The number and age of female recreational runners is increasing, demonstrating a significant number of women of childbearing age running competitively, many who may wish to continue their training while pregnant.
Despite copious evidence suggesting exercise including running is safe during pregnancy, there appears to be a lack of knowledge among obstetric health care professionals and fitness professionals.
This, combined with conflicting recommendations has left pregnant women confused and unsure of what they can do safely.
Appropriate exercise in pregnancy potentially has many benefits. Many countries have national guidelines for prenatal exercise including the UK and USA, produced by national obstetric, and gynaecological institutions.
In recent years, as research grows, the value of these guidelines has been questioned. Many are over ten years old and designed for the general population who may not be active prior to conceiving.
This year, a systematic literature review of prenatal exercise in athletes was published, the first of its kind specifically for recreational and elite athletes, evaluating both the quantity and quality of evidence available. Here’s what it found:
Physiological changes in pregnancy
The body cleverly adapts to pregnancy. Cardiovascular changes include: blood vessels dilation, an increased heart rate (15-20 bpm), increased cardiac output (by as much as 50% compared to pre-pregnancy when at rest) and increased blood volume by up to 50% of pre-pregnancy volume by the end of gestation.
The respiratory rate and tidal volume (amount of air breathed in in one breath) also increases. As the pregnancy progresses the expanding uterus compresses the diaphragm, making breathing uncomfortable which may inhibit running.
Musculoskeletal adaptions also occur to varying degrees; as the uterus expands and breasts grow, the centre of gravity changes and an anterior pelvic tilt occurs with lumbar spine lordosis (arching of lower back), gait changes also occur when running although the significance is unknown.
Perhaps one of the most commonly quoted aspects of exercise in pregnancy is that pregnant women should not overheat during pregnancy. There is a certain amount of truth to this, as during neural tube development of the fetus, raising the core body temperature above 39˚C can cause neural tube development defects such as serious brain maldevelopment or spina bifida.
However, the neural tube finishes developing by the fifth to sixth week of pregnancy, therefore after this time heat exposure should not be a problem. Also, it has been demonstrated that exercising at 60-70% of VO2 max for 60 minutes in a controlled environment did not raise core temperature above 38˚C, however, endurance athletes running for prolonged durations, or outside in hot and humid conditions may see their body temperature spike.
Nutritional requirements & weight gain
Pregnant women need more energy (calories), fluid and nutrients. The additional energy is needed not just for fetal growth but for normal development of the placenta, breasts, uterus and fat stores.
Increased fluids are required to support the increased blood volume, amniotic fluid and other extracellular fluid increases. By late pregnancy, the fetus and placenta can use as much as 30-50% of the maternal glucose supplies.
Active women should ensure they are eating adequate calories for their stage of pregnancy and amount of exercise. Pregnant women may occasionally feel suddenly hungry and faint when exercising so should eat before running and could consider carrying energy gels with them especially if running alone.
Additional daily calorie requirements for the average pregnancy
- 1st trimester: 90kcal/day
- 2nd trimester: 287 kcal/day
- 3rd trimester: 466 kcal/day
For women with a BMI in the normal range, weight gain is expected to be 11-16 kg, with underweight women gaining more and overweight women less.
How much and how far to run
The large majority of studies have discovered that moderate to vigorous cardiovascular exercise (up to 75-80% of aerobic capacity) produces no adverse maternal or fetal effects, so continuing to run is okay as long as the woman is feeling well and comfortable.
Studies in elite athletes have demonstrated transient decreases in fetal heart rate at exercise intensities over 90% of maximum heart rate, and although the significance of this and the effect on fetal outcome is unknown, it is recommended not to exercise at 90% or above of either VO2 or maximal heart rate and there are suggested heart rates (see below), which can be used to monitor intensity.
The volume and pace will depend on the individual women and their training load prior to pregnancy. Studies have shown that women usually voluntarily reduce their training volume during pregnancy and less than one-third continue to run during the third trimester.
Measuring intensity of exercise during pregnancy
A study showed that the rate of perceived exertion (RPE) does not correlate strongly with heart rate in pregnant women, especially in the second and third trimesters. That means women may be exercising at higher heart rates than they realize.
It’s important to take into account more than just heart rate when monitoring effort. Still, heart rate monitors are a good place to start.
Table 1. Recommended heart rates for pregnant women during exercise
- Taken from Mottola MF, Davenport MH, Brun CR, et al. (2006) VO2 peak prediction and exercise prescription for pregnant women. Medicine and Science of Sports and Exercise. 38:138–95.
Theoretically, training at altitude may decrease oxygen delivery to the fetus. So far, no studies have been examined the effects of altitude on pregnant athletes, however, studies on pregnant women at rest at altitude showed no adverse fetal effects. Because there is not enough information, this review advises avoiding high-intensity training at altitudes greater than 1500–2000 m.
