The science of exercise during pregnancy
The Benefits of Exercise During Pregnancy
There are many benefits associated with staying active during pregnancy, providing your pregnancy is progressing well and there are no complications.
Moderate cardio-vascular exercise is not hazardous to the unborn baby; however, in women who continue exercising closer to maximum intensity levels, babies tend to have a lower birth weight.
Some of the benefits to exercising regularly throughout your pregnancy include:
- Keeping fit improves your energy levels and helps you deal with the increased energy demands of pregnancy and labour (women often 'cope' with labour better).
- Your fitness will help you after the birth looking after your new baby.
- Moderate regular exercise has been shown to boost the release of beta endorphins which can provide a sense of well-being and decrease the perception of pain during pregnancy. This can lead to less low back pain, headaches or round ligament pain.
- According to one study, women who didn't exercise regularly only had a 2.5% increase in endorphins with exercise. The women who did exercise regularly over two months had a 57%, 79% and then a 145% increase in endorphin release with exercise.
- Not only does regular exercise boost endorphin release during exercise, it also boosts endorphin release during labour (endorphins – the body's natural drug!).
- Exercise can improve women's self-image and well being during and after pregnancy.
- Reduced low back pain with exercise that targets and strengthens the core stability muscles of the back and pelvic joints.
- Fit individuals have been shown to have better sleep patterns - more slow wave sleep. This will leave you feeling more rested and get a better night's sleep.
- And finally… exercising during and after pregnancy will help you to return to your pre-pregnancy weight earlier and more easily.
Considerations for Exercise During Pregnancy
A woman's body will undergo a number of anatomical and physiological changes during pregnancy. However, it is important to remember that pregnancy is a natural condition, not an illness! Unless you have complications, there is no reason you should not be able to enjoy exercise or activity at some level throughout most of your pregnancy.
Increase in Body Weight (on average 10 - 15 kgs)
The average weight increase during pregnancy is 10 - 15 kilograms, although this can vary. 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 magnitude of jarring forces and joint stress by up to 5 times in activities such as running and jumping.
Change in Body Shape
The change in your body shape moves the body's centre of gravity (COG) forwards and increases the lumbar lordosis. This change in COG 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, the uterus will push up onto the diaphragm. This can make you feel more short of breath than usual when you exercise, and even at rest.
The increase in size and weight of your breasts can also cause rounding of the shoulders and an increased thoracic kyphosis. It is important to be aware of this and try to take extra care with your posture.
Increased Ligamentous Laxity and Hormonal Changes
During pregnancy, the body releases the ovarian hormone, Relaxin. This hormone is designed to gradually loosen the 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 avoid (or take great care) with activities that involve high impacts such as jumping or running, or activities that involve quick changes of direction, jerky or ballistic movements or excessive stretching.
Even the walls of the 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 venous return, ankle swelling and pooling of blood in the legs. Sodium retention in the kidneys may also contribute to swelling of the 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. The body is already in what could be termed 'an exercise state' during pregnancy - the body is working harder - so it is important not to push yourself too hard with any form of aerobic exercise and not to let the heart rate increase too much.
Abdominal Muscle Changes
As the size and weight of the uterus increases, the abdominal muscles will lengthen. Separation of the rectus abdominis at the linea alba can occur, called a diastasis recti. Pregnant women should avoid exercises that strengthen (and therefore tighten) the rectus abdominis, as this can increase the risk of a large diastasis recti.
The increased weight of the uterus on the pelvic floor combined with the effect of relaxin can cause the pelvic floor muscles to stretch and weaken. High impact exercises will also increase the stress on the pelvic floor whilst it is in a stretched and weakened state, and should therefore be avoided. Childbirth itself (vaginal delivery) will also cause damage to the pelvic floor muscles.
It is therefore extremely important to begin conditioning the pelvic floor muscles from the start of pregnancy to prevent complications such as incontinence. Pelvic floor exercises should continue throughout the pregnancy and recommence as soon as is comfortable after the birth.
