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Will cycling use up my heartbeats?

James Witts
27 Jul 2018

If you’ve only got a certain number of heartbeats in your life, will intensive exercise use them up quicker?

There’s a theory that we all have a finite number of heartbeats in our lifetimes, and that once we’ve worked our way through them all – however long it takes – that’s it, we’re dead.

The same is supposedly true for animals, such that small animals with high heart rates and fast metabolisms have shorter lifespans than big animals whose hearts beat slower.

Some sources suggest most animals have a lifespan of about a billion heartbeats, while us humans can expect to have nearer two billion. There are said to be exceptions to this rule, and plenty of people who suspect the theory is bunkum in the first place.

When Cyclist puts the notion to cardiologist and cyclist André La Gerche, he isn’t as quick to dismiss it as we might have suspected: ‘Obviously the idea of a defined number of heartbeats is simplistic,’ he says.

‘But as a broad concept for understanding over-training and the potential risks of high-level sport, it’s an interesting discussion point.’

So let’s discuss it. As a reader of Cyclist, there’s a good chance you spend a fair amount of time pedalling a bike, and when you do your heart rate shoots up.

According to the finite heartbeat theory this shortens your lifespan. Which begs the question: wouldn’t you be better off leaving the bike in the shed and sprawling on the sofa instead?

It’s not that simple. La Gerche offers the example of a recreational rider who might train for two hours at an average heart rate of 150 beats per minute (bpm). That’s 18,000 beats over the course of 120 minutes.

In the same time, a non-exercising, resting adult will average around 80bpm, which adds up to 9,600 beats in two hours – 8,400 fewer beats than the exercising rider.

You might think that would be the end of the debate, but it isn’t. ‘For the other 22 hours of the day, the rider might exhibit an average heart rate around 30bpm lower,’ La Gerche continues.

’That’s 39,600 fewer beats over the 22 hours, leaving the exercising rider’s net total 31,200 beats lower each day.’

Pros and cons

There are plenty of other health benefits associated with regular exercise, of course, including a lower chance of heart vessel disease, cancer, heart attack and diabetes.

But how about comparing the recreational rider or serious amateur cyclist’s heartbeat profile with a pro who might race for 100 days a year, racking up in the region of 14,000km – on top of 15,000-20,000km per year in training?

Are those guys pushing so hard, so often, that they are racing to an early grave?

Let’s take the Tour de France as an example. On average, the riders will race for four to six hours across 21 stages, during which their average heart rate will be around 150bpm.

We also need to take into account the several hours after each stage it will take for their heart rate to return to baseline.

‘This equates to something like 30,000 “extra” beats being used over the norm every day,’ says La Gerche.

‘Even taking into account the eight to 10 hours each day when their heart rate falls to its resting rate, their heart still beats around 20,000 times more than a non-exercising adult who rests for the entire day and night.’

Taking things to extremes, if a rider completed a 52-week Grand Tour, their heart would be so exhausted that health implications would see them keel over at a young age. Clearly this isn’t the case.

‘We know that elite riders actually spend most of the 24 hours each day resting,’ says David James, professor of exercise physiology at the University of Gloucestershire.

And when riders rest, they rest, many refusing to even sit when they could lie, with almost militant preservation of energy stores. We also know that resting heart rates can reach uber-low figures, the most famous example being Miguel Indurain’s 28bpm.

Research undertaken by the Paris Cardiovascular Centre measured the longevity of French riders – 786 in all – who’d completed at least one Tour de France between 1947 and 2003.

The results showed that, on average, Tour riders lived 6.3 years longer than the national average, with a third fewer deaths due to cardiovascular causes – this despite the prevalence of amphetamines, anabolic steroids, human growth hormone, EPO and various other pharmacological concoctions riders indulged in from the 1950s to 2000s.

It seems the heart of a pro is a long-lasting organ, and the reason is something called stroke volume. Allow us to explain…

Bigger is better

An average person’s heart is around the size of a fist and weighs about 300g, while good recreational cyclists who’ve trained regularly and progressively for years may have hearts weighing twice that.

If you’re racing the Tour, that figure can be as high as 1kg.

‘Part of that’s down to a thickening of the walls,’ says La Gerche, ‘but it’s predominantly down to an increase in the size of the chambers, which blow up like a balloon.’

That’s important because chamber size influences stroke volume, which is the volume of blood pumped from the heart with each beat. During exercise your heart pumps out blood at a 70% efficiency rate.

The recreational cyclist’s heart can hold around 250ml of blood, which means pumping out around 175ml of blood with every beat.

Professional cyclists’ chambers can fill with around 400ml of blood, resulting in 280ml of blood pumped out with every beat. 

Apply that difference to cardiac output – the amount of blood pumped out each minute – and you can see why a fit individual requires fewer beats for a greater workload.

For instance, say the professional and recreational rider are cycling at 140bpm. The cardiac output for the pro is 39,200ml, or 39.2 litres of blood each minute; the recreational rider comes in at 24.5 litres of blood each minute.

That’s why, when resting, an elite rider’s heart rate is lower than a recreational rider’s – for instance, 28 versus 60 – and significantly lower than a sedentary individual’s of 80-plus.

All this suggests that pro riders have the strongest hearts and therefore the longest lives, but again, it’s not
quite as simple as that.

La Gerche says, ‘My suspicion from research we’ve done is that the heart is under greatest strain during long rides at a high intensity. We’ve put an ultrasound on riders after five or six hours of intense riding, including many climbs, and you can see that the heart is fatigued.’

There’s a growing body of research that suggests some heart rhythm problems are more common in athletes who train heavily and intensely for significant periods of time. These known arrhythmias can range from completely safe through to life-threatening.

So where does all that leave us? ‘If I was pushed to give an answer as to whose heart beats less over the long term, I’d say it’s the person cycling regularly all their life, no matter what the intensity,’ says James.

La Gerche adds, ‘The best way to use fewer heart beats is to exercise for 30-120 minutes each day, with some sessions including brief bouts of high-intensity exercise.’

There you have it: Cyclist readers, with their lifestyle of regular but not pro-intensity riding, could outlive everyone else. Still, as the saying goes, it’s not the years in your life that count, it’s the life in your years.

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