Abstract

It is unclear whether children with Down syndrome have differing physical activity and sedentary behavior levels compared to typical children. This study addressed this evidence gap in a national sample. Physical activity/sedentary behavior were ascertained by parental report. Findings highlighted that children with Down syndrome were less likely to engage in regular physical activity compared to typical children and had the lowest likelihood of regular physical activity among all subgroups with developmental disabilities/special healthcare needs. Children with Down syndrome were also more likely to watch high volumes of television compared to typical children, although this was nonsignificant upon adjustment for general health. It was concluded that children with Down syndrome are in urgent need for interventions/programs that promote physical activity.

Down syndrome is the most common chromosomal disorder in the United States, occurring in ∼1 in 700 births and prevalent in ∼250,000 individuals (Parker et al., 2010; Presson et al., 2013). Down syndrome is characterized by intellectual disability and risk for comorbidities including congenital heart disease, sleep apnea, gastrointestinal anomalies, and visual and hearing impairments (Roizen & Patterson, 2003). It is furthermore characterized by gross motor deficits and delays in development during childhood that are attributed to muscle hypotonia; joint hypermobility; ligamentous laxity; and abnormal alignment and movement at the foot, ankle, knee, and hip (Mik et al., 2008; Roizen & Patterson, 2003). As such, children with Down syndrome may have a diminished ability to engage in physical activity and, subsequently, may be predisposed towards greater cardiometabolic risk both in adolescence and into adulthood (Fox et al., 2019). For example, children and adults with Down syndrome have higher rates of obesity relative to their peers (Bertapelli et al., 2016; Melville et al., 2005).

Regular physical activity is an essential health behavior for promoting overall health and well-being across the lifespan (Warburton et al., 2006). In children and adolescents, higher amounts of physical activity are favorably linked to indicators of cardiometabolic and bone health (Janssen & Leblanc, 2010). Evidence suggests these health benefits carry forward into adulthood (Fernandes & Zanesco, 2010; Mantovani et al., 2018; Palve et al., 2014). Accordingly, physical activity guidelines recommend children and adolescents engage in ≥60 minutes of moderate-to-vigorous aerobic physical activity (MVPA) daily, as well as bone-strengthening, and muscle-strengthening physical activities for ≥60 minutes at least 3 days a week (Piercy et al., 2018). With recognition that sedentary behavior (e.g., TV viewing, video gaming, computer use, etc.) may constitute a clinically important aspect of a person's physical activity profile that confers health risk irrespective of MVPA (Biswas et al., 2015), some guidelines also recommend children minimize time spent sedentary (Garber et al., 2011; Tremblay et al., 2016). These recommendations apply to most children, including those with Down syndrome.

People with Down syndrome have seldom been included in epidemiological studies on physical activity. Thus, to date, few population-based studies have examined physical activity levels and sedentary time among children with Down syndrome and whether their physical activity levels and sedentary time differ relative to their peers. Although some studies have examined differences in physical activity and sedentary behavior in children with Down syndrome compared to typically developing children, these studies have been limited to small sample sizes of participants (n <30) from a single geographic region and typically recruit from samples of convenience (Fox et al., 2019; Frey et al., 2008). The small sample sizes in prior studies have precluded robust covariate adjustment (with adjustment for only age in some). Furthermore, prior studies have not accounted for important contributing factors (obesity, access to youth sports, health status) or examined whether the differences in physical activity/sedentary behavior between children with Down syndrome and typically developing children are any more pronounced than the difference between typically developing children and children with other special health care needs. The purpose of this study, therefore, was to examine differences in physical activity and sedentary behavior among a population-based sample of children with Down syndrome, children with other special health care needs, and typically developing children.

Methods

Study Population

Data for this analysis come from the 2016 and 2017 National Survey of Children's Health (NSCH), a nationally representative, parent-completed survey of U.S. children aged 0 to 17 years that was funded and directed by the Health Resources and Services Administration's Maternal and Child Health Bureau (MCHB) and conducted by the U.S. Census Bureau. Sample design, data collection procedures, and questionnaire content are available online (www.childhealthdata.org/learn-about-the-nsch/NSCH). Briefly, randomly selected households from all 50 states are mailed a screener questionnaire querying information pertaining to the children in the household, with the opportunity to complete online or via mail. Households with children were identified, and one child from each household was randomly chosen, with oversampling for children with special health care needs using the MCHB's Children With Special Health Care Needs Screener (Bethell et al., 2002). A comprehensive topical questionnaire about this child (and the caregiver) was then completed online or via mail by a parent.

