Exercise in Pregnancy - How and Why to modify

By Taryn Watson, FitRight Physio

As beneficial as it is to keep fit during pregnancy, it is essential to know how to safely modify the way you exercise. It's also important to understand why you are implementing these changes – which modifications are for the safety of the baby, and which modifications are for the benefit of your joints and muscles and will potentially make the post birth recovery process easier? By understanding the ‘why’, pregnant women like you can make informed and empowered decisions about the way in which you stay active.

Assuming that you’re given the medical all clear to exercise, let’s talk about the types of exercises that could negatively affect your unborn baby, and how to safely modify them. These can be divided into three sections:

1. Too Much Load on the Heart and Lungs

During pregnancy, your heart has to pump blood (containing all-important oxygen and nutrients) to two bodies instead of one. This is an extra ‘physiological load’, which even from very early in pregnancy can lead to you feeling more breathless at low levels of exercise, and feeling faint due to low blood pressure or low blood sugar levels.

As the baby grows, all of your abdominal contents are pushed upwards, creating an additional ‘physical load’ on your heart and lungs. This can also lead to you feeling breathless and light headed, and can cause decreases in blood flow to both you and the baby.

Exercise changes need to be considered due these extra loads on the cardiovascular systems.

Use The Talk Test To Monitor Intensity

Firstly, you need to ensure that you exercise at an appropriate intensity so that your body can still provide enough oxygen to your baby.

In general, it has been found that monitoring heart rate in pregnancy is not a very accurate reflection of the blood flow to the baby. Instead, it is recommended to use a ‘Rate of Perceived Exertion’, and to not get above the level of 14 out of 20.

In real terms, this usually means exercising at a level where you could still hold a conversation (but not necessarily still be able to sing!), which is referred to as the ‘Talk Test’. This may differ with elite, high level athletes, who have been shown to be able to exercise at a higher intensity during pregnancy with no ill effect to the baby, but this should be discussed with a health professional.

Don’t Exercise Lying Flat on Your Back

Lying flat on your back when you are more than about 18 weeks of pregnancy can cause ‘Supine Hypotension’. This is a decrease in blood pressure due the weight of your pregnant belly putting pressure on an important blood vessel near the heart called the Inferior Vena Cava.

When this vein is compressed, it can cause you to feel dizzy and light-headed, and could be causing a decrease in blood and oxygen to the baby. This would be much more likely if you were also exercising and getting your heart rate up in this position.

Therefore, it is recommended from about 18 weeks of pregnancy onwards, to modify any exercise lying on your back to a semi-recumbent position, and keep your abdomen lower than your chest when getting your heart rate up.

Avoid Straining and Breath Holding

Straining with effort, also referred to as a ‘Valsalva Maneuver’, usually would happen if you are lifting, pushing or pulling very heavy loads. This can greatly increase the pressure on your uterus and can cause a drop in blood flow to the baby.

Therefore, decreasing the weight and increasing the repetitions during resistance exercises when you are approximately 18 weeks or more pregnant, can ensure that you exercise at a level where the blood flow to the uterus is not compromised.

2. Overheating

Core temperature increases of more than 1.5 degrees can be dangerous to the unborn baby. This is mainly an issue in the first trimester, when important developments in the baby’s neural system require your core temperature to stay within normal limits.

Avoid Spas, Saunas and Bikram Yoga During Pregnancy

Research has shown that these core temperature changes usually occur only in very extreme circumstances, like very hot saunas and spas, or exercising in a heated room, especially if this is something your body isn’t used to.

Always ensure good airflow and ventilation in the exercise space, that regular rests are able to be taken, and that you never feel that you are overheating.

Cardio gym classes in enclosed indoor spaces and exercising in hydrotherapy pools are things to consider the safety of – although it has been shown with recent research that moderate intensity exercise in pools up to 33 degrees Celsius (most hydrotherapy pools are between 31-33 degrees) is very safe for the mother and baby and did not cause an excessive increase in core muscle temperature.

Pregnancy-specific hydrotherapy exercise classes should take overheating into consideration and ensure regular rests and time spent in the shallow end of the pool.

3. Danger of a Force to the Abdomen

Before about 15-20 weeks of pregnancy, the womb is tucked down low in your abdomen and your baby is protected by the pelvic bones. After this time, when your baby is above the pelvic brim, although small forces to the abdomen can be well absorbed by the fluid in the womb, excessive forces could harm your baby.

For this reason, it is recommended to avoid ball sports, contact sports, and exercises with a risk of falling (such as box jumps, trampolining, gymnastics etc) after the time that you start to ‘show’.

Which Types of Exercise Could Be Harmful to My Body?

Once you understand the exercise modifications that you need to make to keep the baby safe during pregnancy, the next thing is to be well informed about the modifications that are recommended for your own health. These are things that can prevent you from experiencing common issues to do with your joints, muscles, connective tissue and organs during and after pregnancy.

