Do you need to keep your heart rate low during pregnancy?
There are a ton of misconceptions, and myths when it comes to exercise during pregnancy. Women who are pregnant are in a very vulnerable part of their life.
Pregnancy is beautiful. But complications occur. Loss may happen. Every instinct in our body tells us to protect that little baby. So it makes sense that we start having questions about exercise during pregnancy.
One of the BIGGEST myths we get asked about on a regular basis is about heart rate and pregnancy. Do we need to stop doing high-intensity cardio?
The Advice: Your heart rate should not get over 140 beats per minute with exercise.
But the big question is … is this true…?
Before we tackle this question, we are going to start with
1. what changes occur to our hearts during pregnancy and
2. where did these recommendations come from?
Changes to our heart and cardiac system during pregnancy.
When we become pregnant, our heart starts to change IMMEDIATELY. Symptoms relating to your heart can be the hint you are pregnant. Your heart rate rising quickly warming up, your resting heart rate being higher and getting carsick are early pregnancy signs.
Let’s breakdown exactly what happens to our cardiovascular system during pregnancy.
1. Your body produces more blood
Your body needs to be able to give blood to your growing baby. Blood carries oxygen and nutrients to your little babe. That means the amount of blood in your body goes up! It increases by 30-50% during pregnancy.
2. Your heart is pumping more blood
Your heart pumping more blood is your cardiac output. It increases the same amount as the increase in your blood (30-50%).
3. Your resting heart rate goes up.
Many of our active to-be mamas know their resting heart rates. When they get pregnant, they are shocked but how much it increases! This is partly due to hormonal changes and partly due to the body’s responding to more blood. This increase is most noticeable during the first and second trimester.
4. Changes in Blood Pressure
In early pregnancy, blood pressure may decrease slightly due to hormonal changes. However, blood pressure tends to gradually rise to pre-pregnancy levels as pregnancy progresses. Rises in blood pressure are a potential complication in pregnancy. Blood pressure is closely monitored by your provider.
5. Blood vessels in the mom’s body, especially in the uterus and placenta, get wider.
The widening of blood vessels is called vasodilation. It helps to get the right amount of blood flow to the baby.
As you can see… it’s a LOT!
So how does this link to exercise?
Where did the limit on heart rate come from?
150 minutes of moderate-intensity exercise is the recommendation of almost all exercise guidelines. This is true if you are pregnant too.
Up until a few years ago, NO research on high-intensity training for pregnant people existed.
Here is how the research process works, especially in pregnancy. First we see what works in people who aren’t pregnant. Then we start with very low intensity for those who are. Then we gradually push boundaries.
This has taken YEARS in the pregnancy space.
Most guidelines and doctors agree that moderate intensity exercise is safe. That is about 50-70% of a person’s max heart rate.
So here is where some of these guidelines come from.
Max heart rate = 220-age
Average age at first birth is 25-30
220- (25- 30) = 190-195 beats per minute
190 x 0.7 = 133 beats per minute
190x 0.7 = 137 beats per minute
Recommendation is to stay below 140 beat per minute
AKA stay in moderate range
Also, there was a study that showed some lower fetal heart rates when moms were working at 100% on a treadmill test. Some important parts of that study is that the group of individuals was VERY small. It has NEVER been repeated and the change in heart rate returned very quickly. All babies were born healthy.
Can we ditch these recommendations?
TLDR: More mounting evidence is pointing to YES
More recent research has looked at vigorous-intensity exercise during pregnancy. This systematic review showed no bad effects on the mom or baby with vigorous-intensity exercise in the third trimester.
It seems that in uncomplicated pregnancies, exercising at ANY intensity is okay.
Is there anything I need to look out for?
Knowing signs of when you are over-exerting during pregnancy is important. This is whether you are exercising or moving around the house.
Signs to stop or slow down include:
Dizziness
Nausea
Blurred Vision
Sudden headache
Chest pain/upper belly pain
Pregnant women are more likely to overheat with exercise. Their heart rate also goes up faster with exercise.
The biggest factor we see with pregnant mamas doing cardio… REBOUND FATIGUE.
You are definitely tired after a hard workout. Everyone is. But when you are pregnant, this is SO MUCH WORSE. If you have other things you need to accomplish in a day, doing a really hard workout will make that a challenge.
If you are worried about YOUR pregnancy, talk to your pelvic floor physical therapist or birth provider about exercise.
References:
1. Beetham KS, Giles C, Noetel M, Clifton V, Jones JC, Naughton G. The effects of vigorous intensity exercise in the third trimester of pregnancy: a systematic review and meta-analysis. BMC Pregnancy Childbirth. 2019;19(1):281. doi:10.1186/s12884-019-2441-1
2. Wowdzia JB, Hazell TJ, Berg ERV, Labrecque L, Brassard P, Davenport MH. Maternal and Fetal Cardiovascular Responses to Acute High-Intensity Interval and Moderate-Intensity Continuous Training Exercise During Pregnancy: A Randomized Crossover Trial. Sports Med. Published online May 22, 2023. doi:10.1007/s40279-023-01858-5
Christina Prevett is a pelvic floor physiotherapist who has a passion for helping women with different life transitions, including postpartum care and menopause.
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