Accelerometer Thresholds for Estimating Physical Activity Intensity Levels in Infants: A Preliminary Study

Lack of physical activity (PA) at a young age can result in health issues. Thus, monitoring PA is important. Wearable accelerometers are the preferred tool to monitor PA in children. Validated thresholds are used to classify activity intensity levels, e.g., sedentary, light, and moderate-to-vigorous, in ambulatory children. No previous work has developed accelerometer thresholds for infancy (pre-ambulatory children). Therefore, this work aims to develop accelerometer thresholds for PA intensity levels in pre-ambulatory infants. Infants (n = 10) were placed in a supine position and allowed free movement. Their movements were synchronously captured using video cameras and accelerometers worn on each ankle. The video data were labeled by activity intensity level (sedentary, light, and moderate-to-vigorous) in two-second epochs using observational rating (gold standard). Accelerometer thresholds were developed for acceleration and jerk using two optimization approaches. Four sets of thresholds were developed for dual (two ankles) and for single-worn (one ankle) accelerometers. Of these, for a typical use case, we recommend using acceleration-based thresholds of 1.00 m/s to distinguish sedentary and light activity and 2.60 m/s to distinguish light and moderate-to-vigorous activity. Acceleration and jerk are both suitable for measuring PA.

Exploring Factors Associated With Accelerometer Validity Among Ethnically Diverse Toddlers

PURPOSE

Studying physical activity in toddlers using accelerometers is challenging due to noncompliance with wear time (WT) and activity log (AL) instructions. The aims of this study are to examine relationships between WT and AL completion and (1) demographic and socioeconomic variables, (2) parenting style, and (3) whether sedentary time differs by AL completion.

METHODS

Secondary analysis was performed using baseline data from a community wellness program randomized controlled trial for parents with toddlers (12-35 mo). Parents had toddlers wear ActiGraph wGT3x accelerometers and completed ALs. Valid days included ≥600-minute WT. Analysis of variance and chi-square analyses were used.

RESULTS

The sample (n = 50) comprised racial and ethnically diverse toddlers (mean age = 27 mo, 58% male) and parents (mean age = 31.7 y, 84% female). Twenty-eight families (56%) returned valid accelerometer data with ALs. Participants in relationships were more likely to complete ALs (P < .05). Toddler sedentary time did not differ between those with ALs and those without.

CONCLUSIONS

We found varied compliance with WT instructions and AL completion. Returned AL quality was poor, presenting challenges in correctly characterizing low-activity counts to improve internal validity of WT and physical activity measures. Support from marital partners may be important for adherence to study protocols.

Randomized controlled trial evaluating a virtual parenting intervention for young children at risk of obesity: study protocol for Parenting Addressing Early Years Intervention with Coaching Visits in Toronto (PARENT) trial

BACKGROUND

The prevalence of overweight (15%) and obesity (6%) in children under 5 years of age in Canada are high, and young children with overweight and obesity are at increased risk of the development of chronic disease(s) in adulthood. Prior research has demonstrated very few published trials on effective obesity prevention interventions in young children at risk of obesity, within primary healthcare settings. The aim of this study is to determine if 18-48-month-old children at risk for obesity, who are randomized to receive the Parents Together program (i.e., intervention group), have reduced body mass index z-score (zBMI), compared to those not receiving the intervention, at a 12-month follow-up. Secondary clinical outcomes between the intervention and control groups will be compared at 12 months.

METHODS

A pragmatic, parallel group, 1:1, superiority, randomized control trial (RCT) through the TARGetKids! Practice Based Research Network will be conducted. Young children (ages 18-48 months) who are at increased risk for childhood obesity will be invited to participate. Parents who are enrolled in the intervention group will participate in eight weekly group sessions and 4-5 coaching visits, facilitated by a trained public health nurse. Children and parents who are enrolled in the control group will receive the usual health care. The primary outcome will be compared between intervention arms using an analysis of covariance (ANCOVA). Feasibility and acceptability will be assessed by parent focus groups and interviews, and fidelity to the intervention will be measured using nurse-completed checklists. A cost-effectiveness analysis (CEA) will be conducted.

