When pregnant, your heart rate should not rise above 140 beats per minute.
About 15 years ago, I was at a kickboxing certification when my friend announced she was pregnant. The other members of the training class told her that while exercising she was essentially putting her baby in a pot of boiling water.
Fast forward to about five months ago when another friend asked me to sub her spinning class. I love teaching classes so subbing for her was no problem. About a week later, she told me she was pregnant and having me sub because she could not keep her heart rate under 140 beats per minute when she was spinning.
The picture that these two stories paint for me is that in over 15 years, so many misconceptions still revolve around exercising while pregnant. Further, many OB/GYNs are giving outdated advice about exercise to their patients. Sadly, the friend I subbed that class for has two degrees in exercise science so the word is definitely not getting out of the masses.
If you read the first myth, you understand that women have not been exercising intensely for very long. In the 50s and 60s, women could not even play both offense and defense in basketball. As a result of this, there was no need for an exercise guideline for pregnancy. Once women started to become more and more active, the American College of Obstetricians and Gynecologists (ACOG) believed that since internal temperatures rose while exercising, placental temperature must also rise and therefore, limits were put on exercise intensity. They believed that the higher the intensity of the exercise, the worse it was for the baby. However, there were no studies or any scientific research to back their claims. Once research began in this field, we documented a well-designed internal placental system that is very capable of not over-heating and remaining safe for the growing fetus.
For years, OB/GYNs have set an arbitrary number of 140 beats per minute as the ceiling for exercising while pregnant. My belief is that they derived this number by assuming the average pregnant was 20 years old and 140 would equate to 70% of heart rate max. [(220-age) x 0.70]. Clearly, there are some issues there. First, not all people who are pregnant are 20. Secondly, the equation to predict maximum heart rate is only a prediction and cannot be generically applied to all people. Further, there is no evidence that exercising over 140bpm will do any harm to the mother or the baby. Finally, taking heart rates while exercising is not only difficult, it can also be highly inaccurate unless taken by someone who is skilled in doing so. The monitors on the equipment at the gym is highly variable and cannot be used with accuracy.
Thanks to the work of Dr. James Clapp, Dr. Raul Artal, and Dr. Daniel Vigil, exercising through pregnancy has been researched and documented and finally, the guidelines have been revised. The governing body for exercise and exercise prescriptions is the American College of Sports Medicine (ACSM) and their current comment regarding the intensity of exercising while pregnant is as follows:
Intensity: Pregnancy is probably not a time for serious competition. For women
who are continuing their regular exercise regimen during pregnancy, exercise
intensity should not exceed pre-pregnancy levels. The intensity of exercise
should be regulated by how hard a woman believes she is working. Moderate
to hard is quite safe for a woman who is accustomed to this level of exercise.
In exercise science terms, we call this monitoring of how hard you are working “ratings of perceived exertion,” or RPE. This chart, seen below, can help determine how hard you should work while exercising. It is easier than taking a heart rate while moving and it helps to keep you in check. Pregnant women should aim to keep their RPE in the moderate to high range or below 17.
As mentioned in myth #1, exercising while pregnant can be for most everyone. However, always consult your doctor before beginning a program, but do not be afraid to question him/her if he/she gives you the 140bpm guideline. The ACOG has revised that guideline, but not all OB/GYNs have listened.
And again, do not exercise if you have one of the contraindicated reasons:
· Pregnancy induced hypertension (high blood pressure)
· Pre-term rupture of membranes
· Pre-term labor during the prior or current pregnancy
· Incompetent or cerclage placement
· Persistent second or third trimester bleeding
· Placenta previa
· Intrauterine growth retardation
If you find you have any of the following, you definitely need to be discuss exercise with your doctor before beginning a new exercise program:
· Chronic hypertension
· Thyroid function abnormality
· Cardiac disease
· Vascular disease
· Pulmonary disease
Once you have determined an appropriate exercise intensity for you, be aware if the following situations occur and report them immediately to your doctor:
· Abdominal pain
· Vaginal bleeding
· Rapid heartbeat
· Muscle weakness
· Shortness of breath
· Decreased fetal movement
In almost all circumstances, the benefits to exercising while pregnant outweigh the risks, we will look at that myth in the next article.