Alison M. McManus

Waist circumference and body mass index in Chinese children: cutoff values for predicting cardiovascular risk factors

Background:Body mass index (BMI) and waist circumference (WC) correlate with cardiovascular (CV) risk factors in childhood which track into adulthood. WC provides a measure of central obesity, which has been specifically associated with CV risk factors. Reference standards for WC, and for WC and BMI risk threshold values are not established in Chinese children.Objectives:To construct reference percentile charts of WC, establish relationships between WC, BMI and other risk factors, and propose WC and BMI threshold values predictive of CV risk factors in Hong Kong ethnic Chinese children.Methods:Weight, height, waist and hip circumference were measured in 2593 (52% boys, 47% girls) randomly sampled Hong Kong school children aged 6–12 years. In 958 of these and 97 additional overweight children (n=1055), the relationships between WC, BMI, waist/hip and waist/height ratio and six age-adjusted CV risk factors (>85% percentile levels of blood pressure (BP), fasting triglycerides, low-density lipoprotein (LDL) cholesterol, glucose and insulin levels, and <15% percentile levels of high-density lipoprotein (HDL) cholesterol) were studied. Receiver-operating characteristic analysis was employed to derive optimal age-adjusted sex-specific WC and BMI thresholds for predicting these measures of risk.Results:WC percentiles were constructed. WC correlated slightly more than BMI with CV risk factors and most strongly with insulin and systolic BP, but poorly or not with LDL and glucose. Optimal WC and BMI risk thresholds for predicting four of these six CV risk factors were ca. the 85th percentiles (sensitivities ∼0.8, specificities ∼0.87) with age-specific cutoff values in girls/boys from ∼57/58 to ∼71/76 cm and 17/18 to 22/23 kg/m2.Conclusion:These are the first set of WC reference data for Chinese children. WC risk cutoff values are proposed which, despite a smaller waist in Chinese children, are similar to those reported for American children. WC percentiles may reflect population risk.

Development and validation of a core endurance intervention program: implications for performance in college-age rowers.

The objective of this study was to examine the effectiveness of a core endurance exercise protocol. Forty-five college-age rowers (age 21 ± 1.0) were assigned to either a core training group [core group] (n = 25), which took part in a core endurance intervention exercise protocol, or to a control training group [control group] (n = 20), which was not given any specialized core training. Training took place 2 days per week for 8 weeks. Trunk endurance was assessed using flexion, extension, and side flexion tests, whereas a variety of functional performance measures were assessed (vertical jump, broad jump, shuttle run, 40-m sprint, overhead medicine ball throw, 2,000-m maximal rowing ergometer test). The results revealed significant improvement in the two side flexion tests for the core group (p < 0.05). Interestingly, significant differences were noted in the trunk extension test endurance times for the control group (p < 0.05), but not for the core group. No significant differences were found for any of the functional performance tests. In summary, the 8-week core endurance training program improved selected core endurance parameters in healthy young men, but the effectiveness of the core intervention on various functional performance aspects was not supported.

Health-related physical fitness and weight status in Hong Kong adolescents

BackgroundThis study was designed to investigate the relation between health-related physical fitness and weight status in Hong Kong adolescents.Methods3,204 students aged 12-18 years participated in the Hong Kong Student Obesity Surveillance (HKSOS) project in 2006-2007. Anthropometric measures (height, weight) and health-related fitness (push-up, sit-up, sit-and-reach, 9-minute run) were assessed. Body mass index (BMI) was computed to classify participants into normal weight, underweight (Grade I, II/III), overweight, and obese groups. The associations of health-related physical fitness with BMI and weight status were examined by partial correlation coefficients and analysis of covariance, respectively.ResultsMore boys than girls were overweight or obese (18.0% vs 8.7%), but more girls than boys were underweight (22.3% vs 16.7%). Boys performed significantly (P < 0.001) better in sit-up (38.8 vs 31.6 times/min) and 9-minute run (1632.1 vs 1353.2 m), but poorer in sit-and-reach (27.4 vs 32.2 cm) than girls. All four physical fitness tests were significantly positively correlated with each other in both sexes, and BMI was only weakly correlated with sit up and sit-and-reach tests in boys. Decreasing performance (P for trend < 0.05) was observed from normal weight to overweight and obese for push-up, sit-up, and 9-minute run in both sexes. From normal weight to Grade I and Grade II/III underweight, decreasing performance (P for trend < 0.05) for sit-up and sit-and-reach in both sexes and for push-up in boys was observed.ConclusionsThe relations between BMI and health-related physical fitness in adolescents were non-linear. Overweight/obese and underweight adolescents had poorer performance in push-up and sit-up tests than normal weight adolescents. Different aspects of health-related physical fitness may serve as immediate indicators of potential health risks for underweight and overweight adolescents.

