Does your sporty patient want to HIIT the gym while pregnant?

A study by Canadian researchers suggests that high intensity interval training (HIIT) appears safe for both people who are pregnant and the fetus.

HIIT involves workouts where one or more minutes of effort raises the heart rate to close to 80% of the maximum heart rate and is interspersed with recovery periods.

Traditionally, physicians recommend moderate exercise for people who are pregnant. This recommendation is based on weak evidence because it has not been well studied, said Patrice Brassard, professor in the department of kinesiology at Laval University and Research Center of the Institut Universitaire de Cardiologie et de Pneumologie de Quebec.

“It's a proof of concept of sorts, showing that, under certain conditions, high-intensity interval training is not necessarily harmful during pregnancy,” Brassard said in a Laval University press release.

The researchers studied 15 women who were pregnant during two types of workouts on stationary bicycles: HIIT and moderate intensity. The women were an average of 27 months pregnant, and most were already physically active.

An initial workout session established their peak fitness, and then a few days later, they had either a 30-minute workout that was between 64% to 76% of their maximum heart rate, or a HIIT workout with 10 repetitions of one-minute intense activity, followed by one minute of recuperation. After at least two days, the women returned to the lab for the second type of workout.

The average heart rate was higher when the women trained using HIIT compared to moderate intensity exercise. Other factors were not significantly different between the two exercise regimes, including cerebral blood velocities, PCA, fetal heart rate and umbilical blood flow. Fetal bradycardia was not detected and umbilical systolic/diastolic (S/D) ratio, resistive index (RI), and pulsatility index (PI) were in normal ranges.

“The body adapts well to the hemodynamic changes induced by pregnancy, so both types of training are well tolerated,” Brassard said.

The results from this small exploratory study may not apply to all forms of HIIT, the researchers note. Further research is needed to determine what types of training are safe in physically active people who wish to pursue HIIT training during pregnancy.

The study involved researchers from Laval University in Québec, University of Alberta in Edmonton and Wilfred Laurier University in Waterloo, Ont. It was published in Sports Medicine.

Read: Do low-risk pregnancies need a third trimester ultrasound?