1 Month Effect of Breaking Up Sedentary Activity on Insulin Sensitivity and Glucose Homeostasis in Free-Living Overweight/Obese Adults (original) (raw)

Sedentary behavior (SB) triggers an inability to adjust substrate use to substrate availability (low metabolic flexibility, MF), which may precede glucose intolerance in the pathogenesis of insulin resistance. We and others have shown that frequent interruptions in SB leads to improved glycemic control, however the underlying role of MF in this process is unknown. This study examined the effects of breaking up SB on MF and glucose metabolism in free-living overweight and obese adults. To distinguish effects of breaking up SB from being physically active, we also studied a group where participants performed a single energy matched continuous bout of exercise. Physically inactive, adults (12F/9M, mean±SD, age: 33±8 yr, BMI: 29.5±3.3 kg/m 2) were randomly assigned to a 4 week intervention consisting of brisk walking for 5 min each hour for 10h, 5 d/wk (MICRO, n=10), or 4 weeks of an intervention consisting of one continuous 45 min bout of exercise per day, 5d/wk (ONE, n=9). Outcomes assessed at baseline and after each intervention included: MF (waking respiratory quotient, RQ, minus sleeping RQ as measured in a whole room calorimeter), insulin sensitivity (SI, IVGTT), 24h glycemia (continuous glucose monitor), 24h glucose oxidation (U 13 C glucose tracer), SB, time spent standing, time spent stepping (ActivPAL) and TEE (double labeled water). Groups were similar on all outcome variables at baseline. Linear mixed models evaluated intervention and intervention-by-group effects. MICRO and ONE decreased time sitting and increased time stepping with no significant changes in TEE. Compared to ONE, MICRO decreased 24h iii glycemic variability (p=0.06), improved the acute whole body insulin sensitivity (p=0.08) and acute insulin response to glucose (AIRg) (p=0.02) , maintained exogenous glucose oxidation (p<0.03) and improved MF (p=0.02). Independent of time sitting and stepping, breaking up SB improves glucose homeostasis and MF. The effects of such an intervention in persons with type 2 diabetes warrants further study. iv ACKNOWLEDGEMENTS I would like to thank the department of Health and Exercise Science, who has led me to this field taught me everything I know about exercise physiology, as well as provided a family like environment to lean on and learn from. This includes Brian Butki, a personal mentor who has been giving me life advice in undergraduate and graduate school, and showed me early on that I am capable of more than I thought, and that big things are sometimes started by just one person. I have also been so grateful to have Josiane Broussard and Christopher Melby on my committee, two people who are that are world class in their fields and have supported and challenged me in this process. My mentors Audrey Bergouignan and Matthew Hickey have also made this process and the past couple of years exciting and enjoyable. Audrey has shown me what work life balance looks like, and that science is exciting and fun, and surrounding yourself with people of this mindset is important and makes things much more fun. I was so lucky to join the family that is her lab, and got to learn from her, such an incredible mind and leader in her field. She has been someone to look up to professionally and personally. Matthew Hickey (aka "Dumbledore") guided me through the journey of a master's thesis as well as a busy and influential time in my life. His wisdom and guidance are very appreciated and have helped shape the person I am today. I would also like to thank my parents, who instilled the love of science in me, and encouraged me to ask questions and be curios at all points in my life. They have supported me in everything I have wanted to do, both academically and personally and have shown me what hard work is, but that hard work should be done out of passion for your field and have a goal of helping others. Finally, I would like to thank Taylor, who has provided me with words of encouragement, breaks from working, and snacks; at all the appropriate times. I would like to thank him for his support of my goals and pursuits both to this point and in the future. v TABLE OF CONTENTS