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Should Pregnant Runners Go the Extra Mile?

June 6, 2017



pregnant woman drinking water at beach

When tennis powerhouse Serena Williams recently announced she was pregnant, commentators marveled at her Australia Open win in January, when she was eight weeks along – a time many women are dealing with overpowering fatigue and nausea.

That revelation has inspired pregnant athletes of all types, and has also raised questions, especially for runners and joggers. Running is one of the most common sports for recreational athletes, with more than 17 million Americans completing a running event in 2015.

In honor of Global Running Day on June 7, Susan M. Joy, MD, co-director of the Kaiser Permanente Sports Medicine Center in Sacramento, provides guidance – what pregnant runners can do, what they should watch for, and if they can indeed go the extra mile.

photo of female physician

Susan Joy, MD, co-director of the Kaiser Permanente Sports Medicine Center in Sacramento, California.

What exercise guidelines should pregnant runners follow?
For decades, pregnant women were told to take it easy. Truth is, during an otherwise normal pregnancy, it is far more problematic for both a mother and her unborn child if she is inactive, gains unnecessary weight and/or develops gestational diabetes than if she continues a smart training and running program.

In general, sports medicine experts recommend that an active runner with no pregnancy-related complications can continue to run during pregnancy, though they should not exceed the intensity of their pre-pregnancy activity. That said, it’s not necessarily the best time to push for a personal best or to start running.

Theoretically, intense exercise could divert blood flow to the working muscles and away from the placenta, which could adversely affect the developing fetus. However, many women have competed in runs late into pregnancy with no adverse outcomes, leading some to question the degree of potential danger.

It is very important for a woman to discuss her exercise habits with her OB/GYN at the start of (or even with her primary physician prior to) the pregnancy.

What physical changes should pregnant runners expect?
Pregnant runners need to be aware of several physiological changes.

With weight gain and a growing uterus, it can feel essentially like running with a bowling ball and thus affect mechanics or alter the body’s center of gravity. This may affect gait and posture and thus could lead to injury, like low back pain, by overloading different areas not accustomed to the changing movement patterns.

Later in pregnancy, the body sees an increase in relaxin, a hormone with effects like it sounds, to help relax tissue and prepare the body for delivery. This has been implicated as a possible risk factor for injury during pregnancy, but thankfully not generally a reason to stop running. Pregnant runners should rather pay attention to their gait patterns and stay attuned to any changes.

Stress-fracture risk increases after pregnancy while nursing due to temporary changes in bone metabolism. Thankfully the lowered bone mass during nursing is reversible once the mom stops nursing.

Should women consider limiting their heart rate?
There used to be recommendations for pregnant women to keep their heart rate lower than 140 beats per minute while exercising. However, there is really no data to support that restriction. If a woman is a fit runner prior to pregnancy, she can certainly start out with the same zones during an uncomplicated pregnancy. At times, some women have to alter their training zones for comfort later in pregnancy. At more moderate levels of training, the “talk test” is a helpful one for monitoring intensity. If a woman is able to run while carrying on a casual conversation, she is exercising at an appropriate level.

Thoughts on training for long distance while pregnant?
The question of whether to train for longer races while pregnant starts with one’s pre-pregnancy training. A “seasoned’ runner experienced with that training could plan to race while pregnant.

However, the reality for most women is that the longer distance races become more difficult as the pregnancy progresses, no matter how savvy the runner.

Also, heat and hydration need to be very carefully considered for longer distance runs as the developing fetus is depending upon the mother’s temperature regulation and circulating blood volume. Similarly, altitude effects can be magnified during pregnancy so women need to take that into consideration as well.

Generally, a woman with an uncomplicated pregnancy can continue with her pre-pregnancy running program after discussing any necessary modifications with her OB/GYN. Staying active in that case is far better for both the mother and her developing child.