Can Pregnant Women Safely Do High-Intensity Workouts?
Share
Staying active during pregnancy is encouraged by most doctors, but how hard can you push your workouts when you're expecting? A new study from Norway has taken a closer look at this, asking: Is high-intensity interval training (HIIT) safe for your baby?
The answer? Mostly yes—if you're healthy, well-trained, and know your limits.
What Is HIIT and Why the Concern?
High-Intensity Interval Training (HIIT) involves short bursts of intense activity followed by brief recovery periods. It's popular because it saves time and builds fitness efficiently. But during pregnancy, intense workouts can raise concerns. Some worry that pushing too hard might reduce blood flow to the baby or cause stress to the fetus.
This study aimed to find out whether these concerns are valid, especially among women who are already very active.
The Study: Who Took Part and What They Did
Researchers worked with 60 pregnant women, including 10 elite athletes and 50 recreational athletes. All were between 26 and 35 weeks pregnant and exercised more than 4 hours a week.
Participants completed five rounds of 5-minute high-intensity intervals on a treadmill one day and on a stationary bike another day. Between each round, doctors monitored fetal heart rate (FHR) and blood flow to the uterus and placenta using ultrasound.
The target intensity was high: about 90% of each woman’s estimated maximum heart rate, or a 17 out of 20 on the perceived exertion scale.
What Did They Find?
Most women tolerated the workouts well. However, there were a few cases where the baby’s heart rate dropped (a condition called bradycardia) or rose too high (tachycardia) for a few minutes during or after exercise.
- Fetal bradycardia occurred six times during treadmill running but none were serious or long-lasting. Heart rates returned to normal within minutes after stopping.
- No prolonged bradycardia occurred during cycling.
- Some babies experienced temporary increases in heart rate (tachycardia), but again, these returned to normal shortly after.
Overall, the babies showed good blood flow, and no long-term issues were observed.
Why Did Running Cause More Changes Than Cycling?
Running had a slightly higher effect on maternal heart rate compared to cycling. Researchers think that upright, weight-bearing exercises like running may cause more blood to shift away from the uterus temporarily. This might explain why fetal heart rate changes were more common with treadmill workouts.
However, the study also noted that as the session continued, the number of abnormal heart responses decreased, suggesting the baby may adapt over time.
Key Takeaways for Expecting Mothers
- High-intensity workouts can be safe—especially for women who were already active before pregnancy.
- Listen to your body. Use tools like the Rate of Perceived Exertion (RPE) scale to stay in a safe zone (aim for “very hard” but not “max effort”).
- Cycling may be gentler than running during later stages of pregnancy.
- Get medical clearance. Always talk to your doctor before starting or continuing intense workouts while pregnant.
- Monitor how you feel. Stop if you notice unusual symptoms like dizziness, pain, or reduced fetal movement.
What This Means for Athletes and Healthcare Providers
This study helps reassure both athletes and doctors that high-intensity interval training isn’t off-limits during pregnancy—at least for healthy, active women. It shows that fetal responses should be monitored, but brief heart rate changes are not necessarily dangerous if they resolve quickly.
The research also highlights the importance of personalised care. Every pregnancy is unique, and so is every athlete’s response to exercise.
The Bottom Line
Pregnant women don’t have to give up challenging workouts entirely. With proper monitoring, rest breaks, and attention to how your body feels, high-intensity interval training can still be part of a healthy prenatal fitness routine. However, more research is needed to understand the long-term effects and how to adapt workouts for different types of pregnancies.
This study, published in BMJ Open Sport & Exercise Medicine, offers an encouraging step forward in giving clearer, evidence-based guidance for pregnant women who want to stay fit and strong.