The paradox of intense physical activity is that in the midst of it we are more likely to trigger a heart attack, even though, done regularly, it reduces our overall risk.

To better understand the relationship between exertion and heart health, a growing body of research has explored the many ways exercise helps our hearts and how can we best mitigate the risk of heart attack.

The ‘best’ exercise is the one you are conditioned for.Credit:Getty

The latest study, in press online ahead of its print publication, looked at 762 Australian adults who have had a heart attack and the type and intensity of exercise they were doing in the lead-up to their diagnosis.

For reasons not yet known the risk was higher among those doing isometric exercise, for example lifting weights, compared with those doing anaerobic exercise, for example going for a long run.

It also found that those who attempted vigorous exercise when they never or rarely did it before had a 77-times higher risk of heart attack.

“It can go up to 135 fold [in risk],” says lead researcher Dr Tom Buckley from the University of Sydney’s Faculty of Medicine and Health. “The risk goes down incrementally. Somebody who already does [vigorous exercise] one-to-two days a week is still 20 fold.

There is an emerging body of literature that to ameliorate your risk during high-intensity activity you have to be exposed to it regularly.

“It’s when you exercise at that level more than four days a week that you really, really lower the risk.”

The risk of heart attack for the “super fit” is still double for the duration of an intense workout and a couple of hours afterwards.

“But then when you’re sitting on the lounge afterwards you’re four times less likely to have a heart attack than if you don’t [exercise],” explains Dr Buckley, an avid cyclist and triathlete.

Separate research from earlier this year found regular exercise can halve the risk of heart attack among healthy people, providing it includes getting the heart rate up.

“People think, ‘Well, I go and do my 30-minute walk four times a week, therefore I'm conditioned,’ but … that type of low-intensity activity doesn’t prepare you for the big risk event.”

This is because a “big risk event” is not confined to doing an F45 class or the City2Surf (though these are the types of vigorous exercise events that can trigger a heart attack in an unconditioned person). They also include picking up large rocks in the garden, catching a heavy piece of furniture that is falling over, sprinting to catch the bus or lifting a boat from the water onto a trailer.

“There is an emerging body of literature that, to ameliorate your risk during high-intensity activity, you have to be exposed to it regularly,” Dr Buckley says. “That was one of the key findings here.”

So the best exercise for our hearts may well be a mix that prepares us for life and all the moments we have to catch, lift and sprint.

“When I explain it to my students, I try to get them to think about how humans have developed over hundreds of thousands of years,” explains Dr Chris Abbiss, associate dean of research in the School of Medical and Health Sciences at Edith Cowan University. “We never developed doing one specific type of exercise… We need a certain amount of strength for everyday activities, we also need prolonged endurance exercise and some intense exercise as well…

“It’s to trigger adaptations, so unless we stress something it’s not going to adapt. Unless we stress the heart the heart won’t adapt to be stronger next time.”

The caveat is ensuring we are medically cleared to do it and making sure we build up slowly, conditioning the body gradually. For some people climbing a flight of stairs is “vigorous”, let alone attempting to enter a “fun run”.

“For me, the best physical activity is the one that is planned, that you warm up for, moderate your level of exertion and ensure enough recovery,” Dr Buckley says.

“Warming up and warming down is just as important because you’re shunting blood flow from organs to muscles.”

Dr Abbiss agrees, adding that the guidelines have shifted dramatically in recent years:

“A lot has changed because of our understanding of risk versus benefit. Gradually increase the volume and intensity … get the right advice and incidental exercise. There is risk, but the benefits far outweigh the costs.”

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