One of the strongest protective factors against a heart attack is your level of fitness. But, the question playing in the back of some people’s minds as they take up a new physical activity is: Does too much exercise, particularly of the vigorous kind, do more harm than good?

Training for a marathon, triathlon, or other endurance event is no easy feat. Each bout of strenuous exercise puts extra pressure on the cardiovascular system, the joints, muscles and the mind.

And as an increasing number of everyday joggers take their training to the ‘next level’, it raises some complex and confronting questions around the safety of extreme sport.

Among the experts leading this discussion from a heart health perspective is Dr Andre La Gerche, a world-renowned sports cardiologist from the Melbourne-based Baker Heart and Diabetes Institute.

He says that the typical demographic of marathon runners has been changing in recent decades, triggering a new wave of research into this area.

“Looking at marathons 30 years ago, it was a younger, fitter population. Now it’s a middle-aged and older population, often without a big history of sporting participation,” Dr La Gerche tells The New Daily.

Watching from the sidelines of any marathon event, and it would seem that he’s right. The typical endurance runner, with their lean, sinewy physique, is no longer the only passing figure on the challenging 42-kilometre course.

Now, it’s your next door neighbour: The weekend warrior who’s usually desk-bound at work; a father of three or your grandmother; or the guy who made it his mission to go from ‘couch to 5k’, and then some.

“From a public health perspective, it’s a really good thing because exercise training is such a positive thing for health. But it presents some unique issues.”

One of these key issues, Dr La Gerche says, is the risk of a heart attack. Over the past couple of years, he’s been leading a joint Australian-Belgian study that is looking into the effects of endurance exercise on heart function, particularly in the long term.

Some of the preliminary findings from the Pro@Heart study will be presented at the institute’s Sports Cardiology Conference taking place in Melbourne from January 19.

Other topics at the conference by leading cardiologists include Exercise as the antidote for the ageing heart and a case study review of heart problems in middle-aged athletes.

Dr La Gerche says it’s not clear if the rate of heart attacks is increasing in middle-aged athletes.

What is known, and widely accepted, is that strenuous exercise is a proven trigger for cardiac events, and if you are going to have a heart attack then training for a marathon is a high-risk time for one.(Cardiologists see more people for heart attacks while training for a marathon than during or after the actual race, Dr La Gerche says).

This is known as the exercise paradox.

“As medical researchers it’s a reminder that there are some people in that group that might have a heart attack, and it would be better if we could predict who those people will be,” Dr La Gerche says.

However, participating in regular exercise reduces a person’s risk of a heart attack in the long run. And that’s when the picture becomes muddier, for both the public and the experts.

“Regular exercise protects your heart. Your heart is stronger, and your heart arteries are less likely to become blocked.

You can’t outrun a heart attack, but you can reduce your overall lifetime risk.”

But, the crux of the issue is the intensity of exercise or physical activity.

A US study published in 2000, Triggering of sudden death from cardiac causes by vigorous exertion, found that the relative risk of sudden death in men during and after 30 minutes of vigorous exertion was 17 times higher than during times of lighter exercise.

The 21,481 men included in the study were in their 40s to 80s and were followed for 12 years during the study period.

However, the male participants who did regular exercise were still far better off than those who were physically inactive, the researchers found.

“Men who exercised at least five times per week had a much lower [relative] risk,” the authors wrote in the paper.

Adding a caveat that “this risk was still significantly higher than that during periods of lighter exertion or none”.

It’s this regular, light to moderate exercise that has been widely touted by official health groups and doctors for decades.

That’s the message from bestselling author and cardiologist Dr James O’Keefe Jr who barracks for the moderately-paced runner in his popular TED Talk from 2012. He suggests, that for longevity and health, runners should hit the pavement regularly, but not too hard or fast, and for fun and enjoyment more often than not.

Australia’s official physical activity guidelines recommend that adults work their way up toward five hours of moderate intensity physical activity, or up to 2.5 hours of vigorous intensity exercise per week.

Dr La Gerche says that people can successfully take up marathon events in middle age or older. Not only can they achieve this goal safely, he argues, but it will also have a positive impact on their cardiovascular health.

Spotting the top warning signs

Experts from both sides agree that getting active far outweighs not doing anything at all, but there are some important warning signs to look out for.

• Chest pain: “We regard chest pain as anything from about the nose to the knees, because it can present in funny ways,” Dr La Gerche says
• Pay particular attention to any chest pain that presents while exercising but goes away at rest
• Shortness of breath, especially if it suddenly worsens
• Heart palpitations or irregular heart rhythm
• Light-headedness or a feeling that you’re going to pass out while exercising

Dr La Gerche says that people should take these symptoms seriously, even if it feels as though the symptoms are minor or unrelated.

“The one that always shakes me is the person who has had clear symptoms and thought, ‘That can’t be my heart because I’m too fit’.”

He advised that people 45 and over have their cholesterol and blood pressure checked, regardless of fitness level, pacing your training efforts over a longer period, rather than overexerting yourself, and seeing a doctor if you notice any symptoms.

“There’s a lot of reasons to be fit, a lot of reasons to train, but it’s not an insurance policy,” he says.

“If people get into sport in a sensible and educated way, overall they’re safe, and if they develop any symptoms or any concerns that’s when they need to see their doctor.”