Clare C.W. Yu

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.

Effects of strength training on body composition and bone mineral content in children who are obese.

The purpose of this study was to test the hypothesis that strength training benefits diet-controlled obese children with respect to lean mass and bone mineral acquisition. Eighty-two Hong Kong school children (aged 10.4 ± 1.0 years, 70 in Tanner stage 1, 12 in stage 2) who were obese/overweight were randomly assigned to receive either a balanced low-energy (900–1200 cal) diet plus strength training (n = 41) (training group) or the diet alone (n = 41) (control group). The training group attended a 75-minute strength exercise program 3 times/week for 6 weeks (phase 1), after which they were offered and 22 children opted to continue a once-weekly program for a further 28 weeks (phase 2). All children were evaluated at baseline, after 6 weeks, and at the end of the 36-week study (including an intervening 2-week introduction to phase 2). Body composition and bone mineral content were measured by dual-energy X-ray absorptiometry, and diet was assessed by food-frequency questionnaire. The results showed that the exercise programs were well accepted, with good attendance at the exercise classes. After 6 weeks, the children in the training group showed significantly larger increases in lean body mass (1 0.8 kg [2.4%] vs. 10.3 kg [1.0%], p < 0.05) and total bone mineral content (146.9 g [3.9%] vs. 133.6 g [2.9%], p < 0.05) than those in the control group. At the end of the study, these trends were maintained in the continued-training subgroup, though no longer reaching statistical significance. We conclude that in diet-controlled prepubertal obese/over-weight children, participation in an exercise program with emphasis on strength training resulted in improved lean mass and bone mineral accrual.

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.

Effects of short-term resistance training on serum leptin levels in obese adolescents

The purpose of this study was to examine the effects of a short-term resistance training program on serum leptin concentrations in obese adolescents. Eighteen Chinese obese adolescents participated in the supervised weight management program. Resistance training was conducted three times a week on alternate days for 6 weeks. Body composition [body fat mass (FM) and body lean mass (LM)] determined by dual-energy X-ray absorptiometry, muscle strength and leptin, insulin and glucose were measured before and after training. Subjects demonstrated significantly improved strength of leg, chest and bicep under conditions of stability in weight, FM and LM. There were positive correlations between leptin and body mass index, FM, %FM, waist girth and hip girth, and negative correlations between leptin and %L M at the resting state before and after 6 weeks of resistance training. No significant relationship was found between leptin concentration and the parameters of muscular strength or concentrations of insulin and glucose. Compared to pre-training values, serum leptin levels were not significantly altered, while relative leptin (leptin/FM) decreased significantly after the short-term resistance training. These results indicate that short-term resistance training enhances muscle strength but does not alter leptin levels in obese adolescents with weight and FM stability. The results also suggest that 6 weeks of resistance training decreases the requirement of leptin per unit of FM and improves leptin sensitivity in obese adolescents.

How Children Move: Activity Pattern Characteristics in Lean and Obese Chinese Children

Physical activity and sedentary behavior are central components of lifetime weight control; however, our understanding of dimensions of these behaviors in childhood is limited. This study investigated free-living activity pattern characteristics and the individual variability of these characteristics in 84 lean and obese Chinese children (7–9 y) during the school day and over the weekend. Activity pattern characteristics were established from triaxial accelerometry (StayHealthy RT3). Results indicated that childrens free-living activity is characterized by many short-duration, low-intensity bouts of movement. Obese children take longer rest intervals between bouts and engage in fewer activity bouts both at school and at home. Intraindividual variability in activity patterns was low during school days but high for the rest intervals between bouts and number of activity bouts per day at the weekend. Finding ways to reduce the rest time between bouts of movement and increase the number of movement bouts a child experiences each day is an important next step.

Orlistat improves endothelial function in obese adolescents: A randomised trial

To investigate the effect of orlistat on endothelial function in obese adolescents.

