The beta-endorphin responses of pregnant women during aerobic exercise in the water.

To determine the effect of pregnancy on the plasma beta-endorphin response to exercise in the water, 12 women were tested during the 15th, 25th, and 35th wk of pregnancy and 10 wk post partum. Each trial consisted of 20 min of lateral supine rest on land, 20 min of immersion to the level of the xiphoid in 30 degrees C water, 20 min of exercise at 60% predicted maximal capacity, and 20 min of lateral supine recovery. Resting beta-endorphin concentrations were elevated during the 15th wk (137.4 +/- 77.4 pg.ml-1) compared to post partum levels (19.8 +/- 17.6). However, neither was different from the 25th (65.6 +/- 68.4) or 35th (48.0 +/- 54.4) wk. Immersion increased beta-endorphin during the post partum trials but resulted in no consistent change during pregnancy. Conversely, exercise had no effect on beta-endorphin post partum but significantly elevated it during pregnancy, the greatest increase occurring during the 15th wk compared to the 25th or 35th wk. Twenty minutes after exercise, beta-endorphin returned to resting levels during all trials. It was concluded that the effect of pregnancy on plasma beta-endorphin is greater than the effect of exercise. Furthermore, pregnancy seems to accentuate the exercise-induced increase in beta-endorphin.