Nicole A. Proudfoot

The health outcomes and physical activity in preschoolers (HOPP) study: rationale and design

BackgroundThe early years are the period of growth for which we know the least about the impact of physical activity. In contrast, we know that more than 90 % of school-aged Canadian children, for example, are not meeting physical activity recommendations. Such an activity crisis is a major contributor to recent trends in childhood obesity, to which preschoolers are not immune. The World Health Organization estimated that more than 42 million children under the age of 5 years were overweight world-wide in 2010. If an activity crisis exists during the preschool years, we should also be concerned about its broader impact on health. Unfortunately, the relationship between physical activity and health during the early years is poorly understood. The goal of the Health Outcomes and Physical activity in Preschoolers (HOPP) study is to describe how the prevalence and patterns of physical activity in preschoolers are associated with indices of health.MethodsThe HOPP study is a prospective cohort study. We aim to recruit 400 3- to 5-year-old children (equal number of boys and girls) and test them once per year for 3 years. Each annual assessment involves 2 laboratory visits and 7 consecutive days of physical activity monitoring with protocols developed in our pilot work. At visit 1, we assess body composition, aerobic fitness, short-term muscle power, motor skills, and have the parents complete a series of questionnaires related to their child’s physical activity, health-related quality of life and general behaviour. Over 7 consecutive days each child wears an accelerometer on his/her waist to objectively monitor physical activity. The accelerometer is programmed to record movement every 3 s, which is needed to accurately capture the intensity of physical activity. At visit 2, we assess vascular structure and function using ultrasound. To assess the associations between physical activity and health outcomes, our primary analysis will involve mixed-effects models for longitudinal analyses.DiscussionThe HOPP study addresses a significant gap in health research and our findings will hold the potential to shape public health policy for active living during the early years.

Noninvasive measures of vascular health are reliable in preschool-aged children

Measures of vascular health are known to be important predictors of cardiovascular disease in adulthood. The reliability of commonly used measures of vascular health has been demonstrated in school-aged children, adolescents, and adults; however, their reliability in preschool-aged children remains to be determined. Twenty 2- to 6-year-old children participated in 2 identical testing sessions on different days. Following 10 min of supine rest, carotid artery blood pressures and common carotid artery images were assessed simultaneously for 10 heart cycles, using applanation tonometry and B-mode ultrasound, respectively, while electrocardiogram (ECG) and infrared measures of arterial pressure waves at the dorsalis pedis were recorded continuously. Brachial artery blood pressures were determined using an automated oscillometric device. Carotid artery diameters and intima-media thickness (IMT) were analyzed using a semiautomated detection software program. Carotid compliance, distensibility, and stiffness index were calculated from carotid diameters and carotid blood pressures. Whole-body pulse-wave velocity (PWV) was determined from the time delay between the R spike of the ECG and the foot of the dorsalis pedis arterial pressure wave. Reliability of all measures was assessed using the coefficient of variation (CV) and the intraclass correlation coefficient (ICC). The most reliable measures were carotid artery IMT and PWV with CVs of 2.6% and 3.5% and ICCs of 0.86 and 0.76, respectively. The lower reliability of carotid compliance and distensibility (ICC≤0.63) is likely attributable to the variability of blood pressure measurements. This study confirms that vascular measurements demonstrate substantial reliability in preschool-aged children as young as 2 years.

