Effects of physical activity on maternal plasma beta-endorphin levels and perception of labor pain.

Thirty-six women in their second or third pregnancies were studied in two groups (control and exercise) to determine whether plasma alpha-endorphin levels could be elevated by exercise conditioning during pregnancy. Aerobic training was performed on a bicycle ergometer. Both groups were monitored throughout pregnancy by frequent gynecologic examinations. During labor, both groups of women had pain perception assessment. Blood was sampled for levels of beta-endorphin, cortisol, human growth hormone, and prolactin. Plasma beta-endorphin was found elevated compared to controls in patients who exercised throughout pregnancy. This difference was maintained throughout labor and pain perception during labor was reduced in the patients who exercised. Cortisol, human growth hormone, and prolactin levels were lowered during labor for the exercise-conditioned patients. Exercise conditioning during pregnancy seems to be beneficial in reducing pain perception during labor (as determined by measurement of visual analog pain scales) and in reducing stress levels during labor.