Thermoregulation of pregnant women during aerobic exercise on land and in the water.

Seven women in their 25th week of pregnancy exercised for 20 minutes on a cycle ergometer at 70% of their maximal heart rate on land and in the water (30 degrees C) to compare thermoregulatory responses. Rectal temperatures increased 0.5 +/- 0.1 degrees C during the land trial and only 0.2 +/- 0.1 degrees C during the water trial (p < 0.05). Mean body temperature rose 0.6 +/- 0.2 degrees C during the land trial, but declined -0.3 +/- 0.1 degrees C during the water trials (p < 0.05). Land exercise caused greater heat storage and sweat loss. The results suggest that normal pregnant women can maintain thermal balance during 20 minutes of exercise at 70% maximal heart rate, whether on land or in the water. Thus, for normal, average fit, pregnant women who wish to participate in a moderate exercise program, heat stress is probably not a major concern.