Across the 2016 and 2017 surveys, 71,811 out of 199,058 (36.1%) eligible households completed the topical questionnaire. Children under age 6 were not administered questionnaires ascertaining physical activity, thus the present analysis is restricted to children aged 6–17 years (n = 51,156). After further excluding children aged 6–17 years with missing data for physical activity measures (n = 965), a total of 50,191participants were included in the final analytic sample. The NSCH study adhered to the Federal Policy for the Protection of Human Subjects (U.S. Department of Health and Human Services, 2014). The NSCH does not undergo an external review by institutional review board. Instead, the process for the review of methods and procedures is incorporated into the responsibilities of the U.S. Census Bureau and Office of Management and Budget officials. All participants provided informed consent.

Classification of Typically Developing Children, Children With Other Special Health Care Needs, and Children With Down Syndrome

Children with special health care needs were identified using the Children With Special Health Care Needs Screener, a widely used tool for identifying children with greater than typical need for healthcare due to chronic illness or disability that was designed to operationalize the MCHB's definition of children with special healthcare needs (Bethell et al., 2002). Children are classified as having special health care needs if they meet at least one of five criteria pertaining to any medical, behavioral, or other health condition lasting or expected to last ≥ 1 year: (1) needing or using a prescription medication; (2) needing or using more health or educational services than is usual for children of the same age; (3) being limited in their ability to do things most children of the same age can do; (4) needing or receiving special therapy (e.g., physical therapy); or (5) needing or receiving treatment or counseling for a chronic emotional, developmental, or behavioral problem. In addition, the NSCH topical questionnaire also ascertained the presence of specific developmental conditions. For each condition other than hearing and vision impairment, parents were asked, “Has a doctor or other health care provider ever told you that this child has [CONDITION]?” The conditions that were queried included “Down syndrome,” “autism or autism spectrum disorder (ASD),” “cerebral palsy,” “intellectual disability (formerly known as mental retardation),” and “developmental delay.” Vision and hearing impairments were determined by parent answer to the questions “Does the child have any blindness or problems seeing even when wearing glasses?” and “Does the child have any deafness or hearing problems?”

Children were categorized into one of five possible groups: typically developing, Down syndrome, or three mutually exclusive other special health care needs comparison groups. The three other special health care needs comparison groups were classified using the following hierarchy: (1) children with a developmental disability that had a high functional impact: autism, cerebral palsy, vision impairment, or hearing impairment; (2) children with a developmental disability, but who did not have Down syndrome or any of the aforementioned high impact developmental disabilities; and (3) children with other special health care needs (e.g., meeting at least one of the five criteria from the Children With Special Health Care Needs Screener but not classified in any of the groups above). Any child not classified as having Down syndrome or other special health care needs (as defined in the three groups above) was classified as a typically developing child.

The selection of three other special health care needs comparison groups is consistent with previous studies that demonstrated Down syndrome, autism, cerebral palsy, visual impairment, and hearing impairment were associated with the greatest health and functional impacts (Boulet et al., 2009; Schieve et al., 2011) and allowed for comparisons of whether the differences in physical activity/sedentary behavior of children with Down syndrome relative to typically developing children are any more pronounced than in children that have other special healthcare needs with similar or lesser functional impact.

Physical Activity and Sedentary Behavior Measures

Physical activity was assessed by parental response to the question, “During the past week, on how many days did this child exercise, play a sport, or participate in physical activity for at least 60 minutes?” with response options of 0 days, 1–3 days, 4–6 days, or every day. Parental report of children's physical activity has been validated against accelerometry (r = 0.41–0.60) and heart rate (0.72–0.82; Sallis, 1991; Sirard & Pate, 2001). Consistent with evidence in youth that suggest that 4 days/week of exercise is sufficient to yield improvements in cardiorespiratory fitness (Baquet et al., 2003), a strong marker of current health among children/adolescents that is predictive of cardiovascular health later in life (Ortega et al., 2008; Ruiz et al., 2009), children were classified as engaging in “regular physical activity” if ≥4 days was reported.

Sports participation was assessed by parental response to the question “During the past 12 months, did this child participate in a sports team or did he or she take sports lessons after school or on the weekends?” with response options of yes or no.

Sedentary behavior was assessed with two items that assessed TV viewing and electronic device use, two of the most common sedentary behaviors among children and adolescents (Atkin et al., 2008; Harrell et al., 2003; Utter, Neumark-Sztainer, Jeffery, & Story, 2003). Time spent in the two sedentary behaviors was assessed by the questions “On an average weekday, about how much time does this child usually spend in front of a TV watching TV programs, videos, or playing video games?” and “On an average weekday, about how much time does this child usually spend with computers, cell phones, handheld video games, and other electronic devices doing things other than schoolwork?” Response options for both of these questions were none, less than 1 hour, 1 hour, 2 hours, 3 hours, or 4 or more hours. Consistent with guidelines for screen time (Strasburger et al., 2013; Tremblay et al., 2016), TV viewing and electronic device use were each dichotomized as ≤2 h/day and >2 h/day.

