But we have recently reviewed the research and shown that vigorous exercise is safe during pregnancy, including in the third trimester. It is not only safe; it is healthy too.
Moderate or powerful?
The safety of moderate intensity exercise during pregnancy has been well established. Walking, swimming and using an exercise bike are all activities that can be considered moderate intensity.
When we talk about vigorous training, it means training to an intensity where you struggle to maintain a conversation, but still manage to manage a meaning. This may include activities such as jogging, circuit-based resistance training or interval training on a stationary bicycle.
In the wider population, it is training at 70 to 90 percent of your maximum heart rate (where the maximum heart rate is about 220 beats per minute minus your age).
For pregnant women, it may feel a little more difficult to achieve vigorous exercise due to some normal changes in the heart and blood that occur during pregnancy.
And the safety of doing vigorous exercise during pregnancy has been more controversial. For example, previous research has suggested that during flowing exercise, the blood is redirected to the muscles and can remove oxygen and nutrients from the growing baby.
We collected all studies that looked at mothers who exert a powerful intensity during the third trimester, to understand how safe this was for mothers and children. Our review included 1
5 studies of a total of 32,703 pregnant women.
What we found should be reassuring for active women with healthy pregnancies: Vigorous exercise seems to be safe for both mother and child, even in the third trimester.
The studies looked at a range of results for both mother and child, and no one showed any meaningful increase in risk. There was no difference in birth weight in infants when their mothers did vigorous exercise; and in particular, no difference in the number of babies born small before gestational age.
For women in the health weight field, vigorous exercise did not affect the amount of weight they gained during pregnancy. That is, they followed the expected path for weight gain as pregnancy continued.
However, in overweight and obese women, for whom it may be more difficult to adhere to the recommended weight gain during pregnancy, vigorous exercise seemed to reduce mothers' weight gain.
It was also associated with a slightly lower chance of a baby being born prematurely and a few extra days of pregnancy.
High-intensity, high-impact exercise
Exercise at more than 90 percent of the maximum heart rate is considered "high-intensity exercise." This is where you can't even string a sentence.
We do not yet know if high intensity exercise involves any risks, so there is still a limit to what expectant mothers may want to do later in a pregnancy. We recommended that they do the "talk test" to make sure they can still talk while they are exercising.
The expectant mothers should also be careful about doing high-impact workouts in the third trimester, such as running, jumping, or lifting heavy weights. The results of our review suggest that these types of effects with great impact are unlikely to affect the child, but it is still unknown whether they can weaken the mother's pelvic muscles, which may contribute to incontinence.
If expectant mothers want to keep these activities up, we recommend that they consult a training staff and their physician.
Every Exercise Is Good
Powerful exercise is an effective strategy to improve a mother's physical and mental health. The benefits to her heart, lungs, muscles and mood are likely to be the same, if not greater, than moderate exercise.
The main purpose of physical activity during pregnancy is to achieve health-enhancing benefits in a way that is safe, fun and sustainable.
Some women may have difficulty being mobile in the third trimester, let alone exercise vigorously. So if you like to do easier exercise, like regular walks, you can feel confident in the benefits you and your child are giving.
Pregnancy-specific yoga or Pilates can also be a milder way to improve muscle strength, heart health and mental health. These activities can help you prepare your body for the upcoming challenge of childbirth and subsequent recovery.
If you struggle to achieve the recommended 150 minutes per week, especially in the third trimester, you can find ways to increase your breathing rate in shorter fits. For example, by taking the stairs, park the car a little further away or take a quick walk on your lunch break.
Mothers will usually receive the most benefit with a little extra support, whether it is a training professional (such as an accredited exercise physiologist), physician or both. Programs can be adjusted to the most suitable training intensity for you.
Kassia Beetham is a lecturer in exercise physiology at Australian Catholic University in Brisbane. This article was originally published on theconversation.com.