Research in Developmental Disabilities 35 (2014) 3081–3088

Contents lists available at ScienceDirect

Research in Developmental Disabilities

Patterns of habitual physical activity in youth with

and without Prader-Willi Syndrome

Diobel M. Castner a, Jared M. Tucker b, Kathleen S. Wilson a, Daniela A. Rubin a,*a Department of Kinesiology, California State University, Fullerton, 800 North State College Boulevard, Fullerton, CA 92834, USAb Healthy Weight Center, Helen DeVos Children’s Hospital, 100 Michigan NE, Grand Rapids, MI 49503, USA

A R T I C L E I N F O

Article history:

Received 4 June 2014

Received in revised form 14 July 2014

Accepted 15 July 2014

Available online

Keywords:

Accelerometer

Physical activity

Prader-Willi Syndrome

Childhood obesity

A B S T R A C T

Children classified as overweight or obese and those with disabilities are at a greater risk of

not meeting the minimum recommendation of 60 min a day of moderate to vigorous

physical activity (PA). Youth with Prader-Willi Syndrome (PWS) appear to participate in

less PA compared to nonsyndromal children, likely due to syndrome-related factors.

However, description of PA patterns in youth with PWS is lacking. The purpose of this

study was to characterize PA in youth with PWS and to compare it to PA in children with

nonsyndromal obesity. Twenty-four youth with PWS (ages 8–16 years) and 40 obese

children without PWS (OB) (ages 8–11 years) wore accelerometers for eight consecutive

days. Data were screened for compliance and classified into PA intensities: sedentary

behavior (SED), light (LPA), moderate (MPA), vigorous (VPA) and moderate plus vigorous

(MVPA). Youth with PWS spent 19.4% less time in weekly LPA (p = 0.007) and 29.8% less

time in weekly VPA compared to OB controls (p = 0.036). All other intensities were similar

between groups. In addition, PWS participated in less LPA and VPA during the weekends

compared to OB, and less LPA on weekdays when compared to OB. There was also a trend

towards PWS participating in less MVPA during the weekends and less VPA during the

weekends than OB controls. There was a trend towards PWS participating in less VPA on

weekends compared to weekdays, while OB participated similarly in VPA on weekdays

and weekend days. On average, neither PWS nor OB children met minimum MVPA

recommendations. The results suggest there is a need to design exercise programs for PWS

youth that focus on integrating vigorous intensity activities, especially during the

weekends when structured PA may not be available.

� 2014 Elsevier Ltd. All rights reserved.

1. Introduction

The United States Department of Health and Human Services recommends that children participate in a minimum of60 min of moderate to vigorous physical activity (PA) per day (U.S. Department of Health and Human Services, 2000).Additionally, PA of at least vigorous intensity should be incorporated at least three days per week. Currently, approximately42% of children ages six to eleven years old meet this PA requirement (Belcher et al., 2010; Troiano et al., 2008). PA levels are

* Corresponding author at: Department of Kinesiology, California State University, Fullerton, 800 North State College Boulevard, KHS-138, Fullerton, CA

92834, USA. Tel.: +1 657 278 4704.

E-mail addresses: dcastner@fullerton.edu (D.M. Castner), jared.tucker@helendevoschildrens.org (J.M. Tucker), kswilson@fullerton.edu (K.S. Wilson),

drubin@fullerton.edu (D.A. Rubin).

http://dx.doi.org/10.1016/j.ridd.2014.07.035

0891-4222/� 2014 Elsevier Ltd. All rights reserved.

D.M. Castner et al. / Research in Developmental Disabilities 35 (2014) 3081–30883082

even lower in children classified as overweight and obese when compared to lean children (Belcher et al., 2010; Dorsey,Herrin, & Krumholz, 2011; Trost, Kerr, Ward, & Pate, 2001). Children with disabilities are also encouraged to meet the samePA recommendation as well as participate in organized sports, recreational activities and spontaneous PA (Murphy &Carbone, 2008). However, it has been suggested that children with disabilities are less physically active compared to childrenwithout disabilities (U.S. Department of Health and Human Services, 2000).

