Journal of Applied Physiology, Vol 55, Issue 1 69-74, Copyright © 1983 by American Physiological Society
Cardiac output and skin blood flow in lean and obese individuals during exercise in the heat
N. B. Vroman, E. R. Buskirk and J. L. Hodgson
Five obese (% body fat greater than or equal to 27%) and five relatively
lean (% body fat less than 20%) men performed upright exercise on a cycle
ergometer at intensities of 30, 50, and 70% of their maximal aerobic power
[VO2max (ml X kg fat-free wt-1 X min-1)] in both a thermoneutral [dry bulb
temperature (Tdb) = 22 degrees C, wet bulb temperature (Twb) = 14 degrees
C] and a hot (Tdb = 38 degrees C, Twb = 20 degrees C) ambient environment.
Cardiac output (Q) was measured by CO2 rebreathing and forearm blood flow
(FBF) was measured by venous occlusion plethysmography. Esophageal
temperature (Tes) was measured by a thermocouple placed in the esophagus at
approximately heart level, and mean skin temperature (Tsk) was calculated
from the average of thermocouple readings from six skin sites. When the
exercise intensity was normalized for metabolic body mass by dividing by
fat-free weight, Q was similar between lean and obese at all exercise
intensities and in both ambient environments. No differences between the
two groups were found in Tes and Tsk under all conditions. The obese had
significantly lower FBF compared with the lean during the higher exercise
intensities in the hot ambient environment. In both ambient environments,
the slope of the FBF-Tes relationship was significantly less in the obese
group. It was concluded that body composition may alter the balance between
the two opposing sets of cutaneous vascular reflexes (baroreceptor-induced
vasoconstriction and thermoregulatory vasodilation) that regulate the
competition for blood flow between the skin and working muscle during
exercise in the heat.
