Pregnancy & postpartum
Do you need to keep your heart rate under 150 while pregnant?
Pregnancy Rules, Revisited: Episode 2
If you've ever finished a workout while pregnant, glanced at your watch, and felt a little panic because your heart rate crept past 140 or 150, this one's for you. It's one of the most common rules I hear, and it causes a lot of unnecessary stress.
Where the rule came from
Back in the 1980s, exercise guidance for pregnancy included a heart rate cap of 140 beats per minute. It was removed from American guidelines in 1994, but it has hung around in conversations, online forums, and even some fitness classes ever since.
Why one number doesn't work
Your resting heart rate naturally rises during pregnancy as your body pumps more blood to support you and baby. On top of that, heart rate varies a lot from person to person based on age, fitness, and genetics. A number that feels easy for one woman could be a hard effort for another.
What the guidelines say now
The 2019 Canadian Guideline for Physical Activity Throughout Pregnancy, led by Dr. Margie Davenport and colleagues, recommends at least 150 minutes of moderate activity per week and uses effort-based checks instead of a heart rate cap. The simplest one is the talk test. If you can still carry on a conversation, you're likely in a good range. Many women who were active before pregnancy can also continue more vigorous exercise with guidance from their provider.
Where the caution came from
Much of the worry about high-intensity exercise traces back to one very small, early study of elite athletes, which saw temporary changes in baby's heart rate during their very hardest efforts. It was an important starting point, but it was too small to tell us much on its own.
What newer research says
Newer, better-designed research from Dr. Davenport's lab found that short bursts of high-intensity intervals were well tolerated by both mom and baby, with no drops in baby's heart rate. And a review that pulled together many studies on vigorous aerobic exercise later in pregnancy, including heart rates above 150, found no adverse effects on baby, along with a slightly lower risk of premature delivery. Your very hardest, sustained efforts still deserve an individualized plan, but the research is far more reassuring than the old rule suggests.
Signs to stop and check in with your provider
Regardless of heart rate, stop exercising and contact your provider if you notice shortness of breath that doesn't improve with rest, chest pain, regular painful contractions, vaginal bleeding, fluid leaking, or dizziness or faintness that doesn't go away.
What this looks like for me
I'll be honest: my aerobic fitness has struggled during this pregnancy. Efforts that used to feel easy can feel really challenging now, and as an endurance athlete, that can be discouraging at times. Letting go of the numbers and paying attention to effort and how I feel has helped me keep moving and give myself some grace along the way.
The takeaway
Instead of chasing a number, pay attention to your effort, your breathing, and how you feel during and after your workout. As always, your training through pregnancy should be discussed with your provider based on your individual needs and goals.
And if you'd like help building a plan that fits your training, that's exactly what I do. Reach out through the interest form or DM me ALIGNED on Instagram.
Research referenced
- Wowdzia et al., 2023. Maternal and fetal cardiovascular responses to high-intensity interval and moderate-intensity continuous exercise during pregnancy. PMID 37213048
- Beetham et al., 2019. The effects of vigorous intensity exercise in the third trimester of pregnancy: a systematic review and meta-analysis. BMC Pregnancy and Childbirth. PMID 31391016
- Salvesen, Hem, and Sundgot-Borgen, 2012. Fetal wellbeing may be compromised during strenuous exercise among pregnant elite athletes. British Journal of Sports Medicine. bjsm.bmj.com/content/46/4/279
- Mottola et al., 2019 Canadian Guideline for Physical Activity Throughout Pregnancy. Read the guideline (PDF)
This post is general education, not medical advice. It isn’t a substitute for an evaluation by a qualified healthcare provider.