Paul Wozny

Vigorous physical activity and longitudinal associations with cardiometabolic risk factors in youth.

Objective:To examine the longitudinal associations between different physical activity (PA) intensities and cardiometabolic risk factors among a sample of Canadian youth.Methods:The findings are based on a 2-year prospective cohort study in a convenience sample of 315 youth aged 9–15 years at baseline from rural and urban schools in Alberta, Canada. Different intensities (light, moderate and vigorous) of PA were objectively assessed with Actical accelerometers. The main outcome measures were body mass index (BMI) z-score, waist circumference, cardiorespiratory fitness and systolic blood pressure at 2-year-follow-up and conditional BMI z-score velocity. A series of linear regression models were conducted to investigate the associations after adjusting for potential confounders.Results:At follow-up, cardiorespiratory fitness increased (quartile 1 vs quartile 4=43.3 vs 50.2; Ptrend<0.01) and waist circumference decreased (quartile 1 vs quartile 4=79.0 vs 72.6; Ptrend=0.04; boys only) in a dose-response manner across quartiles of baseline vigorous-intensity PA. A similar trend was observed for systolic blood pressure (quartile 1 vs quartile 4=121.8 vs 115.3; Ptrend=0.07; boys only). Compared with quartile 1 of vigorous-intensity PA, BMI z-score at follow-up and conditional BMI z-score velocity were significantly lower in the quartile 2 and 3 (P<0.05). Waist circumference at follow-up also decreased (quartile 1 vs quartile 4=75.3 vs 73.8; Ptrend=0.04) across quartiles of baseline moderate-intensity PA.Conclusions:Time spent in vigorous-intensity PA was associated with several positive health outcomes 2 years later. These findings suggest that high-intensity activities in youth help to reduce the risk for several chronic diseases.

Physical activity intensity and cardiometabolic risk in youth.

OBJECTIVE To determine the association between physical activity (PA) intensities and cardiometabolic risk factors in youth. DESIGN Cross-sectional study using data from the 2008 Healthy Hearts Prospective Cohort Study of Physical Activity and Cardiometabolic Health in Youth. SETTING Rural and urban communities in Alberta, Canada. PARTICIPANTS A convenience sample of 605 youth aged 9 to 17 years. Youth were on average aged 12.1 years, 248 were boys (41%), and 157 were overweight or obese (26%). MAIN EXPOSURE Actical accelerometer-measured PA intensity. MAIN OUTCOMES MEASURES The primary outcome was body mass index (calculated as weight in kilograms divided by height in meters squared) z score. Secondary outcome measures included waist circumference, systolic blood pressure, and cardiorespiratory fitness (maximal oxygen consumption [[Vdot]O2max]). RESULTS Body mass index z score, waist circumference, and systolic blood pressure decreased and [Vdot]O2max increased in a dose-response manner across tertiles of vigorous PA (adjusted P < .001). No significant differences in cardiometabolic risk factors were seen across tertiles of moderate or light PA in multivariable analyses. Achieving more than 7 minutes of vigorous PA daily was associated with a reduced adjusted odds ratio of overweight status (0.56; 95% CI, 0.33-0.95) and elevated systolic blood pressure (0.36; 95% CI, 0.16-0.79). The odds of overweight status and elevated blood pressure decreased with increasing time and intensity of PA. CONCLUSIONS Only vigorous PA was consistently associated with lower levels of waist circumference, body mass index z score, systolic blood pressure, and increased cardiorespiratory fitness in youth. These findings underscore the importance of vigorous PA in guidelines for children and adolescents.

Cardiorespiratory fitness and the risk of overweight in youth: the Healthy Hearts Longitudinal Study of Cardiometabolic Health.

