As your baby grows inside you, you will become aware of obvious changes in your body's shape. Less obviously, there are internal physiological changes occurring also, which are essential for your baby`s growth and development. While the extent of both these obvious and hidden changes may differ, they all occur in all women.
What are the changes happening within your body? The hidden ones are the physiological changes needed to provide the right environment for your baby`s development. Changes such as heart enlargement and increased blood volume are not visible, but they are very important factors to consider when planning your exercise program. The obvious changes are — well, obvious! Your weight gain and your altered posture are very visible and can't be ignored.
How will the changes affect your choice of exercise? All of them will affect your ability to exercise in some way. The extent to which the changes affect you and your baby will:
- be different from the extent to which they affect other women and their pregnancies
- depend on the type of exercise you are doing
- depend on the stage of your pregnancy; for example, early in your pregnancy a high temperature is more threatening to your baby's development than later, whereas backache is usually more of a misery for you late in your pregnancy than early on.
THE HIDDEN CHANGES
The sections that follow are a straightforward account of the physiological changes occurring during pregnancy that will have an impact on your choice of exercise. The account is by no means exhaustive; rather, it is a basic overview written so that you can develop a respect for the limitations pregnancy imposes on exercise and plan your program accordingly.
Cardiac changes: During pregnancy your heart naturally becomes more efficient so that it can meet the increased demand for blood to supply your growing baby as well as you. Your heart pumps faster and your heart rate when you are at rest is higher. The muscle of your heart enlarges so that it can pump more blood with every beat
IMPLICATIONS FOR EXERCISE
- the good news is that you can usually achieve aerobic benefits with a lower increase of heart rate (that is, with less work) than when you were not pregnant. Your heart is already working harder than normal to meet the metabolic demands of your pregnancy, so you are always in a slightly aerobic state during pregnancy.
- your resting heart rate is higher, so your warm-up doesn't need to be as vigorous as before you were pregnant; however, both your warm-up and your cool-down should be longer and slower than normal.
- because when you are pregnant the range between your resting heart rate and your heart rate during exercise is smaller than when you were not pregnant, you should limit your level of exertion to what you perceive to be 'somewhat to moderately hard.
Because there is no conclusive research currently available about the maximum safe heart rate during pregnancy, it is difficult to give absolute guidelines. It appears best to use an exercising heart-rate range of between 60 and 75 per cent of your maximum heart rate (see Chapter 5 for an explanation of this), coupled with the perceived level of exertion just described.
- reducing the duration and intensity of the exercise is important as pregnancy progresses. Talk to your medical consultant about what is best for you and your baby.
