Exercise in pregnancy and postpartum: a physiological guide
Introduction
Few recommendations have changed so much in a generation. For decades pregnant women were advised to cut back on activity, avoid lifting and stay under a certain heart rate. Today the major clinical guidelines — among them those of the American College of Obstetricians and Gynecologists — recommend the opposite: stay active throughout pregnancy unless there's a medical contraindication.
The shift rests on accumulated evidence of less gestational diabetes, less pregnancy hypertension, better weight control, less low back pain and better mood, with no increase in the risk of preterm birth or low birth weight in uncomplicated pregnancies.
A necessary caveat before going on: every pregnancy is different, and some situations change the recommendation entirely. What follows is a general framework, not individual guidance; the decision belongs to your midwife or obstetrician.
Pregnancy isn't an injury. It's a period with physiological adaptations worth understanding so you can train with judgment.
What changes in the body
Blood volume and cardiac output rise considerably. Resting heart rate goes up and heart-rate zone formulas stop being useful. This is why the guidelines have moved to recommending perceived effort and the talk test instead of pulse limits.
Relaxin increases ligament laxity. This is one of the most misunderstood points: it doesn't mean joints are fragile or that strength work should be avoided. It means caution with extreme ranges and forced stretching.
The center of gravity shifts forward and up, which alters balance and increases lumbar load. The practical consequence is avoiding activities with a risk of falling.
Respiratory demand rises, and breathlessness appears with efforts that didn't previously cause it.
The pelvic floor carries a growing load, with or without exercise. Training it makes sense during and after.
What to do during pregnancy
The general framework for uncomplicated pregnancies:
- Aerobic activity: about 150 minutes a week at moderate intensity. Walking, stationary bike, swimming, elliptical.
- Strength: two or three sessions a week covering the major muscle groups, with moderate loads and good technique.
- Pelvic floor: specific work several times a week, ideally prescribed by a specialized physical therapist.
- Gentle mobility and breathing work.
Intensity: the practical reference is being able to hold a conversation. If you can't speak in sentences, ease off.
By trimester, broadly:
- First trimester. Usually the hardest because of nausea and fatigue, not risk. You can continue what you were already doing, adjusting volume.
- Second trimester. Typically the best window. Here it's worth avoiding prolonged work flat on your back, which in some women reduces venous return and causes dizziness.
- Third trimester. Less volume, more walking and gentle work, attention to balance and temperature.
What to avoid: contact sports, activities with a risk of falling (mountain biking, skiing, horse riding, climbing), scuba diving, exercise in extreme heat, high altitude if unacclimatized, and sustained Valsalva when lifting.
Hydration and temperature matter more than usual. Avoid very hot environments and long sessions without drinking.
Reasons to stop and seek advice immediately
Stop activity and contact your healthcare professional in case of:
- Vaginal bleeding or fluid leakage.
- Painful, regular contractions.
- Chest pain, dizziness or fainting.
- Severe headache or visual disturbances.
- Calf pain or swelling.
- Breathlessness out of proportion, or before exertion.
- Decreased fetal movement.
There are also absolute contraindications — significant heart disease, advanced placenta previa, cervical insufficiency, preeclampsia, risk of preterm labor, among others — where exercise isn't indicated. Hence the first step is always to ask.
Postpartum
Recovery doesn't start at the gym: it starts with breathing and walking.
Weeks 1 to 6. Short, progressive walks, diaphragmatic breathing, gentle activation of the pelvic floor and transverse abdominis if there's no pain. After a cesarean or a significant tear, all of this is delayed and set by your medical team.
The postpartum check-up isn't an automatic green light. Six-week clearance confirms that healing is going well, not that the pelvic floor is ready to run. Ideally, get an assessment with a pelvic floor physical therapist before returning to impact.
Abdominal separation. Some separation of the rectus muscles is normal at the end of pregnancy and resolves on its own in many cases. What matters isn't so much the distance as the ability to generate tension along the midline. Classic crunches and demanding planks are best delayed until there's control.
Return to running. The criterion most used in physical therapy places the return to impact around three months, and only if simple tests are passed: walking 30 minutes without symptoms, hopping without urine leakage or heaviness, and reasonable single-leg balance and strength.
Warning signs that deserve assessment: urine leakage, a sensation of heaviness or a vaginal bulge, persistent low back or pelvic pain, or pain during sex. These are common, and common isn't the same as inevitable: they're treatable.
Breastfeeding and exercise are compatible. Adequate hydration and nutrition are recommended, and for comfort, training after a feed.
Common mistakes
Stopping altogether "just in case". In uncomplicated pregnancies, inactivity carries more risk than movement.
Going by heart rate. The usual zones don't apply; use perceived effort.
Returning to impact because the calendar says so. Tissues don't read calendars.
Ignoring urine leakage. Very common after birth, and not something to live with.
Chasing your figure before your function. The right order is breathing, pelvic floor and deep core; everything else after.
Final thought
Moving during pregnancy and rebuilding calmly afterward is, for most people, the safest and most useful thing to do. The key isn't intensity but judgment: conversational intensity, no fall risk, attention to warning signs, and a postpartum progression guided by function rather than dates. If you're pregnant or have just given birth, the first conversation isn't with a training plan: it's with your midwife, your obstetrician or a pelvic floor physical therapist.