For much of recent history, pregnant women have been treated as if they had an illness and were confined for fear that any physical activity would harm the fetus. Our understanding of pregnancy, exercise, and health has come a long way.
For the most part, running during pregnancy is safe and even beneficial, especially during the first two trimesters. Exercise during pregnancy has been associated with a reduced risk of developing certain obstetrical complications, including preeclampsia, pregnancy-induced hypertension, and gestational diabetes. It's also associated with better tolerance of labor and a lower risk of C-section childbirth.
- To describe the specific characteristics of pregnancy.
- To understand how pregnancy affects a woman’s running.
- To give recommendations for running during each trimester.
Frequent complaints during pregnancy, including nausea, heartburn, insomnia, varicose veins, back pain, swelling of the extremities, shortness of breath, and leg cramps are reduced in women who remain active while pregnant.
Despite the liberalization of medical guidelines for running during pregnancy, there are certain medical conditions, either pre-existing or that develop during pregnancy, that would prohibit running while pregnant, including heart and lung disease, persistent bleeding in the second and third trimesters, and ruptured membranes. Several other conditions require careful evaluation of the risks and benefits before continuing with a running program, including severe anemia, being extremely underweight, uncontrolled thyroid disease, and inappropriate fetal size and development.
When running while pregnant, always be aware of warning signs, including vaginal bleeding, breathlessness at rest or out of proportion to the effort, dizziness, headaches, chest pain, racing heart rate, muscle weakness, significant swelling in feet or legs, uterine contractions that occur more than 30 minutes after running, decreased fetal movement, pelvic, hip, or back pain, chronic fatigue, and leakage of fluids.
Although women might not look pregnant during the first trimester, most women certainly feel pregnant. Shortly after conception, hormone levels change and the body and uterus adapt to support the growth of the placenta and developing fetus. These changes result in the symptoms that many women experience in the first trimester, including fatigue, morning sickness, and headaches.
Cardiovascular changes, including an increase in maternal blood volume and resting heart rate and stroke volume, occur early in the first trimester. This increase in maternal blood volume allows more oxygen and nutrients to be delivered to the fetus. Stroke volume begins to rise in the first 6 to 8 weeks of pregnancy and increases as much as 10 percent by the end of the first trimester. Resting heart rate increases by 10 to 15 beats per minute.
Since fetal size and, therefore, its oxygen and nutrient needs are small in the first trimester relative to the other trimesters, increases in cardiac output create a circulatory reserve, which is why most women can tolerate running in the first trimester. Some women feel even better running in the first trimester than prior to pregnancy.
Base intensity on effort rather than pace. The pregnancy-induced symptoms in the first semester, including nausea, vomiting, and fatigue, may require an adjustment to the training. If your client experiences morning sickness, decrease her training by 5 to 10 percent and tell her to run at a different time of day.
While women shouldn't race intensely during pregnancy, there are many women who do so early in pregnancy. There are also many case studies of elite athletes tolerating high levels of endurance and interval training without compromising fetal growth or complicating their pregnancy.
During the second trimester, the size of the uterus increases rapidly to accommodate the growing fetus. Accompanying this rapid growth, pregnancy can become more uncomfortable as the woman’s body makes room for the growing uterus and the muscles and supporting pelvic structures are stretched. By the end of the second trimester, the fetus grows to almost four times the size it was at the end of the first trimester. Maternal and fetal oxygen and nutrient needs increase during this time of fetal, uterine, and placental growth.
Cardiac output continues to rise during the second trimester. By 20 to 24 weeks, cardiac output is 30 to 50 percent greater than before pregnancy. By the middle of the second trimester, stroke volume peaks by as much as 30 percent compared to pre-pregnancy levels. Total blood volume continues to rise. These two adaptations allow for adequate nutrients and oxygen to be supplied to the fetus, both at rest and when running.
During pregnancy, blood flow is distributed preferentially to the uterus, kidney, and skin and increases with gestational age. Running results in a redistribution of this blood flow away from the uterus to skin and exercising muscles and is directly proportional to the workout intensity.
These opposing effects could compromise blood flow to the fetus and affect fetal growth and development. However, thanks to the increases in cardiac output and blood volume and placental adaptations that result in greater extraction of oxygen and nutrients, these effects are minimized, particularly with running at moderate intensity. Studies have shown that placental adaptations are greater in women who continue to exercise through the second trimester.
Choose running routes and surfaces that are flat with few obstacles to minimize the risk of falling. In most cases, training can be kept the same in the second trimester as in the first, and total weekly running mileage can even be increased by 5 to 10 perent if your client can tolerate the mileage without increased fatigue, shortness of breath, or back or joint pain.
As the uterus gets larger, a woman’s center of gravity shifts forward, making her more prone to lose her balance. If your client has a history or is at risk of preterm labor, proceed cautiously with strenuous activity in the second trimester.
By the third trimester, most physiological adaptations have peaked. Running will be impacted by the decrease in these adaptations and by the enlarging uterus, weight gain, and the hormones that prepare the woman’s body for delivery. Although total blood volume continues to expand, the increase in heart rate plateaues by the third trimester, and stroke volume and cardiac output begin to decrease.
The enlarging uterus continues to push on the diaphragm, causing a decrease in vertical chest height. As a result, the volume of air that remains in the lungs after each exhalation falls considerably in late pregnancy. This causes a decrease in oxygen reserve. Higher intensity and prolonged running are more challenging.
Only some women are able to run through the end of their pregnancy. Any running in the third trimester should be done in moderation. While the fetus will be buoyed by the movement of the uterus and amniotic fluid when running, reduce the impact if your client experiences low back, hip, or other joint pain.
The better shape a woman is in before delivery, the easier it will be for her to get back in running shape after her baby is born. However, the third trimester is often a time to alter the running program. Every runner is different and alterations that you make to your client’s running depend on how she feels. Many women runners cut down on the frequency and duration of their running. Others substitute non weight-bearing activities. If your client is able to run during her third trimester, limit her runs to 30 to 60 minutes at a moderate intensity.
If your client can’t run, stationary cycling or swimming are good alternatives and can be substituted using the same frequency, intensity, and duration. Swimming is a particularly good alternative to running, as the buoyancy of the water decreases forces on joints, minimizes heat stress, and controls leg swelling.
Hopkins, S.A. and Cutfield, W.S.. (2011). Exercise in pregnancy: Weighing up the long-term impact on the next generation. Exercise and Sport Science Reviews. 39(3): 120-127.
Karp, J.R. and Smith, C.S. (2012). Running for Women. Champaign, IL: Human Kinetics.
Pivarnik, J.M. and Mudd, L.M. (2009). Physical Activity During Pregnancy and Postpartum:
What Have We Learned? President’s Council on Physical Fitness and Sports Research Digest. 10(3).
Smith, C.S. and Van Andel, R. (2001). Pregnancy and north american lifestyles Exercise, work, and diet in pregnancy. Clinics in Family Practice. 3(2).