Short-term muscle power and speed in preschoolers exhibit stronger tracking than physical activity

The purpose of this study was to examine the tracking of short-term muscle power, speed, and physical activity over a 15-month period in a sample of healthy Canadian preschool-aged children. Seventeen preschoolers (age, 4.4 ± 0.8 years) completed exercise testing and physical activity monitoring at baseline and follow-up separated by 14.6 ± 4.1 months. Short-term muscle power was measured using a modified 10-s Wingate test with peak power and mean power normalized to body mass. Speed was assessed with a 25-m dash. Physical activity was measured by accelerometry (Actigraph GT1M) using a 3-s epoch over 7 consecutive days. Total physical activity and moderate-to-vigorous physical activity, expressed as a percentage of accelerometer wear time, were examined. Tracking of the variables between year 1 and year 2 was analyzed using Spearman rank order correlations and Kappa statistics. Paired t-tests were used to assess differences in performance and physical activity between year 1 and year 2. Total physical activity was not significantly different at year 2 (p > 0.05) and showed fair tracking (r = 0.51, p = 0.05; ĸ = 0.30). Moderate-to-vigorous physical activity was increased at year 2 (p = 0.03) and exhibited poor tracking (r = 0.29, p = 0.28; ĸ = 0.00). Short-term muscle power and speed was increased at year 2 (p < 0.0001) and exhibited significant tracking: peak power (r = 0.72, p = 0.001; ĸ = 0.46), mean power (r = 0.83, p = 0.00004; ĸ = 0.82), and 25-m dash (r = 0.82, p = 0.0001; ĸ = 0.47). Moderate-to-vigorous physical activity increased in this sample of boys and girls during the preschool years, and short-term muscle power and speed exhibited stronger tracking than physical activity.

Sedentary Time and Screen-Based Sedentary Behaviors of Children With a Chronic Disease

The objectives of this study were to (i) assess sedentary time and prevalence of screen-based sedentary behaviors of children with a chronic disease and (ii) compare sedentary time and prevalence of screen-based sedentary behaviors to age- and sex-matched healthy controls. Sixty-five children (aged 6-18 years) with a chronic disease participated: survivors of a brain tumor, hemophilia, type 1 diabetes mellitus, juvenile idiopathic arthritis, cystic fibrosis, and Crohns disease. Twenty-nine of these participants were compared with age- and sex-matched healthy controls. Sedentary time was measured objectively by an ActiGraph GT1M or GT3× accelerometer worn for 7 consecutive days and defined as less than 100 counts per min. A questionnaire was used to assess screen-based sedentary behaviors. Children with a chronic disease engaged in an average of 10.2 ± 1.4 hr of sedentary time per day, which comprised 76.5 ± 7.1% of average daily monitoring time. There were no differences between children with a chronic disease and controls in sedentary time (adjusted for wear time, p = .06) or in the prevalence of TV watching, and computer or video game usage for varying durations (p = .78, p = .39 and, p = .32 respectively). Children with a chronic disease, though relatively healthy, accumulate high levels of sedentary time, similar to those of their healthy peers.

Reduced heart rate variability and baroreflex sensitivity in normotensive children with repaired coarctation of the aorta

