The effect of acute high-intensity interval exercise on microvascular function and local skeletal muscle oxygenation

High-intensity interval exercise (HIIE) improves cardiorespiratory fitness through cardiac and skeletal muscle adaptations; however, the relationship between microvascular function and local skeletal muscle oxygenation during HIIE is unclear. Near-infrared spectroscopy at the vastus lateralis (∆ from baseline) was used to assess microvascular function pre- and post-HIIE and oxygenation throughout HIIE (n = 22 enrolled; n = 19 reported with complete oxygenation data, 27 ± 6 yrs., 42% female). HIIE consisted of twelve, 1-min intervals at 85% of peak power output while microvascular function was assessed using vascular occlusion-reperfusion. During HIIE, despite no change in the deoxygenation time constant tau (τ) (all p > 0.059), deoxygenation magnitude progressively increased at intervals 6 and 8 (both p < 0.011) and was greater at interval 11 compared to 1 (-49 ± 13 vs. -41 ± 19%, p = 0.033). Similarly, there was no change in the reoxygenation τ (all p > 0.753) while reoxygenation magnitude was immediately attenuated from interval 2 compared to 1 (-14 ± 18 vs. -6 ± 12%, p = 0.007) and was less at both intervals 6 and 11 compared to 1 (both p < 0.004). Microvascular function assessed as the 2-min hypersaturation area under the curve (AUC) was lower 15 min post- and 2 h post-HIIE compared to pre-exercise (both p ≤ 0.025), while the 10 s saturation upslope remained unchanged when controlling for the occlusion nadir (p = 0.212). The 2-min AUC (ρ = 0.659, p = 0.003) and 10 s upslope (r = 0.481, p = 0.043) correlated with peak cardiorespiratory fitness but were not related to reoxygenation outcomes (all p ≥ 0.113). These findings describe the acute oxygenation environment of HIIE while suggesting that sustained microvascular vasodilation may be lower post-HIIE.