Exercise during pregnancy
Women are often aware of the dos and don'ts in pregnancy, but perhaps they are less aware of the reasons for these, writes Jenny Blizard.
As a physiotherapist that specialises in women’s health, it is my role to promote the benefits of safe exercise during pregnancy. Athletes want to stay as fit as possible during pregnancy, without risking harm to themselves or the foetus. It is possible to maintain and still improve your fitness during pregnancy – as elite athletes such as Paula Radcliffe and more recently Jo Pavey have shown – without harm to you or your baby, provided certain guidelines are followed.
The non-elite athletes without access to specialist services are often confused and worried about the safe levels of exercise during pregnancy with most still being keen to maximise their potential fitness during this period. In pregnancy the aims should be and can be to either maintain or improve a level of cardiovascular fitness.
This article will seek to explain and make sense of the relevance of the guidelines on cardiovascular exercise in terms of the physiological changes to the mother and foetus during pregnancy. It will then allow you to make informed decisions on your choice to exercise and understand what to expect and feel for during exercise to ensure safety.
Although further research is always needed to explain more fully the effects of exercise (not just cardiovascular) during pregnancy, the following benefits are suggested in the research:
» Maintains cardiovascular, respiratory and musculoskeletal health
» Maintains a healthy weight range for the mother
» Improves body awareness, coordination and posture
» Improves circulation
» Increases stamina and endurance
» Increased feelings of social and emotional well-being
» Possible reductions in labour and delivery complications
» Aids a speedier post-natal recovery
» Possible improved placental and foetal growth
The Royal College of Obstetrics and Gynaecology guidelines (2006) for exercise recommend a maximum exercising intensity of no higher than 13 to 14 or “somewhat hard” on the Borg scale rating of perceived rate of exertion (RPE), which is measured between 6 and 20.
Threshold running is designed to significantly improve your aerobic capacity and studies have shown that the Borg rating averaging around 13 to 14 corresponds exactly with threshold running pace. This then determines exactly how you can maintain and even improve your fitness level by working up to this level on a regular basis without detrimental effects. This is provided that there are no specific medical or pregnancy related problems.
This allows the athlete post-natally to return to their pre-pregnancy level quickly by introducing higher-intensity training back into their schedule earlier than those who don’t maintain or improve their aerobic capacity. Again, this is under the proviso that there have been no pregnancy-related complications and should be under the guidance of a qualified coach with experience of helping women back to fitness after a pregnancy.
We will now take a look at the physiological and musculoskeletal changes that take place during pregnancy, which will then make sense of the exercise intensity guidelines and so that you can also make some adjustments along the course of your pregnancy where necessary.
CARDIOVASCULAR CHANGES
The main changes here are that blood volume can increase by up to 50% in the first and second trimesters of pregnancy, which results in increased heart rate and stroke volume (the amount of blood pumped out of the left ventricle of the heart, with each heart beat measured in millilitres) and cardiac output (heart rate multiplied by the stroke volume per minute, measured in litres).
A greater rise in cardiac output in pregnant women during exercise compared to non-pregnant women means that there is a loss of cardiac reserve, which is the difference between the rate at which the heart pumps blood and its maximum capacity for pumping blood at any given time. This reduction in cardiac reserve means that starting exercise too quickly may cause a sudden and extreme shortness of breath, a sharp, sudden rise in heart rate and sudden onset of muscle fatigue.
The first recommendation therefore is to use your heart rate if you have had your threshold zone calculated or RPE as a measure of your running capabilities rather than pace. What will happen throughout pregnancy is that your running pace will drop, but your heart rate will rise – ignoring this rise in heart rate can be harmful.
The second recommendation is to always allow your heart rate to regulate over the first 10 minutes in your recovery zone and once it has stabilised then begin to increase your pace alongside monitoring your heart rate if required. Any fluctuations in heart rate therefore will be noticeable at the lower end and you can decide to have an easier run or stop your run altogether if your heart rate fails to remain consistent and stable for 10 minutes.
Time for a tip! If you are serious about running through to the end of your pregnancy, then it is important to have your heart rate zones calculated. This way you can maximise maintaining a good aerobic base throughout your pregnancy without any harmful effects to yourself or the growing foetus. The RPE is much more subjective based on how you think you feel, but your heart rate tells you exactly.
RESPIRATORY CHANGES
The increased blood volume causes a rise in both tidal volume (amount of air inhaled into the lungs at rest) and respiratory rate. This means that you may feel breathless at relatively low exertion rates. Again, using your heart rate, RPE or both is a better measure than using running pace and ignoring this increased respiratory rate.