DISCUSSION

This study will aim to reflect the social, cultural, and geographic diversity of children in primary care in Toronto, Ontario, represented by an innovative collaboration among applied child health researchers, community health researchers, and primary care providers (i.e., pediatricians and family physicians in three different models of primary care). Clinical and implementation outcomes will be used to inform future research to test this intervention in a larger number, and diverse practices across diverse geographic settings in Ontario.

TRIAL REGISTRATION

ClinicalTrials.gov NCT03219697. Registered on June 27, 2017.

Behavioral, Environmental, and Demographic Factors Associated with Objectively Measured Physical Activity in Infants

Background: To describe objectively measured physical activity (PA) in infants, and to identify demographic, behavioral, and environmental factors associated with infants' PA. Methods: Participants were 6-7-month-old infants and their mothers (N = 143 dyads) from two Southeastern US counties. Infant measures included PA assessed by accelerometers at ankle and waist sites, motor developmental status (i.e., stationary and locomotion), and anthropometric characteristics (i.e., height and weight). Mothers provided information on home environment, child care settings, and family demographic factors. PA levels were compared across demographic subgroups. Correlation coefficients described associations between PA and continuous variables, including motor developmental status and anthropometric characteristics. Multiple linear regression analyses examined factors found to be independently associated with PA. Results: Infants' PA counts were greater at the ankle (77,700 counts/hr) vs. the waist site (32,500 counts/hr). In univariate analyses, a diverse set of environmental, behavioral, and infant-level demographic factors were found to be significantly associated with PA at the ankle site. Multivariate analyses indicated that more advanced motor development status (B = 666.3 ± 329.8, p < 0.05), attendance at home child care settings (B = -13,724.4 ± 5083.9, p < 0.05), greater exposure to tummy time (B = 213.5 ± 79.9, p < 0.05), and white racial/ethnic composition (B = -19,953.4 ± 5888.5, p < 0.01) were independently, associated with infants' PA. Conclusions: In 6-7-month-old infants, objectively measured PA was found to be associated with motor developmental status and physical and social environmental factors, including both demographic moderators and factors that are influenced by parents and caregivers. Longitudinal studies are needed to determine if these relationships persist or change as infants develop.

Early impact of the COVID-19 pandemic on promotion of infant activity, strength and communication: A qualitative exploration

INTRODUCTION

Fostering physical activity, muscle strengthening and communication skills in diverse environments are vital to ensuring healthy infant development; however, promotion of these skills may be impacted by the COVID-19 pandemic. Therefore, the purpose of this study was to explore healthcare workers, parents and childcare providers' perceptions of the pandemic's influence on how they engage with infants to promote physical activity, muscle strength and communication.

METHODS

37 subjects (12 = parents; 12 = childcare providers, 13 = healthcare workers) participated in a semi-structured interview. Data were analyzed via an inductive content analysis.

RESULTS

The majority of caregivers identified concerns related to: limitations in social interactions (especially masks impacting communication), lack of access to peer modeling, fewer opportunities for physical exploration, and a need for creative activities in diverse environments (e.g., home/childcare) for infant development during and after the pandemic.

CONCLUSIONS

Caregivers are concerned about the role COVID-19 is having on infant development. Additional resources on how to promote infant physical activity, muscle strength and communication despite challenges associated with the COVID-19 pandemic are needed.

Inactive Lifestyles among Young Children with Innocent Murmurs or Congenital Heart Disease Regardless of Disease Severity or Treatment

BACKGROUND

Sedentary lifestyle morbidities are common among children with congenital heart disease (CHD). Understanding the physical activity trajectory from early childhood could enhance intervention timing/effectiveness.

