Attenuated Leg Vascular Conductance Responses To Dynamic Knee Extension Exercise In Young Black Men

Abstract

Our group recently showed a blunted increase in skeletal muscle vascular conductance and blood flow during rhythmic handgrip exercise in young black (i.e. African American) individuals with no overt cardiovascular diseases compared with white (i.e. Caucasian American) individuals. These findings, along with reduced endothelium‐dependent forearm vasodilation and augmented forearm vasoconstriction to phenylephrine at rest, suggest that vascular alterations occur early in the lifetime of black individuals, possibly predisposing this population to develop cardiovascular diseases. Notably, research on racial differences in vascular responses has almost exclusively examined upper limbs. However, lower limb vascular diseases are more prevalent and cause more adverse events in the black population than in any other racial group in the U.S. Therefore, for a better understanding of racial differences in vascular health, we tested the hypothesis that vascular responses to lower limb exercise would be attenuated in black individuals compared with their white counterparts. Six black (21 ± 1 years; 23 ± 2 kg/m2) and 4 white (21 ± 0 years; 21 ± 1 kg/m2) healthy men performed dynamic knee extension exercise at the workloads of 10, 20, and 30 watts (W) in an upright sitting position on a custom ergometer. Each exercise trial lasted for 3 min with a minimum rest interval of 5 min. Knee extension cadence was 50 repetitions per min, provided by a metronome and real‐time visual feedback. Common femoral artery blood flow (FABF, Doppler ultrasound) and mean arterial pressure (MAP, finger photoplethysmography) were continuously measured, and leg vascular conductance (LVC) was calculated as FABF/MAP. The participants reported a rating of perceived exertion (Borg Scale 6 – 20) at the end of each trial. Both groups presented LVC increases from rest during dynamic knee extension. While this response was similar between groups at 10 W (White: +1970 ± 138 vs. Black: +1666 ± 173 mL/min/100 mmHg; P = 0.407), the increases in LVC were significantly attenuated in black individuals (mixed‐model ANOVA interaction P = 0.026) at the workloads of 20 W (Whites: +2550 ± 105 vs. Blacks: +1829 ± 179 mL/min/100 mmHg; P = 0.025) and 30 W (Whites: +2528 ± 248 vs. Blacks: +1850 ± 152 mL/min/100 mmHg; P = 0.035). Similarly, FABF responses to dynamic knee extension were lower in black individuals compared with their white counterparts (Interaction P = 0.011). In contrast, increases in MAP were similar between groups (Interaction P = 0.271). The groups reported similar ratings of perceived exertion among trials (Interaction P = 0.817) and achieved similar peak workloads in a dynamic knee extension maximal exercise test (Whites: 48 ± 8 W vs. Blacks: 49 ± 3 W; P = 0.883). These preliminary findings suggest a blunted vasodilator response during leg exercise in black men, further highlighting the early occurrence of vascular alterations in this population.Support or Funding InformationUTA Center of Research and Scholarship Pilot Grant;NIH (1R15HL130906‐01)