Research in Developmental Disabilities 35 (2014) 3081–3088
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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 b
Department of Kinesiology, California State University, Fullerton, 800 North State College Boulevard, Fullerton, CA 92834, USA 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
A B S T R A C T
Article history: Received 4 June 2014 Received in revised form 14 July 2014 Accepted 15 July 2014 Available online
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. ß 2014 Elsevier Ltd. All rights reserved.
Keywords: Accelerometer Physical activity Prader-Willi Syndrome Childhood obesity
1. Introduction The United States Department of Health and Human Services recommends that children participate in a minimum of 60 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, approximately 42% 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: [email protected] (D.M. Castner), [email protected] (J.M. Tucker), [email protected] (K.S. Wilson), [email protected] (D.A. Rubin). http://dx.doi.org/10.1016/j.ridd.2014.07.035 0891-4222/ß 2014 Elsevier Ltd. All rights reserved.
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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 same PA 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 children without 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 in the locus 13-15q. Individuals with PWS have abnormal body composition, characterized by excessive body fat, decreased lean mass and hypotonia. In addition, individuals with PWS present poor muscle strength and coordination, hormonal deficiencies (particularly growth hormone secretion), poor stamina, lethargy, behavioral issues and moderate cognitive disability (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 in fewer activities targeted to promote muscular strength (Rubin, Mouttapa, Weiss, & Barrera-Ng, 2012). Further, adults with PWS engage in less lifestyle PA than other adults with disability (Nordstrøm, Hansen, Paus, & Kolset, 2013) and prefer sedentary 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 exhibited similar PA levels as those without the syndrome (Nardella, Sulzbacher, & Worthington-Roberts, 1983; van den Berg-Emons et al., 2008) when using direct measures of PA (i.e., actometers and pedometers). To date, no study has evaluated the physical activity 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 and nonsyndromal 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 during weekdays 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 this study. Due to the low prevalence of PWS (1 in 15,000 live births), a larger age range was implemented for participation. All PWS 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) and the United States Army Medical Research and Materiel Command. Written informed assent and consent were obtained from all participants and parents prior to participation. Children with confirmed pregnancy, those on lipid-lowering, diabetes or blood 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 history questionnaire regarding their child’s health and participation in moderate- and vigorous-intensity PA. With the help of their parent, 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 the medical history questionnaire for PWS participants, which parents completed. All participants were measured for anthropometrics 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. This study 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 obtained at 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 wallmounted stadiometer (Seca, Ontario, CA). Total body fat percentage was determined using a whole body dual-energy X-ray
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absorptiometry (DXA) scan (GE Healthcare, GE Lunar Corp., Madison, WI). Female participants who had their first menses were 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 elastic belt across the waist line with the accelerometer over the right hip. Accelerometers were initialized following manufacturer specifications 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 accelerometer instructions sheet and a pre-paid envelope to mail back the accelerometer at the end of the eight days. Members of the research team also called the parents during the week to ensure appropriate accelerometer wear. Additionally, participant enrollment in the study was done in cohorts, which resulted in 47 children measured for PA during a school session and 17 children measured for PA during summer break. Accelerometry data were downloaded using the ActiLife5 software version 5.10.0.0 (ActiGraph, LLC, Pensacola, FL). Data were screened for compliance and those with a minimum of 10 h wear time on at least three weekdays and one weekend day were included in the analyses. Non-wear time was determined as 60 consecutive min of zero PA counts. Because participants completed a second visit to CSUF the following Saturday (Day 7) as part of the PA intervention study, data from Saturday 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, and McMurray (2008) cut-points were used to determine the intensity levels (Trost, Loprinzi, Moore, & Pfeiffer, 2011). SED was limited to a window of 6:00 AM to 10:00 PM to omit potential overnight wear time. All PA data were included regardless of time. 2.5. Statistical analysis One-way analysis of variance (ANOVA) tests were conducted to determine group differences for participant characteristics. All PA data were screened for normality using skewness calculations and square root transformations were completed for all intensities except for sedentary behavior. A two (group: PWS vs. OB) by two (day of week: weekday vs. weekend day) multivariate ANOVA (MANOVA) was initially conducted to determine group and day of week differences for all PA intensities. However, because the interaction power was low for all intensities (power < 0.096 for all), separate analyses were conducted to determine (1) group differences for weekly PA, weekday PA and weekend day PA and (2) day of week 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; Belcher et 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 earlypubertal (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 for LPA (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 similar time 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) than OB on weekend days. During weekends, 8% of PWS and 13% of OB met the MVPA recommendation.
