The normal range of maximal values for oxygen consumption, heart rate, cardiac index, and stroke index during treadmill exercise testing are presented for 98 men and 104 women for ages 20–75 yr. These variables decrease with age in both sexes, but men show a significantly greater reduction than women with respect to oxygen consumption (P = 0.05), heart rate (P less than 0.02), and cardiac index (P less than 0.02). Comparison of the normal ranges of oxygen consumption, cardiac index, and stroke index indicated that men have significantly higher values than women (P less than 0.001). The normal range of heart rate was higher in younger men than women, but because of a more rapid decline with age in men, the older women had higher heart rates than the older men. Invasive measurements of cardiac index in 12 normal men and 11 normal women were within the defined normal range. These measurements showed that there was a greater increase in stroke index from supine rest to maximal upright exercise in men compared with the increase in women (means +/- SD, 12 +/- 9 m/m2 vs. 2 +/- 7 ml/m2, P less than 0.01).
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