We assessed the rates of adjustment in oxygen uptake (Vo2) and muscle deoxygenation (ie, deoxygenated hemoglobin and myoglobin, (HHb plus Mb)) during the on-transition to high-intensity cycling initiated from an elevated baseline (work-to-work, w-to-w) before training and at weeks 3, 6, 9, and 12 of low-volume high-intensity interval training (HIIT) and moderate-intensity continuous training (MICT) in type 2 diabetes (T2D). Participants were randomly assigned to MICT (n = 11, 50 min of moderate-intensity cycling), HIIT (n = 8, 10 x 1 min of high-intensity cycling separated by 1 min of light cycling) or nonexercising control (n = 9) groups. Exercising groups trained three times per week. Participants completed two w-to-w transitions at each time point consisting of sequential step increments to moderate- and high-intensity work-rates. (HHb plus Mb) kinetics were measured by near-infrared spectroscopy at the vastus lateralis muscle. The pretraining time constant of the primary phase of Vo2 (Vo2 taup) and the amplitude of the Vo2 slow component (Vo2 As) of the high-intensity w-to-w bout decreased (p < 0.05) by a similar magnitude at week 3 of training in both MICT (from 56 +/- 9 to 43 +/- 6 s, and from 0.17 +/- 0.07 to 0.09 +/- 0.05 L/min, respectively) and HIIT (from 56 +/- 8 to 42 +/- 6 s, and from 0.18 +/- 0.05 to 0.09 +/- 0.08 L/min, respectively) with no further changes thereafter. No changes were reported in controls. The parameter estimates of DELTA (HHb plus Mb) remained unchanged in all groups. MICT and HIIT elicited comparable improvements in Vo2 kinetics without changes in muscle deoxygenation kinetics during high-intensity exercise initiated from an elevated baseline in T2D despite training volume and time commitment being approximately 50% lower in the HIIT group.

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