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Age, Fitness, And Regional Blood Flow During Exercise In The Heat

C. W. Ho, J. L. Beard, P. A. Farrell, C. T. Minson, W. L. Kenney

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Ho, C. W., J. L. Beard, P. A. Farrell, C. T. Minson, and W. L. Kenney. Age, fitness, and regional blood flow during exercise in 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 an increase in cardiac output (Q˙c) and decreases in splanchnic (SBF) and renal blood flows (RBF). To examine interactions between 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, then exercised at 35 and 60% maximal O2 consumption (V˙o 2 max) at 36°C ambient temperature. YF had a significantly higherQ˙c and SkBF than any other group during exercise, but fitness level had no significant effect on any measured variable in the older men. At 60%V˙o 2 max, younger subjects had significantly greater decreases in SBF and RBF than the older men, regardless of fitness level. Total flow redirected from these two vascular beds (ΔSBF + ΔRBF) followed YF >> YS > OF > OS. A rigorous 4-wk endurance training program increased exercise SkBF in OS, but ΔSBF and ΔRBF were unchanged. Under these conditions, older men distribute Q˙c differently to regional circulations, i.e., smaller increases in SkBF and smaller decreases in SBF and RBF. In younger subjects, the higher SkBF associated with a higher fitness level is a function of both a higher Q˙c and a greater redistribution of flow from splanchnic and renal circulations, but the attenuated splanchnic and renal vasoconstriction in older men does not appear to change with enhanced aerobic fitness.