Training state affects plasma volume response to work at similar relative intensities

BACKGROUND: This study determined the difference in change in plasma volume between aerobically trained (T) and sedentary (UT) men cycling at a similar light and heavy relative metabolic work intensity. METHODS: Eight T and eight UT men performed one continuous cycling bout, first at approximately 45% VO₂ peak and then at approximately 80% VO₂ peak. Blood was drawn during supine and seated rest and after 10 minutes of cycling at each workrate. RESULTS: Arepeated measures ANOVArevealed an interaction (P<0.0001) between group and intensity on VO₂ such that the increase in VO₂ was progressively greater from the light (26.4±1.8 vs. 16.9±2.4 mL·min^-1 · kg^-1 for the Tand the UTgroup, respectively) to the heavy (46±3.6 vs. 29.1±4.3 mL · min^-1 · kg^-1 for the Tand the UTgroup, respectively) relative intensity for the Tthan for the UTgroup. There was a main effect of training status such that, when averaged across the light and heavy relative metabolic intensities, the relative decrease in plasma volume was greater (P=0.021) in the UT(12±7.7% and 19.6±3.8%, respectively) than in the T(6.5±2.9% and 14.1±3.7%, respectively) group. CONCLUSIONS: When cycling at similar relative metabolic work intensities, UTmen exhibit greater relative decreases in plasma volume than Tmen. Therefore, for aerobic endurance training, UTindividuals should be assigned a lighter relative metabolic work intensity than well-trained individuals.