Your body will undergo many changes during pregnancy.

Pregnancy brings significant changes to your body. Understanding what is happening and why helps you make sense of the adjustments you may need to make to how you move and exercise. The goal is not to stop exercising. It is to exercise in a way that works with your changing body.

Joint changes

Relaxin and progesterone increase significantly during pregnancy. These hormones loosen the ligaments that support your joints, which allows your pelvis to widen in preparation for birth. This is a normal and necessary change, but it does mean all your joints need more support during exercise, not just your pelvis. Your knees, ankles, wrists, and upper back are all affected.
Your feet also change. The increased weight of pregnancy flattens the arches, and circulation changes can cause puffiness in the feet and ankles as the day goes on.
As your pregnancy progresses and your belly grows, high-impact exercise will become increasingly uncomfortable. Be aware of how your body is responding and adjust accordingly.
To support your joints during exercise:

Wear supportive shoes
Be aware of high-impact exercise and how your body responds to it
Favour double-leg movements over single-leg work
Bring your knees together when changing positions, for example getting out of a car or out of bed
Consider water-based exercise, which reduces load on joints significantly

If you experience pain or notice changes to how you walk, speak with the health professional supporting you through your pregnancy.

Weight and balance changes

Average weight gain during pregnancy is 10-15kg, though this varies. Weight distribution and body shape change significantly as pregnancy progresses.
As the belly grows, the body’s centre of gravity moves forward. This affects balance and coordination, which is why standing on unstable surfaces or performing single-leg movements requires extra care during pregnancy. WHEN’s Exercise and Pregnancy Guidelines recommend modifying or avoiding these movements, particularly in group exercise settings where individual supervision is limited. Exercise & Pregnancy guidelines

Heart and cardiovascular changes

Your heart is already working harder during pregnancy. Your resting heart rate increases to get more blood to your baby, which means your body is doing more even when you are sitting still.
Even if you were exercising at a high level before pregnancy, your cardiovascular system has changed. Growing a baby takes real resources, and those resources are no longer fully available for exercise the way they were before.
The Borg Talk Test is a simple and reliable way to check how hard you are working. If you can sing comfortably, you could work a little harder. If you can hold a conversation you are at a good level. If you cannot hold a conversation, ease back.
Your blood pressure also lowers during pregnancy and your blood volume increases significantly. Getting up quickly can make you feel dizzy or light-headed, so be aware of how you change positions.

Supine position (lying on your back)

From the second trimester (from 12 weeks), lying flat on your back is not recommended. The weight of the growing uterus can compress the vena cava, the major blood vessel that returns blood to your heart, which can make you feel dizzy, light-headed, or faint. This recommendation aligns with RANZCOG guidance.
The evidence is reassuring that your baby will be safe. You are just as important in this picture, and that does not always get said. Fainting is distressing at any time. During pregnancy it can trigger significant anxiety, guilt, and fear about what happened and why. You deserve to move through your pregnancy without that experience.
Safe alternatives include side-lying, seated, standing, or using a wedge for support.

Body temperature

Your body temperature is naturally slightly higher during pregnancy. You may notice you feel warmer than usual, have hot hands and feet, or a stuffy nose. These are all ways your body is helping heat escape to keep you and your baby comfortable. Your body is remarkably good at adapting.
That said, exercising in extreme heat adds extra demand on top of changes that are already happening. Australia’s climate means this is a real consideration, particularly in summer or in hot, poorly ventilated spaces.
To stay comfortable during exercise:

Drink water before, during, and after exercise
Wear lightweight, breathable clothing
Exercise in a cool, well-ventilated space
Be mindful of exercising outdoors in extreme heat
Avoid spas, saunas, and any form of heated exercise classes

Energy levels

Energy levels vary throughout pregnancy. Many women experience fatigue, particularly in the first trimester and again in the third. Iron deficiency is common during pregnancy and can reduce the oxygen available to your muscles, contributing to tiredness. Changes to sleep are also common.
Listen to your body. On days when energy is low, gentle movement such as walking or water-based exercise is still beneficial.

A note on individual variation

Every pregnancy is different. These changes do not affect all women in the same way or at the same time. Use these guidelines as a framework, not a rigid set of rules, and adjust based on how you feel.
For detailed evidence-based guidance on exercise throughout pregnancy, including recommendations on running, weightlifting, pelvic girdle pain, and supine positioning, see WHEN’s Exercise and Pregnancy Guidelines. Exercise & Pregnancy guidelines