Covariates

For the present analysis, age, sex, race, Hispanic ethnicity, household educational achievement, born outside United States, household poverty level, and general health were included as covariates. All covariates were derived from parental responses to the National Survey of Children's Health (NSCH) topical questionnaire. Parental report of the child's race included the following response options: White, Black or African American, American Indian or Alaska Native, Chinese, Asian Indian, Filipino, Japanese, Korean, Vietnamese, Other Asian, Native Hawaiian, Guamanian or Chamorro, Samoan, Other Pacific Islander, or Some Other Race. Race was pooled as White, Black, or Other in the NSCH dataset. The highest level of education was assessed for the child's primary caregivers (up to two). Household educational achievement was defined as the highest reported level of education among the child's primary caregivers. To determine household poverty level, total household income during the past year was queried. A family poverty ratio was calculated as the ratio of total family income and the family poverty threshold, derived from the Census Bureau's poverty threshold, which varies according family size and number of children (Van Dyck et al., 2004). The family poverty ratio is top and bottom coded with values ranging from 50 (total family income is 50% of the family poverty threshold) to 400 (total family income is 400% of the family poverty threshold). Values beyond this range are reported as 50 or 400, respectively. General health of the child was assessed with the question, “In general, how would you describe this child's health?” with response options of excellent, very good, good, fair, and poor (U.S. Census Bureau, 2018). This single-item question was adapted from a self-reported general health item heavily utilized by the Center for Disease Control in national surveys of U.S. adults (Zahran et al., 2005).

We did not adjust for body mass index (BMI) in our primary analyses because BMI classification in the NSCH was limited to only children/adolescents aged 10–17 years. As an exploratory analysis, we additionally included BMI classification as a covariate in a restricted sample (e.g., aged 10–17 years). Age- and gender-specific BMI was calculated from parental report of height and weight. Center for Disease Control recommendations for classifying BMI into weight status categories were created in the NSCH dataset: underweight (<5th percentile), healthy weight (≥5th percentile to <85th percentile), overweight (≥85th to <95th percentile), and obese (≥95th percentile; Kuczmarski et al., 2000).

Statistical Analyses

Characteristics of the sample (e.g., means, frequencies) were calculated stratified by child classification: typically developing children, children with Down syndrome, and children with other special healthcare needs (calculated separately for all three groups: with high-impact developmental disability, without high-impact developmental disability, or other). Cohen's effect size d values (for continuous variables) and h values (for categorical variables) were calculated and used to interpret differences in covariates across child groups, with effect sizes ≥0.20 set as a threshold for meaningful differences between groups (Cohen, 2013).

Logistic regression modeling was used to calculate the odds ratio (OR) for physical activity (regular physical activity, sports participation) and sedentary behavior (TV viewing ≥2 h/d, electronic device use ≥2 h/d) associated with Down syndrome and other special healthcare needs (all three groups) versus typically developing children. Crude ORs were initially calculated. Subsequently, ORs were calculated adjusted for age, sex, race, Hispanic ethnicity, household educational achievement, born outside United States, and household poverty level (Model 1), with further adjustment for general health (Model 2). The analyses were then repeated in a fully adjusted model testing interactions for age (6–11 and 12–17 years) and sex (male and female).

As sports participation may account for differences in physical activity between children with special healthcare needs/Down syndrome and typically developing children, models with regular physical activity as the outcome variable were additionally adjusted for sports participation in a secondary analysis. As previously noted, we did not adjust for body mass index (BMI) in our primary models because BMI classification in the NSCH was limited to only children aged 10–17 years. As an exploratory analysis, the previously described analyses were repeated additionally adjusting for BMI classification in the restricted sample (e.g., aged 10–17 years). All analyses were conducted using SAS version 9.4 (SAS Institute, Cary, NC). Due to the small number of children with Down syndrome in the analytic sample (n = 102), the NSCH sampling weights were not used because of the likelihood of large standard errors and imprecise estimates.

