Glucose Tolerance is Linked to Postprandial Fuel Use Independent of Exercise Dose

PURPOSE The optimal short-term exercise dose to improve glucose tolerance in relation to metabolic flexibility and/or insulin resistance is unknown. Therefore, we tested if short-term, work-matched continuous (CONT) versus interval (INT) exercise training improves glucose tolerance in part by reducing insulin resistance and increasing metabolic flexibility independent of clinically meaningful fat loss in adults with prediabetes. METHODS Subjects (age 60.9±1.4y; BMI 33.5±1.1 kg/m2) were screened for prediabetes using the American Diabetes Association criteria (75g OGTT and/or HbA1c) and were randomized to 60 min/d of supervised CONT (n=17, 70% HRpeak) or work matched INT (n=14; 90% HRpeak for 3 minute and 50% HRpeak for 3 minute) exercise for 12 bouts. Fitness (VO2peak) and body composition were assessed pre- and post-intervention. A 180-minute 75g OGTT was performed and glucose, insulin and free fatty acids (FFA) were collected to calculate glucose tolerance (tAUC180min) and whole-body as well as adipose tissue insulin resistance pre- and post-intervention. Respiratory exchange ratio (RER; indirect calorimetry) was also measured at 0, 60, 120 and 180 minutes of the OGTT to assess fasting and post-prandial metabolic flexibility. RESULTS CONT and INT training improved VO2peak (L/min; P=0.001) and glucose tolerance (P=0.01) and reduced fasting RER (P=0.006), as well as whole-body and adipose insulin resistance (both P=0.02) with no effect on body fat (P=0.18). Increased post-prandial RER was correlated with reduced glucose tAUC180min (r=-0.38, P=0.05), and increased 180 minute RER related to decreased whole-body insulin resistance (r=-0.42, P=0.03). CONCLUSION Independent of exercise dose and fat loss, short-term training improves glucose tolerance in relation to enhanced post-prandial fuel use. Correspondence: Steven K. Malin, PhD, Department of Kinesiology, 210 Emmet St. 225A Memorial Gymnasium, University of Virginia | Charlottesville, VA, Email: skm6n@virginia.edu Funding was supported by the University of Virginia's Curry School of Education and Launchpad Award to S.K.M. The authors have nothing to disclose. The results of the present study do not constitute endorsement by the ACSM. The results of the study are presented clearly, honestly, and without fabrication, falsification, or inappropriate data manipulation. Accepted for Publication: 3 May 2018 © 2018 American College of Sports Medicine

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