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Exercise and how your body changes in pregnancy

Pregnant women in exercise classYour body will undergo a number of anatomical and physiological changes in pregnancy. So how do those changes affect the way you exercise while you are pregnant?

Unless you have complications, you should continue to exercise while pregnant. The general rule is that you can continue with whatever exercise you did before you fell pregnant – although you should avoid sports where there is a risk of falling or being hit in the abdomen (horse riding, martial arts etc). You should always chat to your health care provider after your individual situation before beginning an exercise routine.

Here are some of the ways your body will change during your pregnancy, and how that relates to your exercise.

Exercise and how your body changes in pregnancy

Increase in body weight

The average weight increase during pregnancy is 10-15 kilograms, although everyone is different. Half of this is the uterus, baby, and amniotic fluid, and the other half is body fat stores, fluid, and breast fluid.

This increase in body weight will increase the level of jarring force and stress on your joints by up to 5 times in activities such as running and jumping.

Change in body shape

The change in your body shape moves your body’s centre of gravity forwards and increases the inward curve of your lower back. This change can alter balance and co-ordination and may make activities/sports that require high levels of balance and co-ordination unadvisable (e.g. rollerblading).

As your baby grows, your uterus will push up onto your diaphragm. This can make you feel more short of breath than usual when you exercise, and sometimes short of breath when you’re just resting.

The increase in size and weight of your breasts can also cause rounding of the shoulders and increases the outward curve of your upper back. It is important to be aware of this and try to take extra care with your posture.

Hormonal changes and looser ligaments

During pregnancy, your body releases the ovarian hormone, relaxin. This hormone is designed to gradually loosen your pelvic ligaments to prepare for childbirth. However, all ligaments in the body become affected by relaxin and become gradually looser. This may pre-dispose pregnant women to joint injury and most likely contributes to low back pain and pelvic pain during pregnancy. Many women feel like their pelvis is ‘loose’.  Core abdominal and pelvic floor exercises will be important to help strengthen and stabilise the area.

You should take care with activities that involve high impacts such as jumping or running, or activities that involve quick changes of direction, jerky or ballistic movements (like boxing), or excessive stretching.

Even the walls of your veins are softened by pregnancy hormones and this can contribute to varicose veins.

Increase in blood volume and fluid retention

Blood volume increases by up to 40-50% during pregnancy. Together with the effect of the relaxin hormone, increased blood volume can lead to leg cramps, decreased rate of blood flow back to the heart, ankle swelling, and pooling of blood in your legs.

Sodium retention in your kidneys may also contribute to swelling of your hands and feet.

Increase in resting heart rate and respiratory rate

Resting heart rate increases by 7 beats per minute (bpm) in the first four weeks of pregnancy and 15-20 bpm in mid-pregnancy.

Your body is already in what could be termed ‘an exercise state’ during pregnancy – your body is working harder. This is why it isn’t recommended to use target heart rate to determine the intensity of exercise. Instead the intensity should be measured using the expectant mothers’ rating of perceived exertion. A ‘moderate’ rate of exertion is considered safe during pregnancy.

Abdominal muscle changes

As the size and weight of your uterus increases, your abdominal muscles will lengthen.  Muscle separation can occur if your abdominal muscles (rectus abdominis) are stretched too much and too far away from the connective tissue (linea alba) in the middle – this muscle separate is called a diastasis recti.

Pregnant women should avoid exercises that strengthen (and therefore tighten) the rectus abdominis, as tighter abdominal muscles are more prone to separation, and this can increase the risk of a large diastasis recti.

Pelvic floor

The increased weight of your uterus on your pelvic floor combined with the effect of relaxin can cause your pelvic floor muscles to stretch and weaken. High-impact exercises will also increase the stress on your pelvic floor while it is in a stretched and weakened state, and should therefore be avoided. Childbirth itself (vaginal delivery) can also cause damage to the pelvic floor muscles.

It is important to begin conditioning your pelvic floor muscles from the start of pregnancy to prevent complications such as incontinence or bladder leakage. Pelvic floor exercises should continue throughout the pregnancy and recommence as soon you feel it is comfortable after birth.

When working your pelvic floor, you should focus should on contractions held for about 10 seconds and repeated up to 10 times. Start with 5 repetitions if 10 is too much and build up to 10 per session. You should do this at least 3 times per day.

Pelvic floor exercises are best practiced when your spine is in a neutral position – meaning side lying, standing, or sitting.

Other hints for pelvic floor health are to drink plenty of water during pregnancy (1.5-2 litres per day), avoid constipation, and not push and strain too hard when urinating and defecating.

Decrease in blood pressure

Blood pressure falls during the second trimester due to the development of blood vessels to supply the growing placenta. After about the fourth month, rapid changes of position (e.g. from lying to standing) may cause dizzy spells and should be avoided.

Long periods of lying on your back (e.g. doing leg exercises on your back in exercise classes) should also be avoided after the fourth month as the weight of the baby on major blood vessels in the abdomen can slow down the return of blood to the heart.

Stop exercise immediately and seek medical advice if any of the following is experienced during or after exercise:

  • Elevated heart rate (outside of the norm)
  • Dizziness
  • Headache
  • Uterine contractions
  • Vaginal bleeding
  • Amniotic fluid leakage
  • Nausea or vomiting
  • Shortness of breath (outside of the norm)
  • Faintness
  • Back or pelvic pain
  • Decreased foetal movements
  • Sudden swelling of ankles, hands and face
For more info on exercising during the pregnancy, have a look at our Ultimate Guide to Exercising While Pregnant, and find pregnancy exercise classes near you.
Note: this article should not be used as a replacement for medical advice. If you have any concerns, please consult a medical practitioner.

– this article was kindly supplied by Jenny Birckel, from her manual Preglates

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  1. I just wanted to share how much yoga during pregnancy changed my mental outlook and my birth experience. With my little girl Heidi I walked and swam and that was useful but I often felt breathless and uncomfortable. Pre Natal yoga with my second Tom taught me valuable breathing skills, allowed my very narrow hips and pelvis some time to expand and assisted in connected with my body again – instead of feeling out of control I felt empowered and more connected with my baby. I gained less weight and had a much better labour! I’d love to take this opportunity to thank yoga and promote The Pre Natal Yoga course at Sacred Place Yoga (Blacksmiths NSW) 49 71 6901…were so lucky to have trained midwife as well as a yoga teacher on board. X



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