Results

Participant Characteristics

Demographic characteristics of children with Down syndrome, children with other developmental disabilities or special health care needs, and typically developing children are shown in Table 1. Children with Down syndrome were more likely to live in households with lower incomes and were less likely to have excellent general health compared to typical children. The prevalence of regular physical activity, sports participation, TV viewing ≥2 h/day, and electronic device use ≥2 h/day among children with Down syndrome, children with other developmental disabilities or special health care needs, and typically developing children is shown in Figure 1. The prevalence of regular physical activity was 56.3%, 48.5%, 45.1%, 38.3%, and 32.4% for typically developing children, children with other special health care needs, children without high impact developmental disabilities, children with high impact developmental disabilities, and children with Down syndrome, respectively.

Association of Down Syndrome With Physical Activity and Sedentary Behaviors

In unadjusted and partially adjusted models, children with Down syndrome had a significantly lower odds of engaging in regular physical activity compared to typically developing children (Table 2). Children with developmental disabilities (with or without high functional impact) or other special health care needs also had a significantly lower odds of engaging in regular physical activity in unadjusted and adjusted models compared to typical children, although children with Down syndrome had the lowest likelihood of engaging in regular physical activity (45% less likelihood relative to typical children vs. 8–37% less likelihood for other groups in most adjusted model). Adjustment for general health attenuated the associations; however, all group differences remained statistically significant. Adjustment for sport participation also attenuated the associations; however, children with Down syndrome (OR: 0.63 [95% CI: 0.41, 0.98]), children with high impact developmental disabilities (OR: 0.80 [95% CI: 0.73, 0.88]) and children with other special health care needs (OR: 0.94 [95% CI: 0.90, 0.99]) still were significantly less likely to engage in regular physical activity relative to typical children. Similarly, in unadjusted and adjusted models, children with Down syndrome and children with other developmental disabilities or other special health care needs were significantly less likely to participate in sports relative to typical children. All results were similar with additional adjustment for BMI classification in a sample restricted to ages 10–17 years (data not shown) and did not vary by age or sex (interaction p-values >0.10).

When examining sedentary behaviors, in unadjusted and partially adjusted models (Model 1, Table 2), children with Down syndrome were significantly more likely to watch TV >2 h/day compared to typical children. However, this association was no longer statistically significant after adjustment for general health. There was no significant association comparing children with Down syndrome to typical children for electronic device use >2 hours/day. Compared to typical children, children with high impact developmental disabilities and children with other special health care needs were significantly more likely to watch TV or use electronic devices for >2 hours/day in unadjusted and adjusted models. Results did not vary by age or sex (interaction p-values >0.10).

Discussion

In this large national survey of children in the United States, children with Down syndrome were 45% less likely to engage in regular physical activity and 52% less likely to participate in sports relative to their typically developing peers. Notably, children with Down syndrome exhibited more pronounced reductions in their likelihood of participating in regular physical activity versus typically developing children than children with other developmental disabilities or special health care needs. It was furthermore observed that children with Down syndrome were more likely to watch high volumes of TV (>2 hours/day) compared to typically developing children, albeit this finding was not statistically significant after accounting for general health. These findings highlight children with Down syndrome as a high-risk target population with an urgent need for tailored interventions and community programs that promote physical activity to reduce health disparities.

A recent systematic review identified three studies that evaluated differences in physical activity levels among children with Down syndrome compared to typically developing children (Fox et al., 2019); two of which reported that children with Down syndrome have lower physical activity levels (Matute-Llorente et al., 2013a, 2013b). Accelerometry, the preferred method for assessing physical activity in children, was importantly utilized in these prior studies and provided strong initial evidence that children with Down syndrome have lower levels of physical activity relative to their peers. However, these prior studies were limited in that they had small sample sizes (n <30) and were unable to account for key covariates other than age. When sociodemographic and health characteristics including age, sex, race, income, maternal education, and BMI were accounted for in a study by Whitt-Glover et al. (2006), differences in physical activity between children with Down syndrome and their typically developing siblings, which were significant in unadjusted models, were no longer statistically significant. As such, Pitetti et al. (2013) have contended that the existing data do not allow for investigators to conclude with definitive confidence whether children with Down syndrome have lower levels of physical activity than typically developing children. The present study thus addresses important evidence gaps and confirms and extends upon previous work to show in a population-based sample that children with Down syndrome are less likely to engage in regular physical activity than typically developing children. Importantly, these findings are independent of differences in physical health, sports participation, and overweightness/obesity, as well as key demographic (sex) and socioeconomic (parental education, household income) indicators; potentially contributing factors that were largely unaccounted for in prior studies. Furthermore, the present study is the first to show that the lower rates of regular physical activity in children with Down syndrome are more pronounced than in children with other developmental disabilities or special health care needs. Children with Down syndrome were 45% less likely to engage in regular physical activity compared to typically developing children. In contrast, children with other special health care needs, non-high impact developmental disabilities, or high-impact development disabilities were 8%, 15%, and 37% less likely to engage in regular physical activity compared to typically developing children, respectively. As children with Down syndrome have high rates of obesity (Bertapelli et al., 2016) and given that physical fitness and physical activity have been shown to influence physical and cognitive function in this population (Chen et al., 2015; Cowley et al., 2010; Ptomey et al., 2018), there is a great need for identifying the unique barriers to physical activity in children with Down syndrome and efforts to promote greater physical activity adoption.

