1. The physiological responses to exercise of two groups of industrial workers with moderate and severe anaemia were measured and compared with a group of matched controls, working and living under similar conditions. Exercise was performed on a stationary bicycle ergometer at five consecutive work loads. During the final minute of each exercise periods, oxygen intake, minute ventilation volume, and cardiac and respiratory frequencies were measured. On a separate occasion, blood haemoglobin concentration was measured at rest and cardiac output and blood and plasma volumes were estimated while subjects exercised at a fixed percentage of the maximum aerobic power for 6 min.

2. Oxygen intake for a given work load and ventilation rate was similar in all subjects studied but exercise cardiac output was elevated in the anaemic group. The increased cardiac output was due to an increased heart rate, the stroke volume being similar in the anaemic and control subjects. There was a marked decrement (∼34%) in maximum aerobic power and some evidence of a raised plasma volume in the severely anaemic group.

3. These results suggest that anaemia impairs performance during moderate and near maximum exercise. There is an associated rise of cardiac output and plasma volume.

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