Pancreatic β-cell Function Is a Stronger Predictor of Changes in Glycemic Control After an Aerobic Exercise Intervention Than Insulin Sensitivity

Abstract

Understanding intersubject variability in glycemic control following exercise training will help individualize treatment. Our aim was to determine whether this variability is related to training-induced changes in insulin sensitivity or pancreatic β-cell function. We conducted an observational clinical study of 105 subjects with impaired glucose tolerance or type 2 diabetes. Individual subject changes in fitness (VO2max), glycemia (glycosylated hemoglobin, fasting glucose, oral glucose tolerance test), insulin sensitivity (hyperinsulinemic-euglycemic clamp), oral glucose-stimulated insulin secretion (GSIS), and disposition index (DI) were measured following 12 to 16 weeks of aerobic exercise training. Regression analyses were used to identify relationships between variables. After training, 86% of subjects increased VO2max and lost weight. Glycosylated hemoglobin, fasting glucose, and 2-hour oral glucose tolerance test were reduced in 69%, 62%, and 68% of subjects, respectively, while insulin sensitivity improved in 90% of the participants. Changes in glycemic control were congruent with changes in GSIS such that 66% of subjects had a reduction in first-phase GSIS, and 46% had reduced second-phase GSIS. Training increased first- and second-phase DI in 83% and 74% of subjects. Training-induced changes in glycemic control were related to changes in GSIS (P < .05), but not insulin sensitivity or DI, and training-induced improvements in glycemic control were largest in subjects with greater pretraining GSIS. Intersubject variability in restoring glycemic control following exercise is explained primarily by changes in insulin secretion. Thus, baseline and training-induced changes in β-cell function may be a key determinant of training-induced improvements in glycemic control.