METHODS

154 children (56% male) were recruited at 12-47 months of age for this prospective, longitudinal, observational study. Physical activity and sedentary behaviour (7-day accelerometry) and motor skill (Peabody Developmental Motor Scales-2) were assessed every 8 months until 5 years of age and then annually. Mixed effect repeated measures regression models described outcome trajectories across study assessments.

RESULTS

Children had an innocent heart murmur (n=28), CHD with insignificant hemodynamics not requiring treatment (n=47), CHD treated by catheterization or surgery without cardiopulmonary bypass (n=31), or CHD treated surgically with bypass (n=48). Motor skill was age appropriate (Peabody 49.0±8.4) but participants had lower physical activity (143±41 mins/day) and higher sedentary time (598±89 mins/day) than healthy peers, starting at 18 months of age. Movement behaviours were not related to treatment group (p>0.10), and physical activity was below the recommended 180 mins/day. Over time, physical activity, sedentary time and motor skill were primarily related to the baseline measure of each outcome (p<0.001).

CONCLUSIONS

Children with simple or complex CHD or innocent heart murmurs have an increased risk for sedentary lifestyles. Their physical activity and sedentary behaviours are established prior to 2 years of age, persist until school age, and are unrelated to motor skill. These results emphasize the need for interventions targeting the youngest children seen in a cardiac clinic, regardless of CHD diagnosis or innocent murmur.

Physical Activity and the Home Environment of Pre-School-Aged Children in Urban Bangladesh

Physical activity (PA) is a key determinant of health and development, yet few studies have examined PA levels and risk factors for low PA among young children in low- and middle-income countries. This study aimed to describe the PA and sedentary (SED) behavior levels of preschool-aged children in Dhaka, Bangladesh, and to estimate the associations between potential risk factors in the home built environment and moderate to vigorous PA (MVPA). In a sample of preschool-aged children (n = 65) in Dhaka, PA and SED behavior were measured for 7 days using ActiGraph GT3X-BT accelerometers. Characteristics of the home built environment, socioeconomic factors, and anthropometry were also measured. Linear mixed-effects models were used to estimate multivariable-adjusted associations between characteristics of the home environment and MVPA. Preschool-aged children spent a mean (±standard deviation) 421 ± 48 and 82 ± 23 min per day sedentary and in MVPA, respectively. There were no statistically significant associations between factors in the home built environment (indoor area, presence of an open stairwell, and presence of gross motor activity facilitating items) and MVPA. These findings suggest that the studied characteristics of the home built environment may not significantly influence the MVPA observed among preschool-aged children in Dhaka. Future research should focus on other structural and behavioral factors that facilitate PA among young children in dense urban settings.

Physical Activity and Adiposity in a Racially Diverse Cohort of US Infants

OBJECTIVE

Early life physical activity may help prevent obesity, but objective quantification in infants is challenging.

METHODS

A total of 506 infants were examined from 2013 to 2016. Infants wore accelerometers for 4 days at ages 3, 6, 9, and 12 months. Daily log-transformed physical activity counts were computed, averaged, and standardized across assessments. A linear mixed model was used to examine trends in standardized physical activity counts as well as associations between physical activity and BMI z score, sum of subscapular and triceps skinfold thickness for overall adiposity (SS+TR), and their ratio for central adiposity (SS:TR).

RESULTS

Among infants, 66% were black and 50% were female. For each additional visit, standardized physical activity counts increased by 0.23 (CI: 0.18 to 0.27; P < 0.0001). This translates to 126.3 unadjusted physical activity counts or a 4% increase for each visit beyond 3 months. In addition, a 1-SD increase in standardized physical activity counts (550 unadjusted physical activity counts) was associated with a 0.01-mm lower SS:TR (95% CI: -0.02 to -0.001; P = 0.03). However, standardized physical activity counts were not associated with BMI z score or SS+TR.

CONCLUSIONS

Physical activity increased over infancy and was associated with central adiposity. Despite limitations, researchers should consider objective measurement in infants.

