The Mechanics of Marathon Running

25th September 2016 saw Ethiopia’s Kenenisa Bekele narrowly miss out on a Marathon World Record with a time of 2:03:03 at the Berlin Marathon (the current record is held by Kenya’s Dennis Kimetto at 2:02:57). One question many people may wonder is, over the course of 26.2 miles, what actually happens to the human body when it runs a marathon?


One of the most important considerations for marathon runners is how they fuel their bodies. The notion of a large bowl of pasta the evening before a race is a popular one and, in fact, many people equate long-distance running with high carbohydrate intake. The problem is that the human body can only store so much of this energy that it is being overloaded with. When running, the body first uses up any available glucose before it starts to use the body’s glycogen stores (glycogen is a polysaccharide store of carbohydrates). At around the 18 mile mark, the body will have used up all of the glycogen available and starts to break down its own fat and protein cells to use as energy. Muscle cell glycogen depletion is particularly significant as it is used locally as an immediate energy source for muscle tissue. Without it, muscles start to fatigue resulting in a higher likelihood of injury. In a 1983 article published in the Journal of Applied Physiology, it was found that athletes who, instead of a high-carbohydrate diet, had a high-fat, high-protein diet, had a ‘14% reduction in maximum power output’ [1] which can be translated to running slower.

Running Releases Endocannabinoids

Over the course of the 26.2 miles, muscles also experience micro-damage (small, undetectable tears) caused by the force of the feet hitting the ground. As the body tries to repair the damage caused, swelling can occur. Some researchers say that this same force can also cause the height of a marathoner to decrease by up to 2cm throughout a race. Muscles are also vulnerable to cramp, especially in the later stages of a marathon when the muscles are becoming fatigued. The risk of cramp increases the more dehydrated a person is. Marathon runners can lose up to 8 litres of fluid through a combination of sweating and breathing during a race [2]. It’s not only loss of water that causes runners to become dehydrated – sweat also contains sodium and potassium – which help the body to absorb water, making the body less efficient at rehydrating when drinking more water.


On the other hand, likely due to concerns of dehydration during marathon running, there has been an increase in cases of hyponatremia – that is, drinking too much water. Drinking too much water causes the level of sodium in the blood to decrease due to dilution. Low sodium levels can cause swelling in the brain which can, in some case, be fatal. ‘Hyponatremia (is) more common in slower runners and those who use  NSAIDs (nonsteroidal anti-inflammatory drugs)’ [3] such as aspirin or ibuprofen. This is thought to be because slower runners have more time during a race to drink too much water and because NSAIDs can increase water retention.

Berlin Marathon 2015

Over the years, many articles have been written describing the so-called ‘runner’s high’, a feeling of euphoria many athletes face after a prolonged period of exercise. This is often attributed to the release of endorphins, specifically β-endorphin, which produces a feeling of contentment and joy. However, a 2012 article in the Journal of Applied Physiology found that ‘physical exercise activates the endocannabinoid system’ [4]. The study examined the effects of physical exercise on the levels of anandamide (an endocannabinoid) in the bloodstream. It found that levels increased during physical activity and increased further if the activity was undertaken at higher altitude. In the study the type of physical exercise was mountain hiking, but given the prolonged and lower intensity nature of the exercise, it is comparable to marathon running. Unlike endorphins which can only be produced by specific neurons in the body, most cells in the body are capable of producing endocannabinoids. This, combined with the fact that endocannabinoids are thought to be created in response to stress (as opposed to pain, like endorphins) means that they have a larger potential for how they impact the brain. It’s believed that the naturally produced anandamide, along with β-endorphin and phenethylamine (a stimulant), combine to create ‘runner’s high’.


The human body can sustain a great deal of damage whilst running a marathon. Those 26.2 miles can literally break the body down. Whilst the major consequences of marathon running are clear, there are many factors affecting a runner’s performance, particularly over such a long distance. Most marathon runners are just glad to get to the end in one piece and most of them will never have to consider how to shave off 6 seconds from their time to become a world record holder.




[1] Effect of glycogen depletion on the ventilatory response to exercise (G. J. Heigenhauser, J. R. Sutton, N. L. Jones) Journal of Applied Physiology Published 1 February 1983 Vol. 54 no. 2, 470-474

[2] Know Thy Sweat Rate, Amby Burfoot (1968 Boston Marathon Winner)


[3] The Physiology of Marathon Running (Dr. Jake Emmett)


[4] Effects of exercise stress on the endocannabinoid system in humans under field conditions (Feuerecker M, Hauer D, Toth R, Demetz F, Hölzl J, Thiel M, Kaufmann I, Schelling G, Choukèr A.) Eur J Appl Physiol. 2012 Jul;112(7):2777-81





One Response to “The Mechanics of Marathon Running”
  1. NO Max Shred says:

    There are a lot more things you should learn before you will be able to breakthrough a marathon field. Sometimes you will fail. But it don’t get discourage, because it is only the beginning of your true challenge.

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