Matthew C. Humphries

Effects of exercise training and its cessation on components of the insulin resistance syndrome in obese children

OBJECTIVE: To determine the effect of exercise training (ET) on components of the insulin resistance syndrome (IRS) in obese children.DESIGN: Randomized, modified cross-over study, with subjects assigned to one of two conditions: (1) 4 months of ET followed by 4 months of no-ET; or (2) 4 months of no-ET followed by 4 months of ET. Measurements were made at three time points: 0, 4 and 8 months.SUBJECTS: 79 obese, but otherwise healthy children (age: 7–11 y, percent fat (%fat) 27–61%).MEASUREMENTS: Plasma lipid and lipoprotein concentrations, plasma insulin and glucose concentrations; %fat; submaximal heart rate (HR) as an index of fitness.EXERCISE TRAINING: ET was offered 5 d/week 40 min/d. For the 73 children who completed 4 months of ET, the mean attendance was 80% (that is, 4 d/week) and the average HR during ET was 157 bpm.RESULTS: Significant (P<0.05) group x time interactions were found for plasma triglyceride (TG) and insulin concentrations and %fat. The average change for both groups, from just before ET to just after the 4 month ET was −0.24 mmolċl−1 for TG, −25.4 pmolċl−1 for insulin and −1.6 units for %fat. When Group 1 ceased ET, over the following 4 month period the average change for insulin was +26.6 pmolċl−1 and for %fat +1.3 units.CONCLUSION: Some components (plasma TG, insulin, %fat) of the IRS are improved as a result of 4 months of ET in obese children. However, the benefits of ET are lost when obese children become less active.

General and visceral adiposity in black and white adolescents and their relation with reported physical activity and diet.

Background:Excess body fat accumulation may begin in youth and is linked with increased risk of cardiovascular disease. Examination of physical activity (PA) and diet behaviours predictive of adiposity may help target efforts to reduce chronic disease risk.Objective:We hypothesized that energy intake (EI) from fat, vigorous PA (VPA), and their interaction would predict body fat percentage (%BF) and visceral adipose tissue (VAT) in youth and that sedentary behaviours and intake of dairy, fruit, vegetable and whole grain foods would be related to adiposity.Design:A cross-sectional, observational study of reported PA and diet behaviours and objective adiposity measures.Subjects:Six-hundred sixty-one healthy black and white adolescents aged 14–18 years.Measurements:Diet by 24-h recalls using Nutrition Data Systems for Research (Minneapolis, MN, USA), VPA by previous day physical activity recalls (PAR), and %BF with dual-energy X-ray absorptiometry. VAT by magnetic resonance imaging for 434 subjects.Results:Reported EI and VPA were positively correlated with each other and were negative predictors of %BF. Time spent watching television or movies and %EI from protein were positive predictors of %BF. Adjusted for EI, none of the independent variables predictive of %BF retained their significance. %BF and VAT were highly correlated (r=0.73, P<0.0001). EI was the sole and negative predictor of VAT.Conclusions:Higher energy ‘throughput’, not energy restriction, characterize leaner youths. Youths should be advised to engage in VPA so that they can eat sufficient calories to obtain the nutrients required for optimal health while remaining lean.

Relationship of Visceral Adiposity to Cardiovascular Disease Risk Factors in Black and White Teens

Objective: We tested the hypothesis that visceral adiposity, compared with general adiposity, would explain more of the variance in cardiovascular disease (CVD) risk factors.

Relations of body fatness and cardiovascular fitness to lipid profile in black and white adolescents.

High body fatness is associated with unfavorable cardiovascular disease risk profiles in juveniles. However, the degree to which the deleterious effects attributed to fatness may actually be due to the low cardiovascular fitness (CVF) that is usually confounded with fatness is not known. This study determined in 14- to 18-y-old (n = 398) youths the degree to which percentage body fat (%BF) and CVF explained variability in lipids and lipoproteins. Blood samples were taken after a 12-h fast. %BF was measured with dual-energy x-ray absorptiometry. CVF was determined with a multistage treadmill test. The degree to which %BF and CVF explained variance in outcome variables was determined by regression analyses, controlling for demographic variables before entering %BF or CVF and their interactions with race and sex. Because %BF and CVF were highly correlated (r = –0.69, p < 0.001), they were first entered separately in the regression models before being considered together. Both higher %BF and lower CVF were associated with unfavorable concentrations of total cholesterol to HDLC ratio and triglycerides. However, the effects of %BF and CVF were not additive; once %BF was in the regression model, CVF did not explain additional variance. For Lp(a), only %BF explained a significant portion of the variance. For triglycerides, there was a %BF by race interaction, such that the deleterious effects of high %BF were greater in whites than in blacks. These results suggest that interventions to improve lipid profile in youths should be designed primarily to minimize fatness.