Infants' and toddlers' physical activity and sedentary time as measured by accelerometry: a systematic review and meta-analysis

BACKGROUND

Early experiences in physical activity (PA) are important to shape healthy movement behaviours long-term; as such, it is critical that PA is promoted from infancy, and that detrimental behaviours (e.g., prolonged sedentary time [ST]) are minimized. The purpose of this systematic review and meta-analysis was to examine infants' and toddlers' movement behaviours across daytime hours.

METHODS

Seven online databases were searched for terms related to infants (< 12 months), toddlers (12-35.9 months), PA, ST, and accelerometry. Two independent reviewers examined 4873 articles for peer-reviewed original research, published in English, that assessed infants' (counts/min) and/or toddlers' PA or ST (min/day) using accelerometry across daytime hours. Infants' mean PA level (counts/min) was averaged across studies, and ranges were produced. Estimates of toddlers' movement behaviours were aggregated meta-analytically to produce average daily rates, and accelerometer placement, cut-point validity, device type, and epoch length were tested as a moderating variables.

RESULTS

Twenty-four studies from 16 countries (published 2011-2019), representing 3699 participants, were included in the systematic review. Five studies reported on infants' PA, which ranged from 78.2 to 2580.5 cpm. Across 20 studies, toddlers' total PA, light PA, moderate-to vigorous-intensity PA, and ST ranged from 72.9 to 636.5, 48.5 to 582.4, 6.5 to 89.9, and 172.7 to 545.0 min/day, respectively. After taking into account accelerometer placement, cut-point validity, device type, and epoch length, we found that toddlers engaged in 246.19 min/day (SE = 28.50; 95% CI: 190.34, 302.04) of total PA, 194.10 min/day (SE = 28.76; 95% CI: 137.73, 250.47) of light PA, and 60.16 min/day (SE = 5.88; 95% CI: 48.64, 71.69) of moderate-to vigorous-intensity PA. Toddlers engaged in 337.04 min/day (SE = 32.67; 95% CI: 273.01, 401.07) of ST.

CONCLUSIONS

With limited studies conducted in infants (n = 5), PA estimates are inconclusive and largely heterogeneous. Overall, toddlers tend to exceed the total PA recommendation of 180 min/day; however, very little of this time is spent at higher movement intensities. Even with high PA rates, toddlers still engage in substantial ST. More consistent and valid measurement protocols are needed to improve comparability across studies.

Daily Physical Activity Among Toddlers: Hip and Wrist Accelerometer Assessments

Physical activity (PA) habits seem to track over time from as young as early childhood. For children under age 3 years, wearable sensor-measured PA levels have begun to be investigated. The aims of this study were to evaluate the feasibility of using hip- vs. wrist-worn accelerometers, and to report accelerometer-derived PA metrics among toddlers. A convenience sample of 22 toddlers aged 13 to 35 months and their mothers were recruited for this study. ActiGraph wGT3X-BT accelerometers were attached to wrist bands and waist belts. The mothers were asked to affix a wrist band and a waist belt to their participating children during waking hours for four days. They also completed an acceptability survey. Of the 22 toddlers, 19 (86%) had ≥ 3 valid days of hip data, while only 14 (64%) did so for wrist data (p = 0.16). In terms of acceptability, 18 mothers (82%) responded that the 4-day hip wear was easy, while only 13 (59%) responded that the 4-day wrist wear was easy (p = 0.19). Daily light-intensity PA (LPA) was on average 161 min, and daily moderate- and vigorous-intensity PA (MVPA) was on average 47 min, as determined using published hip accelerometer cut-points. There were no significant differences in LPA or MVPA by age or by sex. In conclusion, this study suggests that hip placement of an ActiGraph accelerometer is more feasible than wrist placement among toddlers.

State Regulations Promoting Infant Physical Activity in Early Care and Education

BACKGROUND

State policies have the potential to improve early care and education (ECE) settings, but little is known about the extent to which states are updating their licensing and administrative regulations, especially in response to national calls to action. In 2013, we assessed state regulations promoting infant physical activity in ECE and compared them with national recommendations. To assess change over time, we conducted this review again in 2018.

