Association Between Cardiorespiratory Fitness and the Determinants of Glycemic Control Across the Entire Glucose Tolerance Continuum

OBJECTIVECardiorespiratory fitness (VO2max) is associated with glycemic control, yet the relationship between VO2max and the underlying determinants of glycemic control is less clear. Our aim was to determine whether VO2max is associated with insulin sensitivity, insulin secretion, and the disposition index, a measure of compensatory pancreatic -cell insulin secretion relative to insulin sensitivity, in subjects representing the entire range of the glucose tolerance continuum.RESEARCH DESIGN AND METHODSA cohort of subjects (N = 313) with heterogeneous age, sex, BMI, and glycemic control underwent measurements of body composition, HbA(1c), fasting glucose, oral glucose tolerance (OGTT), and VO2max. OGTT-derived insulin sensitivity (Si-OGTT), glucose-stimulated insulin secretion (GSIS(OGTT)), and the disposition index (DIOGTT) (the product of Si-OGTT and GSIS(OGTT)) were measured, and associations between VO2max and these determinants of glycemic control were examined.RESULTSA low VO2max was associated with high HbA(1c) (r = -0.33), high fasting glucose (r = -0.34), high 2-h OGTT glucose (r = -0.33), low Si-OGTT (r = 0.73), and high early-phase (r = -0.34) and late-phase (r = -0.36) GSIS(OGTT). Furthermore, a low VO2max was associated with low early- and late-phase DIOGTT (both r = 0.41). Interestingly, relationships between VO2max and either glycemic control or late-phase GSIS(OGTT) deteriorated across the glucose tolerance continuum.CONCLUSIONSThe association between poor cardiorespiratory fitness and compromised pancreatic -cell compensation across the entire glucose tolerance continuum provides additional evidence highlighting the importance of fitness in protection against the onset of a fundamental pathophysiological event that leads to type 2 diabetes.