Do Metabolic and Psychosocial Responses To Exercise Explain Ethnic/Racial Disparities in Insulin Resistance?
This dissertation has been moved to the following series:
Introduction . Non-Hispanic blacks (blacks) are more insulin resistant compared to non-Hispanic whites (whites), increasing their risk for Type 2 diabetes. The role played by ethnic/racial disparities in the response to physical activity in mediating those higher rates of insulin resistance in blacks is unknown. Because the beneficial effects of exercise are transient and require subsequent doses of exercise to maintain the effect; the metabolic and psychosocial responses to single exercise bouts have strong implications for both opposing insulin resistance and raising the probability that an individual will continue to exercise. Purpose . To compare the metabolic and psychosocial responses to individual bouts of exercise, at the intensity and duration corresponding to the current Institute of Medicine guidelines, in blacks and age/gender/BMI-matched whites. Methods . Insulin sensitivity (hyperinsulinemic-euglycemic clamp) and metabolic flexibility (suppression of resting fat oxidation) along with exercise task self-efficacy, mood, and state-anxiety were assessed before and after a bout of exercise in black and white men and women (metabolic n = 21; psychosocial n = 31). Participants walked on a treadmill at 75% of maximum heart rate for 75 minutes. Exercise sessions were repeated on three separate occasions to assess the cumulative change in psychosocial responses to exercise. Results . There were no ethnic/racial differences in baseline measures of whole-body insulin sensitivity (p = 0.95). Black participants demonstrated larger improvements in the insulin sensitivity response to individual bouts of exercise compared to their white counterparts (+18% vs. -1.8%), which was primarily the result of enhanced non-oxidative glucose disposal during the clamp. Additionally, blacks demonstrated a greater capacity to switch from primarily fat oxidation at rest to primarily carbohydrate oxidation during the clamp (p < 0.003). There were no ethnic/racial differences in the psychosocial response to individual bouts of exercise; individual bouts of exercise improved exercise task self-efficacy and reduced psychological distress in both black and white participants (p = 0.006). Black participants reported higher positive in-task mood during all three bouts of exercise (p = 0.003) and lower RPE scores (p = 0.04) during the third exercise bout compared to white participants, despite similar heart rates in both groups. Conclusions . These data demonstrate that metabolic and psychosocial responses to individual bouts of exercise do not help to explain the increased insulin resistance and lower adherence rates to exercise programs reported in blacks compared to whites. If these results are confirmed in a larger, more diverse, free-living population, future research should focus on social determinants of insulin resistance and physical inactivity to obtain a better understanding of the root causes of increased risk of Type 2 diabetes in black populations.