[(Fig._1)TD$IG]
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SED Duration (min/day)
800
600
400
200
0 180
LPA Duration (min/day)
160
*
140 120 100 80 60 40 20 0 50
VPA MPA MVPA Duration (min/day)
40
30
20
10
* 0 PWS
Obese Group
Fig. 1. Weekly sedentary behavior or physical activity (min/day) in youth with PWS and obesity. Data are expressed as mean (standard error). *p < 0.050, where PWS < obese.
3.3. Weekday versus weekend PA within group comparisons For PWS, there were no differences between weekdays and weekends for SED (657.3 21.4 min/day vs. 667.0 21.4 min/day, respectively; p = 0.752) or LPA (132.6 9.7 min/day vs. 125.6 10.4 min/day, respectively; p = 0.495). Fig. 2a presents weekdays versus weekend MPA, VPA and MVPA for PWS. MPA (p = 0.164) and MVPA (p = 0.107) were similar during weekdays and weekend days in PWS. In contrast, there was a trend towards PWS engaging in less VPA on weekend days versus weekdays (p = 0.074). OB participated in similar SED and PA (for all intensities – see Fig. 2b) on weekdays and weekend days (p > 0.101 for all).
[(Fig._2)TD$IG]
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a)
b)
50
50
VPA MPA
VPA MPA
40
MVPA Duration (min/day)
40
MVPA Duration (min/day)
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30
20
10
30
20
10
# 0
0 Weekday
Weekend
Weekday
Day of Week
Weekend
Day of Week
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.
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 children with nonsyndromal obesity. Specifically, in comparison to OB, PWS engaged in less LPA on weekdays and less LPA and VPA on weekends. Additionally, there was a trend for PWS to participate in less VPA on weekdays and less MVPA on weekends compared to OB. MPA was similar between both groups regardless of day of the week. Lastly, there was a trend for youth with PWS 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% of OB obtained 60+ minutes per day of MVPA. The percentage of youth with PWS from Southern California not meeting the recommendations is similar to the 12% of adults with PWS recently reported in Europe (Nordstrøm et al., 2013). Likewise, in youth 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 the general 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 Age (y) Stature (cm) Total body mass (kg) Body mass index (kg/m2)
12/12 11.2 (2.3)* 143.8 (13.3) 62.1 (29.5) 29.4 (12.7)
21/19 9.8 (1.1) 146.3 (8.8) 59.1 (13.3) 27.3 (4.0)
Pubertal development (I–IV) Stage I Stage II Stage III Stage IV
2 8 10 4
9 9 17 5
Body fat mass (%) Lean body mass (kg)
45.8 (11.0) 30.1 (11.4)
44.1 (5.7) 30.9 (5.5)
Data are expressed as frequency or mean (standard deviation). * p < 0.050, where PWS > obese.
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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) Obese (n = 40) p-value
657.3 (15.1) 640.0 (11.7) 0.367
132.6 (9.7) 162.7 (7.0) 0.016b
27.7 (2.9) 29.6 (2.1) 0.611a,c
10.9 (1.4) 14.7 (1.5) 0.090c
38.5 (3.8) 44.3 (3.2) 0.293a,c
Weekend day PWS (n = 24) Obese (n = 40) p-value
667.0 (24.7) 633.3 (19.1) 0.285
125.6 (10.4) 158.3 (8.6) 0.028b
22.6 (2.5) 27.8 (2.7) 0.178
7.9 (1.3) 11.9 (1.5) 0.040c
30.4 (3.3) 39.7 (3.7) 0.085
Data are expressed as mean (standard error). a Adjusted for sex. b Adjusted for puberty status. c Adjusted for school.
