Pushing limits: the acute effects of a heavy-load resistance protocol and supine exercise on fetal well-being.

Objectives: To explore the acute effects of a heavy-load resistance protocol and exercise in the supine position on fetal heart rate (FHR) and uteroplacental blood flow.

Method: In this experimental laboratory study, 48 healthy pregnant athletes (elite: n=7; recreational: n=41) completed 3×8 repetitions with one repetition in reserve in sumo deadlift, bench press and incline bench press. FHR and umbilical and uterine artery pulsatility index (PI) were assessed before and after exercise. Symptoms of vena cava syndrome were recorded following the supine exercise.

Results: Pre- and post-exercise FHR remained within the normal range (110-160 bpm), but there were statistically significant increases after sumo deadlifts (p=0.002) and incline bench press (p=0.008), with no significant change after bench press (p=0.122). Umbilical artery PI did not change, while uterine artery PI significantly decreased after the sumo deadlift (p=0.005), bench press (p<0.001) and incline bench press (p<0.001). No fetal bradycardia was observed after the sumo deadlift or incline bench press, but one case occurred after bench press, resolving shortly after 3 min. Fetal tachycardia (>160 bpm) occurred in four cases after sumo deadlift, five after bench press and three after incline bench press, though none exceeded pathological levels (>180 bpm). One recreational athlete experienced symptoms of vena cava syndrome after the supine exercise, coinciding with a slight decrease in umbilical artery PI, but with stable FHR.

Conclusion: The results indicate that highly active women, especially those with resistance training experience, can safely engage in a heavy-load resistance protocol, including supine exercise, without jeopardising fetal well-being.