Sex differences in vascular adaptations to exercise training within different intensity domains

Cardiorespiratory fitness [commonly assessed as maximal oxygen consumption (V^_ O_2max)] is an independent predictor of risk for cardiovascular disease-related mortality. Endurance exercise training is recognized as a clinically validated intervention to significantly increase V^_ O_2max, and growing evidence exists demonstrating a tight connection between endurance training intensity domain and changes in V^_ O_2max. However, whether the vascular adaptations to exercise training are also influenced by intensity domains is unknown. Also unknown is the potential influence of sex on these responses. Thus, we assessed domain-specific hemodynamic and lower limb vascular adaptations in seventy healthy sedentary adults (35 females and 35 males) that underwent 6 wk of endurance exercise training within five (n ¼ 14/group; 7 females and 7 males) intensity domains: moderate (MOD); lower heavy intensity, HVY1; upper heavy-intensity, HVY2; high-intensity interval training (HIIT) in the severe domain; sprint-interval training (SIT) in the extreme domain. We found that: 1) HIIT was associated with greater changes in resting hemodynamics (i.e., increased in resting mean arterial pressure and femoral artery vascular conductance) compared with MOD; 2) changes in V^_ O_2max were positively associated with changes in resting vascular conductance, femoral artery diameter, and indexes of reactive hyperemia although negatively associated with femoral artery flow-mediated dilation in females; and 3) sex-related associations between changes in V^_ O_2max and peripheral vascular adaptations were more evident in response to HIIT. Taken together, our findings indicate that peripheral vascular adaptations associated with changes in cardiorespiratory fitness are impacted by sex and the exercise intensity domain within which training is performed.