In the present study, children with Down syndrome were less likely to participate in sports, with only 43% participating in sports relative to ∼70% for typically developing children. Prior studies have reported that children with intellectual disability (not exclusive to Down syndrome) participate less often and less frequently in physical activity-based recreational activity relative to their typically developing peers (Chien et al., 2017; Kaljaca et al., 2018; Shields et al., 2014). Thus, the present work confirms these previous findings for the first time in a sample of children with Down syndrome and are of concern given the documented benefits of sports participation, including improved self-efficacy, mood, and social competence (Hoogsteen & Woodgate, 2010; Ozer et al., 2012). Nonetheless, the observed findings are not surprising given the documented barriers to sports participation in this population including lack of access to inclusive sports programs, recreational facilities, and coaches with training or experience in adapted sport/physical activity instruction; lack of motor and social proficiency; and the high need for support from parents, peers, or service providers in order to participate (Kaljaca et al., 2018; McGarty & Melville, 2018).

Previous research suggests that children with Down syndrome spend more time sedentary relative to their typically developing peers (Matute-Llorente et al., 2013a, 2013b). Again, however, these studies are limited by small sample sizes and minimal covariate adjustment. Further, as sedentary time was ascertained via accelerometry, it is unclear what types of sedentary behavior children with Down syndrome typically engage in more often relative to their peers. Such information could be helpful for the development of more targeted sedentary interventions in this population. In the present study, children with Down syndrome were more likely to watch high volumes of TV compared to typically developing children, but no differences were observed for electronic device use. It should be acknowledged that the results for TV viewing were not statistically significant after accounting for general health, suggestive that differences in physical health may account for the observed differences in TV viewing comparing children with Down syndrome to typically developing children. Nonetheless, this finding suggests that reductions in TV viewing and replacement with either physical activity or less passive and more mentally active sedentary behaviors (e.g., reading; Hallgren et al., 2018) that require greater levels of cognitive stimulation and engagement (if physical health precludes more activity) may be warranted in children with Down syndrome.

This study has several limitations. First, all NSCH data, including physical activity and sedentary behavior measures, were assessed by parental report mostly entailing one-item questions for a given topic. As such, there is a likelihood of recall bias and measurement error. Notably, as children typically perform sporadic movements that are brief in duration and varied in activity type, the assessment of physical activity in children via questionnaire is challenging and prone to measurement error. Parental reports of physical activity may be further prone to measurement error because parents may be unable to accurately quantify physical activity levels during school or other times away from the home. Thus, some caution is warranted when interpreting these results. Nonetheless, these findings confirm initial reports that accelerometer-measured physical activity levels were lower in children with Down syndrome relative to their typically developing peers (Matute-Llorente et al., 2013a, 2013b). Future population-based studies that utilize accelerometers to measure physical activity may still be needed to confirm these findings. Second, as a sample survey, the NSCH is subject to nonresponse bias. Third, the survey nature of the NSCH precluded medical professional confirmation of a child having a special health care need. Nor was severity for most conditions documented. Nonetheless, we adjusted for parental report of general health to account for potential differences in health condition severity. Finally, the sample size of children in the NSCH with Down syndrome is relatively small, albeit still comprising one of the largest samples to date to examine physical activity/sedentary behavior levels in this population. The small sample size precluded use of the NSCH sample weights. As such, the reported results are not nationally representative and may have limited generalizability.

In conclusion, in a large national survey of children in the United States, children with Down syndrome were less likely to engage in regularly physical activity compared to typically developing children and had the lowest likelihood among all subgroups of children with other developmental disabilities and special healthcare needs. There is a dearth of published interventions and programs targeting physical activity in populations with intellectual disability (Pitchford, Dixon-Ibarra, & Hauck, 2018). Thus, the present findings underscore an urgent need for researchers, health organizations, community groups, and funding agencies to design and support health promotion programs for children with Down syndrome.

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Author notes

Disclosure of potential conflict of interest: Keith M. Diaz has a son with Down syndrome.