Exercise-induced changes in blood, red cell, and plasma volumes in man

Changes in blood (BV), red cell (RCV), and plasma (PV) volumes were computed from hemoglobin and hematocrit values during submaximal treadmill exercise at 5 work intensities (30, 45, 60, 75, and 90% VO2 max) in 5 male subjects. RCV remained constant under all conditions. Changes in BV (hemoconcentration) could, therefore, be accounted for entirely by decreases in PV at all work levels. PV was a linear function of work intensity from rest through 60% VO2 max. However, a "break" occurred at that point in the data. Modeling of this break was accomplished by the use of one model (the "Fold" catastrophe) taken from the generalized catastrophe therory. However, several limitations to the acceptance of the model are presented, including the need to demonstrate a hysteresis in PV occurring at about 65% VO2 max.