Francisco J. Diaz

Plasma Volume Changes Related to Posture and Exercise

Abstract Plasma volume shifts were investigated in four male subjects who remained in either the upright or low-sit posture on a bicycle ergometer during 60 min of rest, 45 min of exercise, and 45 min of recovery. Rest in the upright and low-sit posture induced plasma volume decreases of 14 and 6.9%, respectively. When postural effects were partialed out, exercise in the upright posture resulted in minimal alterations in plasma volume. Work in the low-sit posture was characterized by hemoconcentration during the early phases of pedalling followed by a slight increase in plasma volume which remained stable for the duration of the exercise period. During recovery, plasma volumes returned rapidly to the pre-exercise levels associated with each seated posture. It is evident that when analyzing fluid shifts, posture and time should be rigorously controlled so as to differentiate between the effects of posture and exercise.