When working the pelvic floor the focus should be 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. This should be done about 3 times per day at least.
Pelvic floor exercises are best practiced when the spine is in a neutral position. This could be in 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 supine (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.
Postural Awareness and Strengthening
Postural alignment is important during pregnancy to reduce the load on the low back. Low back pain is typical in many pregnant women. The laxity in ligamentous structures supporting the back, together with the increase in forward tilt of the pelvis due to increased weight at the front of the body will be placing more stress on the back. Being aware of posture as much as possible and trying not to allow the pelvis to fall into a forward tilt will help reduce the likelihood of serious back pain. Gentle bracing of the core muscles will also offer support for the back and help with posture
Back Care During Pregnancy
During pregnancy it is even more important to ensure that you care for your back. You should always maintain a neutral spine when lifting and use the legs to bend down if picking up a loaded weight. Don't flex forward through the back.
Be conservative about how much you lift. It's better to take more trips to and from the car to unload bags of groceries than to over load the body. Don’t lift heavy weights - including toddlers!
When doing tasks like vacuuming use the legs for the forward and backward motion rather than bending into the task.
Don't twist the back when you are carrying a load.
When performing household or gardening tasks, rather than doing one task for too long, try to do shorter stints on a variety of tasks with short rest periods between.
Always get in and out of bed through a side lying roll where you place the legs over the side of the bed and use the arms to assist your movement up or down. Don't try and sit straight up from lying on the back.
Ergonomically sound supportive seating - ensure the seating in your workplace and at home supports your back.
Maintaining and Training Core Strength
The transverse abdominal muscles are the deep core muscles that encircle the trunk and act as an internal corset. They play an important role in supporting the back and maintaining good posture. In pregnancy, these muscles are placed on stretch as the baby grows. In early pregnancy, it is important to ensure that these muscles are strong so they can continue to give as much support as they can.
Precautions and Advice for Exercise
- Avoid situps or crunches
- Avoid over-heating - try not to exercise in the heat of the day and stay well-hydrated
- Watch your heart rate – a general guide is to keep the heart rate under 150 beats per minute
- Wear a supportive bra
- Do not exercise for long on your back
- Watch your posture - always maintain correct form and posture during exercise
- Avoid heavy weights
- Avoid excessive bouncing - e.g. star jumps, high-impact aerobics
- Avoid excessive breaststroke at the end of your pregnancy – this puts stress on the pelvic joints
- Avoid any exercises which cause pain
Sports That You Should Avoid During Pregnancy
- Scuba diving
- Heavy contact sports
- Sports where a fall could be a consequence - horse riding, rock climbing
STOP EXERCISE IMMEDIATELY AND SEEK MEDICAL ADVICE IF ANY OF THE FOLLOWING IS EXPERIENCED DURING OR AFTER EXERCISE:
- Elevated heart rate
- Uterine contractions
- Vaginal bleeding
- Amniotic fluid leakage
- Nausea or vomiting
- Shortness of breath
- Back or pelvic pain
- Decreased foetal movements
- Sudden swelling of ankles, hands and face
Bramwell, K. and Sherburn, M. (1995). 'Changing Shape: Exercising for Fitness and Wellbeing During and After Pregnancy'. Chapter 3, Guidelines for Minimizing Risks, p. 24-35. ISBM 0 670 85735 1.
Brayshaw, E. and Wright, P. (1994). 'Teaching Physical Skills for the Childbearing Year'. Chapter 2, Physiological Changes and Minor Physical Problems in Pregnancy, P. 19-27. ISBN 1 898507 02 3
Hill, T. (1994). 'The risks and benefits of exercise in pregnancy. Unpublished Masters Thesis, submitted for the dissertation requirements of the Masters of Public Health Degree'. Department of Public Health,
The Pregnancy Centre, More About Exercise in Pregnancy, http://www.thepregnancycentre.com/more_exercise.html
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