Influence of Habitual Physical Activity and Acute Exercise on Lipid Metabolism and Insulin Action.

Abstract

Although a physically active lifestyle is clearly an important contributor to long-term health and disease prevention, it remains unclear how much of these health benefits stem from the acute effects of the most recent session(s) of exercise, and how much can be attributed to physiologic adaptations accrued as a result of habitual active. Importantly, the time course for adaptations that occur in the early stages of adopting a habitually active lifestyle is not clearly understood. Therefore, my dissertation projects were designed to examine key metabolic adaptations that occur in response to a more physically active lifestyle in obese adults who are at risk for developing chronic metabolic diseases, including type 2 diabetes. The major findings of my dissertation studies included: In STUDY#1, using data from the National Health and Nutrition Examination Survey (NHANES), we found that insulin sensitivity was significantly associated with the amount of time participants were engaged in physical activity behaviors (P=0.03), but not with their level of cardiorespiratory fitness. In STUDY #2, contrary to our hypothesis, Insulin Sensitivity Index (ISI) was significantly higher in a group of overweight adults who exercise regularly compared with a well-matched cohort of sedentary overweight adults, even though the regular exercisers abstained from exercise for 3 days. In this study we also found that a single session of moderate-intensity exercise was sufficient to increase ISI the day after exercise by nearly 25% in the previously sedentary overweight adults – but not in the regular exercisers, eliminating the difference in ISI between the groups that was evident at baseline. In STUDY #3, although ISI was not improved in the hours after the first low-intensity exercise training session, after 2 weeks of training, post-exercise ISI was enhanced. We also discovered that a single session of exercise at 50%VO2max (i.e., maximal oxygen uptake) for 40 min may be below a “threshold” for exercise stimulus required to improve insulin sensitivity into the next day in obese adults. These studies provide important new information for optimizing the design of lifestyle interventions specifically aimed at enhancing metabolic health in overweight and obese individuals.