Coarctationoftheaorta(CoA)isassociatedwiththedevelopmentofhypertension and a reduced life expectancy [1]. Despite optimal ana-tomical correction resulting in improved post-coarctation blood flow,individuals with successful repaired CoA maintain an elevated risk forhypertension and early mortality, suggesting that CoA is not simply ananatomical malformation [2]. The mechanisms responsible for thesepersistent late complications remain to be elucidated. In particular,the role of impaired autonomic control has not been thoroughly exam-inedinpatientswithrepairedCoA,eventhoughalterationsinautonomicregulation are hallmark features of primary hypertension [3].Inthepresentstudyweinvestigatedautonomicmodulationandcon-trol using measures of heart rate variability (HRV) and barore flex sensi-tivity(BRS)innormotensivechildrenwithsuccessfullyrepairedCoAandhealthycontrols.Westudied9unmedicatedchildren(age:12±3 years)with anatomically repaired CoA (2 females) and 9 unmedicated healthyage (age: 11±3 years) and sex matche dcontrols(2females),recruitedfrom a local pediatric cardiology unit (McMaster Childrens Hospital,Hamilton, ON, Canada) and the surrounding community. Repaired CoApatients were excluded if they had undergone >1 procedure for theirCoA, had hypertension (resting arm SBP >95th percentile for age),left ventricular hypertrophy (septal and posterior wall dimensions >2z-scores for body surface area), or other moderate to severe associatedintracardiac anomalies.Each participant completed two testing visits, held at the sametime of day (±1 h). During each session continuous supine mea-surements of heart rate (single-lead electrocardiography; 1000 Hz;PowerLab, ADInstruments Inc., Colorado Springs, CO) and bloodpressure(ModelCBM-7000,ColinMedicalInstruments,SanAntonio,TX, USA) were recorded for 10 min after a standard rest period. Discretebrachial blood pressure measurements were also made (Model CBM-7000, Colin Medical Instruments, San Antonio, TX, USA). All procedureswere approved by the Hamilton Health Sciences Research Ethics Board,and informed written consent was ob tained from the parent/guardianand assent from the child before study entry.HRV measures were calculated on a 5 minute epoch edited to re-move non-normal beats (primarily related to movement artifact),whichaccounted for b1%of totaldatain each participant. Specifically,spectral domain (low frequency (LF) power, high frequency (HF) power,andtheLF/HFratio)andtimedomain(standarddeviationsofnormalR-Rintervals (SDNN), the root mean square of successive R-R interval differ-ences (RMSSD), and the percentage of consecutive normal R-R intervalsthat differ by more than 50 ms (pNN50%) measures of HRV were exam-ined [4]. BRS was calculated using the global variability of R-R intervalsand systolic blood pressure [5].Data presented as mean±standard deviations. All comparisonswere completed on the average values of both visits. Normal Gaussiandistributions were assessed using the Kolmogorov–Smirnov test, withnatural logarithmic transformations completed, as required. Unpairedt-tests and Mann –Whitney rank sum tests were used to assess statisti-cal differences between baseline characteristics. HRV and BRSwere an-alyzed using an ANCOVA, to account for baseline differences in bodymassindex(BMI),withTukeyposthocprocedures.Pearsoncorrelationcoefficientswereusedtotestpotentialrelationshipsbetweenvariables.Statistical significance was set at pb0.05.Complete baseline characteristics are available in Table 1. All baselinecharacteristics were similar except for BMI, whichwas higherin repairedCoA. Children with repaired CoA demonstrated signi ficantly lower LFpower, HF power, SDNN, BRS, and a tr end towards lower pNN50%, com-paredwithhealthycontrols( Table2).Correlationanalysesofthestudycohort demonstrated significant associations between BRS and HFpower (r=0.59, pband BRS and SDNN (r=0.54, p0.01) b0.05). Fur-ther correlation analyses did not detect any associations between base-line age, weight, age of surgical repair or years since repair and HRV orBRS measures in the CoA cohort (p>0.05).

Automated ultrasound edge‐tracking software comparable to established semi‐automated reference software for carotid intima‐media thickness analysis

Many commercial ultrasound systems are now including automated analysis packages for the determination of carotid intima‐media thickness (cIMT); however, details regarding their algorithms and methodology are not published. Few studies have compared their accuracy and reliability with previously established automated software, and those that have were in asymptomatic adults. Therefore, this study compared cIMT measures from a fully automated ultrasound edge‐tracking software (EchoPAC PC, Version 110.0.2; GE Medical Systems, Horten, Norway) to an established semi‐automated reference software (Artery Measurement System (AMS) II, Version 1.141; Gothenburg, Sweden) in 30 healthy preschool children (ages 3–5 years) and 27 adults with coronary artery disease (CAD; ages 48–81 years). For both groups, Bland–Altman plots revealed good agreement with a negligible mean cIMT difference of −0·03 mm. Software differences were statistically, but not clinically, significant for preschool images (P = 0·001) and were not significant for CAD images (P = 0·09). Intra‐ and interoperator repeatability was high and comparable between software for preschool images (ICC, 0·90–0·96; CV, 1·3–2·5%), but slightly higher with the automated ultrasound than the semi‐automated reference software for CAD images (ICC, 0·98–0·99; CV, 1·4–2·0% versus ICC, 0·84–0·89; CV, 5·6–6·8%). These findings suggest that the automated ultrasound software produces valid cIMT values in healthy preschool children and adults with CAD. Automated ultrasound software may be useful for ensuring consistency among multisite research initiatives or large cohort studies involving repeated cIMT measures, particularly in adults with documented CAD.

