Effects of hypoxic exercise on 24-hour glucose profile and substrate metabolism in overweight and obese men with impaired glucose metabolism

Hypoxic exercise (HE) may have more pronounced effects on glucose homeostasis than exercise under normoxic conditions (NE), but effects on 24-h glucose profile and substrate utilization remain unclear. We investigated the effects of moderate -inten-sity HE compared with NE on 24-h glucose profile and substrate metabolism in overweight/obese individuals. Ten overweight/ obese men with impaired glucose homeostasis participated in a randomized, single-blind, crossover trial. Participants performed moderate-intensity cycling exercise for 4 consecutive days under mild normobaric hypoxic (FIO2: 15%) or normoxic (FIO2: 21%) con-ditions at similar relative exercise intensity (2 x 30 min/day at 50% of maximal heart rate, with a -4-wk washout period. Twenty-four-hour glucose levels and systemic oxygen saturation (SpO2) were monitored throughout the study. At day 5, plasma metabo-lites and substrate oxidation were determined during a mixed-meal test under normoxic conditions. SpO2 and absolute workload were lower (both P < 0.001), whereas heart rate was comparable during HE compared with NE. HE did not alter mean 24-h, day-time, and nighttime glucose concentrations, and measures of glycemic variability. However, the HE-induced decrease in SpO2 was positively correlated with HE-induced improvements in mean 24-h (rs = 0.683, P = 0.042) and daytime (rs = 0.783, P = 0.013) glucose concentrations. HE at similar relative exercise intensity reduces SpO2 and has comparable effects on mean 24-h glucose concentration and glycemic variability than NE in overweight/obese men with impaired glucose metabolism. Nevertheless, a more pronounced reduction in SpO2 during HE was associated with lower 24-h glucose concentrations, suggesting that a marked hypoxic stimulus is needed to improve glucose homeostasis. NEW & NOTEWORTHY We demonstrate that hypoxic exercise at similar relative exercise intensity (i.e. lower absolute workload) reduces systemic oxygen saturation (SpO2) and has comparable effects on mean 24-h glucose concentrations and glycemic vari-ability than normoxic exercise in men with overweight/obesity and impaired glucose metabolism. A more pronounced reduction in SpO2 during hypoxic exercise, however, was associated with lower 24-h and daytime glucose concentrations. Our findings suggest that a marked hypoxic stimulus may improve glucose homeostasis.