-vigorous activity compared with the 10- to 11-year age group (p < .01). The general trend in total daily physical activity patterns for this sample suggests lifestyles that are more sedentary as children age (Figures 24).

Data also suggested that the amount of daily physical activity has little influence on body composition. Weak relationships exist between physical activity and BMI and physical activity and percent body fat (see Table 4). A small, statistically significant relationship between age and percent body fat (r  =  .23, p < .05) as well as age and BMI (r  =  .40, p < .01) was found. Finally, the general trend of physical activity is decreasing with age, with the exception of the first two age groups. This decrease starts with a significant, positive relationship between age and time spent in sedentary activities and continues with negative, statistically significant decreases in both light (r  =  .31, p < .01) and then moderate-to-vigorous physical activity (r  =  .32, p < .01) as children with Down syndrome increase in age. In this sample, children with Down syndrome were not meeting the minimum guidelines of 60 min of daily moderate or vigorous physical activity.

Table 4

Correlations Between Age, Percentage Body Fat, BMI, BMI Percentile, and Physical Activity Levels

Correlations Between Age, Percentage Body Fat, BMI, BMI Percentile, and Physical Activity Levels
Correlations Between Age, Percentage Body Fat, BMI, BMI Percentile, and Physical Activity Levels

Discussion

The purpose of this study was to examine the physical activity patterns of children with Down syndrome. Results from this study indicate that children with Down syndrome are not meeting the surgeon general's recommendations of accumulating 60 min of moderate or vigorous physical activity (USDHHS, 2010). This is an area of concern given that this is a population already at risk for being overweight. In this cross-sectional sample, physical inactivity was clearly demonstrated by a trend of increased sedentary physical activity and decreased amounts of moderate and vigorous physical activity as youth increase in age. There was an exception among individuals in the 10- to 11-year age group. This group engaged in the least amount of sedentary activity and was the most physically active.

The 14- to 15-year age group was the most sedentary and engaged in the least amount of light, moderate, and vigorous physical activity. These results corroborate previous studies that have found lower levels of physical activity in typically developing adolescents when compared with younger children (Nyberg, Nordenfelt, Ekelund, & Marcus, 2009; Riddoch et al., 2004; Troiano et. al, 2007). A recent study reported declines in moderate-to-vigorous physical activity among children between the ages of 9 and 15 (Nader, Bradley, Houts, McRitchie, & O'Brien, 2008). This same pattern was displayed in this sample of youth with Down syndrome. Potential reasons for this decrease could be explained by the intermittent bouts of activity when children play. As children get older, these informal bouts of activity or play decrease and are replaced with more structured activities. For individuals with Down syndrome, a lack of structured activities and programming has been cited as a reason for not engaging in physical activity (Menear, 2007).

Our results indicate that youth with Down syndrome follow a pattern of physical activity similar to their typically developing peers. This pattern indicates sharp declines in physical activity as children become adolescents. The participants in this study mirror their typically developing peers in both quantity and quality of physical activity, except at a lower level. As a group, very few participants were engaging in vigorous activity. The significant drop in moderate and vigorous physical activity as children age is an area of concern.

This area of concern is particularly problematic because physical activity and physical fitness are related to outcomes other than improved health. Physical fitness in this population has been found to predict performance on a variety of tasks of daily living, including job performance (Cowley et al., 2010). A goal of allied health professionals should be to improve or increase physical activity to keep these individuals independent and productive.

Within this sample of participants, 45.5% were overweight or obese for their age and gender according to CDC (2002) growth charts. These results support previous literature placing the percentage of individuals with an intellectual disability or Down syndrome as obese between 28% and 59% (Illingworth et al., 2003; Rimmer et al., 1993). This result is unique and might suggest that the Down syndrome phenotype or other environmental factors may have a greater influence on maintaining a healthy body composition than physical activity. More research is needed in this area as it is slightly outside the scope of this study.

Also of importance are the implications of childhood physical activity patterns for adult behaviors. This lifespan approach is important for maintaining a healthy lifestyle. Childhood years are critical for maintaining and establishing a physically active lifestyle and a healthy weight for adulthood (USDHHS, 2008). Of specific concern is the pattern of overweight children becoming obese adults as there is evidence that high BMIs and high levels of body fat in childhood are associated with increased body fat in adulthood (Field, Cook, & Gillman, 2005; Freedman et al., 2005).

Various aspects of motor development also may be hindering children's engagement in physical activity (Jobling, 2001). This suspicion warrants further explanation because lifelong community participation has been positively linked to health-related benefits later in life for individuals with Down syndrome (Barnhart & Connolly, 2007; Fujiura, Fitzsimons, Marks, & Chicoine, 1997). As a result, interventions and programming options need to address physical education and community programs to close gaps in motor development that exist between individuals with Down syndrome and their typically developing peers throughout the lifespan.

