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Introduction Higher cardiorespiratory fitness is associated with greater vascular function that leads to improved regulation of skeletal muscle blood flow during exercise. Rapid onset vasodilation (ROV) describes the immediate increase in blood flow following a single contraction, which is integral to support greater blood flow during exercise. As such, blood flow regulation during exercise hyperemia is important. However, it is unclear if cardiorespiratory fitness plays a role in ROV of small muscle mass in young, healthy individuals. Purpose To investigate the relationship of cardiorespiratory fitness on ROV following a single handgrip (HG) contraction in young, healthy adults. Methods Cardiorespiratory fitness (VO2peak) was assessed during a maximal cycle ergometer test in 14 volunteers (M/F, 6/8; 28 ± 5yrs; 24.8 ± 4.1kg/m2). Brachial velocity and diameter were measured using duplex Doppler ultrasound for 10 cardiac cycles prior to and 20 cardiac cycles following the first cardiac cycle after a single 30% of maximal voluntary handgrip contraction. Brachial artery blood flow (FBF) was calculated for each cardiac cycle: (diameter2/2)*π*velocity*60. Peak forearm (brachial) blood flow (FBFpeak) was determined as the maximal FBF from baseline following the first cardiac cycle after the single HG contraction. Time to peak blood flow response was determined as the time to reach FBFpeak and heart rate was measured using a three‐lead ECG. The relationship between FBFpeak and time to peak blood flow was tested using a multivariate regression analysis with cardiorespiratory fitness and sex as independent variables. Results Cardiorespiratory fitness (VO2peak: 30.6 ± 8.0mL/kg/min); β for VO2peak= 0.162 [0.003, 0.327]) was the only predictor of time to peak blood flow response, F(1,12)= 4.602, p= 0.05, R2= 0.217, r= 0.526, while sex (β for time to peak= ‐106.5 [‐156.9, ‐56.2]) was the only predictor of FBFpeak, F(1,12)= 21.245, p<0.001, R2= 0.609, r= 0.799, indicating that females had a lower FBFpeakoverall. Conclusion Our data suggests blood flow responsiveness (e.g., time to peak) is positively associated with cardiorespiratory fitness and these data contribute to our understanding of potential mechanisms between improved blood flow regulation commonly associated with greater cardiorespiratory fitness. More research is necessary to fully elucidate the role biological sex has on these relationships, but our data suggest there may be sex differences in certain blood flow responses.

Introduction Vascular dysfunction increases cardiovascular disease (CVD) risk, whereas aerobic fitness (VO2peak) improves arterial function and decreases CVD risk. However, it is unclear if VO2peak has the same degree of importance across each segment of the arterial tree (e.g., conduit, resistance, and microvasculature). This is relevant given that research has not assessed these three segments in the same cohort. Purpose To examine the relationship of VO2peak and conduit, resistance, and microvasculature arterial function. Methods Graded exercise testing assessed VO2peak in 33 males (41±19 years, 25.6±2.6 kg/m‐2, 41.1±13.6 ml/kg‐1/min‐1) and 28 females (30±12 years, 23.3±4.3 kg/m‐2, 33.6±8.5 ml/kg‐1/min‐1). Concurrent brachial artery flow‐mediated dilation (FMD) and forearm near‐infrared spectroscopy (NIRS) examined conduit, resistance, and microvascular arterial function. FMD measured with ultrasonography to continuously record arterial diameters and Doppler velocities for 1 min baseline, 5 min forearm occlusion (250 mmHg), and 3 min recovery. The maximum percent change in diameter compared with baseline defined FMD (%) and was used to evaluate conduit arterial function. Reactive hyperemia (RH) of forearm resistance arteries was calculated as peak brachial blood flow following cuff release. Forearm tissue saturation index using NIRS during FMD was used to evaluate microvasculature function (reperfusion slope and reperfusion magnitude). Multivariate regression analysis was performed using VO2peak, age, sex, and BMI as independent variables. Results Age was the only predictor of FMD (β ‐0.48 [‐0.02, ‐0.01], p=0.001), sex was the only predictor of RH, females exhibited lower RH, (β ‐0.66 [‐0.30, ‐0.15], p<0.001), and VO2peak only predicted reperfusion slope (β 0.56 [1.46, 4.52], p< 0.001) and reperfusion magnitude (β 0.36 [3.15, 41.66], p=0.02). Conclusion In our cohort, aerobic fitness was associated with microvascular function when age, BMI, and sex were included in the model. Only age was associated with conduit artery function, and only sex was associated with resistance arterial function. Each segment of the arterial tree was affected differently by VO2peak, age, and sex. These data show the importance of including several potentially important variables when investigating the association between VO2peak and arterial function.