Evaluation of Internal Medicine Residents as Exercise Role Models and Associations With Self-Reported Counseling Behavior, Confidence, and Perceived Success

Background: Patients perceive physicians who practice healthy personal behaviors as more credible and better able to motivate patients to make healthy lifestyle choices. Purposes: To evaluate internal medicine resident physicians as role models for promoting exercise by an assessment of physician physical activity behavior, cardiovascular fitness, physical activity knowledge, personal use of behavior modification techniques, attitudes toward personal physical activity practice, and confidence (i.e., self-efficacy) in the knowledge and personal utilization of behavior modification techniques and to explore the associations with self-reported patient counseling behavior, confidence, and perceived success. Methods: Cross-sectional study of internal medicine resident physicians with a self-administered survey, treadmill fitness testing, and a 7-day physical activity recall. Results: Fifty-one resident physicians agreed to participate (response rate = 81%). Fitness levels were below average for 60%, average for 25%, and above average or excellent for 15%. The mean energy expenditure was 234 kcal/kg/week, with 41% of physicians meeting recommended physical activity guidelines. Few reported high self-efficacy (33%) or perceived success (25%) in the ability to be regularly active. Few demonstrated adequate knowledge useful for patient counseling (e.g., listing 3 ways to integrate physical activity into daily life [27%], calculating target heart rate [29%], and identifying personal exercise stages of change [25%]). Personal use of behavior modification techniques was reported infrequently. Although 88% reported confidence in the knowledge of exercise benefits, less than half reported confidence in the knowledge of local facilities, American College of Sports Medicine (ACSM) guidelines, and behavior modification techniques. Multiple linear regression demonstrated that a higher level of training (p =. 02) and a greater confidence in the knowledge of ACSM guidelines (p =. 048, total R2 =. 21) independently predicted more frequent self-reported counseling. Sex (i.e., male; p =. 01) and greater physical activity self-efficacy (p =. 017, total R2 =. 23) independently predicted greater perceived counseling success. Greater physical activity enjoyment (p =. 03) and greater perceived success at engaging in regular physical activity (p =. 028, total R2 =. 28) independently predicted greater counseling self-efficacy. Conclusions: Most internal medicine resident physicians may not be adequate role models for promoting exercise adherence. Confidence in the knowledge of current guidelines, personal physical activity enjoyment, and perceived success and self-efficacy in engaging in regular physical activity may be useful targets for enhancing resident physician physical activity counseling for their patients.

Relations of adiposity and effects of training on the left ventricle in obese youths.

PURPOSE 1) To determine the relations of left ventricular (LV) structure and function to total body composition, visceral adipose tissue (VAT), and hemodynamics in obese children; 2) to determine the effects of 4-month of physical training (PT) on LV structure and function and hemodynamics; and 3) to explore determinants of individual variability in response to PT. METHODS Measurements included LV structure/function with echocardiography, total body composition with dual-energy x-ray absorptiometry, VAT with magnetic resonance imaging (MRI), and resting and exercising hemodynamics with a Dinamap monitor and Doppler-echocardiography. Youths were randomly assigned to engage in PT for the first or second 4-month periods of the 8-month intervention period. RESULTS Correlation and regression at baseline showed that elevated LV mass was associated with excess general and visceral adiposity, and elevated cardiac output. Although the PT had favorable effects on percent body fat and VAT, no significant changes were found in LV or hemodynamic variables. Over the 4-month period of the PT intervention, those who increased the most in VAT tended to increase the most in LV mass. CONCLUSION General and visceral adiposity were associated with elevated LV mass. However, no evidence was provided that 4 months of PT had a significant effect on LV or hemodynamic variables.