METHODS

We reviewed regulations for all US states for child care centers (centers) and family child care homes (homes) and compared them with three national recommendations: (1) provide daily tummy time; (2) use cribs, car seats, and high chairs for their primary purpose; and (3) limit the use of restrictive equipment (e.g., strollers). We performed exact McNemar's tests to compare the number of states meeting recommendations from 2013 to 2018 to evaluate whether states had made changes over this period.

RESULTS

From 2013 to 2018, we observed significant improvement in one recommendation for homes-to use cribs, car seats, and high chairs for their primary purpose (odds ratio 11.0; 95% CI 1.6-47.3; p = 0.006). We did not observe any other significant difference between 2013 and 2018 regulations.

CONCLUSIONS

Despite increased awareness of the importance of early-life physical activity, we observed only modest improvement in the number of states meeting infant physical activity recommendations over the past 5 years. In practice, ECE programs may be promoting infant physical activity, but may not be required to do so through state regulations.

Hip and Wrist-Worn Accelerometer Data Analysis for Toddler Activities

Although accelerometry data are widely utilized to estimate physical activity and sedentary behavior among children age 3 years or older, for toddlers age 1 and 2 year(s), accelerometry data recorded during such behaviors have been far less examined. In particular, toddler’s unique behaviors, such as riding in a stroller or being carried by an adult, have not yet been examined. The objective of this study was to describe accelerometry signal outputs recorded during participation in nine types of behaviors (i.e., running, walking, climbing up/down, crawling, riding a ride-on toy, standing, sitting, riding in a stroller/wagon, and being carried by an adult) among toddlers. Twenty-four toddlers aged 13 to 35 months (50% girls) performed various prescribed behaviors during free play in a commercial indoor playroom while wearing ActiGraph wGT3X-BT accelerometers on a hip and a wrist. Participants’ performances were video-recorded. Based on the video data, accelerometer data were annotated with behavior labels to examine accelerometry signal outputs while performing the nine types of behaviors. Accelerometer data collected during 664 behavior assessments from the 21 participants were used for analysis. Hip vertical axis counts for walking were low (median = 49 counts/5 s). They were significantly lower than those recorded while a toddler was “carried” by an adult (median = 144 counts/5 s; p < 0.01). While standing, sitting, and riding in a stroller, very low hip vertical axis counts were registered (median ≤ 5 counts/5 s). Although wrist vertical axis and vector magnitude counts for “carried” were not higher than those for walking, they were higher than the cut-points for sedentary behaviors. Using various accelerometry signal features, machine learning techniques showed 89% accuracy to differentiate the “carried” behavior from ambulatory movements such as running, walking, crawling, and climbing. In conclusion, hip vertical axis counts alone may be unable to capture walking as physical activity and “carried” as sedentary behavior among toddlers. Machine learning techniques that utilize additional accelerometry signal features could help to recognize behavior types, especially to differentiate being “carried” from ambulatory movements.

Greenspace, physical activity, and BMI in children from two cities in northern Mexico

Numerous previous studies have reported positive associations between exposure to greenspace and children's physical activity, but in high-income countries only. Prior studies have also examined greenspace and obesity in children, but these have yielded inconsistent results and focused mostly on older children. The purpose of this study was to assess associations between time children spent in greenspace as the primary exposure and our outcomes of interest, including 1) minutes of physical activity, and 2) body mass index (BMI) z-score. Our sample was 102 children ages 3 to 5 years living in Ensenada and Tijuana, Mexico. We fit linear mixed models to estimate associations between greenspace and children's physical activity and BMI z-score. After adjustment for potential confounders, greater time in greenspace was associated with decreased sedentary time (−0.08 min per hour for each additional 30 min in greenspace; 95% CI −0.13, −0.04; p = 0.002) and increased moderate-to-vigorous physical activity (MVPA) (0.06; 95% CI 0.03, 0.10; p < 0.001). Results were driven primarily by children in Tijuana (−0.22; 95% CI −0.38, −0.06; p = 0.008 for sedentary time and 0.15; 95% CI 0.06, 0.38; p = 0.007 for MVPA). Time in greenspace was not associated with BMI z-score in children in Ensenada (0.001; 95% CI −0.008, 0.01; p = 0.83) or Tijuana (−0.009; 95% CI −0.02, 0.004; p = 0.17). Greater time in greenspace was associated with physical activity but not BMI in our sample of children—more so in Tijuana compared to Ensenada. Given high rates of obesity, interventions should aim to increase physical activity in young children in Northern Mexico.