It is an unfortunate fact that certain exercises will predispose you to urinary incontinence, vaginal prolapse, pelvic joint pain, abdominal muscle separation and more, and it’s important to understand which exercises these are and how you may choose to modify them.

1. Protecting the Pelvic Floor Muscles

The pelvic floor is an extremely important group of muscles and connective tissue that runs between the pubic bone and the tail bone, and outwards to the sit bones, literally making up the floor of your pelvis. It is responsible for:

• Keeping your bladder and bowel from leaking
• Supporting your pelvic organs to prevent vaginal prolapse
• Supporting your lower back and pelvic joints
• Helping to keep sexual intercourse enjoyable

Pregnancy can stretch and weaken the pelvic floor in two ways.

It can be from the physical load of the weight of the growing baby and uterus, and it can also be from the physiological relaxing of the muscles and ligaments due to the pregnancy hormone relaxin, which makes the area more flexible for childbirth. A vaginal birth would then stretch the pelvic floor muscles further, and potentially injure them.

It could be helpful to your pelvic floor to keep exercise low impact and low load during pregnancy.

Some types of exercise can repetitively increase pressure on this already challenged muscle, and weaken them, such as:

  • High impact exercise like running, jumping, skipping
  • Abdominal muscle exercises such as crunches, planks, pull ups and Russian Twists
  • Heavy weight training

While these exercises are not in the category of those that could harm the baby, it is worth considering the pros and cons of continuing exercises that would put extra pressure on an area that is already at risk of damage, and avoiding them could improve the recovery of the pelvic floor after birth. This would be especially important during the second and third trimesters as the baby’s weight increases.

You can exercise these muscles to keep them strong and functioning well, which is discussed in more depth in Step 5.

2. Preventing Strain on Separated Abdominal Muscles

No doubt you’ve heard about abdominal muscle separation (or diastasis) during and after pregnancy, and you’re wondering how to avoid it. The reality is, however, that every woman who reaches full term in her pregnancy will need her ‘six pack’ abdominal muscles to stretch apart from each other in the midline, otherwise there wouldn’t be enough space for the baby to grow.

While separation is normal and a necessary adaptation during pregnancy, what needs to be realized is that:

  • In the midline of a pregnant belly there is only thin tissue rather than thick muscles
  • The six pack muscle is at a big mechanical disadvantage and can’t work as efficiently as usual

Repetitive strain through the separated muscles, especially when it causes ‘doming’ or ‘coning’ when the midline bulges outwards, could set you up for abdominal hernias, back pain and difficulty training the six pack muscles to return to their normal state after you give birth.

Modifying Abdominal Muscle Exercises During Pregnancy

So what impact does this have on exercise in pregnancy, and how should you modify your program to avoid putting strain through the weakened tissue in the midline of your pregnant belly?

It is recommended that after the muscles start to separate, which is usually around 16-20 weeks, you should avoid anything that would put strain through the weakened midline:

  • Sit ups
  • Planks
  • Pull ups
  • Muscle ups
  • Russian Twists

You or your trainer can monitor whether these or any other exercises cause the typical ‘doming’ through your belly that would indicate strain.

This doesn’t mean that you can’t do abdominal muscle exercises, you just need to talk to a qualified physiotherapist or fitness professional about what type of core muscle exercises (usually ones that target the deeper layers of abdominal muscles) that you can do without ‘doming’. This is discussed further in Step 4.

3. Avoiding Pelvic Joint Pain and Dysfunction

We have three ‘pelvic girdle’ joints – the pubic symphysis joint at the front of your pelvis, and the two sacroiliac joints on either side of the back of your pelvis, where your pelvis joins to the lower spine.

Pain in one or more of these joints occurs in up to half of pregnant women, and usually occurs when the joints are loaded when you put weight down through one leg, like with getting out of the car, or getting up from the floor. Usually it will occur as a sharp, sudden pain, and/or a clicking sensation, at the front or back of the pelvis. If you experience pain like this, it is important to get it assessed by a physiotherapist who specialises in pregnancy, as it can get progressively worse without good management.

You should also modify your exercise program so that you avoid single-leg-loaded activities if they cause pain, for example

  • Lunges
  • Step ups
  • Running

You may wish to pre-emptively avoid these single-leg-loaded exercises during pregnancy to avoid stress through potentially vulnerable joints.

There are many variations of these exercises that involve weight bearing through both legs together, or having a smaller base of support, which may decrease your risk of experiencing pelvic girdle pain.

So, in summary, these modifications in this section are recommended to avoid common joint, muscle and connective tissue problems while you’re pregnant. It is important to note that if you choose to still participate in high impact exercise or do abdominal muscle exercises during pregnancy, the research has not shown any link to this and any harm to the unborn baby.

Note: The views and advice expressed on this blog post are those of the author and are not representative of the Pregnancy Babies & Children's Expo.

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