We assessed the time-course of changes in oxygen uptake (VO2) and muscle deoxygenation (ie, deoxygenated hemoglobin and myoglobin (HHb+Mb)) kinetics during transitions to moderate-intensity cycling following 12 wk of low-volume high-intensity interval training (HIIT) versus moderate-intensity continuous training (MICT) in adults with type 2 diabetes (T2D). Participants were randomly assigned to MICT (n = 10, 50 min of moderate-intensity cycling), HIIT (n = 9, 10x1 min at approximately 90% maximal heart rate), or nonexercising control (n = 9) groups. Exercising groups trained three times per week, and measurements were taken every 3 wk HHb+Mb kinetics were measured by near-infrared spectroscopy at the vastus lateralis muscle. The local matching of O2 delivery to O2 utilization was assessed by the delta HHb+Mb / delta VO2 ratio. The pretraining time constant of the primary phase of VO2 (tauVO2p) decreased (p < 0.05) at wk 3 of training in both MICT (from 44 +/- 12 to 32 +/- 5 s) and HIIT (from 42 +/- 8 to 32 +/- 4 s) with no further changes thereafter, whereas no changes were reported in controls. The pretraining overall dynamic response of muscle deoxygenation (tauHHb+Mb) was faster than tauVO2p in all groups, resulting in delta HHb+Mb/VO2p showing a transient "overshoot" relative to the subsequent steady-state level. After 3 wk, the delta HHb+Mb/VO2p overshoot was eliminated only in the training groups, so that tauHHb+Mb was not different to tauVO2p in MICT and HIIT. The enhanced VO2 kinetics response consequent to both MICT and HIIT in T2D was likely attributed to a training-induced improvement in matching of O2 delivery to utilization.

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