Reduced leg vascular responses to dynamic knee extension exercise in young black men

Background: Our group and others have shown that non-Hispanic Black young adults exhibit reduced vasodilatory responses in active skeletal muscle during exercise, reduced endothelium-dependent vasodilation, and augmented vasoconstriction to phenylephrine in comparison with their White counterparts. Notably, racial disparities in vascular responses have been tested mostly in the upper limbs. A single study that has examined lower limbs found that Black and White young men show similar blood flow and vascular conductance during dynamic plantar flexion. It remains unknown whether exercise involving a larger muscle group, such as knee extension, would elicit distinct vascular responses between young Black and White men. Hypothesis: We hypothesized that leg blood flow and vascular conductance would be lower in Black men compared with their White counterparts during knee extension exercise. Methods: Young healthy White (n=11; 22±4 years; 22±2 kg/m 2 ) and Black (n=12; 22±5 years; 25±3 kg/m 2 ) men (P >0.05 for age and body mass index), born and raised in the US, performed 6 trials of a single-leg (right) dynamic knee extension exercise (mainly engaging the quadriceps muscle group). Exercise was performed at 5, 10, 15, 20, 25, and 30 watts (W), at 50 repetitions per minute, in an upright seated position (custom ergometer). Each trial lasted 3 minutes, followed by a 5-minute rest interval. Common femoral artery blood flow (LBF; duplex Doppler ultrasound) and mean arterial pressure (MAP; automated sphygmomanometer) were used to calculate leg vascular conductance (LVC=LBF/MAP). An incremental knee extension test was conducted to measure peak workload and calculate relative exercise intensities. Right leg lean mass (RLLM; DEXA) was measured in 11 Black and 9 White participants for normalization of vascular responses (i.e., LBF/RLLM, and LVC/RLLM). Results: Both groups achieved similar peak workloads in the incremental test (White: 48±12 W vs. Black: 50±11 W; P=0.694). LBF, MAP, and LVC were similar between groups at rest (P >0.05), and increased from rest during exercise (P< 0.001 for Workload) with no significant difference between groups (P >0.05 for Interaction Workload x Group). Notably, RLLM was significantly greater in Black participants than in White participants (White: 9.5±0.8 kg vs. Black: 11.0±2.0 kg; P=0.039). After RLLM normalization, Black participants exhibited lower normalized LVC (P< 0.001 for Workload, P< 0.001 for Group, P=0.003 for Interaction Workload x Group) and LBF (P< 0.001 for Workload, P=0.012 for Group, P=0.051 for Interaction Workload x Group) than the White participants. Conclusion: Although vascular conductance and blood flow were similar between groups during single-leg dynamic knee extension exercise, normalizing for leg lean mass revealed a lower vascular response in Black compared to White men. This study extends previous research, suggesting altered vascular responsiveness in the lower limbs of Black men during exercise. Funding: UTA Center of Research and Scholarship Pilot Grant and NIH (1R15HL130906-01) This abstract was presented at the American Physiology Summit 2026 and is only available in HTML format. There is no downloadable file or PDF version. The Physiology editorial board was not involved in the peer review process.