Prader-Willi Syndrome (PWS) is the best characterized form of congenital childhood obesity (Cassidy, Schwartz, Miller, &Driscoll, 2012). PWS is a genetic disease stemming from an alteration or lack of expression of the paternal chromosome 15 inthe locus 13-15q. Individuals with PWS have abnormal body composition, characterized by excessive body fat, decreasedlean mass and hypotonia. In addition, individuals with PWS present poor muscle strength and coordination, hormonaldeficiencies (particularly growth hormone secretion), poor stamina, lethargy, behavioral issues and moderate cognitivedisability (Eiholzer & Whitman, 2004; Holm et al., 1993; Reus et al., 2011).

In general, individuals with PWS participate in less PA compared to nonsyndromal controls (Butler, Theodoro, Bittel, &Donnelly, 2007; van den Berg-Emons, Festen, Hokken-Koelega, Bussmann, & Stam, 2008; van Mil et al., 2000) and engage infewer activities targeted to promote muscular strength (Rubin, Mouttapa, Weiss, & Barrera-Ng, 2012). Further, adults withPWS engage in less lifestyle PA than other adults with disability (Nordstrøm, Hansen, Paus, & Kolset, 2013) and prefersedentary behaviors such as watching television, playing computer games and arts and crafts (Dykens, 2012). However,some studies have suggested that generalizing PA habits in PWS is premature, as some individuals with PWS have exhibitedsimilar PA levels as those without the syndrome (Nardella, Sulzbacher, & Worthington-Roberts, 1983; van den Berg-Emonset al., 2008) when using direct measures of PA (i.e., actometers and pedometers). To date, no study has evaluated the physicalactivity patterns of children and adolescents with PWS, including the intensity and timing of PA throughout the week.

Therefore, the purpose of this study was to compare PA duration and intensity between youth with PWS andnonsyndromal obese controls. A secondary purpose was to evaluate differences in weekly patterns of PA (i.e., weekdays vs.weekend days) between youth with and without PWS. By identifying potential deficiencies in PA engagement in PWS duringweekdays or weekends, more focused intervention strategies can be designed to meet the needs of this population.

2. Methods

2.1. Participants

Twenty-four youth with PWS ages eight to sixteen years and 40 obese children without PWS ages eight to eleven years(OB = body fat percentage> 95th percentile for age and sex) (McCarthy, Cole, Fry, Jebb, & Prentice, 2006) participated in thisstudy. Due to the low prevalence of PWS (1 in 15,000 live births), a larger age range was implemented for participation. AllPWS participants provided genetic testing documentation to confirm diagnosis with this syndrome: uniparental deletion(n = 10), uniparental disomy (n = 3), either uniparental disomy or imprinting defect (n = 3) and positive DNA methylation(n = 8). PWS participants exhibited other associated conditions including type I diabetes (n = 1), type II diabetes (n = 1),asthma (n = 6), sleep apnea (n = 6), hip dysplasia (n = 2), seizures (n = 5), hypothyroidism (n = 1) and scoliosis (n = 5).Additionally, some participants with PWS reported engaging in physical therapy either currently (n = 7) or previously(n = 15). Most youth with PWS also reported current (n = 15) or previous (n = 6) growth hormone replacement therapy(GHRT). This study was approved by the Institutional Review Boards from California State University, Fullerton (CSUF) andthe United States Army Medical Research and Materiel Command. Written informed assent and consent were obtained fromall participants and parents prior to participation. Children with confirmed pregnancy, those on lipid-lowering, diabetes orblood pressure medications, or those unable to participate in moderate plus vigorous PA were excluded from participation.

2.2. Study procedures

Participants completed one Saturday visit at the CSUF campus. Parents of participants completed a medical historyquestionnaire regarding their child’s health and participation in moderate- and vigorous-intensity PA. With the help of theirparent, obese controls completed a previously validated self-report questionnaire to determine pubertal development(Petersen, Crockett, Richards, & Boxer, 1988). The Pubertal Developmental Scale questionnaire was integrated into themedical history questionnaire for PWS participants, which parents completed. All participants were measured foranthropometrics and body composition. At the end of the visit, participants received a GT3X triaxial accelerometer(ActiGraph, LLC, Pensacola, FL) attached to an elastic belt that they were asked to wear during the following eight days. Thisstudy was part of a larger research effort devoted to investigating the effectiveness of a 24-week home-based PA program(Rubin, Wilson, Wiersma, Weiss, & Rose, 2014). All measurements included in this manuscript are measurements obtainedat the baseline visit before the completion of the PA intervention.