the low rate of MVPA participation is alarming. The results demonstrate that youth with PWS are at an enormous risk for physical inactivity. 4.3. Low LPA and VPA Youth with PWS participated in less LPA throughout the week compared to obese children. Previous studies have shown that individuals with PWS exhibit lower spontaneous PA energy expenditure (Butler et al., 2007) and participate in less lifestyle PA when compared to controls (Nordstrøm et al., 2013). Preference for sedentary over physical activities have also been demonstrated in PWS (Dykens, 2012; Nordstrøm et al., 2013; van den Berg-Emons et al., 2008). Likely, lower LPA participation 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 (White et al., 2012). It is possible that more stamina, better cardiovascular fitness (Rowlands, Eston, & Ingledew, 1999) and motor proficiency (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. PWS participants 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), coinciding with results from previous studies (Butler et al., 2007; Rubin et al., 2013). In addition, low strength has been shown in young women with PWS, who presented 50% and 70% less isokinetic strength during knee flexion and extension, respectively, when compared to age- and sex-matched obese and lean controls (Capodaglio et al., 2009). Last, youth with PWS have been shown to produce significantly lower relative peak power output (watts per kg of lean body mass) during cycling in comparison to lean and obese controls (Castner et al., 2013). Therefore, it is likely that low muscle mass, strength and power characteristics of the syndrome contribute to low PA participation, which, in turn, largely impacts participation in VPA (Butler et al., 2007; Capodaglio et 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 has been 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 not meet 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 and 62.9% of adults with PWS (Rubin et al., 2012). This preference for walking may explain the similar MPA between those with and without PWS. Another possible factor contributing to similar minutes of MPA during weekdays in both groups could be structured PA (i.e., physical education at school or therapies). van den Berg-Emons et al. (2008) found that as a group, youth with PWS were less active than other children; however, half of the PWS participants had similar activity levels as age- and gender-matched healthy children when PA was measured over two school weekdays (van den BergEmons et al., 2008). Therefore, it seems that if there is a structure in place for PA participation, those with PWS may benefit from it.
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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 that after completing a structured 3-month calf exercise training program in youth with PWS, there was a significant increase from 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 on structuring activities that youth with PWS will enjoy, but will also yield physiological benefits (i.e., weight bearing/muscle strengthening activities). Additionally, our results suggest that youth with PWS are at higher risk of not participating in VPA during the weekends, where structured PA, such as physical education, is likely less frequent. In those with PWS, a larger percentage 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, these children may have been more inclined to participate in PA during the measurement period of this study because of their willingness to participate in the home-based PA program. Lastly, the specific type of PA (i.e., structured or unstructured) was not 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 and programs 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 MVPA recommendations. Youth with PWS engaged in less overall PA than obese youth without PWS. Of particular concern is a tendency for PWS youth to engage in less light- and vigorous-intensity activity than their nonsyndromal peers, on both weekends and throughout the week. Exercise interventions and programs should focus on integrating activities of vigorous intensity, along with activities that the child will enjoy, as well as providing more opportunities to engage in spontaneous PA of low intensity. Acknowledgements The authors would like to thank the participants and their families. This study was supported by the US Army Medical Research and Materiel Command Award W81XWH-09-1-0682. References Ainsworth, B. E., Haskell, W. L., Herrmann, S. D., Meckes, N., Bassett, D. R., Jr., & Tudor-Locke, C. 