The primary objective of this longitudinal study was to determine the association between cardiorespiratory fitness and the risk of overweight status in youth. To accomplish this aim we analyzed data from annual school‐based surveys of cardiorespiratory fitness and anthropometry conducted between 2004 and 2006. The first analysis was performed on a cohort of 902 youth aged 6–15 years followed for 12 months to assess the association between cardiorespiratory fitness levels determined from a graded maximal field test and the risk of becoming overweight. The second analysis was conducted on a cohort of 222 youth followed for 2 years to assess the continuous association between annual changes fitness and weight gain. Children with low cardiorespiratory fitness were characterized by higher waist circumference and disproportionate weight gain over the 12‐month follow‐up period (P < 0.05). Within the entire cohort, the 12‐month risk of overweight classification was 3.5‐fold (95% confidence = 2.0–6.0, P < 0.001) higher in youth with low cardiorespiratory fitness, relative to fit peers. A time series mixed effects regression model revealed that reductions in cardiorespiratory fitness were significantly and independently associated with increasing BMI (r = −0.18, P < 0.05) in youth. Accordingly, low cardiorespiratory fitness and reductions in fitness over time are significantly associated with weight gain and the risk of overweight in children 6–15 years old. An assessment of cardiorespiratory fitness using a common field test may prove useful for the identification of youth at risk of overweight and serve as a potential target for obesity prevention.

Outdoor Time Is Associated with Physical Activity, Sedentary Time, and Cardiorespiratory Fitness in Youth

OBJECTIVE To determine whether time spent outdoors was associated with increased moderate-to-vigorous physical activity (MVPA) and related health benefits in youth. STUDY DESIGN We performed a cross-sectional study of 306 youth aged 13.6 ± 1.4 years. The exposure of interest was self-reported time spent outdoors after school, stratified into three categories: none, some, and most/all of the time. The main outcome of interest was accelerometer-derived MVPA (Actical: 1500 to >6500 counts/min). Secondary outcomes included sedentary behavior, cardiorespiratory fitness, overweight status, and blood pressure. RESULTS Among the 306 youth studied, those who reported spending most/all of their after-school time outdoors (n = 120) participated in more MVPA (61.0 ± 24.3 vs 39.9 ± 19.1 min/day; adjusted P < .001), were more likely to achieve the recommended minimum 60 min/day of MVPA (aOR 2.8; 95% CI, 1.3-6.4), spent less time in sedentary activities (539 ± 97 min/day vs 610 ± 146 min/day; adjusted P < .001), and had higher cardiorespiratory fitness (49 ± 5 vs 45 ± 6 mL/kg/min; adjusted P < .001) than youth who reported no time outdoors (n = 52). No differences in overweight/obesity or blood pressure were observed across the groups. CONCLUSIONS Time spent outdoors is positively associated with MVPA and cardiorespiratory fitness in youth and negatively associated with sedentary behavior. Experimental trials are needed to determine whether strategies designed to increase time spent outdoors exert a positive influence on physical activity and fitness levels in youth.

175 FITNESS DOES NOT MITIGATE WEIGHT GAIN-ASSOCIATED BLOOD PRESSURE INCREASES IN CHILDREN

Background: : Both excessive weight and weight gain are associated with a disproportionate increase in blood pressure in children. The purpose of this analysis was to determine if physical fitness and/or activity could mitigate changes in blood pressure associated with obesity or excessive weight gain. Methods: This study was carried out from an analysis of the Health Hearts cohort, a group of school children who had been prospectively followed for cardiometabolic status in relation to physical activity, physical fitness and weight status. The current cohort represented a sub-set for whom data was available for three consecutive years, 2008–2010. Yearly fitness was measured by Leger shuttle run, activity by accelerometry, and blood pressure by automated device. Results: This study included 565 children ages 9–16; 315 boys and 250 girls. As expected both BMI and waist:hip ratio correlated with systolic blood pressure (SBP) (r = .49, p<.0001; r = .47, p < .0001, respectively). Change in BMI also correlated with change in SBP (r = .19, p < .0001). Categorically, change in weight status correlated with change in blood pressure status (p = .005). Higher levels of activity and fitness were associated with lower BMI and SBP independently. However, in covariate analysis, BMI determined SBP independent of activity/fitness. Similarly, after adjustment for adiposity, physical activity/fitness did not influence SBP. Conclusions: Blood pressure in children is significantly influenced by adiposity, and while physical activity and fitness can influence the latter, they do not seem to independently reduce the blood pressure-raising effects of weight gain or obesity.