Age, fitness, and regional blood flow during exercise in the heat

Ho, C. W., J. L. Beard, P. A. Farrell, C. T. Minson, and W. L. Kenney. Age, fitness, and regional blood flow during exercisein the heat. J. Appl. Physiol. 82(4):1126-1135, 1997.During dynamic exercise in warm environments,the requisite increase in skin blood flow (SkBF) is supported by anincrease in cardiac output (c) and decreases insplanchnic (SBF) and renal blood flows (RBF). To examine interactionsbetween age and fitness in determining this integrated response, 24 men, i.e., 6 younger fit (YF), 6 younger sedentary (YS), 6 older fit (OF), and 6 older sedentary (OS) rested for 50 min, thenexercised at 35 and 60% maximalO₂ consumption(O_{2 max}) at36°C ambient temperature. YF had a significantly higherc and SkBF than any other group during exercise,but fitness level had no significant effect on any measured variable inthe older men. At 60%O_{2 max}, younger subjects had significantly greater decreases in SBF and RBF than theolder men, regardless of fitness level. Total flow redirected fromthese two vascular beds (SBF + RBF) followed YF >> YS > OF > OS. A rigorous 4-wk endurance training programincreased exercise SkBF in OS, but SBF and RBF were unchanged.Under these conditions, older men distribute cdifferently to regional circulations, i.e., smaller increases in SkBFand smaller decreases in SBF and RBF. In younger subjects, the higherSkBF associated with a higher fitness level is a function of both ahigher c and a greater redistribution of flow fromsplanchnic and renal circulations, but the attenuated splanchnic andrenal vasoconstriction in older men does not appear to change withenhanced aerobic fitness.