Effect of training on the aerobic power and anaerobic performance of prepubertal girls

The purpose of this study was to investigate the effects of two, three times a week, 8‐week training programmes on the aerobic power and anaerobic performance of 30 prepubescent girls, with a mean age of 9.6 y. Peak oxygen uptake assessed by an incremental discontinuous treadmill test, and peak power in 5 s and mean power over 30 s estimated from a Wingate anaerobic test were used as the criterion measures. Twelve girls trained using a continuous cycle ergometer programme, 11 girls followed a sprint running programme and the control group consisted of 7 girls. Both training groups significantly (p < 0.05) increased their peak oxygen uptake and peak power in 5 s. However, the increases reported here are lower than those generally observed in adolescents following training. The control group demonstrated no significant (p > 0.05) change in either variable. No significant (p > 0.05) changes in mean power over 30 s were observed in any group.

Contextual barriers to lifestyle physical activity interventions in Hong Kong.

PURPOSE Increased lifestyle physical activity, for instance, use of active transport, is a current public health target. Active transport interventions that target stair climbing are consistently successful in English-speaking populations yet unsuccessful in Hong Kong. We report two further studies on active transport in the Hong Kong Chinese. METHODS Pedestrians on a mass transit escalator system (study 1) and in an air-conditioned shopping mall (study 2) were encouraged to take the stairs for their cardiovascular health by point-of-choice prompts. Observers coded sex, age, and walking on the mass transit system, with the additional variables of presence of children and bags coded in the shopping mall. In the first study, a 1-wk baseline was followed by 4 wk of intervention (N = 76,710) whereas in the second study (shopping mall) a 2-wk baseline was followed by a 2-wk intervention period (N = 18,257). RESULTS A small but significant increase in stair climbing (+0.29%) on the mass transit system contrasted with no significant changes in the shopping mall (+0.09%). The active transport of walking on the mass transit system was reduced at higher rates of humidity and temperature, with steeper slopes for the effects of climate variables in men than in women. CONCLUSIONS These studies confirm that lifestyle physical activity interventions do not have universal application. The context in which the behavior occurs (e.g., climate) may act as a barrier to active transport.

Using heart-rate feedback to increase physical activity in children

OBJECTIVE The objective of this study was to test whether heart-rate feedback prompts increased physical activity (PA) in primary school students. METHODS A controlled trial with 210 9-11 year olds from subsidized Hong Kong Government primary schools was completed in December 2006. Schools were randomly assigned to one of three groups: Control (CG); Educational program (EG); No-educational program (NEG). INTERVENTION In a short-term school-based intervention, heart-rate feedback was given either in combination with an educational program (EG) or in isolation (NEG). Long-term retention was assessed in comparison to the control group after 6 months follow-up. MAIN OUTCOME MEASURES Physical activity and changes in attraction to PA. RESULTS In the short-term, heart-rate monitor feedback increased total daily PA by an average of 24% (p<0.001) and vigorous PA by 0.6% (p<0.05). No change was found for moderate PA. Increases occurred regardless of involvement in the educational program, and in the absence of any change in attitudes towards PA. No long-term retention was apparent. CONCLUSIONS The findings from the study suggest that feedback from heart-rate monitors encourages low intensity PA, but when removed increases do not persist.

Maximising the Clinical Use of Exercise Gaseous Exchange Testing in Children With Repaired Cyanotic Congenital Heart Defects The Development of an Appropriate Test Strategy

AbstractImplicit in deciding upon an exercise test strategy to elucidate cardiopulmonary function in children with congenital heart disease are appropriate application of gas exchange techniques and the significance of the data collected to the specific congenital heart disorder. Post-operative cardiopulmonary responses to exercise in cyanotic disorders are complex and, despite a large body of extant literature in paediatric patients, there has been much difficulty in achieving quality and consistency of data.Maximal oxygen uptake is widely recognised as the best single indicator of cardiopulmonary function and has therefore been the focus of most clinical exercise tests in children. Many children with various heart anomalies are able to exercise to maximum without adverse symptoms, and it is essential that test termination is based on the same criteria for these children. Choosing appropriate, valid indicators of maximum in children with congenital heart disease is beset by difficulties.Such maximal intensity exercise testing procedures have been challenged on the grounds that they do not give a good indication of cardiopulmonary function that is relevant to real life situations. Furthermore, they are prone to much interindividual variability and error in the definition of maximal exertion. Alternative strategies have been proposed which focus upon dynamic submaximal and kinetic cardiopulmonary responses, which are thought to be less dependent on maximal voluntary effort and more suited to the daily activity patterns of children. These methods are also not without problems. Variability in anaerobic threshold measurements and controversy regarding its physiological meaning have been debated.It is recommended that an appropriate cardiopulmonary exercise gas exchange test strategy, which provides clinically useful information for children with cyanotic congenital heart disease, should include both maximal and submaximal data. The inclusion of oxygen uptake kinetics and ventilatory data are encouraged, since they may allow the distinction between a pulmonary, cardiovascular or inactivity related exercise limitation.