Longer term follow up of aerobic capacity in children affected by severe acute respiratory syndrome (SARS)

Background: A study was undertaken to investigate the aerobic capacity and pulmonary function of children 6 and 15 months after the diagnosis of severe acute respiratory syndrome (SARS). Methods: Thirty four patients of mean age 14.7 years completed both pulmonary function and maximal aerobic capacity tests at 6 months. All had normal clinical examination and were asymptomatic. Their exercise responses were compared with a group of healthy controls. Complete data were collected on 27 of the original 34 cases at 15 months. Results: Compared with normal controls, the patient group had significantly lower absolute and mass related peak oxygen consumption (peak V˙o2 (p<0.01)), higher ventilatory equivalent for oxygen (p<0.01), lower oxygen pulse (p<0.01), and a lower oxygen uptake efficiency slope (p<0.01) at 6 months. This impairment was unexpected and out of proportion with the degree of lung function abnormality. Residual high resolution computed tomography of thorax (HRCT) abnormalities were present in 14 patients. Those with abnormal HRCT findings had significantly lower mass related peak V˙o2 than subjects with normal radiology (p<0.01). Absolute and mass related peak V˙o2 in the patient group remained impaired at 15 months despite normalisation of lung function in all patients. Conclusions: The mechanism for the reduced aerobic capacity in children following SARS is not fully understood, but it is probably a consequence of impaired perfusion to the lungs at peak exercise and deconditioning.

Association Between Leisure Time Physical Activity, Cardiopulmonary Fitness, Cardiovascular Risk Factors, and Cardiovascular Workload at Work in Firefighters

Background Overweight, obesity, and cardiovascular disease risk factors are prevalent among firefighters in some developed countries. It is unclear whether physical activity and cardiopulmonary fitness reduce cardiovascular disease risk and the cardiovascular workload at work in firefighters. The present study investigated the relationship between leisure-time physical activity, cardiopulmonary fitness, cardiovascular disease risk factors, and cardiovascular workload at work in firefighters in Hong Kong. Methods Male firefighters (n = 387) were randomly selected from serving firefighters in Hong Kong (n = 5,370) for the assessment of cardiovascular disease risk factors (obesity, hypertension, diabetes mellitus, dyslipidemia, smoking, known cardiovascular diseases). One-third (Target Group) were randomly selected for the assessment of off-duty leisure-time physical activity using the short version of the International Physical Activity Questionnaire. Maximal oxygen uptake was assessed, as well as cardiovascular workload using heart rate monitoring for each firefighter for four “normal” 24-hour working shifts and during real-situation simulated scenarios. Results Overall, 33.9% of the firefighters had at least two cardiovascular disease risk factors. In the Target Group, firefighters who had higher leisure-time physical activity had a lower resting heart rate and a lower average working heart rate, and spent a smaller proportion of time working at a moderate-intensity cardiovascular workload. Firefighters who had moderate aerobic fitness and high leisure-time physical activity had a lower peak working heart rate during the mountain rescue scenario compared with firefighters who had low leisure-time physical activities. Conclusion Leisure-time physical activity conferred significant benefits during job tasks of moderate cardiovascular workload in firefighters in Hong Kong.

central adiposity and the propensity for rehearsal in children

Background: There is increasing evidence that continuous activation of the hypothalamic-pituitary adrenal axis and the central sympathetic nervous system contributes to the pathogenesis of central adiposity via increased psychological stress. The purpose of this study was to examine the link between central adiposity and the propensity for Chinese children to rehearse emotionally upsetting events, a dimension of psychological stress. Additionally, gender differences in this relationship were explored. Methods: Waist circumference, which is a marker of central adiposity and associated risks of developing cardiovascular disease, was measured and the propensity for rehearsal was assessed twice over two consecutive years in Hong Kong Chinese children (n = 194, aged 7–9 years), using a psychometric tool. Results: Children with waist circumference indicative of a risk of cardiovascular disease displayed higher rehearsal scores than children categorized as “not at risk”, as did boys compared with girls. Our results suggest that central adiposity and the propensity for rehearsal of emotionally upsetting events may be linked in Chinese children. Conclusion: Future prospective studies examining the direction of causality between central adiposity and rehearsal can potentially have valuable clinical implications.

Follow up of aerobic capacity in children affected by severe acute respiratory syndrome

Background and objective:  The aim of this study was to investigate the aerobic capacity of children 3 years after they were diagnosed with severe acute respiratory syndrome (SARS).