There is a positive association between cardiorespiratory fitness and cognitive health but the interaction between cardiorespiratory fitness and aging on cerebral hemodynamics is unclear. These potential interactions are further influenced by sex differences. The purpose of this study was to determine the sex-specific relationships between cardiorespiratory fitness, age, and cerebral hemodynamics in humans. Measurements of unilateral middle cerebral artery blood velocity (MCAv) and cerebral pulsatility index obtained using transcranial Doppler ultrasound and cardiorespiratory fitness (VO2max) obtained from maximal incremental exercise tests were retrieved from study records at 3 institutions. A total of 153 healthy participants were included in the analysis (age=42±20 y, range=18-83 yrs). There was no association between VO2max and MCAv in all participants (p=0.20). The association between VO2max and MCAv was positive in women, but no longer significant after age adjustment (univariate: p=0.01; age-adjusted: p=0.45). Additionally, there was no association between VO2max and MCAv in men (univariate: p=0.25, age-adjusted: p=0.57). For VO2max and cerebral pulsatility index, there were significant negative associations in all participants (p<0.001), in men (p<0.001) and women (p<0.001). This association remained significant when adjusting for age in women only (p=0.03). In summary, higher cardiorespiratory fitness was associated with lower cerebral pulsatility index in all participants and the significance remained only in women when adjusting for age. Future studies are needed to determine the sex-specific impact of cardiorespiratory fitness improvements on cerebrovascular health.

Age‐related declines in cerebral blood flow have been linked to greater risk for cognitive decline. Habitual exercise is recommended to prevent or delay cognitive impairment. Previous studies have found a positive correlation between cardiorespiratory fitness and middle cerebral artery blood velocity (MCAv) in men; however, there is limited data on this relationship in women. This study aimed to examine the relationships between cardiorespiratory fitness, age and MCAv in women. We hypothesized that MCAv would decline with advancing age and there would be a positive association between MCAv and cardiorespiratory fitness in women. Data from 74 women (age = 46 ± 21 y, range = 18 – 83 yrs.) were collected at 4 institutions (University of Kansas Medical Center; University of Wisconsin‐Madison; Université Laval; Mayo Clinic) as part of previously conducted studies. All participants were determined to be of low risk for cardiovascular disease according to the American College of Sports Medicine criteria. MCAv, mean arterial pressure, end tidal carbon dioxide and cardiorespiratory fitness (maximal oxygen consumption: VO2max) were retrieved from study records. MCAv was collected unilaterally at rest using a transcranial Doppler ultrasound. VO2max was collected during either cycling ergometry (n = 61) or treadmill ergometry (n = 13) tests. Associations were assessed using a Pearson product‐moment correlation. In the 74 women, the absolute VO2max was 2089 ± 622 ml·min‐1 and average relative VO2max was 34 ± 10 ml·kg‐1·min‐1. The average MCAv for the entire group was 64 ± 16 cm·s‐1. As expected, there was an inverse association between age and MCAv (r = ‐0.310; p = 0.007) such that women who were older demonstrated lower MCAv. There was a positive association between absolute VO2max and MCAv (r = 0.310; p = 0.007). Likewise, there was a positive association between relative VO2max and MCAv (r = 0.309; p = 0.007) such that women with higher cardiorespiratory fitness demonstrated higher MCAv. However, the relationship between VO2max and MCAv was no longer significant when adjusted for age (absolute VO2max; r = ‐0.105, p = 0.375; relative VO2 max; r = ‐0.089, p = 0.452). Cardiorespiratory fitness is positively associated with MCAv in women. This suggests that habitual exercise may be protective against age‐related declines in cerebral blood flow. However, because the association between cardiorespiratory fitness and MCAv is attenuated when it is adjusted for age, future studies could utilize non‐linear modeling to understand how age, MCAv and cardiorespiratory fitness are related in women.