Short-term aerobic exercise training in obese humans with type 2 diabetes mellitus improves whole-body insulin sensitivity through gains in peripheral, not hepatic insulin sensitivity.

CONTEXT: Short-term aerobic exercise training can improve whole-body insulin sensitivity in humans with type 2 diabetes mellitus; however, the contributions of peripheral and hepatic tissues to these improvements are not known. OBJECTIVE: Our objective was to determine the effect of 7-d aerobic exercise training on peripheral and hepatic insulin sensitivity during isoglycemic/hyperinsulinemic clamp conditions. DESIGN: Subjects were randomly assigned to one of two groups. The energy balance group consumed an isocaloric diet consisting of 50% carbohydrate, 30% fat, and 20% protein for 15 d. The energy balance plus exercise group consumed a similar diet over the 15 d and performed 50-min of treadmill walking at 70% of maximum oxygen consumption maximum during the second 7 d of the 15-d study period. Each subject underwent an initial isoglycemic/hyperinsulinemic clamp after 1-wk dietary control and a second clamp after completing the study. SETTING: The study was performed at Ohio State University's General Clinical Research Center. PARTICIPANTS: There were 18 obese, mildly diabetic humans included in the study. INTERVENTION: Aerobic exercise training was performed for 7 d. MAIN OUTCOME MEASURES: Whole-body, peripheral, and hepatic insulin sensitivity were measured. RESULTS: Exercise training did not have an impact on peripheral glucose uptake or endogenous glucose production during the basal state or low-dose insulin. Likewise, it did not alter endogenous glucose production during high-dose insulin. However, 1-wk of exercise training increased both whole-body (P<0.05) and peripheral insulin sensitivity (P<0.0001) during high-dose insulin. CONCLUSION: Improvements to whole body insulin sensitivity after short-term aerobic exercise training are due to gains in peripheral, not heptic insulin sensitivity.

Importance of aerobic fitness in cardiovascular risks in sedentary overweight and obese African-American women.

BACKGROUND: Whether the level of aerobic fitness significantly impacts cardiovascular disease (CVD) risks in healthy, nondiabetic, overweight or obese African-American women remains uncertain. OBJECTIVE: To examine the clinical and metabolic risk factors of CVD in nondiabetic, sedentary overweight or obese African-American women with varying degrees of aerobic fitness. METHODS: Forty-eight African-American women, with mean age of 43 +/- 4.2 years and body mass index of 32.3 +/- 3.6 kg/m2, participated in the study. Fasting and 2-hr postprandial serum glucose, insulin, and C-peptide levels were obtained during oral glucose tolerance test. Insulin sensitivity was calculated by Homeostasis Model Assessment (HOMA-IR). Aerobic fitness was categorized empirically as very low aerobic fitness (VLAF; n = 17, VO2max < 21 ml/kg/min), low aerobic fitness (LAF; n = 12, between 21 and 24.4 ml/kg/min), and moderate aerobic fitness (MAF; n = 19, >24.4 ml/kg/min). RESULTS: Significant differences were found in serum glucose, insulin, and C-peptide levels, and HOMA-IR in the VLAF vs. LAF and MAF groups. Mean HOMA-IR was statistically greater in the VLAF and LAF when compared to MAF. Mean fasting serum cholesterol, triglycerides, and low-density lipoprotein cholesterol levels were higher in the VLAF group compared to the MAF group, whereas high-density lipoprotein cholesterol was lower in the VLAF group. Despite differences in the obesity indices and insulin resistance in the three groups, the atherogenic lipids and lipoproteins were within normal limits, irrespective of degree of VO2max. DISCUSSION: Modest aerobic fitness has significant impact on insulin sensitivity and atherogenic lipids and lipoprotein parameters and the overall risks for CVD in sedentary overweight or obese African-American women. Whether modest physical fitness translates into prevention of type 2 diabetes and CVD in African-American women remains to be determined.

Dietary composition influences short-term endurance training-induced adaptations of substrate partitioning during exercise.

The purpose of the current study was to examine the influence of dietary composition on short-term endurance training-induced adaptations of substrate partitioning and time trial exercise performance. Eight untrained males cycled for 90 min at approximately 54% aerobic capacity while being infused with [6,6(2)H]glucose before and after two 10-d experimental phases separated by a 2-week washout period. Time trial performance was measured after the 90-min exercise trials before and after the 2nd experimental phase. During the first 10-d phase, subjects were randomly assigned to consume either a high carbohydrate or high fat diet while remaining inactive (CHO or FAT). During the second 10-d phase, subjects consumed the opposite diet, and both groups performed identical daily supervised endurance training (CHO+T or FAT+T). CHO and CHO+T did not affect exercise metabolism. FAT reduced glucose flux at the end of exercise, while FAT+T substantially increased whole body lipid oxidation during exercise and reduced glucose flux at the end of exercise. Despite these differences in adaptation of substrate use, training resulted in similar improvements in time trial performance for both groups. We conclude that (a) 10-d high fat diets result in substantial increases in whole body lipid oxidation during exercise when combined with daily aerobic training, and (b) diet does not affect short-term training-induced improvements in high-intensity time trial performance.

Evaluation of a step-counter during treadmill walking in 7-12 year old African-American children.

The primary purpose of this study was to evaluate the accuracy of the Digiwalker step-counter in recording the number of steps by African-American children during level treadmill walking and the accuracy of the Digiwalker when placed inside a pouch at midline rather than when placed at midline of the thigh. A secondary purpose of this study was to examine the relationship between the number of steps and physiological response to walking. Study subjects were a sub-set of thirty-one children recruited from a larger study evaluating the effects of an after school program on cardiovascular risk factors in this population. The Digiwalker was consistent in the steps recorded when time and speed were held constant and the Digiwalker was able to detect increases in steps with small increases in walking speed. In addition, the use of a soft-cased pouch appears to be an appropriate alternate placement site for the Digiwalker.