2.3. Anthropometric and physiologic measurements

Participants removed shoes before all measurements. Body mass was measured using a digital scale (ES200L, Ohaus,Pinewood, NJ) while participants wore a t-shirt and shorts. Height was measured at the end of inhalation using a wall-mounted stadiometer (Seca, Ontario, CA). Total body fat percentage was determined using a whole body dual-energy X-ray

D.M. Castner et al. / Research in Developmental Disabilities 35 (2014) 3081–3088 3083

absorptiometry (DXA) scan (GE Healthcare, GE Lunar Corp., Madison, WI). Female participants who had their first menseswere required to complete a pregnancy test prior to completing the DXA scan.

2.4. PA measurement

During the visit, families completed an accelerometer training session. Participants were instructed to wear the elasticbelt across the waist line with the accelerometer over the right hip. Accelerometers were initialized following manufacturerspecifications at 5-s epochs. Participants were instructed to wear the device for eight consecutive days (Sunday to Sunday)during all waking hours, except while bathing, showering or swimming. Parents were provided with an accelerometerinstructions sheet and a pre-paid envelope to mail back the accelerometer at the end of the eight days. Members of theresearch team also called the parents during the week to ensure appropriate accelerometer wear. Additionally, participantenrollment in the study was done in cohorts, which resulted in 47 children measured for PA during a school session and 17children measured for PA during summer break.

Accelerometry data were downloaded using the ActiLife5 software version 5.10.0.0 (ActiGraph, LLC, Pensacola, FL). Datawere screened for compliance and those with a minimum of 10 h wear time on at least three weekdays and one weekendday were included in the analyses. Non-wear time was determined as 60 consecutive min of zero PA counts. Becauseparticipants completed a second visit to CSUF the following Saturday (Day 7) as part of the PA intervention study, data fromSaturday were omitted. Accelerometry data were then categorized into five intensity levels: sedentary behavior (SED), low(LPA), moderate (MPA), vigorous (VPA) and moderate plus vigorous (MVPA). Evenson, Catellier, Gill, Ondrak, andMcMurray (2008) cut-points were used to determine the intensity levels (Trost, Loprinzi, Moore, & Pfeiffer, 2011). SED waslimited to a window of 6:00 AM to 10:00 PM to omit potential overnight wear time. All PA data were included regardless oftime.

2.5. Statistical analysis

One-way analysis of variance (ANOVA) tests were conducted to determine group differences for participantcharacteristics. All PA data were screened for normality using skewness calculations and square root transformationswere completed for all intensities except for sedentary behavior. A two (group: PWS vs. OB) by two (day of week: weekdayvs. weekend day) multivariate ANOVA (MANOVA) was initially conducted to determine group and day of week differencesfor all PA intensities. However, because the interaction power was low for all intensities (power< 0.096 for all), separateanalyses were conducted to determine (1) group differences for weekly PA, weekday PA and weekend day PA and (2) day ofweek differences in PA for either PWS or OB. Thus, MANCOVAs controlling for sex, age, pubertal development or school year/summer were used. These covariates were selected based on previous research (Baker, Birch, Trost, & Davison, 2007; Belcheret al., 2010; Long et al., 2013) linking them to PA. Only significant covariates in each analysis were kept for each model.Significance level for all statistical analyses was set at p< 0.050. Values in the text are presented as mean� standard error.Raw PA data values were reported in lieu of transformed data for ease of interpretation. IBM SPSS Statistics 20.0 for Windows(SPSS, Inc., Chicago, IL) was used for the statistical analysis. Sigma Plot for Windows version 10.0 (Systat Software, Inc., San Jose,CA) was used to generate Figs. 1 and 2.

3. Results

3.1. Participant demographics and characteristics

Participant demographics and characteristics are presented in Table 1. As expected, PWS were older than OB (p = 0.001).All other characteristics were similar between groups. 42% of PWS and 45% of OB reported being at either pre- (I) or early-pubertal (II) stages.