The following limitations should be observed when interpreting the results of this study. The waist was selected for accelerometer placement to increase compliance in this population. The children were more compliant when the monitor was not immediately obvious (visually). However, the use of a single waist-mounted accelerometer may have underestimated actual movement by not detecting upper body movements or specific non-weight-bearing activities, such as cycling (Welk, 2002). In addition, the use of cut points established for typically developing children may not be representative of energy expenditure in children with Down syndrome. Research has found that individuals with Down syndrome exercising at the same intensity as their typically developed peers were found to exercise at a higher percentage of their VO2 peak and to expend more energy (Mendonca, Pereira, & Fernhall, 2009). Finally, because of the cross-sectional design of the study, we could not conclude that there is an age-related decline in physical activity, only that differences among the age groups suggested a potential decline in physical activity as children age.

Results of this study indicate a decline in physical activity as children with Down syndrome get older. These differences appear as a trend of decreased physical activity as age increased. Nearly 80% were engaging in moderate or vigorous activities for at least 30 min. Only 20.6% of the sample exceeded the recommended 60 min of moderate-to-vigorous physical activity combined. These results are interesting when considering the BMIs of the sample. Over 45% of the participants were either overweight or obese. One goal should be to better understand the role physical activity plays in moderating body weight and potentially body fat in this population.

Guidelines for physical activity have been established and are based on minimal criteria; the youth in this study were not meeting these basic guidelines of accumulating 60 min of physical activity daily with a majority of those minutes being moderate or vigorous in intensity. Closer examination of the breakdown of physical activity levels suggests that these youth spent most of their time in sedentary activity. When these children were physically active, they spent more time in moderate physical activity and little time spent in vigorous physical activity. Many of these individuals might be missing out on the health benefits associated with vigorous activity. With a population already at risk for becoming overweight, perhaps this population could benefit from additional activity beyond the minimum recommendations.

It is imperative to continue to examine, quantify, and understand the physical activity patterns of individuals with Down syndrome and the impact of physical inactivity to determine the risk for chronic diseases that can be attributed to inadequate physical activity (Draheim, McCubbin, & Williams, 2002). We have taken an initial step in globally describing the physical activity patterns of children and early adolescents with Down syndrome. Future studies should focus on the influence of families, schools, and the community on physical activity and should include both younger and older individuals to better understand this population.

