Running Intensity when Pregnant: How to Adjust
How do I adjust my running intensity when pregnant? How do I know if I’m not overdoing it? How do I know if I’m running in a “safe zone” for me and my Baby?
Sometimes it’s hard to know what to do, whether to scale back or whether to keep on with your regular routine.
Lots of things change when you become pregnant. In relation to your running, your pace, posture and intensity will certainly be adjusting to your growing belly. (Looking for more pregnancy related info? Click HERE.)
Read on for research-based guidelines for adjusting your running intensity while pregnant.
Disclaimer: Although I am a physical therapist by profession, I am not YOUR physical therapist. This article is for informational and educational purposes only, does not constitute medical advice and does not establish any kind of therapist-patient relationship with me. I am not liable or responsible for any damages resulting from or related to your use of this information.
Did you know?
- Recreational and elite runners typically decrease how much they run (overall volume of training) during pregnancy
- Only 1/3 of women continue to run into their 3rd trimester and at a decreased running intensity compared to pre-pregnancy
- It has been shown that women who are pregnant and run, can increase their overall fitness during pregnancy
How do I know what my running intensity should be when pregnant?
There are a few ways you can gauge your intensity while running pregnant: Using heart rate, the “talk test” and/or RPE.
Let’s talk about each one of these a little bit more.
Using Heart Rate to Modify or Monitor Running Intensity
The American College of Obstetricians and Gynecologists (ACOG) exercise guidelines to keep HR <140bpm is outdated. This guideline is from 1985!!
Physiologically, there is an elevation in resting heart rate early on in pregnancy, so regular exercisers will typically notice this as the first sign they are pregnant.
HR then becomes more stable/normal as overall cardiac output improves. Not until mid-pregnancy (2nd trimester, on) can HR be used as a useful tool to gage running intensity.
In a 2006 study by Mottola, et al., they were able to use a treadmill test to predict VO2peak for pregnant women. They tested women between the ages of 20 and 39 and between 16 and 22 weeks pregnant. This stage of pregnancy was chosen because typically the first trimester symptoms like nausea and fatigue have subsided and most women have been cleared to exercise. Here are the guidelines that they came out with:
Fit Pregnant Women
If you are a “fit” pregnant woman (defined as having a VO2 peak >75th percentile for age group):
And between the ages of 20 and 29, exercising at 60-70% of aerobic capacity, you should exercise at a target HR of 145-160bpm.
Or between the ages of 30 and 39, target HR should be between 140-156bpm.
Active Pregnant Women
Now if you fall into the second category and are an “active” pregnant woman (defined as having a VO2peak between the 25th and 75th percentile for age):
And between the ages of 20-29, target HR should be between 129-144bpm.
Or between the ages of 30-39, target HR should be between 128-144bpm.
No, that’s not a typo, the HR ranges are essentially the same for these two “active” groups.
It should be noted that they also recommended HR training should be used in conjunction with the “talk test” and the RPE scale (more on this below).
Using your Known Max HR
Another study conducted by Salvesen et al. in 2011, tested 6 Olympic level athletes (ages 28-37) at 23-29 weeks pregnant while they ran at 60-90% of max oxygen consumption on a treadmill.
They monitored maternal-fetal circulation and determined that running at greater than 90% of maximal HR may compromise fetal HR and overall well being. So the take-away here is to stay below 90% of your maximal HR (ONLY if you know your pre-pregnancy max HR!).
Using the “talk test” to Modify or Monitor Running Intensity
Most MD’s are not familiar with the current guidelines, which have been updated as recently as April 2020 by the ACOG.
Because HR varies throughout pregnancy, ACOG now recommends using the Borg Rating of Perceived Exertion (RPE) Scale and the “talk test” rather than a blanket HR target of the original <140bpm.
What is the “talk test”?
The “talk test” means that you should be able to carry on a conversation without being short of breath while exercising. If you can do this, then you’re likely not over-exerting yourself. And therefore, exercising at a safe intensity for you and Baby.
Using the RPE scale to Modify or Monitor Running Intensity
There are actually two RPE (Rating of Perceived Exertion) Scales. This first is the Borg Scale which starts at a 6 and goes up to a 20. A 6 is equivalent to no exertion at all and a 20 is considered maximal exertion.
On this scale, exercising at moderate intensity correlates with a “somewhat hard” level, somewhere between a 12 and a 14. These levels are deemed to be safe for pregnant exercisers.
On the 10 point RPE scale, where 0 is no perceived effort and a 10 is a maximal effort, intensity should be targeted between 3 and 4 for pregnant exercisers.
Running Intensity Take Away:
You can use HR as a measure:
- keep it between 129 and 160bpm, or
- keep it below 90% of your max pre-pregnancy HR (if you know it),
- and only use HR as a measure from your 2nd trimester onward
Using RPE:
Keep it between a 12 and 14 (on the 6-20 scale) or a 3-4 (on the 0-10 scale)
Using the “talk test”
Make sure you can maintain conversation while exercising
Really, it’s best to use a combination of the intensity measures described above, rather than just one alone.
So how do I apply this to my running?
You definitely shouldn’t be exercising at your maximum intensity while pregnant.
Your goal of running while pregnant should be to stay moving for as long as you want or is comfortable.
You really should not have any pace goals during pregnancy, unless you can meet the intensity guidelines as stated above.
In order to decrease running intensity, you may need to do one or more of the following:
- decrease your overall pace
- decrease the overall duration of your runs
- run non-continuously, so you’re doing some run: walk intervals for recovery and comfort
A final word on running intensity:
Most resources suggest that pregnant women should exercise at no more than at a moderate or somewhat hard intensity.
However, ACOG guidelines state that
“Although upper level of safe exercise intensity has not been established, women who were regular exercisers before pregnancy and who have uncomplicated, healthy pregnancies should be able to engage in high-intensity exercise programs…with no adverse effects. High intensity or prolonged exercise in excess of 45 minutes can lead to hypoglycemia; therefore, adequate caloric intake before exercise, or limiting the intensity or length of the exercise session, is essential to minimize this risk.”
In the end, most women who are running and pregnant, self-modify anyway as pregnancy progresses. The belly gets bigger, things feel more strained or difficult, and that’s ok.
Do what you can within the confines of what your body will allow. If you need to make adjustments, do it. If you need to transition from running to walking at any point, do that too.
Most importantly, make sure you’re still enjoying getting out there! And remember, running will still be there on the other side waiting for you after your birth recovery.
Questions/Comments
I’d love to hear from you. How have you had to modify your running as your pregnancy progressed?
Love this post? Save the tips here. PIN IT!
Other Articles of Interest:
FREE Guide: Strengthening for Pregnant Runners
How Pregnancy Affects Running Posture
