Physiological Responses to Physical Activity
With Sophie and Marcus, Biology & Physiology Specialist
Key Takeaways
- Because midwives advise women on exercise throughout pregnancy and postnatally, and that advice needs to be evidence-based and physiologically informed — not just generic reassurance.
- Multiple systems respond acutely.
- Heart rate and cardiac output increase to deliver oxygen to working muscles.
- The cardiovascular system is already working harder.
- This doesn't mean exercise is harmful — it means intensity needs to be modulated, and women should avoid supine exercise after the first trimester.
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Full Transcript
Sophie: We're finishing the anatomy series by looking at physiological responses to physical activity. I'm Sophie, with Marcus, our Biology and Physiology Specialist. Marcus, why is exercise physiology relevant for midwives?
Marcus: Because midwives advise women on exercise throughout pregnancy and postnatally, and that advice needs to be evidence-based and physiologically informed — not just generic reassurance.
Sophie: What happens in the body when we exercise?
Marcus: Multiple systems respond acutely. Heart rate and cardiac output increase to deliver oxygen to working muscles. Breathing deepens and quickens. Blood is redirected from the gut to the muscles. Core temperature rises.
Sophie: Do these responses change in pregnancy?
What should learners understand about physiological responses to physical activity?
Marcus: Significantly. The cardiovascular system is already working harder. Cardiac reserve is reduced. This doesn't mean exercise is harmful — it means intensity needs to be modulated, and women should avoid supine exercise after the first trimester.
Sophie: Why is the supine position problematic?
Marcus: The gravid uterus compresses the inferior vena cava when lying flat, reducing venous return to the heart and potentially causing hypotension and dizziness — which reduces uteroplacental blood flow.
Sophie: What are the benefits of exercise in pregnancy?
Marcus: Strong evidence supports reduced risk of gestational diabetes, pre-eclampsia, excessive gestational weight gain, and postnatal depression. Pelvic floor exercises reduce incontinence. Birth outcomes may also improve.
Why is physiological responses to physical activity important in midwifery practice?
Sophie: Are there situations where exercise should be avoided or restricted?
Marcus: Yes — placenta praevia, cervical incompetence, severe anaemia, and uncontrolled hypertension are key contraindications. Midwives should screen for these before giving exercise advice.
Sophie: What about the muscular adaptations to regular exercise?
Marcus: With training, muscle fibres become more efficient at oxidative metabolism — they use oxygen more effectively and fatigue less quickly. Cardiovascular adaptations include increased stroke volume and lower resting heart rate.
Sophie: Postnatally, how soon can women resume activity?
What should learners understand about physiological responses to physical activity?
Marcus: Low-impact activity can begin from days postnatally, but impact exercise should wait until pelvic floor function has been assessed — typically around 12 weeks. Rushing this risks long-term prolapse and incontinence.
Sophie: So exercise advice is a clinical conversation, not just a general encouragement.
Marcus: Exactly. Personalised, evidence-based, and timing-sensitive. Understanding the physiology behind it is what allows a midwife to advise with confidence and appropriate caution.