Plasma volume changes in trained and untrained men during submaximal and maximal work

The acute change in plasma volume (PV) was compared in nine aerobically trained and nine untrained men cycling at the same absolute work rate and after maximal work. Subjects cycled for 7 minutes at each of 60,120, and 180 W. Thereafter, work rate was increased 60 W every 2 minutes until fatigue. The relative metabolic work intensity at 60, 120, and 180 W was significantly greater for the untrained (32.6, 54.4, and 82.2% peak oxygen consumption [VO₂ peak], respectively) than for the trained group (19.9, 31, and 45.7% VO₂peak respectively). There was a significant (p < 0.05) interaction between group classification and work rate reflected in a change in PV so that, as work rate increased, the mean percent PV decrease was progressively greater for the untrained (3.9, 9.2, and 16.2%, respectively) than for the trained (3.9, 6.8, and 12.5%, respectively) group. The acute PV decrease was similar (18.6%) in both groups after maximal work. Thus, when cycling at the same absolute work rates, untrained men exhibit a progressively greater PV decrease during incremental exercise than trained men.