Abstract
Insulin resistance (IR) is characterized by reduced insulin-mediated glucose uptake from the blood. Studies in vitro suggest that IR muscle is not resistant to contraction-mediated glucose uptake (i.e. exercise), but studies in vivo are lacking. PURPOSE To compare blood glucose uptake and total carbohydrate utilization during exercise in IR and insulin-sensitive (IS) women while controlling for body fatness and habitual physical activity. We hypothesized that, total carbohydrate utilization during exercise would be the the same in IR and IS individuals METHODS 12 overweight, sedentary but otherwise healthy women aged 22–45 participated in the study. Insulin resistance was determined by incorporating glucose and insulin responses to an oral glucose load into a mathematical model (composite insulin sensitivity index, C-ISI). The women were divided into 2 groups (n = 6): insulin-resistant (IR, BMI = 28.5 ± 1.6, %body fat = 38.4 ± 3.5, C-ISI = 3.0 ± 0.7) and insulin sensitive (IS,BMI = 27.2 ± 1.9,%body fat 44.6 ± 4.4, C-ISI = 7.7 ± 0.9). Blood glucose uptake, carbohydrate oxidation, and estimated muscle glycogen utilization were assessed using stable isotope dilution and indirect calorimetry during 50 minutes of treadmill walking at 45% VO2max. RESULTS Insulin concentrations were significantly higher in IR at rest (IR = 85.85 pM ± 40.66, IS = 44.81 pM ± 17.19) and remained higher during exercise (IR = 68.94 pM ± 11.45, IS = 33.28 pM ± 1.77). Mean carbohydrate oxidation (CHOox g/min) was significantly higher in IS(0.75 ± 0.14) compared to the IR(0.51 ± 0.14) group during exercise (p < .05). Blood glucose, lactate and FFA concentrations were similar at rest and during exercise. CONCLUSION These data suggest that, when body fatness and physical activity are matched, total carbohydrate utilization during exercise is significantly lower in IR women compared to IS. Group differences in blood glucose kinetics and/or muscle glycogen utilization may explain difference seen in total carbohydrate oxidation. Supported by UMASS/Baystate CBRP.
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