"Towards the end of your pregnancy the growing bump can impact on the depth of your breathing rate and again you may notice an increased respiratory rate to accommodate for the shallower breath"
Towards the end of your pregnancy the growing bump can impact on the depth of your breathing rate and again you may notice an increased respiratory rate to accommodate for the shallower breath. It is important to relax during the day and take time for regular deep breaths throughout your pregnancy. This will help to maintain your maximum lung volumes ready for running post-natally. As physiotherapists, we all too often see women with poor breathing patterns.
MUSCULOSKELETAL CHANGES
Pregnancy results in a natural, yet gradual weight gain, which causes changes to the centre of gravity (COG) and balance as well as the normal spinal curves. These changes will alter body biomechanics during running and specifically there will be increased joint and bone stress, which can be positive or negative depending on the amount of stress. Good joint and bone stress means that, provided there is enough rest to stimulate changes, your bones will increase in density and strength. Persistent niggles are a sign of negative stress and obviously need addressing.
The effect of hormonal influences from six weeks gestation can result in joint laxity and this may sometimes lead to minor pains and some mild joint dysfunction. The joint laxity (increased mobility) is essential to allow for the widening of the pelvis and birth canal in anticipation of delivery, but persistent pain should be assessed, especially if you are intending to continue with an exercise programme. Ignoring pains may result in a diffcult labour and long-term consequence post-childbirth.
Running at or below your threshold pace will ensure that your joints are not overstressed in this phase of laxity. If in doubt seek help from a specialist women’s health physiotherapist, who will also be able to help you with other aspects of having a healthy pregnancy.
PHYSIOLOGICAL CHANGES TO THE FOETUS DURING EXERCISE
During exercise, the growing foetus responds by increasing its heart rate and blood pressure to facilitate oxygen and carbon dioxide transfer across the placenta and therefore protecting itself from harm. One of the risk factors for exercise during pregnancy is the potential for over-heating (hyperthermia), which carries a risk for the foetus. The normal foetal core temperature is 0.6C higher than the mother’s. This along with other cardiovascular changes tends to make the mother feel warmer than usual. This in itself acts as a safety mechanism for prevention of hyperthermia provided that the mother takes note of it while exercising. Most women would instinctively limit their exercise intensity and duration to a level which is safe for the foetus.
"It's important that you take regular drinks during your runs and more so than you would normally to prevent hyperthermia"
As we are enjoying the warmth of the summer, it’s important that you take regular drinks during your runs and more so than you would normally to prevent hyperthermia. Keep your runs to cooler times in the day if at all possible too. Monitoring heart rate will also ensure that you don’t overheat.
For the majority of women, continuing with their usual exercise during pregnancy should be an enjoyable and uncomplicated experience. It is important however, to be fully aware of the risks associated with exercise and you should always discuss these with your GP, midwife or physiotherapist prior to continuing or starting with exercise as soon as pregnancy is confirmed. It should be noted that this article is aimed at women undertaking athletics, although usual exercise in terms of contact sports such as horse-riding and cycling are deemed unsafe.
All women should stop exercising immediately and seek advice from a midwife or doctor if they experience:
» Abdominal pain
» Leakage of amniotic fluid
» Pelvic pain and resultant difficulty in walking
» Vaginal bleeding
» Shortness of breath, dizziness, faintness, palpitations or rapid heart rate
» Persistent severe headache
» Calf pain
» Absence of or reduced foetal movements
Tiredness is common in pregnancy, particularly in the first trimester and in the later stages. This is thought to be due to a rapid rise in the hormone progesterone. You can’t fight or “get round” this fatigue – you just have to work with it. Running through it regardless will just have a compounding effect, so you just need to be sensible and adjust your training as necessary.
Fatigue in pregnancy can also be related to iron-deficiency anaemia, which is common in pregnancy and even more so a potential risk for pregnant athletes. Iron is essential for making haemoglobin, the protein in red blood cells that carries oxygen to other cells. During pregnancy, the amount of blood in your body increases until you have almost 50% more than usual. You need more iron to make more haemoglobin for all that additional blood. You also need extra iron for your growing baby and placenta.
Many women start pregnancy without sufficient stores of iron to meet their body’s increased demands, particularly in the second and third trimesters. Your levels of iron are usually checked early in your first trimester and again later. It is therefore worth mentioning to your GP that you are still training so that you can take action early if this is a problem.
Here is some further recommended reading: pelvic obstetric and gynaecological physiotherapy pogp.csp.org.uk/publications/fit-safe-physiotherapists-exercise-childbearing-year
» Jenny Blizard is a chartered physiotherapist who competed for GB in athletics, triathlon and duathlon. You can visit blizardphysiotherapy.co.uk or email [email protected]
