Time-course of (V)over dotO2 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)over dotO(2)) and muscle deoxygenation (i.e., deoxygenated hemoglobin and myoglobin, [HHb + 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 x 1 min at similar to 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 O-2 delivery to O-2 utilization was assessed by the Delta[HHb + Mb]/Delta(V)over dotO(2) ratio. The pretraining time constant of the primary phase of (V)over dotO(2) (tau(V)over dotO(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 (tau'[HHb + Mb]) was faster than s(V)over dotO(2p) in all groups, resulting in Delta[HHb + Mb]/(V)over dotO(2p) showing a transient overshoot relative to the subsequent steady-state level. After 3 wk, the Delta[HHb + Mb]/(V)over dotO(2p) overshoot was eliminated only in the training groups, so that tau'[HHb + Mb] was not different to s(V) over dotO(2p) in MICT and HIIT. The enhanced (V) over dotO(2) kinetics response consequent to both MICT and HIIT in T2D was likely attributed to a training-induced improvement in matching of O-2 delivery to utilization. NEW & NOTEWORTHY High-intensity interval training and moderate-intensity continuous training elicited faster pulmonary oxygen uptake ((V)over dotO(2)) kinetics during moderate-intensity cycling within 3 wk of training with no further changes thereafter in individuals with type 2 diabetes. These adaptations were accompanied by unaltered near-infrared spectroscopy-derived muscle deoxygenation (i.e. deoxygenated hemoglobin and myoglobin concentration, [HHb+Mb]) kinetics and transiently reduced Delta[HHb+Mb]-to-Delta(V)over dotO(2) ratio, suggesting an enhanced blood flow distribution within the active muscles subsequent to both training interventions.

Automated summary

This study compared the effects of low-volume high-intensity interval training (HIIT) and moderate-intensity continuous training (MICT) on oxygen uptake and muscle deoxygenation kinetics in patients with type 2 diabetes. The results showed that both training methods improved oxygen uptake kinetics, but had no significant effect on muscle deoxygenation kinetics.