Vascular remodeling enhances high-flow muscle oxygen delivery following aerobic exercise training

BACKGROUND: This research demonstrates how two distinct training modalities, high-intensity interval training (HIIT) and moderate-intensity continuous training (MICT), influence oxygen transport dynamics and microvascular remodeling. METHODS: Twenty-five healthy sedentary men and women (median age 21 years) were randomly assigned to HIIT or MICT for 8 weeks. VO2max improvement was assessed in all participants. Non-invasive maximal cardiac output measurements (Qmax) were performed in 15 participants. Biopsies from vastus lateralis were obtained, cleared and immunolabeled for VE-cadherin and alpha-smooth muscle actin, in 10 subjects, to observe microvasculature architecture. A computational hemodynamic model was constructed to estimate muscle flow dynamics. RESULTS: VO2max and Qmax increased significantly in both training groups, with a greater improvement for VO2max in HIIT that was accompanied by a significant increase in capillaries pericyte coverage. No formation of new capillaries nor anastomoses (angiogenesis) was detected in either group. Modelisation estimated higher shear stress during HIIT than MICT and pericyte recruitment was modelized to adapt to shear stress level limiting excessive capillary dilation. CONCLUSION: HIIT induces superior improvements in VO2max and distinct microvascular structural adaptations rather than angiogenesis. HIIT is thought to induce protective capillary adaptation, limiting dilation during maximal effort and improving oxygen diffusion. CLINICAL TRIAL REGISTRATION: https://clinicaltrials.gov/study/NCT07237854, identifier NCT07237854.