Insulin sensitivity, cardiorespiratory fitness, and physical activity in overweight Hispanic youth

OBJECTIVE: To determine whether cardiorespiratory fitness and/or physical activity (PA) were related to measures of insulin sensitivity and secretion independent of body composition in overweight Hispanic children. RESEARCH METHODS AND PROCEDURES: Ninety-five Hispanic children (n = 55 boys; n = 40 girls; 8 to 13 years old) participated in this investigation. The frequently sampled intravenous glucose tolerance test was used to determine the insulin sensitivity index (SI), the acute insulin response, and the disposition index. Cardiorespiratory fitness [maximal oxygen uptake (VO(2max))] was evaluated using a treadmill protocol, and PA was determined by an interviewer-administered questionnaire. Body composition was measured using DXA. RESULTS: Unadjusted correlations indicated that VO(2max) (milliliters of O(2) per minute) was negatively related to SI (r = -0.46, p < 0.05) and disposition index (r = -0.31, p < 0.05) and positively associated with fasting insulin (r = 0.29, p < 0.05), but these relationships were no longer significant once gender, Tanner stage, fat mass, and soft lean tissue mass were included as covariates (all p > 0.05). Multivariate linear regression analysis showed that body fat mass explained 53% of the variance in SI and that VO(2max) (milliliters of O(2) per minute) was not independently related to SI. Cardiorespiratory fitness was positively related to both fat mass (r = 0.43, p < 0.001) and soft lean tissue mass (r = 0.89, p < 0.001). PA was not related to any measure of insulin sensitivity and secretion. DISCUSSION: Cardiorespiratory fitness, as determined by VO(2max) (milliliters of O(2) per minute), was not independently related to insulin sensitivity or secretion, suggesting that VO(2max) influences insulin dynamics indirectly through fat mass.