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Long, M. W., Sobol, A. M., Cradock, A. L., Subramanian, S. V., Blendon, R. J., & Gortmaker, S. L. (2013). School-day and overall physical activity among youth. American Journal of Preventive Medicine, 45(2), 150–157. McCarthy, H. D., Cole, T. J., Fry, T., Jebb, S. A., & Prentice, A. M. (2006). Body fat reference curves for children. International Journal of Obesity, 30(4), 598–602. Murphy, N. A., & Carbone, P. S. (2008). Promoting the participation of children with disabilities in sports, recreation, and physical activities. Pediatrics, 121(5), 1057–1061. Myers, S. E., Whitman, B. Y., Carrel, A. L., Moerchen, V., Bekx, M. T., & Allen, D. B. (2007). Two years of growth hormone therapy in young children with Prader-Willi syndrome: Physical and neurodevelopmental benefits. American Journal of Medical Genetics Part A, 143(5), 443–448. Nardella, M. T., Sulzbacher, S. I., & Worthington-Roberts, B. S. (1983). Activity levels of persons with Prader-Willi syndrome. American Journal of Mental Deficiency, 87(5), 498–505. Nordstrøm, M., Hansen, B. H., Paus, B., & Kolset, S. O. (2013). Accelerometer-determined physical activity and walking capacity in persons with Down syndrome, Williams syndrome and Prader-Willi syndrome. Research in Developmental Disabilities, 34(12), 4395–4403. Petersen, A. C., Crockett, L., Richards, M., & Boxer, A. (1988). A self-report measure of pubertal status: Reliability, validity, and initial norms. Journal of Youth and Adolescence, 17(2), 117–133. Reus, L., Zwarts, M., van Vlimmeren, L. A., Willemsen, M. A., Otten, B. J., & Nijhuis-van der Sanden, M. W. (2011). Motor problems in Prader-Willi syndrome: A systematic review on body composition and neuromuscular functioning. Neuroscience and Biobehavioral Reviews, 35(3), 956–969. Rowlands, A. V., Eston, R. G., & Ingledew, D. K. (1999). Relationship between activity levels, aerobic fitness, and body fat in 8- to 10-yr-old children. Journal of Applied Physiology, 86(4), 1428–1435. Rubin, D. A., Cano-Sokoloff, N., Castner, D. L., Judelson, D. A., Wright, P., & Duran, A. (2013). Update on body composition and bone density in children with PraderWilli syndrome. Hormone Research in Paediatrics, 79(5), 271–276. Rubin, D. A., Mouttapa, M., Weiss, J. W., & Barrera-Ng, A. (2012). Physical activity in children with Prader-Willi Syndrome: A parents’ perspective. Californian Journal of Health Promotion, 10(Special Issue: Obesity Prevention & Intervention), 57–66. Rubin, D. A., Wilson, K. S., Wiersma, L. D., Weiss, J. W., & Rose, D. J. (2014). Rationale and design of active play @ home: A parent-led physical activity program for children with and without disability. BMC Pediatrics, 14, 41. Schlumpf, M., Eiholzer, U., Gygax, M., Schmid, S., van der Sluis, I., & l’Allemand, D. (2006). A daily comprehensive muscle training programme increases lean mass and spontaneous activity in children with Prader-Willi syndrome after 6 months. Journal of Pediatric Endocrinology and Metabolism, 19(1), 65–74. Troiano, R. P., Berrigan, D., Dodd, K. W., Masse, L. C., Tilert, T., & McDowell, M. (2008). Physical activity in the United States measured by accelerometer. Medicine and Science in Sport and Exercise, 40(1), 181–188. Trost, S. G., Kerr, L. M., Ward, D. S., & Pate, R. R. (2001). Physical activity and determinants of physical activity in obese and non-obese children. International Journal of Obesity and Related Metabolic Disorders, 25(6), 822–829. Trost, S. G., Loprinzi, P. D., Moore, R., & Pfeiffer, K. A. (2011). Comparison of accelerometer cut points for predicting activity intensity in youth. Medicine and Science in Sport and Exercise, 43(7), 1360–1368. U.S. Department of Health and Human Services (2000). Healthy people 2010: Understanding and improving health (2nd ed.). Washington, DC: US Government Printing Office. van den Berg-Emons, R., Festen, D., Hokken-Koelega, A., Bussmann, J., & Stam, H. (2008). Everyday physical activity and adiposity in Prader-Willi syndrome. Journal of Pediatric Endocrinology and Metabolism, 21(11), 1041–1048. van Mil, E. G., Westerterp, K. R., Kester, A. D., Curfs, L. M., Gerver, W. J., & Schrander-Stumpel, C. T. (2000). Activity related energy expenditure in children and adolescents with Prader-Willi syndrome. International Journal of Obesity and Related Metabolic Disorders, 24(4), 429–434. White, E. W., Schroeder, L., Wright, P., Rubin, D. A., Rose, D. J., & Wiersma, L. D. (2012). Reliability of the Bruininks-Oseretsky test of motor proficiency in children and adolescents with Prader-Willi Syndrome. Medicine and Science in Sport and Exercise, Abstract 1978, 44(Suppl. 2.5), 487. Wrotniak, B. H., Epstein, L. H., Dorn, J. M., Jones, K. E., & Kondilis, V. A. (2006). The relationship between motor proficiency and physical activity in children. Pediatrics, 118(6), e1758–e1765.
