Marathon Man – What Running Does to Your Heart

Consider the runner as an abstract, and you’ll probably picture someone along the following lines: lean, focused, determined and ruthlessly fit. Unlike the artificial movements we create by lifting weights in the gym, there’s an element of risk and adaptability involved with running, as well as a noteworthy ascetic advantage – bye bye strip-lights, grunting steroid bros and the hum of air-conditioning, hello fresh air and varied terrain. With our existences increasingly eked out indoors in offices, on public transport and in queues at supermarkets, it’s not surprising that an increasing number of people are choosing to exercise al fresco.

Traditionally considered a solo enterprise, it’s not surprising that humans have found a way to add a competitive edge to running – first came apps which allow you to post your run-time, route and distance on social media, then came the explosion in mass-popularity of marathons. The importance of aerobic exercise is well-documented and its benefits are barely worth rehashing here: but what about its bigger, bolder, tougher cousin? How does running 26 miles or so affect your heart, and does it benefit your body or not?

What Happens When You Run?
As with any cardiovascular activity, running causes your body to redirect blood away from less active muscles and towards the ones that are doing the work, causing an increase in blood flow/volume to and from the heart. Over time, your heart adapts and enlarges, meaning it increases in capacity and can pump a higher volume of blood with each beat. Long distance runners typically have a lower resting pulse and larger, thicker left ventricles than their less active counterparts [1] – however, controversy arises from two sources. Does marathon running confer any additional benefits which shorter runs do not? And can it actually be dangerous?

The Human Heart While Running

Is Bigger Better?
Evidence suggests that excessive endurance training can cause ‘pathologic structural remodeling of the heart and large arteries’, as well as ‘overload of the atria and right ventricle’ [2] – basically, your heart is working to such capacity that it’s getting injured and the long term, this could lead to a plethora of issues including coronary artery calcification and large-artery wall stiffening.

When you think about the muscle-strengthening process, this is entirely logical – exercising causes small tears in the muscle called microtraumas, which the body then repairs, allowing your muscles to grow stronger in a process called hypertrophy [3]. If the trauma is too great or too frequent, it causes injury which the body struggles to repair, resulting in damage. However, evidence linking this kind of damage with endurance exercising is still hypothetical – long-term vigorous exercisers generally have low mortality rates and excellent physical health.

There is, however, evidence that regular moderate running confers the same benefit as long-distance running – it appears that, like any good thing, there’s an optimum level to achieving peak results. A 15-year study of 52,000 adults found that running distances of 1-20 miles a week, speeds of 6-7 miles per hour and frequencies of 2-5 days per week all conferred a lower rate of mortality, while increasing pace, mileage or frequency garnered no additional benefits. As little as 15 minutes of running per day can be enough to achieve substantial health benefits [2].

So, good news for those wishing to abstain from the mass marathon milieu which has us sacrificing our weekends and setting our alarms for 5.45 every morning – on balance, you’re probably better off with a forty-five minute jog round the park a few times a week instead.

[1] http://www.ncbi.nlm.nih.gov/pubmed/3902253
[2] http://www.ncbi.nlm.nih.gov/pmc/articles/PMC3538475/
[3] http://jap.physiology.org/content/97/3/1119

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