Joanne S. Harrell

Energy costs of physical activities in children and adolescents

PURPOSE The primary aim was to determine the energy expenditure (EE: kcal.kg(-1).h(-1)) in terms of caloric cost and metabolic equivalents of activities commonly performed by children and adolescents. Secondary aims were to determine at what age and pubertal developmental stage values approach those of adults. METHODS In this descriptive study, 295 volunteer youth 8-18 yr of age completed 18 common physical activities (including rest) while EE was measured continuously with a portable metabolic system. Three sets of activities were assigned in random order for each subject. Activities ranged from television viewing and video game play to running and rope skipping. Pubertal development was estimated from a self-report questionnaire. RESULTS At rest, VO(2) and EE were highest in the youngest children and decreased with advancing age and higher pubertal stage in both genders. The age-adjusted and puberty-adjusted energy expenditure values were generally lower than the compendium MET values for sedentary and moderate activities but were more varied for high-intensity activities. However, the ratio of activity EE to REE was comparable in children and adults. CONCLUSIONS Energy expenditure per kilogram of body mass at rest or during exercise is greater in children than adults and varies with pubertal status, thus using the definition of a MET in the compendium of physical activities without adjustment is inadequate for energy estimation in children, until a child reaches Tanner Stage 5. However, the ratio of activity EE to resting EE in children appears to be similar or slightly less than in the compendium, suggesting that the compendium MET increments used with our adjusted EE values more closely approximate the true EE of activities in children than present adult norms.

Effects of a school-based intervention to reduce cardiovascular disease risk factors in elementary-school children: The Cardiovascular Health in Children (CHIC) Study

OBJECTIVE To test a classroom-based intervention to reduce cardiovascular disease risk factors in elementary school children. STUDY DESIGN This was a randomized, controlled field trial in 12 schools across North Carolina, stratified by geographic region and urban/rural setting. Subjects were 1274 third and fourth graders (48% boys). The intervention, taught by regular classroom and physical education teachers, provided all children an 8-week exercise program and 8 weeks of classes on nutrition and smoking. Data were analyzed at the school level with survey regression models and at the individual level with multivariate analysis of variance and analysis of covariance models; 95% confidence intervals were computed. RESULTS Children in the intervention group had significantly greater knowledge (7.9% more correct) and a significant increase in self-reported physical activity than children in the control group. Trends for the intervention group were a reduction in total cholesterol level (-5.27 mg/dl), an increase in aerobic power, a reduction in body fat, and smaller rise in diastolic blood pressure than control children. CONCLUSIONS This classroom-based, public health approach improved childrens cardiovascular disease risk profiles; it is practical and fairly easy to incorporate into the school day. All children directly receive the potential benefits of the intervention without a risk of labeling. This program can improve health knowledge, habits, and health outcomes of young children at a time when health habits are being formed.

Changes in common activities of 3rd through 10th graders: the CHIC study.

PURPOSE This study was a longitudinal examination of the change in both the activities done and the intensity of those activities from childhood to adolescence. METHODS Common activities were assessed by questionnaire initially on 656 subjects from 21 elementary schools; 50.5% were female, 83.4% were Caucasian, 20.6% African-American, and 6.0% were other races. RESULTS Girls more often reported sedentary activities overall. Weighted least squares analyses showed boys consistently reported more vigorous activities than girls (P < 0.0008). African-American girls reported fewer vigorous activities than Caucasian or other race girls (P = 0.027). Sedentary activities were more frequently reported with increasing age (X2 P < 0.001). The youngest African-American and Caucasian boys reported similar activity patterns. However, boys from other races reported more intense activities until sixth and seventh grades when African-American boys began reporting more sedentary activities than Caucasians or other races (P = 0.004). During sixth-eighth grades, Generalized Estimating Equations (GEE) models show that girls with more advanced pubertal status reported more sedentary activities than girls who were less developed (P < 0.0001). For high school girls, race was a marginally significant predictor (P = 0.05) of activity status. Neither race nor pubertal status were significant factors in activities chosen by middle school boys. However, for male high school students, Caucasians were more likely than African-Americans to report vigorous activities (P = 0.005). CONCLUSIONS Variation in activities by race within gender suggests that establishing activity patterns in youth may be race-specific as well as gender-specific and must be accounted for in designing physical activity interventions. Also, pubertal maturation is a factor in activity choices in middle school girls.

