Circulatory response to prolonged severe exercise

Four subjects worked on a treadmill or a bicycle ergometer for 180 min at oxygen uptakes of 75% of the individual's max Vo2; after 90 min rest, the exercise was resumed and a maximal work load was tried. Repeated circulatory studies were made. The body weight decreased 3.1 kg (3.2–5.2%), but the reduction in blood volume was less than 5%. During submaximal exercise the major change in the hemodynamic response was a decrease in stroke volume (from 126 to 107 ml). Oxygen uptake and cardiac output increased slightly. There was a decrease of about 10% in systolic, diastolic, and mean arterial blood pressure during the 180 min of exercise. When the work was performed in a supine position there was the same reduction in the stroke volume as in the sitting work position. At the maximal work oxygen uptake, cardiac output, heart rate, and blood pressure attained almost normal values but there was a marked decrease in both work time and blood lactates. dehydration; blood volume; arterial blood pressure; circulatory reaction Submitted on January 31, 1964