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 b
Department of Kinesiology, California State University, Fullerton, 800 North State College Boulevard, Fullerton, CA 92834, USA 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
A B S T R A C T
Article history: Received 4 June 2014 Received in revised form 14 July 2014 Accepted 15 July 2014 Available online
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. ß 2014 Elsevier Ltd. All rights reserved.
Keywords: Accelerometer Physical activity Prader-Willi Syndrome Childhood obesity
1. Introduction The United States Department of Health and Human Services recommends that children participate in a minimum of 60 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, approximately 42% 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: [email protected] (D.M. Castner), [email protected] (J.M. Tucker), [email protected] (K.S. Wilson), [email protected] (D.A. Rubin). http://dx.doi.org/10.1016/j.ridd.2014.07.035 0891-4222/ß 2014 Elsevier Ltd. All rights reserved.
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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 same PA 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 children without 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 in the locus 13-15q. Individuals with PWS have abnormal body composition, characterized by excessive body fat, decreased lean mass and hypotonia. In addition, individuals with PWS present poor muscle strength and coordination, hormonal deficiencies (particularly growth hormone secretion), poor stamina, lethargy, behavioral issues and moderate cognitive disability (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 in fewer activities targeted to promote muscular strength (Rubin, Mouttapa, Weiss, & Barrera-Ng, 2012). Further, adults with PWS engage in less lifestyle PA than other adults with disability (Nordstrøm, Hansen, Paus, & Kolset, 2013) and prefer sedentary 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 exhibited similar PA levels as those without the syndrome (Nardella, Sulzbacher, & Worthington-Roberts, 1983; van den Berg-Emons et al., 2008) when using direct measures of PA (i.e., actometers and pedometers). To date, no study has evaluated the physical activity 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 and nonsyndromal 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 during weekdays 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 this study. Due to the low prevalence of PWS (1 in 15,000 live births), a larger age range was implemented for participation. All PWS 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) and the United States Army Medical Research and Materiel Command. Written informed assent and consent were obtained from all participants and parents prior to participation. Children with confirmed pregnancy, those on lipid-lowering, diabetes or blood 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 history questionnaire regarding their child’s health and participation in moderate- and vigorous-intensity PA. With the help of their parent, 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 the medical history questionnaire for PWS participants, which parents completed. All participants were measured for anthropometrics 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. This study 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 obtained at 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 wallmounted stadiometer (Seca, Ontario, CA). Total body fat percentage was determined using a whole body dual-energy X-ray
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absorptiometry (DXA) scan (GE Healthcare, GE Lunar Corp., Madison, WI). Female participants who had their first menses were 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 elastic belt across the waist line with the accelerometer over the right hip. Accelerometers were initialized following manufacturer specifications 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 accelerometer instructions sheet and a pre-paid envelope to mail back the accelerometer at the end of the eight days. Members of the research team also called the parents during the week to ensure appropriate accelerometer wear. Additionally, participant enrollment in the study was done in cohorts, which resulted in 47 children measured for PA during a school session and 17 children measured for PA during summer break. Accelerometry data were downloaded using the ActiLife5 software version 5.10.0.0 (ActiGraph, LLC, Pensacola, FL). Data were screened for compliance and those with a minimum of 10 h wear time on at least three weekdays and one weekend day were included in the analyses. Non-wear time was determined as 60 consecutive min of zero PA counts. Because participants completed a second visit to CSUF the following Saturday (Day 7) as part of the PA intervention study, data from Saturday 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, and McMurray (2008) cut-points were used to determine the intensity levels (Trost, Loprinzi, Moore, & Pfeiffer, 2011). SED was limited to a window of 6:00 AM to 10:00 PM to omit potential overnight wear time. All PA data were included regardless of time. 2.5. Statistical analysis One-way analysis of variance (ANOVA) tests were conducted to determine group differences for participant characteristics. All PA data were screened for normality using skewness calculations and square root transformations were completed for all intensities except for sedentary behavior. A two (group: PWS vs. OB) by two (day of week: weekday vs. weekend day) multivariate ANOVA (MANOVA) was initially conducted to determine group and day of week differences for all PA intensities. However, because the interaction power was low for all intensities (power < 0.096 for all), separate analyses were conducted to determine (1) group differences for weekly PA, weekday PA and weekend day PA and (2) day of week 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; Belcher et 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 earlypubertal (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 for LPA (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 similar time 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) than OB on weekend days. During weekends, 8% of PWS and 13% of OB met the MVPA recommendation.
