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I’m pregnant. Should I be monitoring my heart rate when I exercise?
This is a super common question and something that causes a lot of stress and confusion for pregnant women.
And you know what? The recommendation for pregnant women to keep their heart rates below 140 bpm was big in the 90s. But just like big perms, shoulder pads and flowery maternity dresses, things go out of date.
And these guidelines have certainly gone out of date.
In this episode, I’m diving deep into why monitoring your heart rate during exercise is oh-so 1990s and I’ll break down what you should be doing instead.
Hello, and welcome to episode 8 of The Mana Women’s Wellness Podcast. I’m your host, Rachel and today I wanna do something a little different and we’re going to have a Q&A Wednesday. And we’ll call it Q&A Wednesday because this podcast episode is coming out on a Wednesday, and I’m not super creative. But more importantly, I am answering a question that’s been sent to me.
So thank you Danni for asking me a question, and if there’s something you want to know about please feel free to send me a DM on Instagram and I’ll do my very very best to answer it on an upcoming episode.
So, Danni asks – I’m currently 5 months pregnant. Should I be monitoring my heart rate when I exercise? I’ve been reading a lot about keeping it below 140 bpm and I’m wondering if this is something I should be sticking to?
Now this is a really common question that is asked over and over and over and there is a lot of conflicting information out there about this one.
At the time I’m recording this episode it is 2020. The recommendation for pregnant women to keep their heart rates below 140bpm was big in the 90s. I was born in 1990, so that means this recommendation is about 30 years old.
Now this means that this recommendation was the in-thing when my mum was pregnant with me. I’ve never really asked her, but I’m betting she wasn’t at the gym getting her sweat on while she was pregnant with me. I’ll tell you this much though, I’ve seen pictures of her pregnant though and she had a mad perm and wore flowery maternity dresses with big lacy collars. It was surely trendy at the time, but my point is that things go out of date.
There were previous pregnancy exercise guidelines released by the American College of Obstetrics & Gynaecology (who we call ACOG) and these guidelines recommended that for exercise during pregnancy, women kept their heart rate below 140bpm. However, more research discovered that like most things in pregnancy, and in life, the heart rate response to exercise varies considerably between women.
So a set target heart rate isn’t appropriate for monitoring exercise intensity in all pregnant women. And so, 10 years later in 2002, ACOG released a new set of guidelines which are still current at the time I’m recording this and here they recommended using something called the Borg Scale so women could monitor exercise intensity and not worry about tracking their heart rate throughout.
I’ll come back to the Borg Scale soon, but first I want to dive deeper in to how our heart rate changes during pregnancy.
The entire circulatory system – and by this I mean your heart, blood vessels, arteries, veins – all of this changes early on in pregnancy to support the needs of both mother and baby. These changes can begin as early as 4-5 weeks gestation and may peak during the second and early third trimesters.
It is these changes in the circulatory system that cause many of the unpleasant symptoms of pregnancy, so nausea, light-headedness, fatigue, cravings, constipation, bloating and that highly annoying and frequent need to urinate.
Elevated hormone levels during pregnancy cause an increase in both blood volume and the elasticity of blood vessels. As a result, there is a reduced amount of blood pumped out by, and returning to, the heart. This phenomenon is known as “underfill” and is the cause of many early pregnancy symptoms.
Gradually the body will adapt to these cardiovascular changes, which is why most side effects and symptoms resolve after the first trimester.
Cardiac output, the volume of blood pumped out by the heart, may increase by as much as 40% during pregnancy. This means women have around 1.5 extra litres of blood in their circulatory system. High blood volume maintains good blood flow to the uterus and placenta to provide nutrition and oxygen to your growing baby, and it also helps to reduce the impact of blood loss that you experience during birth.
Interestingly, despite the increase in blood volume, red blood cell numbers remain the same, which means that levels are lower relative to the amount of blood in the entire circulatory system. Red blood cells contain haemoglobin which carries oxygen and iron around the body. Increased blood volume basically ‘dilutes’ the amount of red blood cells in the blood. This means iron and oxygen levels are also reduced, and this is the cause low iron levels (or anaemia) and fatigue which are both really common during pregnancy.
Heart rate (beats per minute) also increases, which is why pregnant women do not need to work as hard to increase their heart rate when exercising. This is why previous ACOG guidelines suggested that pregnant women take it easy when exercising.
