Time course of changes in VO2peak and O2 extraction during ramp cycle exercise following HIIT versus moderate-intensity continuous training in type 2 diabetes

In the present study, we assessed the time course of adaptations in peak oxygen uptake (V^_ O_2peak) and muscle fractional oxygen (O₂) extraction (using near-infrared spectroscopy) following 12 wk of low-volume high-intensity interval training (HIIT) versus moderate-intensity continuous endurance training (MICT) in adults with uncomplicated type 2 diabetes (T2D). Participants with T2D were randomly assigned to MICT (n = 12, 50 min of moderate-intensity cycling) or HIIT (n = 9, 10 × 1 min at ~90% maximal heart rate) or to a nonexercising control group (n = 9). Exercising groups trained three times per week and measurements were taken every 3 wk. The rate of muscle deoxygenation (i.e., deoxygenated hemoglobin and myoglobin concentration, D[HHb + Mb]) profiles of the vastus lateralis muscle were normalized to 100% of the response, plotted against % power output (PO), and fitted with a double linear regression model. V^_ O_2peak increased (P < 0.05) by week 3 of MICT (+ 17%) and HIIT (+ 8%), with no further significant changes thereafter. Total increases in V^_ O_2peak posttraining (P < 0.05) were 27% and 14%, respectively. The %D [HHb þ Mb] versus %PO slope of the first linear segment (slope₁) was reduced (P < 0.05) beyond 3 wk of HIIT and MICT, with no further significant changes thereafter. No changes in V^_ O_2peak or slope₁ were observed in the control group. Low-volume HIIT and MICT induced improvements in V^_ O_2peak following a similar time course, and these improvements were likely, at least in part, due to an improved microvascular O₂ delivery.