[(Fig._1)TD$IG]
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SED Duration (min/day)
800
600
400
200
0 180
LPA Duration (min/day)
160
*
140 120 100 80 60 40 20 0 50
VPA MPA MVPA Duration (min/day)
40
30
20
10
* 0 PWS
Obese Group
Fig. 1. Weekly sedentary behavior or physical activity (min/day) in youth with PWS and obesity. Data are expressed as mean (standard error). *p < 0.050, where PWS < obese.
3.3. Weekday versus weekend PA within group comparisons For PWS, there were no differences between weekdays and weekends for SED (657.3 21.4 min/day vs. 667.0 21.4 min/day, respectively; p = 0.752) or LPA (132.6 9.7 min/day vs. 125.6 10.4 min/day, respectively; p = 0.495). Fig. 2a presents weekdays versus weekend MPA, VPA and MVPA for PWS. MPA (p = 0.164) and MVPA (p = 0.107) were similar during weekdays and weekend days in PWS. In contrast, there was a trend towards PWS engaging in less VPA on weekend days versus weekdays (p = 0.074). OB participated in similar SED and PA (for all intensities – see Fig. 2b) on weekdays and weekend days (p > 0.101 for all).
[(Fig._2)TD$IG]
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a)
b)
50
50
VPA MPA
VPA MPA
40
MVPA Duration (min/day)
40
MVPA Duration (min/day)
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30
20
10
30
20
10
# 0
0 Weekday
Weekend
Weekday
Day of Week
Weekend
Day of Week
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.
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 children with nonsyndromal obesity. Specifically, in comparison to OB, PWS engaged in less LPA on weekdays and less LPA and VPA on weekends. Additionally, there was a trend for PWS to participate in less VPA on weekdays and less MVPA on weekends compared to OB. MPA was similar between both groups regardless of day of the week. Lastly, there was a trend for youth with PWS 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% of OB obtained 60+ minutes per day of MVPA. The percentage of youth with PWS from Southern California not meeting the recommendations is similar to the 12% of adults with PWS recently reported in Europe (Nordstrøm et al., 2013). Likewise, in youth 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 the general 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 Age (y) Stature (cm) Total body mass (kg) Body mass index (kg/m2)
12/12 11.2 (2.3)* 143.8 (13.3) 62.1 (29.5) 29.4 (12.7)
21/19 9.8 (1.1) 146.3 (8.8) 59.1 (13.3) 27.3 (4.0)
Pubertal development (I–IV) Stage I Stage II Stage III Stage IV
2 8 10 4
9 9 17 5
Body fat mass (%) Lean body mass (kg)
45.8 (11.0) 30.1 (11.4)
44.1 (5.7) 30.9 (5.5)
Data are expressed as frequency or mean (standard deviation). * p < 0.050, where PWS > obese.
