Time-course of V^-O₂ kinetics responses during moderate-intensity exercise subsequent to HIIT versus moderate-intensity continuous training in type 2 diabetes

We assessed the time-course of changes in oxygen uptake (V^_ O₂) and muscle deoxygenation (i.e., deoxygenated hemoglobin and myoglobin, [HHb þ Mb]) kinetics during transitions to moderate-intensity cycling following 12 wk of low-volume high-intensity interval training (HIIT) vs. 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, 10 1 min at ~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 þ 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 D[HHb þ Mb]/DV^_ O₂ ratio. The pretraining time constant of the primary phase of V^_ O₂ (sV^_ O_2p) 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 (s'[HHb þ Mb]) was faster than sV^_ O_2p in all groups, resulting in D[HHb þ Mb]/V^_ O_2p showing a transient “overshoot” relative to the subsequent steady-state level. After 3 wk, the D[HHb þ Mb]/V^_ O_2p overshoot was eliminated only in the training groups, so that s'[HHb þ Mb] was not different to sV^_ O_2p in MICT and HIIT. The enhanced V^_ O₂ 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.