The amount of blood circulated by the heart increases early in pregnancy and levels off during the third trimester at 30-50% above normal values.

Results:

Since aerobic exercise also requires increased blood to be pumped by the heart, exercise during pregnancy is more difficult at any workload.

Your heart rate at rest increases 10-15 beats per minute during pregnancy. During exercise, heart rate also increases. Heart rate during weight-bearing activities is elevated in direct proportion to weight gain. Also, recovery rates are much slower during pregnancy..

Results:

At the same workload, your heart rate will be higher than it was before you became pregnant. You may need to decrease the intensity of your activity to keep your heart rate from becoming too high during exercise. It may also take as long as 15 minutes for your heart rate to recover to resting values following an exercise session.

During pregnancy, blood flow to the skin increases to help cool the body. Blood flow to the kidneys, lungs and uterus also increases.

Results:

Exercise requires an increase in blood flow to the heart and working muscles which may compete with other body systems at high levels of activity.

You may notice a decrease in blood pressure during the first two trimesters and also a decreased ability of the body to return blood to the heart quickly. This is sometimes linked to the dizzy sensation that is experienced by some pregnant women.

Results:

Activities which contract the muscles (i.e. exercise) help stimulate return blood flow to the heart.

The total volume of blood in the body increases up to 50% by the end of the second trimester. The water component of the blood increases faster than the red blood cell component, which contributes to anemia in many women.

Results:

In some women, exercise capacity may decrease, since red blood cells carry oxygen to body cells (including muscles).