Exercise training and orthostatic intolerance: A paradox?

Abstract

To summarise the present view, orthostatic intolerance in deconditioned subjects is related to hypovolaemia and possibly to cardiac atrophy (Pawelczyk et al. 2001) and to attenuated carotid baroreflex responsiveness and a larger compliance of the heart in the highly fit. The debate as to the effect of physical training on an individual's tolerance to orthostatic stress may come to an end by accepting the existence of an 'optimal level of fitness', ill-defined as it is, located between the deconditioned and the highly trained state. To advise people who do not easily tolerate standing to exercise seems logical but to what extent they should exercise is less certain (Wieling et al. 2002). Intuitively leg resistance training may reduce venous pooling by increasing muscle tone but e.g. swimming training does not lead to greater orthostatic tolerance than running training (Franke et al. 2003). Tensing the leg muscles attenuates the postural reduction in cerebral perfusion (van Lieshout et al. 2001) and the instructions given to students in military schools to 'walk' in their shoes and to stand on the balls of their feet during parade may also be of relevance to athletes.