Is fetal well-being jeopardised during high-intensity interval training?

Area of Science:

• Sports Medicine
• Maternal-Fetal Medicine
• Exercise Physiology

Background:

• Understanding the impact of intense exercise on pregnancy is crucial for maternal and fetal health.
• High-intensity interval training (HIIT) is popular but its effects during pregnancy require careful evaluation.

Purpose of the Study:

• To investigate the acute effects of high-intensity interval training on fetal heart rate (FHR) and uteroplacental blood flow in athletes.
• To assess the safety of HIIT for both mother and fetus during pregnancy.

Main Methods:

• 10 elite and 50 recreational athletes underwent 5x5-minute HIIT intervals on a treadmill and cycle ergometer.
• Fetal heart rate and uteroplacental blood flow were measured during 4-minute recovery periods between intervals.
• Target intensity was 17 on Borg's Rating of Perceived Exertion (RPE) and 90% of maximal maternal heart rate (MHRmax).

Main Results:

• Exercise intensity averaged 16.0-16.4 RPE and 84.6-89.4% MHRmax.
• Six instances of fetal bradycardia (<100 bpm) occurred during running, leading to exercise termination, but normalized within 8 minutes.
• No prolonged fetal bradycardia was observed during cycling; however, fetal tachycardia (≥180 bpm) led to exercise termination in 5 participants.

Conclusions:

• HIIT can induce transient fetal heart rate alterations, including bradycardia and tachycardia.
• Despite these events, highly active pregnant women appear to tolerate HIIT without significant long-term harm to fetal well-being.
• Individualized monitoring and exercise prescription are recommended for pregnant athletes engaging in high-intensity exercise.