School-based Interventions Improve Heart Health in Children With Multiple Cardiovascular Disease Risk Factors

Objective. To determine the immediate effects of two types of elementary school-based interventions on children with multiple cardiovascular disease (CVD) risk factors. Design. Randomized, controlled field trial. Setting. Conducted in 18 randomly selected elementary schools across North Carolina. Study Participants. Four hundred twenty-two children age 9 ± 0.8 years with at least two risk factors at baseline: low aerobic power and either high serum cholesterol or obesity. Intervention. Both 8-week interventions consisted of a knowledge and attitude program and an adaptation of physical education. The classroom-based intervention was given by regular teachers to all children in the 3rd and 4th grades. The risk-based intervention was given in small groups only to children with identified risk factors. Children in the control group received usual teaching and physical education. Outcome Measures. The primary outcome measure was cholesterol; additional measures were blood pressure, body mass index, body fat, eating and activity habits, and health knowledge. Results. Both interventions produced large reductions in cholesterol (−10.1 mg/dL and −11.7 mg/dL) compared with a small drop (−2.3 mg/dL) in the controls. There was a trend for systolic blood pressure to increase less in both intervention groups than in the controls. Both intervention groups had a small reduction in body fat and higher health knowledge than the control group. Conclusions. Both brief interventions can improve the CVD risk profile of children with multiple risk factors. The classroom-based approach was easier to implement and used fewer resources. This population approach should be considered as one means of early primary prevention of CVD.

Prevalence of abnormal lipid and blood pressure values among an ethnically diverse population of eighth-grade adolescents and screening implications

OBJECTIVES. Our goal was to report the prevalence of elevated blood pressure and lipid levels among eighth-grade adolescents from 3 US locations and differences by gender, ethnicity, and overweight percentile group. METHODS. Fasting blood samples and blood pressure levels were obtained from 1717 eighth-grade students from 12 predominantly minority schools in 3 states (Texas, California, and North Carolina) during spring 2003. Age, gender, ethnicity, weight, and height were ascertained and BMI calculated. The presence of abnormal total cholesterol, high-density lipoprotein cholesterol, low-density lipoprotein cholesterol and triglycerides, prehypertension, hypertension, at risk for overweight, and overweight were calculated and compared with the findings of previous youth studies. We examined whether prevalence differed by gender, ethnicity, or BMI group. RESULTS. A total of 23.9% of participants had high blood pressure, 16.7% had borderline total cholesterol, 4.0% had high total cholesterol, 10.5% had borderline low-density lipoprotein cholesterol, 3.9% had high low-density lipoprotein cholesterol, 13.3% had low high-density lipoprotein cholesterol, and 17.2% had high triglycerides. A total of 19.8% of participants were at risk of overweight (BMI ≥85th percentile, <95th percentile) and 29% were overweight (BMI ≥95th percentile). The prevalence of risk factors was associated (P < .05) with the overweight group and differed by age and gender. CONCLUSIONS. Prevalence of elevated blood pressure was higher in this sample than in previous national surveys in which subjects were less overweight. Associations between overweight and both elevated lipid and blood pressure levels suggest that adolescents overweight or at risk for overweight should be screened for elevated blood pressure and lipid levels.

Tracking of physical activity and aerobic power from childhood through adolescence

PURPOSE To evaluate the tracking of physical activity levels (PA) and aerobic power (VO2max) in African-American (AA) and Caucasian (CA) youth as they age from 8 to 16 yr. METHODS Subjects were 529 girls and 535 boys for whom data were obtained at least three times over 7 yr and a subset of 387 girls and 404 boys who participated in all years. PA levels were obtained from a survey. VO2max was predicted from a cycle ergometer test. RESULTS Spearman correlation for VO2max for years 1-7 for AA boys and girls were similar (rho approximately 0.53). Year 1-7 correlations for VO2max for the CA boys and girls were similar (rho approximately 0.50-0.53). The year 2-7 correlations for PA were similar for the AA and CA girls but higher for the AA than the CA boys. The kappa (kappa) statistics for VO2max indicated substantial year-to-year agreement on categorization (high, moderate, and low), with AA girls having the highest agreement and AA boys the lowest. The kappa statistic for high, moderate, and low PA groupings in girls of either ethnicity was quite low, whereas the kappa statistics for the boys were somewhat better. The general estimating equation (GEE) stability coefficients for tracking of VO2max were similar between the sexes and ethnicities (P<0.0001). The GEE stability coefficient for PA was better for the boys than girls and slightly better for the AA than CA. CONCLUSION Although aerobic power and physical activity levels decline from childhood through adolescence, aerobic power tracks better than physical activity levels. Because tracking within the cohort is only moderate, change is possible if we intervene early in these youth.

A public health vs a risk-based intervention to improve cardiovascular health in elementary school children: the Cardiovascular Health in Children Study.

OBJECTIVES This study sought to determine the population effects of both classroom-based and risk-based interventions designed to reduce cardiovascular disease risk factors in children. METHODS Elementary school children (n = 2109; age range: 7-12 years) were randomized by school to a classroom-based intervention for all third and fourth graders, a risk-based intervention only for those with 1 or more cardiovascular disease risk factors, or a control group. The 8-week interventions involved both knowledge--attitude and physical activity components. RESULTS School-level analyses showed that physical activity in the risk-based group and posttest knowledge in the classroom-based group were significantly higher than in the control group. With regard to trends shown by individual-level analyses, cholesterol dropped more in the classroom-based than in the control group, and skinfold thickness decreased 2.9% in the classroom-based group and 3.2% in the risk-based group (as compared with a 1.1% increase in the control group). CONCLUSIONS Both classroom-based and risk-based interventions had positive effects on physical activity and knowledge, with trends toward reduced body fat and cholesterol. However, the classroom-based approach was easier to implement and evidenced stronger results than the risk-based intervention.

