Effects of Exercise On the Body
Overview
Every individual responds differently to exercise, whether pregnant or
not pregnant. Factors that influence the response to exercise include age, body composition, body weight and physical condition (3).
Studies have shown that pregnant women have to expend more energy in weight-dependent activities (e.g. walking or running) because of their increased weight gain. However, there is no evident change in energy expenditure for weight-supported activities such as stationary cycling or swimming (4).
Risk of Hypoxia (Lack of Oxygen to the Fetus)
One major concern of exercising during pregnancy is changes in uteroplacental blood flow. The concern is that the demands of exercising muscle divert blood flow away from the placenta, raising the theoretical risk of decreasing the oxygen supply to the fetus- hypoxia. This phenomenon is relatively difficult to study because there is no way to determine exactly how much blood is getting to the fetus. Researchers do know that the placenta is a 'volume-dependent organ,' which means that changes in blood volume have a greater effect on placental blood flow to the fetus than do changes in the nervous system that alter blood pressure (1). Some researchers claim that although the body selectively redistributes the blood supply to the most needy organs within the body during exercise, placental blood flow is favoured. This would ensure adequate oxygen supply to the fetus (3). A more recent report claims that increased maternal hematocrit (oxygen carrying blood cells) and oxygen extraction appear to prevent impairment of oxygen to the fetus (2).
Hyperthermia
Dehydration and hyperthermia are other conditions of worry that exercise places on the mother and fetus. Strenuous exercise will raise the internal body temperature of the mother which can have damaging effects on the fetus. Not drinking enough water adds to the overheating of the body, and so contributes to the onset of hyperthermia (1). Adaptive changes are made during pregnancy to prevent hyperthermia. Increased minute ventilation and skin blood flow augment heat dissipation and offset somewhat the potential hyperthermic effects of exercise. So although hyperthermia should be watched for, it is not a reason for ceasing to exercise- JUST BE CAUTIOUS! (2)
Balance
Balance skills required to participate in activities such as ice skating, skiing, and tennis are
affected by the enlarging uterus and the resulting changes in the center of gravity
(Click
for more info).
Joint laxity, and an increase in interstitial fluid volume during
pregnancy lead
to decreased kinesthetic sensation and diminished coordination. These
changes in the coordination
of a pregnant women increase the risk of ligament strains and bone fractures during a
fall. Activities such as contact sports, gymnastics, downhill skiing, and
in-line skating should
be avoided during the 2nd and 3rd trimesters for these reasons (1).
Trauma
Before 12-15 weeks gestation, the uterus is relatively protected by the bony structures of the pelvis. After 20 weeks gestation, when the uterus has expanded into an abdominal organ there is little or no protection for the developing fetus. At this time participation in competitive sports that pose a risk of trauma, such as contact sports like basketball or soccer, are very risky. Each women develops differently through pregnancy, so a good rule of thumb to follow is between 15-20 weeks participation in risky activities should be analyzed by the athlete, doctor, and coach (1).
The Supine Position
Pregnancy alters the number of safe positions to perform various types of exercise in. The mother should refrain from exercising in the supine position during the later stages of pregnancy (after pregnancy). In this position the pregnant uterus compresses the inferior vena cava, making venous return to the heart difficult. This can decrease blood flow to other areas of the body during exercise such as the brain and muscles, often leading to dizziness, and lightheadedness (1).
Exercise and the Fetus
A common worry of pregnant mothers is the effect of exercise on decreasing fetal birth weight.
Current studies show that moderate to vigorous exercise has little to no effect on fetal birth
weight. In a recent study, babies born to active mothers were the same birth weight or heavier
than the babies born to sedentary mothers. As long as the proper caloric intake is met, exercise
has relatively little effect on fetal birth weight (2).
REFERENCES
1. Araujo, D. (1997) Expecting questions about exercise and pregnancy. The Physician and Sportsmedicine,
25(4).
2. Artal, R. (1999) Exercise During Pregnancy: Safe and Beneficial for Most. The Physician and
Sportsmedicine 27(8).
3. Holstein, B. (1989, June). Exercise During Pregnancy. Idea Today, pp. 1-5
4. Wolfe, Larry A. (1993). Pregnancy. In J. Skinner, Exercise Testing and Exercise Prescription for Special
Cases (pp. 363- 385). Philadelphia: Lea & Febiger.
(Nutrition) (Exercise on your Body) (Effects of Pregnancy) (Exercise Guidelines)
(Precautions & Contraindication) (Benefits of Exercise) (Exercise Programs) (Perinatal Dangers)
(Hints for Around the House) (Tips for Fitness Instructors)