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Greater time in greenspace was associated with decreased sedentary time.

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Greater time in greenspace was associated with increased physical activity.

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Associations were mainly driven by children in Tijuana compared to Ensenada.

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Time spent in greenspace was not associated with body mass index z-score.

Accelerometry-measured physical activity and sedentary behaviour of preschoolers in Nova Scotia, Canada

The objective of this study was to describe the levels and bouts of physical activity (PA) and sedentary behaviour (SB) among preschoolers in Nova Scotia, Canada, and the proportion meeting PA and step guidelines. Children (75 boys, 49 girls; mean age = 4.2 (range = 3-5 years)) participating in the Physical Literacy in the Early Years (PLEY) study provided data. Average time (minutes, % of day) spent sedentary, in light PA (LPA), moderate-to-vigorous PA (MVPA), and total PA; average frequency; and duration of bouts of MVPA (≥5 min, ≥10 min) and sedentary bouts (≥10 min) per day were determined using published cut-points, using 15-s epochs. The proportion of children meeting PA and step guidelines was determined, and differences by sex explored. Children spent the majority (70.8%) of their day active; nearly all (≥97%) met PA guidelines. Most children met step guidelines on a weekly basis, but not daily. Only LPA differed by sex (greater in girls; p = 0.001). Little time was spent in sustained SB (bouts ≥10 min). Boys had greater and longer bouts of MVPA and spent more of their day in these (p < 0.05). Girls spent less time in sustained SB (p = 0.009). This is the first study to describe the PA and SB of Nova Scotia preschoolers using accelerometry. Findings suggest preschoolers spend the majority of their day active, and that there are sex-related differences in PA and SB, warranting further examination.

Individual and environmental correlates of school-based recess engagement

The purpose of this study was to examine individual variables associated with children's levels of recess physical activity (PA), as well as environmental influences that influence children's engagement during recess. Participants (n = 146) were 4–6th grade students across seven schools. PA data were collected using the Fitbit Flex. Psychological need satisfaction at recess data were collected with a basic psychological need satisfaction for recess PA survey. Observations of recess activity engagement and the quality of the recess environment were also collected at 134 recess periods (n = 8340 children) across nine schools. Results of multi-level regression analyses indicated that gender and recess time were significant predictors of physical activity during recess. In examination of the environmental level factors, multi-level regression analyses revealed that ‘adult engagement and supervision’ was the only significant predictor for recess engagement in boys and girls. These findings suggest the amount of time allocated, and the quality of the recess environment must be included in evaluation of the critical factors relevant to engagement of students in physically active recesses.

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Psychological need satisfaction did not predict recess physical activity.

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Recess time and gender were significant predictors of recess activity.

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Adult engagement and supervision was related to student engagement at recess.

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27% of physical activity recorded during the school day was at recess.

The longitudinal association between temperament and physical activity in young children

OBJECTIVE

To examine the longitudinal association of negative affect and physical activity in a population of preschool children.

STUDY DESIGN

Participants included 763 children (53% male) attending scheduled health supervision visits in their primary care physicians' offices. Data were collected at two time points at mean ages 27 (SD=5.4) and 47 (SD=6.2) months. Negative affect (NA) was measured using the Negative Affectivity (frustration/anger, decreased soothability) domain of the Children's Behavior Questionnaire. Physical Activity (PA) was assessed using a parent-report questionnaire. Multiple regression analyses tested the association between NA and PA, adjusting for child age, sex, z-BMI, PA at Time 1, maternal education, household income, and season, and examined for sex differences in the relationship between NA and PA.