Is physical activity or aerobic power more influential on reducing cardiovascular disease risk factors

PURPOSE This study determined the relationship between aerobic power (VO2max), physical activity (PA), and cardiovascular disease (CVD) risk factors. The study also determined how increased VO2max and increased PA levels influence CVD risk factors of 576 low-fit adults (VO2max < 30 mL.kg-1.min-1). METHODS PA (Baeke questionnaire) and VO2max (submaximal cycle test) of 1664 law enforcement trainees were evaluated with respect to the CVD risk factors of total cholesterol, blood pressure (BP) [BP], smoking, and obesity using separate logistic regression, adjusting for age, gender, and the other major CVD risk factors. RESULTS Compared with the lowest tertile of VO2max, the highest tertile had a reduced relative risk (RR) for elevated cholesterol (RR, 0.56; CI, 0.36-0.43), BP (RR, 0.32; CI, 0.15-0.62) and obesity (RR, 0.09; CI, 0.06-0.12). The middle tertile of VO2max compared with the lowest had reduced RR for elevated diastolic BP (RR, 0.44; CI, 0.23-0.66) and obesity (RR: 0.38; CI 0.28-0.50). High PA tertile, compared with low PA tertile, only had lower RR for high systolic BP (RR, 0.48; CI, 0.23-0.95). Compared with the low PA tertile, moderate or high PA had no reduction in any of the RR (P > 0.05). Participation in a 9-wk exercise program by low-fit individuals resulted in a 9% increase in PA levels (P < 0.02); however, only those subjects who increased VO2max (> 3 mL.kg-1.min-1; N = 345) had a reduction in RR for high cholesterol (RR: 0.62; CI 0.42-0.92) and systolic BP (RR: 0.57; CI 0.40-0.80). No reduction in RR were noted for diastolic BP or obesity. CONCLUSIONS Aerobic power appears to have more of an influence on CVD risk factors than PA levels. Further, in low-fit persons, it appears that PA resulting in an increased aerobic power is associated with a reduction in CVD risk factors of cholesterol and BP in as little as 9 wk.

The association between insulin resistance and cytokines in adolescents: the role of weight status and exercise

Increased adiposity is associated with insulin resistance (IR) and an inflammatory response in adults. We tested the hypotheses that cytokines associated with adiposity are also correlated with IR in early adolescents and that these relationships are moderated by weight status, levels of vigorous physical activity (VPA), or maximal aerobic power (pVO2max). Body mass, stature, and a fasting blood sample were obtained from 120 midpubertal adolescents (60 girls and 60 boys). Habitual VPA was obtained by a survey. Predicted VO2max was determined using a cycle ergometer test. Weight status was based on body mass index (BMI) percentiles (normal weight=BMI<75th percentile, overweight=BMI>95th percentile). Glucose, insulin, adiponectin, resistin, tumor necrosis factor-alpha (TNF-alpha), and interleukin-6 were measured; and IR index was based on the Homeostatic Model Assessment. Adiponectin, resistin, and TNF-alpha were associated with IR in all adolescents (R2=0.329, P<.001; R2=0.152, P=.001; and R2=0.141, P=.002; respectively); but interleukin-6 was not (R2=0.148, P=.114). The degree of association between adiponectin and IR was stronger in overweight than in normal-weight adolescents (P<.050). When regression models included weight status, neither TNF-alpha nor resistin was significantly related to IR (P>.050). Exercise did not moderate the association between these cytokines and IR. However, higher levels of VPA and/or pVO2max were associated with higher adiponectin, lower resistin, and lower TNF-alpha in at least one of the sexes. Our results indicate that the pathophysiology of obesity is already established in early adolescents. Increased adiposity, resulting in reduced adiponectin and increased resistin and TNF-alpha, may link these cytokines with IR in adolescents.

LEISURE TIME ACTIVITIES OF ELEMENTARY SCHOOL CHILDREN

The three most common leisure time activities of 2,200 third and fourth grade children (mean age 8.8 + 0.8; 50.7% girls) and the association of the intensity levels of those activities with demographic variables and risk factors for cardiovascular disease are reported. Activities reported most often by boys were playing video games (33%), playing football (32%), bicycling (31%), watching television (28%), and playing basketball (26%). The girls reported doing homework (39%), bicycling (31%), watching television (30%), dancing (27%), and reading (23%). Overall, the children, especially girls, reported fairly sedentary activities, with an average metabolic equivalent level of 4.2 for girls and 4.8 for boys. Among boys, African Americans reported more vigorous activities than Whites, but the activities reported by White girls were somewhat more vigorous than those reported by non-White girls. Children from a higher socioeconomic status (SES), especially boys, reported a greater proportion of sedentary activities than lower SES children. The risk factors of cholesterol, blood pressure, skinfold thickness, and body mass index were not significantly associated with total activity score. However, significantly more nonobese than obese children reported a vigorous (high-intensity) activity as one of their top three activities.