Here’s a fun fact for you – Women who exercise regularly may actually realise they are pregnant sooner than a pregnancy test would reveal because their heart rates may increase more than usual during a workout. How is that for knowing your body? I love it!
During exercise your baby often sleeps, so it is normal to feel less movement when you are being active. This is a safety mechanism to draw blood away from the baby and back to the mother’s working muscles. When you stop exercising, blood returns to baby and so increased movement is felt once again. This is why a good, proper cool-down is essential after exercising to allow that blood flow to return to baby.
Previous guidelines for exercising during pregnancy recommended keeping your maximum heart rate below 140 beats per minute.
However, a woman’s heart rate response will change during her pregnancy. It increases initially during early pregnancy, then gradually falls throughout later pregnancy.
So what’s the problem with the old and outdated guidelines? They assume that all pregnant women with a heart rate of 140 bpm are exerting exactly the same amount of effort during physical activity. As wise women, we know that all women are different, so a set target heart rate is not appropriate for monitoring exercise intensity in all pregnant women.
You’ve got to keep in mind that the appropriate workout intensity for you will depend on how physically fit you were before pregnancy. If you were very unfit, you may have to keep your heart rate well below 140 bpm, while fitter women and gym junkies may be able to reach a heart rate of up to 170 bpm with no negative effects.
And so, in 2002, ACOG released some newer guidelines. And for the past 20 years, they have continued to release updates about their recommendations for safe exercise during pregnancy. And coincidentally, ACOG released their latest opinion piece in April of this year.
So, what’s changed? In 2002, these guidelines started to recommend using the Borg Scale that I talked about earlier – the Borg Rating of Perceived Exertion so women can monitor their exercise intensity without having to track their heart rate during workouts.
This means that women are now encouraged to work in a target training zone of 12 to 14 on the Borg Scale, or a “Somewhat hard” intensity. Now if you head over to today’s show notes I’ll make sure include a picture of The Borg Scale so you can see what this scale looks like and how it works. So that will be over at www.fertilityco.com.au//8 The Borg Scale allows women to self-monitor their exercise intensity with confidence. Because like anything else, it’s all about listening to your body not focusing on a bunch of numbers on a screen. Using the Borg scale, you can adjust the intensity of your workout if it feels like you’re working too hard, and you can also modify your workouts as your pregnancy progresses and your physical fitness and comfort levels change.
The current exercise guidelines are so much better because they take into account the individual differences in heart rates and physical fitness among pregnant women and eliminates that one size fits all approach. The Borg Scale gives women a far more accurate idea of how hard they should be working during pregnancy.
Athletes or intense exercisers who are used to pushing through discomfort while exercising may be encouraged to wear a heart rate monitor to track their exercise intensity. Athletes may have more difficulty sticking to the Borg Scale and if this sounds like you, I’d recommend working really closely with your doctor or coach to really work out what is most suitable and safe for you.
Now of course, if your doctor has specifically told you to keep your heart rate below a set point during exercise, please follow their advice. Your doctor’s individual recommendations are always going to overrule what you’ve heard in a podcast. Right?
Well, being a very clever and important organisation, they acknowledge that physical activity and exercise is extremely important during all phases of life – and this includes pregnancy. Long gone are those days of pregnancy being a condition that women needed to be on bed rest for 9 months.
The guidelines say that physical activity and exercise in pregnancy carries minimal risks and have been shown to benefit most women, although some women will need to change their exercise routines because of the normal changes that occur during pregnancy both inside our bodies, like changes in our circulatory system, as well as the obvious anatomical changes – like the growing belly that makes lying on your stomach a little difficult.
Now, you’ll be working closely with a medical team during your pregnancy and it’s really important that you speak with your doctor and get that all clear before starting an exercise program. This is particularly important for women have never really exercised before and for those who are used to exercising at a high intensity. But medical clearance is essential for all women because there are certain medical conditions that mean that you should NOT be exercising during pregnancy.
So, once you’ve gotten the all-clear from your doctor, current recommendations for women with uncomplicated pregnancies are 20-30 minutes of moderate intensity exercise at least 5 days a week. You should not exercise for longer than 45 minutes at a time. Rest days are just as important as active days to allow your body to recover and repair.
Work around your schedule to stay consistent. You can divide your workouts into three separate 10 minute sessions if this is more convenient to you – it all still counts! Make sure you include a combination of cardio, stretching and strengthening exercises in your workouts.
