While the evidence has been clear that moderate intensity exercise is safe and beneficial in pregnancy, little has been researched on the safety of high intensity (>90% heart rate max) exercise in pregnancy. A new study in May 2023 has shed some new light on the matter and found vigorous exercise to be safe for pregnant women and their fetuses.

The study included women from 24-30 weeks of pregnancy. Each conducted a high intensity interval workout and also a moderate intensity workout at different times and in randomized order. The high intensity interval workout included intervals of 1 minute of effort x10 at >90% heart rate max. The moderate intensity workout included 30 minutes of continuous exercise at 64-76% of heart rate max. Multiple maternal and fetal cardiovascular metrics were monitored. Maternal heart rate, blood pressure, and middle and posterior cerebral artery blood velocity were monitored continuously. Fetal heart rate, as well as umbilical systolic/diastolic ratio, resistive index, and pulsatility index were assessed immediately before and after exercise. All metrics were found to be in safe ranges for both moderate and vigorous workouts. Aside from increased maternal heart rate with vigorous exercise, no major differences were found in any cardiovascular metrics for mother or fetus in moderate vs vigorous exercise bouts.

While this research is encouraging, it is only just a start. This looked acutely at the effects of vigorous exercise. What might change in long term metrics with continued vigorous exercise in pregnancy? How frequent of vigorous exercise is safe or beneficial? Can vigorous exercise extend beyond 10, 1 minute intervals? Further research will help guide the refining of exercise recommendations for pregnant women.

At Mend, pelvic health physical therapy in Boulder and Lafayette, we don’t perpetuate fear-based pregnancy recommendations. Rather, we use the latest research and each’s individualized needs to help guide women through pain free fitness in pregnancy.

*please consult with your medical provider to identify your individual needs before starting a vigorous exercise routine

Wowdzia JB, Hazell TJ, Berg ERV, Labrecque L, Brassard P, Davenport MH. Maternal and Fetal Cardiovascular Responses to Acute High-Intensity Interval and Moderate-Intensity Continuous Training Exercise During Pregnancy: A Randomized Crossover Trial. Sports Med. 2023