Vascular adaptation in athletes: is there an ‘athlete's artery’?

Abstract

Whilst the existence of a specific phenotype characterized as 'athlete's heart' is generally acknowledged, the question of whether athletes exhibit characteristic vascular adaptations has not been specifically addressed. To do so in this symposium, studies which have assessed the size, wall thickness and function of elastic, large muscular and smaller resistance arteries in athletes have been reviewed. Notwithstanding the caveats pertaining to cross-sectional comparisons between athletes and 'matched' control subjects, these studies reveal increased conduit artery size, including enlargement of epicardial arteries and those supplying skeletal muscle. Evidence that peak limb blood flow responses are enhanced in athletes further suggests that resistance arteries undergo increases in total cross-sectional area. Such increases can be localized to those arteries supplying active muscle leading to speculation, supported by exercise training studies in humans and animal and cellular data, that arterial enlargement is associated with repetitive episodic increases in arterial shear stress which elicit endothelium-mediated remodelling. Such structural remodelling at conduit and resistance artery level may play a role in accommodating the substantial increase in cardiac output apparent in endurance athletes; arterial pressure is not increased at rest or during exercise in athletes (versus control subjects). Arterial wall remodelling also occurs in athletes but, in contrast to the impact of shear stress on remodelling of arterial lumenal dimensions, the impact of endurance athletic status on wall thickness may be a systemic, rather than localized, phenomenon. Finally, the question of whether the arteries of athletes exhibit enhanced function is moot. Somewhat paradoxically, measures of conduit and resistance artery endothelial function may not be enhanced, compared with healthy control subjects. This may relate to the inherent difficulty of improving arterial function which is already normal, or the time course and transient nature of functional change. It may also relate to the impact of compensatory structural remodelling, as arterial lumen size and wall thickness both affect functional responsiveness. In summary, there is clear evidence for an impact of athletic status on arterial structure and function, at least with respect to the impact of endurance training. Arterial adaptation may, to some extent, emulate that evident in the hearts of endurance athletes, and it is tempting to speculate that similar mechanisms may be at play.

Brachial artery characteristics and micro‐vascular filtration capacity in rock climbers

“…Larger vessels are also a feature in the upper-body of wheelchair athletes (Zeppilli et al, 1995). An enlargement of the arteries in trained individuals may contribute to an improvement in performance through an enhanced blood flow and oxygen delivery (Green et al, 2012;Welsch, Blalock, Credeur and Parish, 2013). Although it is appreciated that local blood flow is regulated by the resistance vessels we have previously demonstrated resistance vessel adaptation resulting in an enhanced limb blood flow capacity and functional hyperaemia in climbers (Ferguson and Brown, 1997).…”

“…The key physiological stimulus proposed to be responsible for the remodelling of the conduit arteries is the repetitive shear stress produced during exercise (Langille and O'Donnell, 1986;Tinken et al, 2010;Green et al, 2012) which activates a number of signalling cascades within the endothelial cells resulting in an altered endothelial cell phenotype (Chien, 2007) and consequent remodelling. Independent of, or indeed in addition to the effects of shear stress, there may be contributions from other stimuli e.g.…”

“…In accordance with the 'athletes paradox' theory (Green et al, 2012) it was hypothesised that rock climbers would exhibit an enlarged artery diameter, suggestive of arterial remodelling, but there would be an absence of any functional 4 adaptations. It was also hypothesised that rock climbers would exhibit an enhanced capillary filtration capacity, reflective of a greater capillary density (Brown, Jeal, Bryant and Gamble, 2001).…”

“…Structural adaptations, including a relatively greater diameter of the conduit arteries have been observed (Huonker, Schmid, Schmid-Truckäss, Grathwohl and Keul, 2003;Rowley, Dawson, Birk, Cable, George, Whyte, Thijssen and Green, 2011a;Rowley, Dawson, Hopman, George, Whyte, Thijssen and Green, 2011b) despite a lack of a functional improvement or in some cases a functional decrease (Petersen et al, 2006;Rowley et al, 2011b). This phenomenon has recently been called the 'athletes paradox' (Green, Spence, Rowley, Thijssen and Naylor, 2012).…”

“…Although improved function has been observed with exercise training in patients with cardiovascular disease (Hambrecht et al, 2003), the same has not been observed in healthy athletic populations (Tinken, Thijssen, Black, Cable and Green, 2008;Rowley et al, 2011b). It is now apparent that an 'athlete paradox' exists, whereby despite the expectation of greater vascular function in highly trained individuals, this group exhibit functionally 'normal' arteries (Green et al, 2012). This lack of functional adaptation can be also explained by appreciating the time-course of artery adaptation to exercise training.…”