Rachel Simpson


So many women are confused about how to exercise safely during pregnancy. Everyone seems to have a different answer – doctors, family and friends, personal trainers – and the research and recommendations for safe exercise during pregnancy are changing regularly. It wasn’t so long ago that women were told not to exercise at all during pregnancy. Twenty years ago, women were told to exercise but to monitor their heart rate carefully. Now, women are told to go for it. It’s no wonder we’re all so confused!

Previous pregnancy exercise guidelines released by the American College of Obstetrics & Gynaecology (ACOG) recommended that pregnant women keep their heart rates below 140 beats per minute (bpm) when exercising. However, more research discovered that the heart rate response to exercise varies considerably between women and throughout pregnancy. The entire circulatory system – the heart, blood vessels, arteries and veins – will change early on in pregnancy to support the needs of both mother and baby. These changes may begin as early as 4-5 weeks gestation and may peak during the second and early third trimesters. These changes cause the heart rate response to increase initially during early pregnancy, and will gradually fall in later pregnancy.

The problem with the previous ACOG guidelines is that they assumed that all pregnant women exercising at a heart rate of 140 bpm are exerting exactly the same amount of effort during physical activity. We now know that a set target heart rate is not appropriate for monitoring exercise intensity in all pregnant women. The appropriate workout intensity for you will depend on how physically fit you were before pregnancy. If you are new to exercise or would consider yourself to be unfit, you may have to keep your heart rate well below 140 bpm, while athletes and more active women may be able to reach a heart rate of up to 170 bpm with no negative effects.

This means that a set target heart rate isn’t appropriate for monitoring exercise intensity in all pregnant women. For the past twenty years, ACOG have continued to release updates about their recommendations for safe exercise during pregnancy and since 2002, ACOG have recommended that women use the Borg Scale to monitor their exercise intensity without needing to track their heart rates. The Borg Scale, also called the Borg Rating of Perceived Exertion, allows women to monitor their exercise intensity without having to track their heart rate during workouts.

 Women are encouraged to work in a target training zone of 12 to 14 on the Borg Scale, or a “Somewhat hard” intensity. 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. 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 now 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.

Another simple way to monitor your exercise intensity is with 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. It is also important to take note of your body’s response to exercise. If you are sweating, it is a sign that your body is trying to cool down and you are working hard enough. If you are short of breath and red in the face you are working too hard.

You should consult your doctor before starting a new program or if you are new to exercise. If your doctor has specifically told you to keep your heart rate below a set point during exercise, please follow their advice. Make sure you have addressed any problems or discomfort you may have during pregnancy and check if you should be taking any special precautions. Pregnancy is not the time to be trying a new and strenuous activity for the first time. Aim to start gently with low impact exercises such as walking or swimming. Some women prefer to wait until the second trimester once morning sickness and fatigue have settled, but there is no risk in starting in the first trimester if you are feeling well.

Long gone are those days of pregnancy being a condition that puts women on bed rest for 9 months. ACOG now recognises how important physical activity is during pregnancy. 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 to avoid overheating, and remember that rest days are just as important as active days to allow your body to recover and repair.

Remember, your heart rate will change throughout your pregnancy and so it is not a reliable guide. Always listen to your body. Stop and 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. 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.

Stop exercising immediately and consult your doctor if you feel unwell during exercise or if you experience any of the following:

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


Rachel Simpson is a Women’s Health Educator for women who want to understand their bodies. An Australian-trained physiotherapist, nutrition and health coach and natural fertility educator, she teaches women all those things they never learnt in health class – periods, pregnancy and pelvic floor.

Through her knowledge-packed podcast, free resource library and her digital guides, she’s here to answer all those questions you’ve been secretly Googling (you know the ones!). She believes that knowledge is power – because when women understand their bodies, they are empowered to make informed decisions about their health.

A few of her favourite things? Cuddles with her border collie Bonnie, gluten-free baking and salted-caramel everything!

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