IntensityThe intensity of exercise

IntensityThe intensity of exercise should be at a level that is moderate to somewhat hard during pregnancy. It is not accurate to limit the intensity of exercise based on a specific heart rate. During pregnancy, the use of a training heart rate to measure intensity during exercise has been determined to be a poor indicator of maternal exertion level. During early pregnancy, vessel dilation (a response to hormones being produced that relax blood vessels) and the resulting vascular underfilling will cause a woman’s heart to beat more rapidly to make up for the drop in volume. If she exercises at her usual prepregnancy level, her heart rate response will be much higher than normal because of her body’s attempt to pump blood through her system. As pregnancy progresses, blood volume increases to correct the changes in circulatory volume, causing cardiac output to rise. The amount of blood pumped into the system is increased, so the heart does not need to pump as rapidly to meet exercise needs. By late pregnancy, the combined effects of exercise and cardiac output may make it difficult for a pregnant woman to get her heart rate into a training range, even though she may feel that she’s working at a somewhat hard level.