The objectives of this study were to identify the independent effect of physical activity and fitness on insulin dynamics in a cohort of European-, African-, and Hispanic-American children (n = 215) age 7–12 years and to determine if racial/ethnic differences in insulin dynamics could be statistically explained by racial/ethnic differences in physical activity or fitness. An intravenous glucose tolerance test and minimal modeling were used to derive the insulin sensitivity index (SI) and acute insulin response to glucose (AIRg). Fitness was assessed as VO2-170 and physical activity by accelerometer. Multiple regression models were tested for contributions of fitness and physical activity to SI and AIRg. Fitness was a stronger predictor of SI and AIRg than physical activity regardless of ethnicity; racial/ethnic differences in insulin dynamics were not accounted for by differences in fitness and/or physical activity.
Krista Casazza, Barbara A. Gower, Amanda L. Willig, Gary R. Hunter and José R. Fernández
Margaret A. Forster, Gary R. Hunter, Donna J. Hester, Donna Dunaway and Kathy Shuleva
Maximal oxygen uptake (VO2max), submaximal grade-walking oxygen uptake, and anthropometric measures were measured in a group of 19 children in 1988 and in 1992. The children were 5.2 ± .9 years old in 1988 and 9.2 ± 1.0 in 1992. The VO2max did not change relative to body weight over the 4 years (44.6 ml·kg−1·min−1 in 1988 versus 43.3 ml·kg−1·min−1 in 1992). Lower specific weight-relative oxygen uptakes were seen at the submaximal work levels in 1992 than in 1988, indicating an improvement in grade-walking economy.
Kathleen M. Shuleva, Gary R. Hunter, Donna J. Hester and Donna L. Dunaway
This study compared submaximal and maximal oxygen uptake (V̇O2 max) in children ages 3–4 and 5–6 years. Methods appropriate for this age group were developed to elicit maximal performance on the exercise tests. Subjects (N = 22) performed progressive treadmill walking tests. The criteria used to determine whether V̇O2 max was reached were a plateauing of oxygen uptake, HR > 195, and an R > 1.00. The V̇O2 max for the 3- and 4-year-olds (44.5 ml•kg−1•min−1) was not significantly different from that of the 5- and 6-year-olds (44.1 ml•kg−1•min−1). At submaximal levels, 5- and 6-year-olds had significantly lower relative oxygen uptake, indicating better economy in walking. A large proportion of children met testing criteria for V̇O2 max. Test-retest results indicated that the tests were reliable.
Stephen J. Carter, Eric P. Plaisance, Gordon Fisher, Jose R. Fernandez, Barbara A. Gower and Gary R. Hunter
African American (AA) and European American (EA) women often exhibit differences in hemoglobin (Hb) and 25-hydroxyvitamin D [25(OH)D], both of which can be altered by calorie restriction leading to weight loss. Given these known differences, it is of clinical interest to examine the potential for race-specific, adverse responses to weight loss. Sixty-four overweight (BMI 27–29.9 kg/m2), premenopausal women consumed a standardized, very-low calorie diet to reduce BMI < 25 kg/m2. Ancestry informative markers provided estimates of African admixture, an objective mean of expressing race. Blood sampling and anthropometric measures were performed at baseline and upon meeting target BMI. At baseline, in the overweight state, Hb (g/dL) (AA, 11.7 ± 0.9 vs. EA, 12.5 ± 0.8; p < .01) and 25(OH)D (nmol/L) (AA, 35.7 ± 12.9 vs. EA, 57.0 ± 20.0; p < .01) were lower in AAs. After weight loss, Hb decreased (AA, -0.5 ± 0.7 vs. EA, -0.4 ± 0.6; p = .48) to a similar extent among races. Conversely, 25(OH)D increased (AA, 43.4 ± 14.0 vs. EA 68.2 ± 24.3; p < .01) though the magnitude of change (Δ) was not different (AA, +7.8 ± 13.5 vs. EA, +11.2 ± 16.7; p = .37) between races. Multiple linear regression revealed a positive association between ΔHb and Δ25(OH)D (r = .386; p < .01) adjusted for African admixture, Δtestosterone, and Δbody fat%. Path analyses revealed a significant indirect effect of Δbody fat% on ΔHb through Δ25(OH)D, β =-0.023, CI [-0.06, -0.004]. Following 15% weight loss, participants with the largest increase in serum 25(OH)D exhibited the smallest decrease in Hb. Future research should clarify the optimal degree of calorie restriction to stimulate weight loss while mitigating the potential risk of anemia associated with dieting efforts.
David W. Brock, Olivia Thomas, Charles D. Cowan, David B. Allison, Glenn A. Gaesser and Gary R. Hunter
Numerous public health organizations have adopted national physical activity recommendations. Despite these recommendations, over half of the US population does not meet the minimum recommendation for physical activity, with large variations across individual US states.
Using the 2005 Behavioral Risk Factor Surveillance System (BRFSS) prevalence data for physical activity and obesity by state, we performed a weighted least squares regression using prevalence of obesity (BMI ≥ 30 kg/m2) as the dependent variable and insufficiently physically active (included completely sedentary), age, race, gender, and median household income as the independent variables.
The unadjusted weighted least squares regression revealed a strong correlation between a state’s prevalence of obesity and the prevalence of insufficiently physically active (R = .76, R 2 = .58, P < .0001). After adjusting for age, gender, race, and median household income, the prevalence of insufficiently physically active is still a significant predictor of the state prevalence of obesity (partial R = .44, R 2 = .19 P = .004).
Macroenvironmental and sociopolitical disparities between individual US states that transcend simple state-level demographic factors need to be examined more rigorously to identify unique barriers and promoters of physical activity.