RESULTS

The longitudinal association between NA at Time 1 and PA at Time 2 was moderated by sex (p<0.001). After adjusting for covariates, females with greater NA at Time 1 had decreased PA at Time 2 (p=0.01), whereas males with greater NA at Time 1 had increased PA at Time 2 (p=0.01). Specifically, among females, every 1 unit increase in NA at Time 1 was associated with a 9.9min/day decrease in PA at Time 2 (95% CI: -17.1, -2.8).

CONCLUSIONS

NA and PA were associated early in childhood and the effects of NA on PA were gender specific. These findings underscore the importance of longitudinal and gender-specific analyses in mood-obesity research.

The cost of simplifying complex developmental phenomena: a new perspective on learning to walk

Researchers can study complex developmental phenomena with all the inherent noise and complexity or simplify behaviors to hone in on the essential aspects of a phenomenon. We used the development of walking as a model system to compare the costs and benefits of simplifying a complex, noisy behavior. Traditionally, researchers simplify infant walking by recording gait measures as infants take continuous, forward steps along straight paths. Here, we compared the traditional straight-path task with spontaneous walking during 20 minutes of free play in 97 infants (10.75-19.99 months of age). We recorded infants' footfalls on an instrumented floor to calculate gait measures in the straight-path and free-play tasks. In addition, we scored videos for other critical aspects of spontaneous walking-steps per bout, shape of walking path, and step direction. Studying infant walking during free play incurred no cost compared with the straight-path task, but considerable benefits. Straight-path gait was highly correlated with spontaneous gait and both sets of measures improved with walking age, validating use of the straight-path task as an index of development. However, a large proportion of free-play bouts were too short to permit standard gait measures, and most bouts were curved with omnidirectional steps. The high prevalence of these "non-canonical" bouts was constant over development. We propose that a focus on spontaneous walking, the phenomenon we ostensibly wish to explain, yields important insights into the problems infants solve while learning to walk. Other areas of developmental research may also benefit from retaining the complexity of complex phenomena.

Physical Activity in Pediatric Pulmonary Arterial Hypertension Measured by Accelerometry. A Candidate Clinical Endpoint

RATIONALE

The development of evidence-based treatment guidelines for pediatric pulmonary arterial hypertension (PAH) is hampered by lack of pediatric clinical trials. Trial design is hampered by lack of a feasible clinical endpoint in this population.

OBJECTIVES

To evaluate the use of accelerometry for measuring physical activity (PA) in pediatric PAH and to investigate its correlation with clinical disease severity markers.

METHODS

We included children from the Dutch National Network for Pediatric Pulmonary Hypertension. Control patients were recruited from the outpatient cardiology clinic of the Beatrix Children's Hospital. Children were asked to wear the accelerometer for 7 days. Vector magnitude counts per minute (VM CPM) and time per day spent in different PA intensity levels were defined as accelerometer outcomes.

MEASUREMENTS AND MAIN RESULTS

VM CPM was lower in children with PAH (n = 29) than in controls (n = 60; 647 vs. 921; P < 0.001). Children with PAH spent less time in moderate and vigorous PA (13 vs. 29 min/d and 2 vs. 13 min/d, respectively; P < 0.001). Time spent in moderate and vigorous PA correlated inversely with World Health Organization functional class. Time spent in moderate PA correlated positively with 6-minute-walk distance. In post hoc analyses, VM CPM and time spent in moderate/vigorous combined and vigorous PA were associated with outcome (P ≤ 0.044).

CONCLUSIONS

PA is markedly decreased in children with PAH. Accelerometer output correlated with clinical disease severity markers and may predict outcome. We showed an exciting potential of PA as a meaningful endpoint for clinical trials in pediatric PAH, although its clinical utility and prognostic value need to be further validated.