References

References
Balic
,
M. G
.,
Mateos
,
E. C
.
Blasco
,
C. G
.,
&
Fernhall
,
B
.
(
2000
).
Physical fitness levels of physically active and sedentary adults with Down syndrome
.
Adapted Physical Activity Quarterly
,
17
,
310
321
.
Barnhart
,
R. C
.,
&
Connolly
,
B
.
(
2007
).
Aging and Down syndrome: Implications for physical therapy
.
Physical Therapy
,
87
,
1399
1406
.
Block
,
M. E
.
(
1991
).
Motor development in children with Down syndrome: A review of the literature
.
Adapted Physical Activity Quarterly
,
8
,
179
209
.
Centers for Disease Control and Prevention
. (
2002
).
Prevalence of overweight children and adolescents: United States
.
Washington, DC
:
NCHA Health E-Stats
.
Cowley
,
P. M
.,
Ploutz-Snyder
,
L. L
.
Baynard
,
T
.
Heffernan
,
K
.
Jae
,
S. Y
.
Hsu
,
S
.,
&
… Fernhall
,
B
.
(
2010
).
Physical fitness predicts functional tasks in individuals with Down syndrome
.
Medicine and Science in Sports and Exercise
,
42
,
388
393
.
Davis
,
W. E
.,
&
Kelso
,
J. A. S
.
(
1982
).
Analysis of “invariant characteristics” in the motor control of Down's syndrome and normal subjects
.
Journal of Motor Behavior
,
14
,
194
212
.
Draheim
,
C. C
.,
McCubbin
,
J. A
.,
&
Williams
,
D. P
.
(
2002
).
Differences in cardiovascular disease risk between nondiabetic adults with mental retardation with and without Down syndrome
.
American Journal on Mental Retardation
,
107
,
201
211
.
Fernhall
,
B
.,
&
Unnithan
,
V. B
.
(
2002
).
Physical activity, metabolic issues, and assessment
.
Physical Medicine and Rehabilitation Clinics of North America
,
13
,
925
947
.
Field
,
A. E
.,
Cook
,
N. R
.,
&
Gillman
,
M. W
.
(
2005
).
Weight status in childhood as a predictor of becoming overweight or hypertensive in early adulthood
.
Obesity Research
,
13
,
163
169
.
Foley
,
J. T
.,
Bryan
,
R. R
.,
&
McCubbin
,
J. A
.
(
2008
).
Daily physical activity levels of elementary school-aged children with and without mental retardation
.
Journal of Developmental and Physical Disabilities
,
20
,
365
378
.
Freedman
,
D. S
.,
Khan
,
L. K
.
Serdula
,
M. K
.
Dietz
,
W. H
.
Srinivasan
,
S. R
.,
&
Berenson
,
G. S
.
(
2005
).
The relation of childhood BMI to adult adiposity: The Bogalusa heart study
.
Pediatrics
,
115
,
22
27
.
Frey
,
G. C
.,
Stanish
,
H. I
.,
&
Temple
,
V. A
.
(
2008
).
Physical activity of youth with intellectual disability: Review and research agenda
.
Adapted Physical Activity Quarterly
,
25
,
95
117
.
Fujiura
,
G. T
.,
Fitzsimons
,
N
.
Marks
,
B
.,
&
Chicoine
,
B
.
(
1997
).
Predictors of BMI among adults with Down syndrome: The social context of health promotion
.
Research in Developmental Disabilities
,
18
,
261
274
.
Goran
,
M. I
.,
Ball
,
G. D. C
.,
&
Cruz
,
M. L
.
(
2003
).
Obesity and risk of type 2 diabetes and cardiovascular disease in children and adolescents
.
Journal of Clinical Endocrinology and Metabolism
,
88
,
1417
1427
.
Illingworth
,
K
.,
Moore
,
K. A
.,
&
McGillivray
,
J
.
(
2003
).
The development of the Nutritional and Activity Knowledge Scale for use with people with an intellectual disability
.
Journal of Applied Research in Intellectual Disabilities
,
16
,
159
166
.
Jobling
,
A
.
(
1998
).
Motor development in school-aged children with Down syndrome: A longitudinal perspective
.
International Journal of Disability, Development, and Education
,
45
,
283
.
Jobling
,
A
.
(
2001
).
Life be in it: Lifestyle choices for active leisure
.
Down's Syndrome, Research and Practice
,
6
(
3
):
117
122
.
Latash
,
M
.,
Wood
,
L
.,
&
Ulrich
,
D. A
.
(
2008
).
What is currently known about hypotonia, motor skill development, and physical activity in Down syndrome
.
Down's Syndrome, Research and Practice
,
doi: 10.3104/reviews.2074
Masse
,
L. C
.,
Fuemmeler
,
B. F
.
Anderson
,
C. B
.
Matthews
,
C. E
.
Trost
,
S. G
.
Catellier
,
D. J
.,
&
Treuth
,
M
.
(
2005
).
Accelerometer data reduction: A comparison of four reduction algorithms on select outcome variables
.
Medicine and Science in Sports and Exercise
,
37
,
S544
S554
.
Mendonca
,
G. V
.,
Pereira
,
F
.,
&
Fernhall
,
B
.
(
2009
).
Walking economy in male adults with Down syndrome
.
European Journal of Applied Physiology
,
105
,
153
157
.
Menear
,
K
.
(
2007
).
Parents' perceptions of health and physical activity needs of children with Down syndrome
.
Down's Syndrome, Research and Practice
,
12
,
60
68
.
Nader
,
P. R
.,
Bradley
,
R. H
.
Houts
,
R. M
.
McRitchie
,
S. L
.,
&
O'Brien
,
M
.
(
2008
).
