Anatomical and physiological changes of pregnancy and exercise

INTRODUCTION

In the past two decades, a large quantity of data has provided evidence that historical, restrictive guidelines for exercise in pregnancy can and should be modified. In the absence of medical or obstetrical complications, pregnant women should be encouraged to continue and maintain an active lifestyle during their pregnancies. Regular aerobic exercise during pregnancy appears to maintain or improve physical fitness [1]. Maternal physiological adaptations to pregnancy should be considered, however, and some modification in exercise routines or activity patterns may be necessary because of the normal anatomical changes in pregnancy and fetal requirements.

Current information on physiological responses to exercise during pregnancy, including physiological variables that are evaluated during exercise, will be reviewed here. These variables are assessed to determine fitness, ability to engage in various forms of exercise, and corresponding metabolic adjustments. Recommendations for exercise during pregnancy and the puerperium are discussed separately. (See "Recommendations for exercise during pregnancy and the postpartum period" and "Exercise physiology".)

ANATOMICAL CHANGES

Pregnancy results in anatomical changes or conditions which could have an impact on a woman's ability to engage in physical activities. The most significant pregnancy induced change is the expansion of the uterus to accommodate the growing fetus and products of conception. The uterus expands from a strictly abdominal organ at 12 weeks to become an abdominal organ for the remainder of gestation.

The expanding uterus causes an anterior cephalad shift in the center of gravity and progressive lumbar lordosis. Lumbar lordosis leads to low back pain in 40 to 50 percent of all pregnant women [2]. To compensate for the lumbar lordosis, pregnant women increase the anterior flexion of the cervical spine, resulting in kyphosis. Prominent kyphosis can be associated with paresthesias and motor weakness over the distribution of the ulnar and/or median nerve [3].

Although prominent lordosis and kyphosis can interfere with the ability to engage in physical activities, physical therapy, weight control, and specific exercise routines can minimize or prevent these problems. Avoiding excessive weight gain is important because a 20 percent weight gain will increase the biomechanical force exerted on a joint by as much as 100 percent, thereby increasing the risk of joint injuries during certain physical activities [4]. Physical therapy and exercises that strengthen muscles at major joints may prevent or minimize this risk. (See "Weight gain in pregnancy".)