Abstract

Cardiorespiratory responses to two levels of exercise (133 and 200 W) on a bicycle ergometer were measured in nine subjects before and after a 1-h outdoor run of 12.8 km completed in ambient temperatures of 20-25 degrees C. After the run, the subjects showed a mean weight loss of 1.49 kg; the laboratory exercises produced higher mean levels of 02 consumption than before the run (1.91 and 2.66 l/min compared with 1.80 and 2.46 l/min) and higher mean heart rates (141 and 158 beats/min compared with 115 and 140 beats/min); and lower levels of stroke volume (83 and 85 ml compared with 109 and 101 ml) and of cardiac output (11.6 and 13.3 l/min compared with 12.6 and 14.1 l/min). Five subjects were studied in a similar way on a second occasion when they consumed 1.25 l of a dextrose-electrolyte solution during the first 45 min of the outdoor run. Differences in the exercise variables measured before and after the outdoor run were now small or insignificant. It is postulated that in the first study uncompensated loss of body water reduced plasma volume and cardiac filling, thus reducing stroke volume and cardiac output. Such changes jeopardize body temperature regulation during exercise. Verf.-Referat