Moderate-to-vigorous physical activity from ages 9 to 15 years
.
Journal of the American Medical Association
,
301
,
2095
2098
.
Nyberg
,
G. A
.,
Nordenfelt
,
A. M
.
Ekelund
,
U
.,
&
Marcus
,
C
.
(
2009
).
Physical activity patterns measured by accelerometry in 6-to 10-yr-old children
.
Medicine and Science in Sports and Exercise
,
41
,
1842
1848
.
Pfeiffer
,
K. A
.,
McIver
,
K. L
.
Dowda
,
M
.
Almeida
,
M
.,
&
Pate
,
R. R
.
(
2006
).
Validation and calibration of the actical accelerometer in preschool children
.
Medicine and Science in Sports and Exercise
,
38
,
152
157
.
Puyau
,
M. R
.,
Adolph
,
A. L
.
Vohra
,
F. A
.,
&
Butte
,
N. F
.
(
2002
).
Validation and calibration of physical activity monitors in children
.
Obesity Research
,
10
,
150
157
.
Puyau
,
M. R
.,
Adolph
,
A. L
.
Vohra
,
F. A
.
Zakeri
,
I
.,
&
Butte
,
N. F
.
(
2004
).
Prediction of activity energy expenditure using accelerometers in children
.
Medicine and Science in Sports and Exercise
,
36
,
1625
1631
.
Reid
,
G
.,
&
Block
,
M
.
(
1996
).
New approaches to Down syndrome
.
In
B
.
Stratford
&
P
.
Gunn
(
Eds.
),
Motor development and physical education
(pp.
309
340
).
London, England
:
Cassell
.
Riddoch
,
C. J
.,
Andersen
,
L. B
.
Wedderkopp
,
N
.
Harro
,
M
.
Klasson-Heggebo
,
L
.
Sardinha
,
L. B
.,
&
… Ekelund
,
U
.
(
2004
).
Physical activity levels and patterns of 9- and 15-yr-old European children
.
Medicine and Science in Sports and Exercise
,
36
,
86
92
.
Rimmer
,
J. H
.,
Braddock
,
D
.,
&
Fujijura
,
G
.
(
1993
).
Prevalence of obesity in adults with mental retardation: Implications for health promotion and disease prevention
.
Mental Retardation
,
31
,
105
110
.
Roizen
,
N. J
.,
&
Patterson
,
D
.
(
2003
).
Down's syndrome
.
Lancet
,
361
,
1281
1289
.
Rowlands
,
A. V
.
(
2007
).
Accelerometer assessment of physical activity in children: An update
.
Pediatric Exercise Science
,
19
,
252
266
.
Slaughter
,
M. H
.,
Lohman
,
T. G
.
Boileau
,
R. A
.
Horswell
,
C. A
.
Stillman
,
R. J
.
VanLoan
,
M. D
.,
&
Bemben
,
D. A
.
(
1988
).
Skinfold equations for estimation of body fatness in children and youth
.
Human Biology
,
60
,
709
723
.
Troiano
,
R. P
.,
Berrigan
,
D
.
Dodd
,
K. W
.
Masse
,
L. C
.
Tilert
,
T
.,
&
McDowell
,
M
.
(
2007
).
Physical activity in the United States measured by accelerometer
.
Medicine and Science in Sports and Exercise
,
40
,
181
188
.
Trost
,
S. G
.,
McIver
,
K. L
.,
&
Pate
,
R. R
.
(
2005
).
Conducting accelerometer-based activity assessments in field-based research
.
Medicine and Science in Sports and Exercise
,
37
,
S531
S543
.
Ulrich
,
D. A
.,
Lloyd
,
M. C
.
Tiernan
,
C. W
.
Looper
,
J. E
.,
&
Angulo-Barroso
,
R. M
.
(
2008
).
Effects of intensity of treadmill training on developmental outcomes and stepping in infants with Down syndrome: A randomized trial
.
Physical Therapy
,
88
,
114
122
.
Ulrich
,
D. A
.,
Ulrich
,
B. D
.
Angulo-Kinzler
,
R. M
.,
&
Yun
,
J
.
(
2001
).
Treadmill training of infants with Down syndrome: Evidence-based developmental outcomes
.
Pediatrics
,
108
((
5
)):
E84
.
U.S. Department of Health and Human Services
. (
2000
).
Healthy people 2010: Understanding and improving health (2nd ed.)
.
Washington, DC
:
U.S. Government Printing Office
.
U.S. Department of Health and Human Services
. (
2002
).
Healthy people 2010: Physical activity and fitness.
. .
U.S. Department of Health and Human Services
. (
2008
).
2008 physical activity guidelines for Americans
.
Washington, DC
:
U.S. Government Printing Office
.
U.S. Department of Health and Human Services
. (
2010
).
The surgeon general's vision for a healthy and fit nation
.
Rockville, MD
:
U.S. Department of Health and Human Services, Office of the Surgeon General
.
Welk
,
G. J
.
(
2002
).
Use of accelerometry-based activity monitors to assess physical activity
.
In
G. J
.
Welk
(
Ed.
),
Physical activity assessment for health-related research
(pp.
125
140
).
Champaign, IL
:
Human Kinetics
.
Whitt-Glover
,
M. C
.,
O'Neill
,
K. L
.,
&
Stettler
,
N
.
(
2006
).
Physical activity patterns in children with and without Down syndrome
.
Journal of Developmental Neurorehabilitation
,
9
,
158
164
.

Author notes

Editor-in-Charge: Steven J. Taylor

Authors:

Phil E. Esposito (e-mail: p.esposito@tcu.edu), TCU Box 297730, Department of Kinesiology, Texas Christian University, Fort Worth, TX 76129, USA; Megan MacDonald, Oregon State University; Joseph E. Hornyak, University of Michigan; and Dale A. Ulrich, University of Michigan.