3.2. Group differences for weekly, weekday and weekend PA

Weekly PA data are presented in Fig. 1. PWS and OB spent similar time in SED (660.5� 15.1 min/day vs. 638.7� 11.7 min/day, respectively; p = 0.257), MPA (26.2� 2.4 min/day vs. 28.9� 1.9 min/day, respectively; p = 0.359) and MVPA (36.1� 3.2 min/day vs. 43.0� 2.9 min/day, respectively; p = 0.138) throughout the week. PWS participated in less weekly PA compared to OB forLPA (130.3� 9.4 min/day vs. 161.7� 7.0 min/day, respectively; p = 0.007) and VPA (9.9� 1.2 min/day vs. 14.1� 1.3 min/day,respectively; p = 0.036). In general, 8% of PWS and 18% of OB met the 60 min per day MVPA recommendation.

Group differences for weekday and weekend PA are presented in Table 2. During weekdays, both groups spent similartime in SED, MPA and MVPA (p> 0.293 for all). PWS spent less time in LPA (p = 0.016) and there was a trend towards less VPA(p = 0.090) than OB on weekdays. Additionally, 17% of PWS and 20% of OB met the MVPA recommendation on weekdays.During weekends, both groups engaged in similar SED and MPA (p> 0.178). However, PWS engaged in less LPA (p = 0.028)and VPA (p = 0.040) than OB on weekend days. There was also a trend towards PWS engaging in less MVPA (p = 0.085) thanOB on weekend days. During weekends, 8% of PWS and 13% of OB met the MVPA recommendation.

[(Fig._1)TD$FIG]

SED

Dur

atio

n (m

in/d

ay)

0

200

400

600

800

Group

PWS Obese

MV

PA

Dur

atio

n (m

in/d

ay)

0

10

20

30

40

50VPAMPA

LP

A D

urat

ion

(min

/day

)

0

20

40

60

80

100

120

140

160

180

*

*

Fig. 1. Weekly sedentary behavior or physical activity (min/day) in youth with PWS and obesity. Data are expressed as mean (standard error). *p< 0.050,

where PWS< obese.

D.M. Castner et al. / Research in Developmental Disabilities 35 (2014) 3081–30883084

3.3. Weekday versus weekend PA within group comparisons

For PWS, there were no differences between weekdays and weekends for SED (657.3 � 21.4 min/day vs.667.0 � 21.4 min/day, respectively; p = 0.752) or LPA (132.6� 9.7 min/day vs. 125.6 � 10.4 min/day, respectively; p = 0.495).Fig. 2a presents weekdays versus weekend MPA, VPA and MVPA for PWS. MPA (p = 0.164) and MVPA (p = 0.107) were similarduring weekdays and weekend days in PWS. In contrast, there was a trend towards PWS engaging in less VPA on weekend daysversus weekdays (p = 0.074). OB participated in similar SED and PA (for all intensities – see Fig. 2b) on weekdays and weekenddays (p> 0.101 for all).

[(Fig._2)TD$FIG]

Day of Week

Weekday Weekend

MV

PA

Du

rati

on (

min

/day

)

0

10

20

30

40

50VPAMPA

Day of Week

Weekday Weekend

MV

PA

Du

rati

on (

min

/day

)

0

10

20

30

40

50VPAMPA

a) b)

#

Fig. 2. Weekday versus weekend day moderate plus vigorous physical activity (min/day) in (a) youth with PWS and (b) obesity. Data are expressed as mean

(standard error). #p = 0.074, indicating a trend towards weekday>weekend.

D.M. Castner et al. / Research in Developmental Disabilities 35 (2014) 3081–3088 3085

4. Discussion

4.1. Overview

The results of this study showed that throughout the week, youth with PWS engaged in less LPA and VPA than childrenwith nonsyndromal obesity. Specifically, in comparison to OB, PWS engaged in less LPA on weekdays and less LPA and VPA onweekends. Additionally, there was a trend for PWS to participate in less VPA on weekdays and less MVPA on weekendscompared to OB. MPA was similar between both groups regardless of day of the week. Lastly, there was a trend for youth withPWS to participate in less VPA during weekends compared to weekdays.

