Comparative Exercise-Cardiorespiratory Performance of Normal Men in the Third, Fourth, and Fifth Decades of Life

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Abstract
The circulatory and respiratory responses to five levels of treadmill exercise were recorded for 75 normal males divided equally in the age groups 20 to 29, 30 to 39, and 40 to 49 years. Parameters studied included heart rate, cardiac output, stroke volume, intra-arterial blood pressure, minute ventilatory volume, oxygen uptake, and carbon dioxide elimination. Values for peripheral vascular resistance, left ventricular work, and stroke work indices were calculated. Intergroup and intragroup differences were analyzed by modified covariance technique using oxygen uptake per square meter of body surface area as the concomitant variable reflecting a specific midrange work level. Significant differences were observed between groups in cardiac output, stroke volume, systolic, diastolic, and mean arterial blood pressure as well as pressure-related variables with regard to absolute values and trend over the exercise spectrum. The results indicate that normal untrained males in the fourth and fifth decades of life react to moderate and heavy upright exercise with statistically significant systemic pressure elevations as compared to 20-year-olds. A tendency toward initially high cardiac output and stroke volume during light exercise was observed in the older men. Relatively small subsequent increments in cardiac output with resultant low absolute values during heavier work were also characteristic for this group as reflected in their decreasing stroke output at submaximal loads.