Active video games and physical activity recommendations: A comparison of the Gamercize Stepper, XBOX Kinect and XaviX J-Mat

OBJECTIVES The current study was designed to evaluate the intensity levels of three exergames and determine the association with physical activity recommendations that correspond to specific outcomes. The variation in cardiovascular responses between the three exergames was also examined. DESIGN We employed a cross-sectional laboratory design. METHODS We recruited 18 girls to participate in a peak VO2 test and to play Gamercize, Kinect River Rush, XaviX J-Mat at three separate exergaming sessions. Linear regression equations of heart rate and percentage of peak VO2 were calculated for each participant to determine the intensity of exergame play. Differences in intensity between the three exergames and time spent in the recommended moderate (heart rate at ≥ 55% peak VO2) and vigorous (heart rate at ≥ 75% peak VO2) intensity levels were analyzed. We calculated the coefficient of variation for the mean heart rate to determine the difference in variance in heart rate values for the three exergames. RESULTS When playing Gamercize and Kinect the girls did not play at recommended moderate or vigorous levels. Although the girls did not play at vigorous levels when playing XaviX J-Mat, our results showed that when playing XaviX J-Mat they did play at moderate intensity levels. No significant differences in the coefficient of variation between the three exergames were apparent. CONCLUSIONS If active gaming is to be used to increase physical activity levels then individual differences in levels of exertion and specific activity recommendations need to be taken into consideration.

Play pattern of seated video game and active "Exergame" alternatives

The purpose of the study was to compare the play pattern of “exergames” and seated internet-based video games between boys and girls. Seventy-nine participants (40 boys, 39 girls) aged 9 to 12 years (M = 10.85 ± 0.9) were involved in two 1-hour video game sessions. Play pattern in terms of frequency, duration and intensity were assessed from observation, accelerometry and heart rate monitoring. Results indicated that children spent half of the available time playing the activity-promoting exergames (XaviX bowling 47.6 ± 14.9%; XaviX J-Mat 48.8 ± 12.8%). No differences between the boys and girls were apparent for total time played, number of play bouts or duration per bout (p ≥ 0.05). Boys however played both exergames more actively than the girls (XaviX bowling RT3 counts.s−1: boys 10.47 ± 4.71, girls 6.34 ± 2.76; XaviX J-Mat RT3 counts·s−1: boys 66.37 ± 13.84, girls 51.94 ± 17.83). This study concludes that both boys and girls choose to play exergames for similar periods of time, but play style during the XaviX bowling was often inactive in the girls and during the XaviX J-Mat less active in the girls than the boys. Reasons underlying choice of play was similar between the girls and boys. Active video games appear to be suitable for longer-term physical activity interventions in children, but attention will need to be given to the intensity of game play in girls.

Prevalence of exercise and non-exercise physical activity in Chinese adolescents

Non-exercise physical activity (NEPA) is an important part of energy expenditure. This study aimed to investigate the prevalence of exercise and NEPA among adolescents. In the HKSOS project 2006-2007, the proportions of Hong Kong Chinese adolescents (N = 32,005) achieving 60-minute exercise and 60-minute NEPA per day were analyzed. Exercise was defined as structured and planned physical activities, and NEPA was defined as unstructured and unplanned physical activities including walking for transportation and climbing stairs. The prevalence of exercise was higher in boys than girls (after school: 63.8% vs 39.6%; holidays: 78.7% vs 60.0%), but the prevalence of NEPA in boys was similar to that in girls (after school: 72.2% vs 68.0%; holidays: 80.3% vs 79.4%). In general, the prevalence of both exercise and NEPA decreased with age in boys and girls, but was more marked for exercise than NEPA. In conclusion, the prevalence of exercise was lower in adolescent girls than boys, and decreased more rapidly with age than NEPA. NEPA seems to be easier to accumulate than exercise among adolescents regardless of sex and age.