This research, says Clapp, suggests that pregnancy improves cardiovascular and metabolic function. "I think a woman's body undergoes some fundamental changes when she's pregnant that could change her body's response to exercise," he says. Many of these changes parallel what happens to an athlete who works out with weights or who does endurance training in hot weather. For instance:
•Women find their legs feel stronger after pregnancy, possibly because they were carrying an average of 25 additional pounds.
•During pregnancy a woman's heart rate increases, as does her stroke volume, which is the amount of blood the heart pumps with each beat. Both phenomena improve fitness.
•Her blood volume increases by as much as 40%. Her red-blood-cell count rises slightly, but plasma accounts for most of the increase in volume.
Additional plasma allows athletes who train in hot weather to sweat more profusely. Their blood also circulates near the surface of the body more easily because the smaller ratio of red blood cells to plasma means that the blood flows more freely in the tiny capillaries near the skin. As a result, the athlete's body can dissipate heat more effectively. Similarly, Clapp discovered that pregnant women begin to sweat when their bodies are at a lower temperature than women who aren't pregnant. "I figure that pregnant women are about 33 percent more efficient at getting rid of heat," says Clapp.
All other factors being equal, such physiological changes could enhance performance. Rumors have been circulating in the track world that some Eastern European athletes take advantage of these apparent benefits by becoming pregnant just before crucial competitions. Such unconfirmed stories are difficult to believe, because these women would have to abort after big meets. However, Der Spiegel, the West German news magazine, reported that top women athletes commonly take high doses of birth control pills, which contain hormones that stimulate physiological changes that mimic the early stages of pregnancy.
So far, though, scientists are just guessing that the physiological changes brought on by pregnancy improve performance and that they persist after the baby is born. In theory, finding out how pregnancy affects world-class athletic performance ought to be simple. All that's required are tests before, during and after the pregnancies of elite athletes. Such tests have probably been performed in East Germany and the Soviet Union, where accumulating data is easier because athletes live together in training centers. In this country, only one such study has been done, and it focuses on just one subject, champion triathlete Liz Applegate.
In 1982 Applegate, a lecturer in the nutrition department at UC Davis, won the U.S. Triathlon Series event in San Francisco and the California Championship Triathlon in Folsom. At that time Bob Holly, a sports physiologist and assistant professor of physical education at Davis, did tests on Applegate similar to those performed in the famous 1975 Dallas study of elite male runners. Before she conceived, he tested Apple-gate's VO2max, which is a measure of the body's ability to absorb and use oxygen during all-out exertion. Holly also checked her body fat and maximum heart rate, both of which were consistent with those of an elite athlete.
Applegate continued exercising throughout her pregnancy before having a 7-pound, 2-ounce baby boy in December 1983. Two days after delivering, Applegate was running again. Holly continued to test her at regular intervals. Within 5½ months Applegate had returned to competition, having regained her prepregnancy levels of fitness.
Seven months after Applegate had given birth, she and Holly were astonished to see that her VO2max had increased by 5%. This is a phenomenal improvement for a highly conditioned athlete. A woman who goes from being an overweight couch potato to being able to run a 10K might expect a dramatic jump, perhaps as much as 25%, but such an increment is rare for someone already high on the fitness scale. Applegate cautions that her results don't prove the existence of a pregnancy effect. "This is just one case study," she says.