Disclaimer: This post does not constitute medical advice, and is based on my opinion and my research. Always check with your doctor about your exercise recommendations.
I recently was browsing the website for the hospital associated with my doctor, and noticed there were some educational pages under their “maternity” section. One of the pages was on exercise, and I was a bit shocked to see that the page still stated that pregnant women should raise their heart rate “no more than 140 beats per minute during exercise.”
The ACOG actually removed the 140 beats per minute recommendation from their guidelines back in 1994. Outdated information drives me a little crazy, and this particular piece of information is prevalent in so many places – baby forums, doctor’s websites, patient education handouts, etc. In fact, a 2010 study of 93 practicing physicians and midwives found that 64% of all respondents believed that maternal exercise heart rate should not exceed 140 beats per minute. This was more than 15 years after the recommendation was removed!
[To my doctor’s office credit, they don’t recommend this number. When I brought up that this recommendation was still on the hospital website, they were surprised and said they’d look into getting it taken down.]Instead, the ACOG (along with other organizations) state that with your doctor’s go ahead, you should be able to continue the exercise regimen you had before you were pregnant, perhaps with some modifications. You should not exercise until absolute exhaustion, and you should be able to maintain a conversation.
For example, the Mayo Clinic states…
“Years ago, some experts recommended a heart rate of no more than 140 beats a minute for exercise during pregnancy. Today, however, heart rate limits aren’t typically imposed during pregnancy. For healthy women, the Department of Health and Human Services recommends at least 150 minutes a week of moderate-intensity aerobic activity preferably spread throughout the week without any specific heart rate limits.”
For me, a conversational pace is somewhere around 160 to 170 beats per minute – quite a ways above the 140 guideline. Despite having been pretty into fitness for the last five or six years, my heart rate still jumps pretty high during cardio. That’s normal for me. In fact, 2 minutes into my run last weekend, my heart rate was already over 150. If I stuck to 140 beats per minutes, I’m not sure I could even do a brisk walk from the back of the parking lot into Target (exaggerating a bit, but you get my drift).
Plus, I’m someone that likes to stick with research. And from what I’ve seen, there is no research out there that shows exceeding 140 beats per minute is dangerous to the fetus. Most research shows the many benefits of exercise – improved mood, reduced risk of gestational diabetes (or better glycemic control if you have gestational diabetes), better sleep quality, and more.
There are only a few recent studies that look at heart rate intensity, and only one I could find that had a negative effect with intense exercise. That particular study was among 6 Olympic elite athletes, and only saw a negative effect on the fetus (additional reduced blood flow compared to baseline) when the athletes were above 90% of their max heart rate. So, essentially, you had hardcore athletic women, and if you made them push themselves to the brink, there was a reduction in blood flow to the baby (and just to note, even that normalized quickly after exercise). But there were no negative effects found below 90% of max heart rate. Plus, an elite athlete working above 90% of their max heart rate is not working out at a conversational/non-exhausting pace – they were likely pushing themselves hard.
Of course, exercise recommendations are certainly individualized and beneficial to check with your MD regarding your specific situation. Some women will have certain medical conditions that prohibit any exercise during pregnancy. For those that can exercise, keep in mind there are a considerable number of factors that influence how your body responds to activity – and as such, how your heart rate responds. And if you never exercised before pregnancy, your doctor may recommend starting with low intensity exercises like walking or swimming.
The takeaways:
- Talk to your doctor about exercise recommendations. If they mention 140 bpm, inquire more about why they recommend that number, as ACOG no longer recommends a heart rate restriction.
- Unless you have a medical condition that prohibits exercise, you should be able to keep up with your pre-pregnancy exercise routine without specific heart rate restrictions (in this sense, I’m talking about cardio – there are potentially modifications to make with heavy strength training, but that’s another post).
- Exercise at a pace that seems comfortable to you – one where you can still get through a conversation, and where you are not pushing yourself to exhaustion.
- If you really want a specific number to stick to, the research only suggests athletes should avoid exercising above 90% of your max heart rate. You can guess your max by using the 220 minus age formula, though this isn’t super accurate. (For example, this puts my max heart rate around 190, and it’s definitely higher than that. I can easily go up to 200-210 when I push myself running outside of pregnancy).
Share with me: What have your pregnancy exercise experiences been like?
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My doctor had given me a restriction of 110 bpm in the first trimester, indicating that there are concerns of birth defects in the baby if the mom’s core temperature is elevated too high. I was then given a restriction of 140 in my second trimester. It’s been a challenge as I was a moderately active person pre-pregnancy, even teaching some fitness classes. Due to the restrictions I’ve limited myself to prenatal yoga, light elliptical, powerwalking treadmill, light machine weights, and swimming or water aerobics classes. I’m still very frustrated by the 140 bpm because I know I can do soo much more.
Hi Katie! Thanks so much for commenting. I completely get being frustrated – I would be too. Standard disclaimer – I’m not a doctor, so of course you would want to follow what your doctor recommended.
In general this topic frustrates me, because there’s no current medical guidelines to stay under a certain heart rate UNLESS there are contraindications with the mother (like a history of certain health conditions). With regards to core temperature rising and birth defect risk, that is true, but as far as I know there is no hard and fast rule that X BPM equals the amount of temperature increase related to risk. And I would imagine that’d vary highly across each individual based on their current resting HR, max HR, and level of fitness. In general, those risks during exercise can be minimized/eliminated by exercising at a conversational pace, staying hydrated, and avoiding exercise in extreme temperatures.
But again, your doctor knows your medical history far better than an internet blogger, so certainly follow what they tell you – he could have a good reason to make the recommendations based on your individual history. 🙂 But if you’re questioning why you have that restriction, you could most definitely bring it up with them in your next appointment!