Chemistry is something I have always loved, unlike many others. And well before I started appreciating my long runs. But how much do chemistry and running have in common? Pretty much, I would say. 

Let’s start from the human body. While we run, chemical reactions transform fuel into the energy we need. We don’t run on gasoline, but sugar (or more specifically, glucose). Glucose is converted (we could say burnt) with oxygen into water, carbon dioxide… and a lot of energy. Well, the efficiency of this process is low. About 80% of what we burn is lost as heat. This is also why it is so hard to run in hot weather conditions!

When it is about running and alimentation, the most used measure unit for energy is the kcal (kilo calorie). It is the quantity of energy required to increase the temperature of a kilogram of water by 1 °C (thank you metric system to make things easy!)

Anaerobic and aerobic processes

The molecule storing energy in this process is called adenosine triphospate (or better, ATP). This energy storage molecule is produced by the mitochondria (finally we know what is the role of these guys in the cells!).

In normal (aerobic) conditions, there is enough oxygen to burn the sugars effectively. But what if the effort is high intensity, running intervals or lifting weights for example?

In this case the body can be unable to supply enough oxygen to the process: therefore, we have to use a mechanism less efficient. The anaerobic respiration creates a byproduct well know as symptom for muscular post training pain: lactic acid.

Let’s go back to the aerobic training. I just said that to get energy, we need to burn sugars. But where do these sugars come from? There are two sources: carbs and fats. Fat is – as we all sadly know! – a way for the body to store energy (yes, we could call these extra kilos energy storages!). Your body has the ability to burn both fat and carbohydrates for energy, but given the choice, it will go with carbs because it is fast and efficient.

If the effort is , say a one hour walk, the body will understand that the effort is continuous and not particularly hard, and switch to “low quality” fuel (fat). Fat oxydation processes will in this case support the energy generation. If you want to burn more fat, it is easier to do it with a long walk, than a short run.

Another interesting thing is what happens when the effort sustained continues for long. During a marathon, for example. The amount of sugars we can store in our blood is roughly proportional to our body weight. But also the calories we burn are proportional to our weight. This means that we tend to finish our glucose storage after the same point (again, more or less). When this happens, we are like a car running out of gasoline. Our ability to go shuts down, and it is like hitting a wall.

Different people can run out of sugar reserves in similar times

For this reason, marathon runners often refer to hit the 30 Km (or 20 miles) wall, the threshold where we may deplete our energy reserve. The best way to avoid, or to limit this, is to replenish the reserve by constant hydratation and carbohydrates supplies.

There are commercially available gel bars which have a content in carbs quite high. Replenish our sugar reserves using these gels or alternative sources (fruit bites, for example) is extremely important while running long distances.


Speaking of hydration, we should not forget what is there. Water, sure, but also the electrolytes. These elements (potassium sodium, magnesium among others) or better, their ionic form, are facilitating many processes in our body. We could say that they let the body behave like a battery, and transmitting the electrical impulses used by the muscles – and remember, the heart is a muscle too!

We lose the electrolytes when we sweat, therefore for long runs, water alone is not enough. Electrolyte deficit can lead to cramps, dizziness, symptoms quite usual during long-distance races. Although for short runs water may be OK (we wouldn’t be able to deplete our electrolyte reserves so easily), that may not be the case when the mileage is higher. Isotonic drinks have a electrolyte content in a concentration similar to the normal one in the body.

Obviously, also weather conditions are important: we don’t need a PhD in chemistry to agree that the hotter, the more we need to drink!


Another famous class of chemical compound associated with running are the endorphins.

Our body releases hormones called endorphins. They help prevent muscle pain and are often considered responsible for the “runner’s high”, an euphoric state during or after the training.

It is proven that the body releases endocannabinoids, substances similar to the cannabis (!) and naturally produced by our body. New studies indicate that these mulecules could be the ones responsible for the runner’s high, and have benefic effects, like reducing anxiety and pain.


I hope you liked this trip into the chemistry of running. I think the main takeaway is: the body runs like a machine. Let’s take care of it, supporting the chemistry behind. It can only help us to be better, maybe faster… but most importantly, to live better!


Did you like this post? Please contact me for any question or if you find info to be rectified!

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