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.

Lack of research

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. 

WATCH | Study suggests some intense exercise may be fine during pregnancy:

Study suggests some intense exercise may be fine during pregnancy

New research from Alberta on pregnant women doing high-intensity interval training suggests rigorous workouts may be both safe and beneficial, but the study’s small sample size is unlikely to change national guidelines.

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.'”

No adverse effects

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.

“Both the mother and the baby responded quite normally, exactly as we would expect and tolerated the exercise very well. We didn’t see any adverse effects,” Davenport said.

Canada is one of the only countries that allows research that allows research in pregnant people working out at a maximal heart rate, which makes the study relatively unique, according to Davenport. She said the findings aren’t enough to change the guidelines, but believes other research can build on what they found. 

The participants were in their late second or early third trimesters, and ranged in age from their late 20s to mid 30s.  Davenport said many of the women had done HIIT workouts previously. They were all carrying singleton pregnancies, and none had any contraindications.

Encouraging results

Even though there were only 15 participants, the findings are important, said Dr. Milena Forte, a family physician at Mount Sinai Hospital and associate professor at the University of Toronto.

“We know that a minimal amount of exercise is really important. We haven’t really had good data on what the upper limit of exercise is in elite athletes and in women and pregnant patients that choose to exercise above the recommendations,” she said.  

Like Davenport, Forte worked on the 2019 Canadian exercise guidelines, but was not involved in the new study.

Forte, who has been delivering babies for 24 years, said that physical activity is beneficial for the majority of pregnant patients, and that absent specific kinds of contraindications, a pregnant person can do moderate exercise without checking with their practitioner. 

She said the type of activity depends on the individual and what they did before pregnancy, but she recommends everything from walking and strength training to pelvic floor exercises.

“I think sedentary behaviour is what we need to start thinking about as causing harm, not physical activity,” she said.

Forte said evidence has been mounting to show that exercise can help reduce risks and complications such as high blood pressure, diabetes, depressive symptoms and back pain. 

Dr. Sandeep Sharma, chief of obstetrics-gynecology and medical director of maternal child program at Oakville Trafalgar Memorial Hospital in Oakville, Ont., also finds the results encouraging.

“I think sedentary behaviour is what we need to start thinking about as causing harm, not physical activity.”​​​​​– Dr. Milena Forte

Sharma said he sees patients who are intense CrossFit athletes, personal trainers and otherwise very active who are all keen to continue with their activities.

When determining what type and how much physical activity to do, a good place to start is to consider fitness level before pregnancy, he said. 

“Because if someone’s not used to doing, for example, intense exercise, maybe pregnancy is not the time to just start out of the blue,” he said. 

Sharma said having a good fitness level can also help with labour outcomes. 

That’s one of the reasons Manca is continuing to exercise when she feels up to it. 

“It’s probably going to be hard regardless, but just being able to continue some activity and maintain some strength going into that feels like it gives me a bit more confidence,” she said.