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 ± 1.4 yr, body mass index = 33.5 ± 1.1 kg·m^-2) were screened for prediabetes using the American Diabetes Association criteria (75 g oral glucose tolerance test [OGTT] and/or HbA_1c) and were randomized to 60 min·d^-1 of supervised CONT (n = 17, 70% HR_peak) or work-matched INT (n = 14; 90% HR_peak for 3 min and 50% HR_peak for 3 min) exercise for 12 bouts. Fitness (VO_2peak) and body composition were assessed pre-and postintervention. A 180-min 75-g OGTT was performed, and glucose, insulin, and free fatty acids were collected to calculate glucose tolerance (tAUC_180min) and whole-body as well as adipose tissue insulin resistance pre-and postintervention. RER (indirect calorimetry) was also measured at 0, 60, 120, and 180 min of the OGTT to assess fasting and postprandial metabolic flexibility. Results CONT and INT training improved VO_2peak (L·min^-1; 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 postprandial RER was correlated with reduced glucose tAUC_180min (r =-0.38, P = 0.05) and increased 180-min 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 postprandial fuel use.