Effects of short-term and prolonged immersion on the cardiovascular responses to exercise. 
The primary purpose of this investigation was to examine the effects of water immersion in 35 degrees C water, per se, and the effects of 3 h of water immersion on the physiological responses to exercise.  Experiments in air were conducted after 15 min of water immersion and after 3 h of water immersion.  After each condition, exercises of 20%, 40%, 60%, 80%, and 100% of the subject's maximum oxygen consumption were performed on a cycle ergometer.  Oxygen consumption (VO2), cardiac output, heart rate (HR), stroke volume, and blood pressure were determined.  At submaximal workloads, no significant differences in the data were observed.  The VO2 at the maximal workload after 3 h of immersion (3.32 +/- 0.15 L.min-1) was significantly higher than the value after 15 min of immersion (3.03 +/- 0.20 L.min-1).  Both of these values were significantly lower than the value in air (3.83 +/- 0.30 L.min-1).  The peak HR's were significantly higher after 3 h of immersion (167 +/- 2 b.min-1).  These observations suggest that 3 h of immersion can cause alterations in the cardiovascular responses to maximal exercise; however, submaximal responses were unaffected.