4.2. Meeting the MVPA recommendation

Neither group met the MVPA recommendations, with more youth with PWS being inactive as only 8% of PWS and 18% ofOB obtained 60+ minutes per day of MVPA. The percentage of youth with PWS from Southern California not meeting therecommendations is similar to the 12% of adults with PWS recently reported in Europe (Nordstrøm et al., 2013). Likewise, inyouth with Down Syndrome, only 20.6% of the study sample met the PA recommendation (Esposito, MacDonald, Hornyak, &Ulrich, 2012). Despite that, in the U.S., 42% of 6–11-year-olds without disability currently meet the PA recommendation(Belcher et al., 2010; Troiano et al., 2008). In the present study, a much smaller proportion of the children with obesity (18%)met this recommendation. It is possible that levels of MVPA in the children from the current study may be lower than in thegeneral population as these measurements were obtained at baseline in participants of a PA intervention study. Nonetheless,

Table 1

Participant demographics and characteristics by group.

PWS (n = 24) Obese (n = 40)

Male/female 12/12 21/19

Age (y) 11.2 (2.3)* 9.8 (1.1)

Stature (cm) 143.8 (13.3) 146.3 (8.8)

Total body mass (kg) 62.1 (29.5) 59.1 (13.3)

Body mass index (kg/m2) 29.4 (12.7) 27.3 (4.0)

Pubertal development (I–IV)

Stage I 2 9

Stage II 8 9

Stage III 10 17

Stage IV 4 5

Body fat mass (%) 45.8 (11.0) 44.1 (5.7)

Lean body mass (kg) 30.1 (11.4) 30.9 (5.5)

Data are expressed as frequency or mean (standard deviation).

* p< 0.050, where PWS> obese.

Table 2

Differences in sedentary behavior or physical activity (min/day) in youth with PWS and obesity during weekdays and weekend days.

SED LPA MPA VPA MVPA

Weekday

PWS (n = 24) 657.3 (15.1) 132.6 (9.7) 27.7 (2.9) 10.9 (1.4) 38.5 (3.8)

Obese (n = 40) 640.0 (11.7) 162.7 (7.0) 29.6 (2.1) 14.7 (1.5) 44.3 (3.2)

p-value 0.367 0.016b 0.611a,c 0.090c 0.293a,c

Weekend day

PWS (n = 24) 667.0 (24.7) 125.6 (10.4) 22.6 (2.5) 7.9 (1.3) 30.4 (3.3)

Obese (n = 40) 633.3 (19.1) 158.3 (8.6) 27.8 (2.7) 11.9 (1.5) 39.7 (3.7)

p-value 0.285 0.028b 0.178 0.040c 0.085

Data are expressed as mean (standard error).a Adjusted for sex.b Adjusted for puberty status.c Adjusted for school.

D.M. Castner et al. / Research in Developmental Disabilities 35 (2014) 3081–30883086

the low rate of MVPA participation is alarming. The results demonstrate that youth with PWS are at an enormous risk forphysical inactivity.

4.3. Low LPA and VPA

Youth with PWS participated in less LPA throughout the week compared to obese children. Previous studies have shownthat individuals with PWS exhibit lower spontaneous PA energy expenditure (Butler et al., 2007) and participate in lesslifestyle PA when compared to controls (Nordstrøm et al., 2013). Preference for sedentary over physical activities have alsobeen demonstrated in PWS (Dykens, 2012; Nordstrøm et al., 2013; van den Berg-Emons et al., 2008). Likely, lower LPAparticipation in PWS compared to obese controls is related to less preference for movement leading to less lifestyle PA(Ainsworth et al., 2011).

Additionally, youth with PWS may be at a disadvantage to engage in VPA due to their inherent poor stamina (Butler,Hanchett, & Thompson, 2006), cardiovascular fitness (Castner, Rubin, Judelson, & Haqq, 2013) and motor proficiency (Whiteet al., 2012). It is possible that more stamina, better cardiovascular fitness (Rowlands, Eston, & Ingledew, 1999) and motorproficiency (Wrotniak, Epstein, Dorn, Jones, & Kondilis, 2006) would contribute to higher PA participation in youth with PWS,specifically in activities of vigorous intensity.