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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) Obese (n = 40) p-value
657.3 (15.1) 640.0 (11.7) 0.367
132.6 (9.7) 162.7 (7.0) 0.016b
27.7 (2.9) 29.6 (2.1) 0.611a,c
10.9 (1.4) 14.7 (1.5) 0.090c
38.5 (3.8) 44.3 (3.2) 0.293a,c
Weekend day PWS (n = 24) Obese (n = 40) p-value
667.0 (24.7) 633.3 (19.1) 0.285
125.6 (10.4) 158.3 (8.6) 0.028b
22.6 (2.5) 27.8 (2.7) 0.178
7.9 (1.3) 11.9 (1.5) 0.040c
30.4 (3.3) 39.7 (3.7) 0.085
Data are expressed as mean (standard error). a Adjusted for sex. b Adjusted for puberty status. c Adjusted for school.
the low rate of MVPA participation is alarming. The results demonstrate that youth with PWS are at an enormous risk for physical inactivity. 4.3. Low LPA and VPA Youth with PWS participated in less LPA throughout the week compared to obese children. Previous studies have shown that individuals with PWS exhibit lower spontaneous PA energy expenditure (Butler et al., 2007) and participate in less lifestyle PA when compared to controls (Nordstrøm et al., 2013). Preference for sedentary over physical activities have also been demonstrated in PWS (Dykens, 2012; Nordstrøm et al., 2013; van den Berg-Emons et al., 2008). Likely, lower LPA participation 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 (White et al., 2012). It is possible that more stamina, better cardiovascular fitness (Rowlands, Eston, & Ingledew, 1999) and motor proficiency (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. PWS participants 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), coinciding with results from previous studies (Butler et al., 2007; Rubin et al., 2013). In addition, low strength has been shown in young women with PWS, who presented 50% and 70% less isokinetic strength during knee flexion and extension, respectively, when compared to age- and sex-matched obese and lean controls (Capodaglio et al., 2009). Last, youth with PWS have been shown to produce significantly lower relative peak power output (watts per kg of lean body mass) during cycling in comparison to lean and obese controls (Castner et al., 2013). Therefore, it is likely that low muscle mass, strength and power characteristics of the syndrome contribute to low PA participation, which, in turn, largely impacts participation in VPA (Butler et al., 2007; Capodaglio et 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 has been 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 not meet 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 and 62.9% of adults with PWS (Rubin et al., 2012). This preference for walking may explain the similar MPA between those with and without PWS. Another possible factor contributing to similar minutes of MPA during weekdays in both groups could be structured PA (i.e., physical education at school or therapies). van den Berg-Emons et al. (2008) found that as a group, youth with PWS were less active than other children; however, half of the PWS participants had similar activity levels as age- and gender-matched healthy children when PA was measured over two school weekdays (van den BergEmons et al., 2008). Therefore, it seems that if there is a structure in place for PA participation, those with PWS may benefit from it.
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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 that after completing a structured 3-month calf exercise training program in youth with PWS, there was a significant increase from 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 on structuring activities that youth with PWS will enjoy, but will also yield physiological benefits (i.e., weight bearing/muscle strengthening activities). Additionally, our results suggest that youth with PWS are at higher risk of not participating in VPA during the weekends, where structured PA, such as physical education, is likely less frequent. In those with PWS, a larger percentage 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, these children may have been more inclined to participate in PA during the measurement period of this study because of their willingness to participate in the home-based PA program. Lastly, the specific type of PA (i.e., structured or unstructured) was not 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 and programs 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 MVPA recommendations. Youth with PWS engaged in less overall PA than obese youth without PWS. Of particular concern is a tendency for PWS youth to engage in less light- and vigorous-intensity activity than their nonsyndromal peers, on both weekends and throughout the week. Exercise interventions and programs should focus on integrating activities of vigorous intensity, along with activities that the child will enjoy, as well as providing more opportunities to engage in spontaneous PA of low intensity. Acknowledgements The authors would like to thank the participants and their families. This study was supported by the US Army Medical Research and Materiel Command Award W81XWH-09-1-0682. References Ainsworth, B. E., Haskell, W. L., Herrmann, S. D., Meckes, N., Bassett, D. R., Jr., & Tudor-Locke, C. 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