Date of Award

12-2011

Degree Type

Dissertation

Degree Name

Doctor of Philosophy (PhD)

Department

Exercise Science

Advisor(s)

Jill A. Kanaley

Keywords

Appetite, Insulin, Insulin Secretion, Meal Frequency, Physical Activity

Subject Categories

Endocrinology

Abstract

Long, uninterrupted bouts of sedentary behavior are thought to negatively influence insulin sensitivity, and may impact metabolic function regardless of adherence to general physical activity guidelines. The purpose of this study was to determine the combined effect of physical activity (1 h continuous exercise v. intermittent exercise throughout the day) and meal consumption on glucose excursions, insulin secretion, and appetite markers in obese individuals with prediabetes. Methods: Eleven healthy, obese subjects (>30 kg/m2) with prediabetes underwent 3, 12 h study days including sedentary behavior (SED), exercise (EX; 1h morning exercise, 60-65% VO2 max), and physical activity (PA; 12 hourly, intensity-matched 5-minute bouts). Meals were provided every 2 h. Blood samples were taken every 10 min for 12 h. Baseline and area under the curve (AUC) for serum glucose, insulin, c-peptide, total PYY concentrations, and subjective appetite ratings; as well as insulin pulsatility were determined. Results: No significant differences in baseline glucose, insulin or c-peptide concentrations across study days were observed (P>0.05). Glucose AUC (12 h and 2 h) were significantly different across study days, with AUC attenuated in the PA condition compared to the EX condition (P<0.05). The 12 h incremental insulin AUC was reduced by PA compared to SED (173,985±3556.8 v. 227,352±4581.2 pmol/L*min for 12 h, respectively; P<0.05). Similarly, a significant main effect of condition in the 2 h insulin AUC was found, with the PA condition being reduced compared to SED condition (P<0.05), but no differences between the EX and SED conditions. A significant reduction in 2 h c-peptide AUC was demonstrated with EX and PA compared to the SED condition (P<0.05). Deconvolution analysis of insulin secretion revealed no significant differences between experimental conditions. There were no significant differences in total PYY between experimental conditions, though subjective measures of hunger and satiety were reduced with continuous and intermittent exercise. Conclusions: Short bouts of physical activity throughout the day attenuate glucose excursions and improve insulin clearance compared to an exercise day with 1 h of morning exercise. Further, both continuous and intermittent exercise mechanisms that improve satiety in obese individuals are not related to changes in concentrations of PYY.

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