In addition, muscle mass, muscle strength and power production all contribute to movement characteristics. PWSparticipants in this study (age range: 8–16 years) presented a similar lean mass as the obese controls (age range: 8–11 years).However, when comparing only those with PWS ages 8–11 years (n = 15) to the age-matched nonsyndromal obese controls(n = 40), PWS had significantly less lean mass than controls (24.7� 1.4 kg vs. 30.9� 0.9 kg, respectively; p< 0.001), coincidingwith results from previous studies (Butler et al., 2007; Rubin et al., 2013). In addition, low strength has been shown in youngwomen with PWS, who presented 50% and 70% less isokinetic strength during knee flexion and extension, respectively, whencompared to age- and sex-matched obese and lean controls (Capodaglio et al., 2009). Last, youth with PWS have been shown toproduce significantly lower relative peak power output (watts per kg of lean body mass) during cycling in comparison to lean andobese controls (Castner et al., 2013). Therefore, it is likely that low muscle mass, strength and power characteristics of thesyndrome contribute to low PA participation, which, in turn, largely impacts participation in VPA (Butler et al., 2007; Capodaglioet al., 2009; Castner et al., 2013).

A factor worth mentioning is that 57.7% of the PWS participants in the present study reported current GHRT. GHRT hasbeen shown to increase muscle mass and physical activity levels in infants (Myers et al., 2007) and youth (Eiholzer et al.,1998) with PWS. These results are optimized when GHRT is combined with physical training (Schlumpf et al., 2006).Therefore, our results suggest that despite that a large proportion of participants with PWS were on GHRT, they still did notmeet the PA recommendations.

4.4. Participation in MPA

Walking is reported as the most frequent activity of moderate intensity in 75% of children, 81.5% of adolescents and62.9% of adults with PWS (Rubin et al., 2012). This preference for walking may explain the similar MPA between thosewith and without PWS. Another possible factor contributing to similar minutes of MPA during weekdays in both groupscould be structured PA (i.e., physical education at school or therapies). van den Berg-Emons et al. (2008) found that as agroup, youth with PWS were less active than other children; however, half of the PWS participants had similar activitylevels as age- and gender-matched healthy children when PA was measured over two school weekdays (van den Berg-Emons et al., 2008). Therefore, it seems that if there is a structure in place for PA participation, those with PWS maybenefit from it.

D.M. Castner et al. / Research in Developmental Disabilities 35 (2014) 3081–3088 3087

4.5. Structuring PA for youth with PWS: weekdays versus weekend days

Based on present findings, the low participation in LPA and VPA in PWS is a concern. Eiholzer et al. (2003) showed thatafter completing a structured 3-month calf exercise training program in youth with PWS, there was a significant increasefrom pre- to post-training for physical activity (walking distance: 11.1 km vs. 17.4 km, respectively) and physical capacity(calf exercise: 22.7 repetitions vs. 57.3 repetitions, respectively) (Eiholzer et al., 2003). More emphasis needs to be placed onstructuring activities that youth with PWS will enjoy, but will also yield physiological benefits (i.e., weight bearing/musclestrengthening activities). Additionally, our results suggest that youth with PWS are at higher risk of not participating in VPAduring the weekends, where structured PA, such as physical education, is likely less frequent. In those with PWS, a largerpercentage met recommendations during weekdays than weekend days (17% vs. 8%).

4.6. Study limitations

The sample for the current study was drawn from children who consented to begin a home-based PA program. Therefore,it is possible that their typical activity levels may differ from other children with and without PWS. Additionally, thesechildren may have been more inclined to participate in PA during the measurement period of this study because of theirwillingness to participate in the home-based PA program. Lastly, the specific type of PA (i.e., structured or unstructured) wasnot evaluated for this study. Further studies should evaluate both quantitative (i.e., accelerometers) and descriptive (i.e.,daily logs) measures of PA in order to better interpret PA preferences and potentially design better interventions andprograms that will effectively increase PA participation in PWS youth.

5. Conclusion

In a cohort enrolled to begin a PA program, both youth with and without PWS did not meet the minimum MVPArecommendations. Youth with PWS engaged in less overall PA than obese youth without PWS. Of particular concern is atendency for PWS youth to engage in less light- and vigorous-intensity activity than their nonsyndromal peers, on bothweekends and throughout the week. Exercise interventions and programs should focus on integrating activities of vigorousintensity, along with activities that the child will enjoy, as well as providing more opportunities to engage in spontaneous PAof low intensity.

Acknowledgements

The authors would like to thank the participants and their families. This study was supported by the US Army MedicalResearch and Materiel Command Award W81XWH-09-1-0682.

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