The effects of activity and thermal environment on creatinine clearance

Summary Rates of creatinine clearance (C_Cr) were measured in 3 healthy young men while standing at rest, walking at 5.6 km/hr, or jogging at 9.6 km/hr for 1 hr in environments set at water vapor tensions equal to about 10 mm Hg and dry bulb temperatures of 10, 25, or 40 ° C. The purpose was to study the differential effects of activity and thermal environment on glomerular filtration rate (GFR). C_Cr was always greater for walking than for standing in each environmental situation considered. For jogging, C_Cr decreased below standing values in the hot and temperate environments, but in the cold C_Cr for jogging did not differ from that for standing. Furthermore, during the jogging experiments C_Cr decreased in a linear fashion for each subject as heat stress (sweat rate) increased. We conclude that in comparison with rest the effects of mild and moderate exercise on GFR can be directionally different. With increasing heat stress, these differences in GFR can be accentuated.