In the beginning i was uncertain and needed additional information to decide whether exercise during pregnancy was a good idea, a bad idea, or didn’t make any difference at all. On the other hand, physical activity was such an integral part of life that was difficult to understand how it could be harmful to something as important as the reproductive process.
On the other hand, it was equally difficult to understand why things like a sudden marked increase in temperature or a 50 percent decrease in blood flow to the womb would not harm the developing baby.
Because there were many theoretical concerns, little factual knowledge, and a growing number of women exercising vigorously during pregnancy, i decided to analyze the information from the first 10 women who wanted to participate in our survey. During very early pregnancy, their heart rates suddenly went sky high, both at rest and during exercise.
It was so early and dramatic that it alarmed several of the women, but it turned out to be simply an early, previously unrecognized sign of healthy pregnancy. Later in pregnancy the heart rates of these women during exercise come back down.
By late pregnancy, it was hard for most women to get their exercise heart rates up to the levels recorded before pregnancy, even though their workloads were the same or higher. Energy requirements during exercise also decreased, indicating that their metabolic efficiency were much lower at rest and during exercise. Finally during pregnancy, their blood sugar levels fell during and after exercise, which was the reverse of what happened before they became pregnant.
These unexpected and dramatic changes were exciting because they meant that understanding the effects of exercise on the course and out come the pregnancy might be straightforward. It looked as if many functional changes induced by the hormonal signals of pregnancy had modified various aspects of the exercise response in a manner that would protect the unborn baby.
It also appeared that exercise induced cardiovascular and metabolic training effects enhanced the functional chenges of pregnancy in a manner that was also protective. Although this train of thought proved to be naive, it did provide a vital element of early understanding.
Indeed, once the basic principles underlying the physiological interaction between regular exercise and pregancy are understood, it is easy to design and appropriate, individualized exercise regimen for any healthy woman who is either considering pregnancy or already pregnant.