Journal of Applied Physiology, Vol 39, Issue 6 958-964, Copyright © 1975 by American Physiological Society
Cardiac limitation to maximal oxygen transport and changes in components after jogging across the US
R. A. Bruce, F. Kusumi, B. H. Culver and J. Butler
Observations were made before and 3-5 days after prolonged endurance
jogging an average of 42 miles/day, 6 days/wk for 2.5 mo by a young male
adult who voluntarily initiated a run across the United States. Both
arterial PO2 and lactic acid increased. In each instance, the first
limitation in circulatory delivery of oxygen was a plateau in stroke volume
and cardiac output. Afterward, pulse deficit and systemic arterial pressure
fell with exercise and heart rate accelerated. Although there was no change
in oxygen transport (Q X CAO2), a reduction in stroke volume was exactly
balanced by a rise in arterial oxygen content. Vital capacity, residual
volume, and total lung capacity and diffusion capacity for carbon monoxide,
hematocrit, and red cell mass increased, while plasma volume diminished and
heart size and total blood volume were unchanged.
