The effects of blood loss on the performance of physical exercise.

Seven male subjects were studied before and up to 53 days after the loss of 11 of blood. The resting hematocrit fell from 44.0 to 38.7% and returned to control level after 3 weeks. Maximal oxygen uptake decreased from 4.00 1/min to 3.54 1/min and returned to the initial level within 2 weeks. Submaximal oxygen uptake, pulmonary ventilation, maximal heart rate and blood lactate were not found to change significantly. Submaximal heart rate was increased from 125 beats . min-1 to about 135 beats . min-1 and remained elevated for 3 weeks, whereas blood lactate was increased only in the first week. Maximal work time decreased from 5.1 min to 3.8 min and remained low for the first 2 weeks, but rose thereafter above the starting level. Comparison with a control study suggested that there is some training effect, which, when allowed for, indicates that maximal work time returns to starting values at the same time as does the maximal oxygen uptake. It is concluded that the drop in Hct, maximal oxygen uptake and work capacity, found after the loss of 11 of blood, are related to each other both in magnitude and duration.