Short bursts of intense exercise may be fine during pregnancy, a new study suggests

Cycling up hills is harder than it used to be, but at 27 weeks pregnant with twins, Terra Manca isn't ready to park her bike.

Manca, 39, is a longtime athlete. The Edmontonian was on the varsity cross-country running team while in university, competed in road races as a cyclist and also cross-country skis.

Being able to continue with those sports throughout her pregnancy has helped her stay energetic, feel comfortable and remain social.

"I've been exercising throughout with whatever my body is up to and whatever I find fun and worthwhile," she said.

Manca's family doctor has been supportive of her continuing to exercise, but advised backing off if she starts to experience certain symptoms. 

"I plan to continue biking for as long as I fit on my bike and feel comfortable. Twin pregnancies — you can get pretty big, so it could potentially get pretty uncomfortable," she said. 

Many studies have found that exercise can help reduce the risk of pregnancy complications. The 2019 Canadian guideline for physical activity throughout pregnancy recommends 150 minutes per week of moderate exercise for people who are not experiencing health factors or concerns that could make exercising a risk.

But there's very little research into what happens if a pregnant person works out beyond what's recommended, which is a real problem, said Margie Davenport, a pregnancy researcher with the University of Alberta's Faculty of Kinesiology, Sport and Recreation.

"In the area of exercise and pregnancy, there are a lot of longstanding, often theoretical concerns. And so because of that we've basically been prevented from actually testing these concerns to see if they're correct or incorrect," said Davenport, who is a professor and is director of the univesrsity's program for pregnancy and postpartum health. 

She was one of the authors of the 2019 recommendation. Now, a study published in Sports Medicine Journal  by her and a team at the U of A found that short bursts of intense physical activity may be safer than previously believed.

"Many [pregnant women] will continue to do high-intensity exercise well beyond what we have in current recommendations," Davenport said. "By doing the research, we can provide them with the evidence to be able to safely say 'You can do this and you can't do this.'"

For the study, the 15 pregnant participants did one 30-minute moderate intensity workout and one shorter high-intensity interval training workout (HIIT) on different days. 

The HIIT workout was done on a spin bike and saw the women complete 10 one-minute sprints at at least 90 per cent maximum heart rate, with active rest in between the intervals. 

During the workout, the researchers monitored both the women and their fetuses' heart rates and other metrics, such as blood flow to the fetus.