Impact of Hypoxic Versus Normoxic Training on Physical Fitness and Vasculature in Diabetes

Background: Exercise training improves physical fitness, insulin resistance, and endothelial function in type 2 diabetes. Hypoxia may further optimize these beneficial effects. The aim of this study was to compare the effects of hypoxic versus normoxic exercise training on physical fitness, endothelial function, and insulin resistance in type 2 diabetes. Methods: Peak oxygen consumption, flow mediated dilation (endothelial function), and glucose homeostasis were assessed in 19 patients (55+/-7 years) before and after an 8-week intervention. Subjects were randomly allocated to normoxic (21% O-2, n = 9) or hypoxic (16.5% O-2, n = 10) exercise training. Endothelium-independent dilation was examined using sublingual administration of glyceryl trinitrate, and used to calculate the ratio between endothelium-dependent and -independent dilation. Results: Exercise training improved physical fitness and brachial artery ratio between endothelium-dependent and -independent dilation (both p < 0.05), whilst these exercise training-induced changes were similar in both groups (interaction-effects p > 0.05). Exercise training did not significantly change brachial artery flow-mediated dilation or glyceryl trinitrate-response, superficial femoral artery flow-mediated dilation, or glucose homeostasis, whilst hypoxia did not alter the impact of exercise training. Conclusion: Contrary to our hypothesis, hypoxia does not potentiate the effect of exercise training on physical fitness, vascular function, or glucose homeostasis in type 2 diabetes.