Extreme Exercise: Is Our Obsession With Ever Harder Fitness Challenges Bad For Our Hearts?

Is it just us or is everyone doing some ridiculous endurance challenge these days?

Half our friends are already in training for next year's London Marathon and the rest have taken on Tough Mudders, Iron Mans or in some extreme cases Ultramarathons and Olympic triathlons.

We look at these (crazy) people in awe at their physical prowess and dedication to being fit and healthy. But there's something to make us gym-a-couple-of-times-a-week-and-that's-it types feel better about our fitness choices - heavy endurance exercise could actually be bad for the heart.

According to new research endurance exercise can 'interfere with heart rhythms' and people who train to this level are more likely to experience disturbances or heart arrhythmias

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Not that we're wishing any heart problems on our friends of course! But it does make us question the safety of these ever more extreme fitness challenges.

Everyone knows that running a marathon isn't 'good' for you. Not really. It's an incredible achievement and the mental challenge and dedication most likely are good for you as a whole, but your body will pay in many sore ways in the weeks and months following the event. And let's not forget the tragedies when runners die during or shortly after running marathons.

Research on mice by the British Heart Foundation suggests that this sort of training affects the body's inbuilt pacemaking process. It causes a decrease in HCN4, which is an important protein that's responsible for low heart rate - something elite athletes experience.

But let's not get too ahead of ourselves and think that not exercising is probably safer. The risk of heart rhythm problems for even elite athletes is still fairly low, while the benefits of exercising, even to this level are plentiful.

Prof Boyett, who lead the study, said: "Although endurance exercise training can have harmful effects on the heart, it is more than outweighed by the beneficial effects."

If you are concerned, exercising but not to super-endurance levels is definitely a safer bet. But if you're after the mental challenge and the satisfaction these events bring, just make sure you're training sensibly and get your heart checked out before you taken on a major challenge.