Strength and flexibility training
Light to moderate strength training can be performed effectively and safely during pregnancy. Despite theories that increased relaxin levels results in joint instability, there are no studies examining joint range of motion during pregnancy or the effect of flexibility training during pregnancy.
As discussed, there is no reason runners should not continue to train at a moderate intensity throughout the entire pregnancy providing they feel well and comfortable, however there are a variety of pregnancy complaints and complications varying in severity and likelihood of occurrence which may (or may not) effect the ability to run. In the case of any complications or concerns, seek medical advice.
Nausea and vomiting
Nausea and vomiting are common in the first trimester, and despite the name, morning sickenss is not always limited to the morning. Depending on the severity, nausea may restrict a woman’s ability to run. Hyperemesis gravidarum is far more rare and symptoms include severe and persistent vomiting, weight loss, dehydration and electrolyte imbalances. Medical advice should be sought if vomiting is persistent or severe.
Fatigue is common in pregnancy and might not impact a woman’s ability to run. Medical advice should be sought if there is persistent and severe fatigue to rule out anemia or hypothyroidism.
Oedema refers to the accumulation of excessive watery fluid in cells and tissues. It is very common during the third trimester and usually of no concern, however, it is occasionally linked to pre-eclampsia and hypertension. It should not affect running.
Pelvic girdle pain (PGP)
PGP is common in pregnancy and is characterized by pelvic pain especially around the sacroiliac joint. The link (if any) between PGP and high-impact exercise is unclear, however, there is some evidence that people who participated in high-impact exercise had a lower likelihood of PGP than those who didn’t. Anecdotally, PGP may be exacerbated by running and may be a reason for switching to low-impact exercise.
Pelvic floor dysfunction
Urinary incontinence (UI) is common during pregnancy. In elite athletes, the prevalence was higher in high-impact sports. Medical advice should be obtained for UI persisting into the post-natal period. Pelvic floor exercises have been shown to be effective, however, the majority of people are not able to perform them correctly so seek appropriate instruction and advice.
A potentially serious condition characterized by high blood pressure and the presence of protein in the urine. Pre-eclampsia is not common and lack of physical activity and obesity increases the risk. It can have serious consequences for both the fetus and the mother if left unmanaged. Other symptoms include; headaches, abdominal pain and altered vision. Most studies found exercise beneficial in minimizing the risk of pre-eclampsia.
This is rare and involves repeated high blood pressure measurements during pregnancy. It is often a pre-cursor to pre-eclampsia and there are no studies evaluating exercise as a treatment.
This sometimes occurs in approximately 10% of the population, however, the likelihood is lower in active, non-overweight women. It is tested for during the second trimester and can be appropriately managed.
Anxiety and depression
Specific pregnancy-related anxiety can occur, as well as anxiety about being able to return to ‘normal’ both aesthetically and fitness-wise. Exercise is associated with decreased risk of depression, however, athletes may have anxiety about performance or fear about being unable to return to compete at the same level. Seek medical advice if depressive feelings persist or become more severe.
In summary, providing you have a routine pregnancy, continuing to run throughout the entire pregnancy is possible. Most women finding they feel able to run as usual during the second trimester once nausea has subsided before decreasing both the distance and intensity or stopping completely during the third trimester. Some women find the increasing bump size and resulting pelvic pain mean they have to switch to another form of exercise towards the end of pregnancy.
Tips for running in pregnancy
- Don’t aim for personal bests.
- Run for enjoyment and physical and mental wellbeing without any pressure to stick to a plan.
- Stay hydrated and ensure adequate food intake.
- Many women find maintaining regular running hard in the first trimester due to nausea and fatigue, however, this usually subsides during the second trimester and many women feel able to return to more regular running throughout the second, and some, into the third trimester.
- If you start to find running too uncomfortable, switch to static cycling, appropriate strength training, swimming, walking or yoga.
- Continue appropriate strength training, start pelvic floor exercises, ensuring you are doing them correctly and timing appropriately with abdominal muscle contraction (seek advice if unsure).
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- Bo, K., Artal, R., Barakat R., Brown, W., Davies, G, L., Dooley, M., . . . Khan, K., (2016). Exercise and pregnancy in recreational and elite athletes: 2016 evidence summary from the IOC expert group meeting, Lausanne. Part 1—exercise in women planning pregnancy and those who are pregnant. British Journal of Sports Medicine, 50, 571-589.
- Mottola, M,F., Davenport, M,H., Brun, C,R., et al. (2006) VO2 peak prediction and exercise prescription for pregnant women. Medicine and Science of Sports and Exercise. 38:138–95.
Last updated on March 2nd, 2021.