What happens to your body during a marathon?

what changes in your body from start to finish?
07 March 2017



What happens to your body during a marathon?


Chris Smith put biologist Aimee Eckert from the University of Sussex through her paces...

Aimee - Yes. Apart from getting tired. Oh, there’s a lot of things. Because you’re running for such a long distance you’re going to use up all the glucose reserves in your blood, in your muscle cells, and also in the carbohydrate stores in your liver.

Carbohydrates is your body’s preferred source of energy and once you deplete all of that your body starts working on fat cells and also muscle cells. So that is going to lead to you feeling incredibly tired, incredibly sore, and the phenomenon called the ‘runner’s wall.’ People describe that as a complete inability to continue and being really unable to focus on anything.

Another thing that happens is you loose a lot of fluid, obviously, through sweating and when you complete a marathon you arrive over the finish line (hopefully) 2 centimetres shorter than when you started because you’ve lost so much fluid between the discs in the vertebrae of your spine. But, if you rehydrate properly, you’ll be back to normal in 24 hours.

Chris - Is this something you spotted on YouTube as well or is that a fact that actually, people are 2 centimetres shorter after a marathon?

Aimee - I don’t know what you’re trying to say about my scientific credentials, but I’ve done my homework Chris.

Chris - I’m just referring to your kitten data. So Mo Farah is 2 centimetres shorter, on average, after he completes the London Marathon in record time?

Aimee - Yes.

Chris - Goodness! And does he inflate again? Presumably he does, otherwise he’d be miniscule by now wouldn’t he with the number of marathons he’s run?

Aimee - Yeah. Rehydrate and you’ll be back to normal,yeah, to your original height.

Chris - And what other effects are there - anything else?

Aimee - Yeah. There’s a few more things. Your body needs oxygen to work and do all that exercise so that’s loads of airflow going through your respiratory tract. This really dries out your nose and so the mucus producing cells in your nose work really, really hard and so your nose will be running a lot, as well as your feet!

Your immune system gets suppressed. I’ve heard from runners that they often get a bad cold after doing a marathon. I’m not sure why your immune system gets suppressed in this way; maybe it’s trying to deal with the inflammation in the body from broken and injured muscle cells.

Chris - This all sounds like bad news. Is there evidence that marathon runners ultimately end up less healthy than the average person, because this doesn’t sound like a recipe for being healthy?

Aimee - I think it’s pretty extreme exercise, yeah.

Chris - So... with care?

Aimee - Yeah.


It would be a good idea to revisit this with Dr Christof Schwiening from the Department of Physiology, Development and Neuroscience at the University of Cambridge. He's an experienced marathon runner who has been a bit of a guru to the Cambridge running community. He knows a great deal about the adaptations marathon runners's bodies go through when they're training.

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