Validity of field assessments to predict peak muscle power in preschoolers

Field-based fitness assessments are time- and cost-efficient. However, no studies to date have reported the predictive value of field-based musculoskeletal fitness assessments in preschoolers. The purpose of this study was to determine the validity of 2 field assessments to predict peak muscle power in preschool-aged children. Four-hundred and nineteen 3- to 5-year olds participated (208 girls, 211 boys; mean age: 4.5 ± 0.9 years). Peak power (PP) was evaluated using a modified 10-s Wingate protocol as the criterion standard. Standing long-jump was measured in inches to the back of the heel using a 2-footed takeoff and landing. Shuttle-run time was measured using a shuttle-run protocol, which required children to sprint 50 feet (15.2 m), pick up a small block, and sprint back, with time measured to the closest tenth of a second. Regression modelling was used to calculate the predictive power of each field-based measurement, adjusting for weight (kg), age, and sex. Both standing long-jump distance and shuttle-run time were significantly correlated with PP (r = 0.636, p < 0.001, and r = -0.684, p < 0.001, respectively). Linear regression analysis determined that a childs PP can be predicted from the childs weight, age, and sex and either standing long-jump or shuttle-run time (adjusted R2 = 0.79, p < 0.001, and 0.81, p < 0.001, respectively). The standing long-jump and the Bruininks Oseretsky Test of Motor Proficiency 2nd Edition shuttle-run are both significant predictors of peak muscle power in preschool children. Either measure can be used as a cost- and time-efficient estimate of musculoskeletal fitness in preschoolers.

Tracking of physical activity and fitness during the early years

The early years are characterized by rapid physical growth and the development of behaviours such as physical activity. The objectives of this study were to assess the 12-month changes in and the tracking of physical activity and fitness in 400 preschoolers (201 boys, 4.5 ± 0.9 years of age). Physical activity data, expressed as minutes per day and as the percentage of time spent at various intensities while wearing an accelerometer, were collected in 3-s epochs for 7 days. Short-term muscle power, assessed with a 10-s modified Wingate Anaerobic Test, was expressed as absolute (W) and relative (W/kg) peak power (PP) and mean power (MP). Aerobic fitness, assessed with the Bruce Protocol progressive treadmill test, was expressed as maximal treadmill time and heart rate recovery (HRR). Light physical activity decreased by 3.2 min/day (p < 0.05), whereas vigorous physical activity increased by 3.7 min/day (p < 0.001), from year 1 to year 2. Physical activity exhibited moderate tracking on the basis of Spearman correlations (r = 0.45-0.59, p < 0.001) and fair tracking on the basis of κ statistics (κ = 0.26-0.38). PP and MP increased from year 1 (PP, 94.1 ± 37.3 W; MP, 84.1 ± 30.9 W) to year 2 (PP, 125.6 ± 36.2 W; MP, 112.3 ± 32.2 W) (p < 0.001) and tracked moderately to substantially (PP, r = 0.89, κ = 0.61; MP, r = 0.86, κ = 0.56). Time to exhaustion on the treadmill increased from 9.4 ± 2.3 min to 11.8 ± 2.3 min (p < 0.001) and tracked strongly (r = 0.82, κ = 0.56). HRR was unchanged at 65 ± 14 beats/min (p = 0.297) and tracked fairly (r = 0.52, κ = 0.23). The findings indicate that fitness tracks better than physical activity over a 12-month period during the early years.