Plasma Volume Changes in Middle-Aged Male and Female Subjects during Marathon Running.

摘要

Circulatory fluid shifts were studied in middle-aged runners (6 males and 5 females, ages 32-58 yr) during a 42.2-km marathon racerun in mild weather (dry-bulb temperature = 17.5 -20.4 C). Running times for the subjects were 3:12 - 4:40 (mean values were 3:3 for males and 4:10 for females). By the end of the race, hypohydration had reached 3.2% in male subjects and 2.9% in female subjects and 8.6% in female subjects, but PV n both groups remained stable. Sweat rates during the race averaged 545 and 429 g.m-2.h-1 for male and female subjects, respectively, with ad lib. water intake replacing 21-72% of fluid loss. Increases in plasma protein concentration throughout the race reflected the observed initial decrease in PV. The interpretation of PV responses to exercise and/or hypohydration is critically dependent on selection of base-line conditions; we were able to control for posture-exercise effects by treating the early exercise (6 km) sample as the base line for examining the effects of later fluid loss. Under these conditions, the vascular compartment resisted volume depletion. The ability to maintain stable PV can be explained in part by relationships among oncotic and hydrostatic pressures in the intra- and extravascular fluid compartments.