If you already have a moderate exercise routine, keep it up. Your pre-pregnancy workouts can be modified by reducing the frequency, intensity and duration of your exercise sessions.
If you are not used to doing regular exercise, walking 4-5 days a week is an easy way to start. Start walking for 10 minutes, then gradually work up to 30 minutes. Take it slow and steady.
And remember – Don’t rely on monitoring your heart rate as a way to monitor how hard you are working. Your heart rate will change throughout your pregnancy and so it is not a reliable guide. Remember, the 90s was a long time ago!
The most important advise I can give you is to listen to your body. Stop or rest if you start to feel tired or unwell to prevent overheating or getting injured. Make sure you warm up before and cool down afterwards, and do not work too hard. A super simple check of your exercise intensity is the “Talk Test”. If speaking in a full sentence while exercising is hard because you are too breathless and fatigued, you are working too hard.
Another good test is to take note of your body’s response to exercise. If you are sweating, your body is trying to cool down and so you are working hard enough. If you are short of breath and red in the face you are working too hard. Remember to work at your own pace and do not compete if you are in a class.
Closely monitor your body’s response during and immediately after exercise to make sure your workouts aren’t causing any issues that could affect baby’s development. Pay particular attention to changes in your body temperature, hydration and blood sugar levels. And take note of baby’s behaviour during and after exercise. Remember that baby often falls asleep during exercise, and so reduced movement is normal. Baby will then become more active when your workout has finished.
You should be able to feel your baby moving around within 20-30 minutes after you have stopped exercising. Feeling baby moving and even contractions of your uterus are great indicators of baby’s wellbeing. If you are ever concerned, consult your doctor.
Athletes or women who are used to intense workouts might feel a little frustrated by the limitations that pregnancy places on their physical activity. They will likely experience reduced agility, slower running speed and generally just moving in a sluggish way. Don’t get too discouraged and don’t overdo it! Regardless of your level of physical fitness, you cannot avoid the effects of pregnancy on your soft tissues and joints and you will be at increased risk of injury if you over-train, no matter how fit you are.
If you were active before your pregnancy, exercising a few times a week for 20-30 minutes at a moderate intensity is sustainable. You should continue to adjust your workouts as your pregnancy progresses. Sessions lasting longer than 45 minutes can increase your risk of overexertion, overheating and a drop in blood sugars, so make sure you’re eating well, drinking plenty of water and don’t over-do it!
What’s the mantra of this episode? Listen to your body!
Every woman and every pregnancy is very different, so while some women may be able to continue with intense training during their pregnancy, this level may not be appropriate for others. Upper limits of exercise intensity have not been studied for obvious safety reasons, so stick to the guidelines.
Now before we wrap things up today on our very. First Q&A Wednesday, I just want to go over the signs to stop exercising immediately and consult your doctor.
And they are:
o Vaginal bleeding or loss of fluid from your vagina
o Regular painful contractions or signs of preterm labour
o Deep, severe pubic or back pain
o Shortness of breath (especially if you were experiencing this before you started exercising)
o Chest or stomach pain
o Calf pain or swelling
o If you’re feeling dizzy, like you might faint, or you have a headache
o Difficulty walking, muscle weakness that’s affecting your balance
o You notice that baby has reduced movement after exercising
o Having heart palpitations or unusually slow heart beat
o Extremely tired
Be aware of baby’s movements when exercising. Rest if the movements seem to slow down or stop. Your baby may be quiet when you are exercising, but if things don’t feel right, stay cautious and always consult your doctor.
If you want me to answer your questions about periods, pregnancy or pelvic floor, I’d love to hear from you! Send me an DM and let me know what you want me to talk about. This podcast is for you and so I want to talk about the things that are most important to you!
And if you want to know more about safe exercise during pregnancy, you can grab my free guide 10 Exercises to Avoid During Pregnancy (and what to do instead). I’ll make sure to link to it in today’s shownotes or you can head on over to www.fertilityco.com.au/8 for a link there too and for a visual guide to the Borg Scale that I talked about in this episode.
I will see you in next week’s episode, bye for now and don’t forget that knowledge is power!
When you truly understand your body, you are empowered to make informed decisions and take control of your health!
Until next time.
Want to make sure you’re exercising safely during your pregnancy? Get your Free Guide: 10 Exercises to Avoid During Pregnancy
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