Having a baby is possibly the most important goal of your life. So when you Google exercising when trying to get pregnant and find that the advice ranges from ‘exercise will make you more fertile’ to ‘exercise can make you infertile,’ you may feel stuck on what to do. Will exercise hurt or benefit your fertility? What about after implantation? Will exercise increase the risk of miscarriage?
We examined the research on exercise safety for women trying to get pregnant and what doctors advise their patients to do so that you can make the best decision for your health and goal of having a baby.
What is moderate or vigorous exercise?
This varies person to person based on your individual past exercise experience and level of fitness. To understand your own individual intensity level, you can either simply check in with how you feel during exercise or use your heart rate.
Perceived intensity is easy to measure. If you are doing low intensity exercise, it will feel easy. Moderately intense exercise feels somewhat hard. Your breath is faster, but you can still talk and might be sweating slightly. Vigorous or high intensity exercise feels hard and challenging. You are out of breath; you can feel that your heart rate is high, and you can’t say more than a few words.
For a more accurate measurement, you can calculate your maximum heart rate by subtracting your age from 220. So if you are 38 years old, your maximum heart rate would be 182 beats per minute.
The American Heart Association generally recommends a target heart rate of:
- Moderate exercise intensity: 50% to about 70% of your maximum heart rate
- Vigorous exercise intensity: 70% to about 85% of your maximum heart rate
Keeping with the example above, if your maximum heart rate is 182, your heart rate should be between about 91 to 127 or, for vigorous exercise, between about 127 to 154.
Once you are pregnant or if you are new to exercise, ask your doctor what target heart zone is best for you. For further clarification, please refer to the Centers for Disease Control and Prevention’s classification of exercises that fall under moderate and vigorous.
Why isn’t the answer clear on whether exercise is safe or not?
Let’s get something straight right off the bat. Exercise is fantastic for your health — that is not what is in question. The question is, how much exercise is safe and at what intensity? Research shows conflicting results on whether or not intense exercise is harmful because so many factors need to be taken into account and may influence the results. Factors like body weight, how much you currently exercise, and nutrition all play a major role when it comes to exercising safely while trying to get pregnant (and early pregnancy).
For example, if you are overweight, any type of exercise will likely help increase your fertility. If you are a normal weight, however, it is possible that too much exercise, especially without sufficient caloric intake, leads to negative energy balance. A negative energy balance can lead to temporary infertility due to not meeting the energy requirements of your reproductive functions (Loucks et al., 1998).
Here’s a perfect example of conflicting research. The Nurses’s Health Study II found that more hours of vigorous exercise reduced risk of ovulatory infertility (Rich-Edwards et al., 2002; Chavarro et al., 2007). Another study found, on the other hand, that women exercising 4 or more hours per week were 40% less likely to have a live birth and twice as likely to have an implantation failure (Published by Oxford University Press on behalf of the European Society of Human Reproduction and Embryology). It should be noted that in the Oxford study, these women were undergoing fertility treatment and may have been under a great deal of stress or had other physiological issues unrelated to exercise.
What could happen if I exercise too much?
The idea of too much exercise seems counterintuitive, but it is possible to have too much of a good thing.
Here are risk factors of too much exercise:
- Irregular periods
- Amenorrhea (no period)
- High milage
- High intensity
- Low body weight
- Low body fat
- Poor nutrition (especially protein)
Amenorrhea, or not having a period, may be caused by too much vigorous exercise and low body weight. If your calorie intake is considerably lower than the energy output, the body enters a “starvation state” and shuts down organs that are not absolutely essential for survival, including the reproductive system. If you experience any of the above symptoms, please check with your doctor for the best course of action.
You can keep track of your exercise and weight along with your cycle information in a paper journal or a fertility tracking app — like my company’s, Kindara — to ensure that you are staying in the zone that’s safe for you.
So what should I do?
The general recommendation is that you can continue to exercise just as you have been, even through early pregnancy, with the approval of your doctor.
While physical activity tends to help increase fertility, it may be best to stay on the safe side and not be too vigorous with exercise. In fact, the Mayo Clinic states that strenuous, intense exercise of more than five hours a week has been associated with decreased ovulation. If you have irregular cycles and/or are not getting pregnant after several months of trying, then you may consider trying to reduce your exercise intensity to moderate exercise.
If overweight or obese, physical activity of any type is shown to improve fertility, but be sure to talk to your doctor about how much exercise is appropriate for your individual needs.
If you are still worried about how much to exercise when trying to conceive, keep in mind that research consistently shows that moderate exercise is beneficial and can significantly improve fertility, your pregnancy, and post-delivery recovery.
For safe exercise examples while trying to conceive, check out https://priyaring.com/blog/safe-workout-plans-for-women-trying-to-conceive/exercise/fertility.