Why Isn’t Flow-Mediated Dilation Enhanced in Athletes?

Abstract

Studies performed in animals and humans strongly suggest that exercise training and physical activity enhance arterial endothelial function. Studies of athletes have, however, been less definitive. We recruited a range of Olympic and world class athletes who participate in upper or lower limb predominant activities and examined brachial and superficial femoral artery diameter responses to 5-min ischemia (flow-mediated dilation [FMD]) and glyceryl trinitrate, wall thickness (WT) and wall-to-lumen ratio using Doppler and two-dimensional ultrasound. Subjects were elite male canoe paddlers (n = 12), squash players (n = 13), lower limb dominant athletes (i.e., runners/cyclists/triathletes, n = 13), or age- and sex-matched control subjects (n = 16). Athletes demonstrated lower superficial femoral artery FMD than controls (P < 0.05), whereas in the brachial artery, a lower FMD was found in squash players (P < 0.05). Both arteries showed a significant inverse correlation between diameter and FMD (P < 0.05), and a significant inverse relationship was apparent between wall-to-lumen ratio and FMD in the superficial femoral artery (P < 0.05). Although artery FMD was lower in athletes, artery size was larger and WT smaller than controls. The apparent reduction in artery FMD may relate to the profound structural remodeling in the diameter and WT of the conduit arteries of athletes. These findings have implications for the interpretation of FMD data, particularly as it pertains to the effect of athletic endeavor on cardiovascular health.