Marathons: Blood, sweat and... poo?

Can anyone learn to run a marathon?
24 April 2018

Interview with 

Christof Schweining, University of Cambridge


This week, many brave individuals have been taking part in the London Marathon, which was a little bit of a hot one. But is running a marathon possible for anyone, and what does training do to your body? Georgia Mills and Chris Smith were joined by one of those brave individuals, Christof Schwiening, who is a physiologist at Cambridge University and joined them straight after running the marathon himself.

Christof - I’m fine. It was a bit of struggle getting there; the coach didn’t turn up so we had a bit of a rush to get down there but wonderful day. A really lively atmosphere and great weather. The support was fantastic; it was really really positive.

Chris - You’re saying the journey was harder than the marathon?

Christof - Oh, yeah, yeah. Because you know a last minute change of plan and suddenly you’re shooting down the motorway in a car not sure where you’re going to park up, and whether you’re going to get there or not. And, of course, are you going to get to the toilet stop in time and that’s really, for most marathon runners, a major thing.

Chris - It didn’t bother Paula Radcliffe!

Christof - Well, yeah.

Chris - She popped behind a tree.

Christof - I know she did.

Chris - Not today obviously. She wasn’t running today.

Christof - It happens to an awful lot of runners. More runners lose time over a toilet stop than pretty much anything other than simply’ hitting the wall,’ I guess.

Chris - Is that because they’re taking a lot of water in because they’re worried about over-hydrating or is there a physiological reason? Is there a reason why you need a wee more if you run more?

Christof - It’s not so much the wee I’m afraid.

Chris - Oh right, number twos?

Christof - It’s number twos. It’s because the whole stress of running a marathon actually causes, if you’ve still got food in your digestive tract to head downwards. And once it hits that internal sphincter and bounces around you’re on a limited fuse.

Chris - So what do you do? As well as what you do if you end up in that position?

Christof - If you’re lucky you get to a loo in time.

Chris - But dietary, is there anything you can do ahead of the marathon to limit that?

Christof - Yes there is. Every individual is different, but I know my gut transit time. So I know if I stop eating at 4 o’clock in the afternoon the day before a marathon, I’m absolutely fine. If I were to indulge, as the rest of the family were, in chips in the evening, then it’s going to get messy out on the course.

Chris - And there was me thinking when you see these athletes looking at their watches, that they’re looking at their track time, actually they’re not, they’re looking how far it is to the next loo stop.

Christof - Entirely possible.

Georgia - Wow. That’s a side to the marathon I hadn’t even considered. What I was thinking about is the temperature. It’s been absolutely gorgeous today, but how did that affect the run and what does it do to your body?

Christof - It’s so multifactorial. Heat plays on just about every physiological system. The really big threat of the heat is that you increase the amount of sweat that you produce and so you’re effectively running along as if you’ve almost been shot. You’re losing it out this fluid from your blood, the blood plasma, it’s leaking away…

Chris - Because it’s being turned into sweat?

Christof - Because it’s being turned into sweat. And that turning into sweat isn’t just a simple process, it’s a highly trainable process. So if you’re somebody who’s trained to sweat a lot then you can lose the sweat that is really very diluted, it’s almost like pure water and you can actually osmotically pull water out of your intracellular fluid compartments.I didn’t drink in today’s marathon, I was mainly splashing water on myself and I got faster as I went along, so the second half of the marathon I finished it one minute faster than the first half.

This dehydration that you get as a result of sweating doesn’t need to be performance limiting for the elites. They’ll dump about four to five litres of water out of their body so by the time they’re finishing the marathon and hammering down the Mall, they’re actually lighter and so they need less energy to go faster. While the guys at the back who are drinking a lot, they’re heavier by the time they’re finishing and it’s getting progressively harder and harder.

Chris - You said, Christof, that it’s trainable to control sweating, so in what way is it trainable and to what extent can you constrain how much or how little you sweat then?

Christof - It’s trainable in many different ways. First at the level of the skin itself, these sweat glands and you’ve got millions of them across the surface of your skin. You can grow them and make bigger sweat glands, and the biggest sweat glands can not just push out more sweat, but they’ll also reabsorb more sodium, so you lose less sodium. But also the drive to them, this thing that we call the sympathetic nervous system. It’s part of your peripheral nervous system that you have little conscious control over, you can train that as well so you get a big adrenal gland. All of that supports this ability to sweat for prolonged periods of time and to not lose so much circulating blood volume.

Georgia - So that’s one way that training for a marathon changes, you get this sort of super-sweater, but what else happens to your body? How does your body change to be able to do this?

Christof - One of the other major changes that occurs is this increase in blood volume, which most people notice as a gradually fall in their heart rate as they do exercise. What’s actually happening is - there are multiple different theories, but the most likely is that as you exercise you’re actually pushing a protein called albumin out of the interstitial space, which is outside of the blood vessels all around your body…

Georgia - Not the same stuff as you get in eggs?

Christof - I’m afraid it is, yeah. You’ve got it floating around and it enters into the actual circulatory system and attracts water with it, and that builds a larger circulatory system. And that larger circulatory system means, of course, you can push more blood through your whole body to the skin to lose heat and also though other muscles, but you’ve got more fluid in the first place when you start off running. So that loss of two or three litres of fluid during the course of the marathon has less of an impact.

Chris - But muscles themselves also change don’t they? The composition, the biochemistry of your muscles as you train?

Christof - Absolutely! At that level, there are literally thousands of changes and this is what makes predicting the time you can actually do to finish a marathon so difficult. You change the energy that’s stored within the muscles, the capillarisation that is the ability to get the blood down to the mitochondria - you get mitochondrial biogenesis. You’re actually growing more of these powerhouses within the muscle and you get this gradual change in what looks like the fibre type.

Georgia - Right. Talking about training, running a marathon I’d rather get into a spiders’ pit I think; it fills me with fear! Can anyone learn to run a marathon and how do you go about getting ready for one?

Christof - Everybody already has what’s necessary to run a marathon. And Georgia, you could certainly run a marathon right now; it’s just a matter of how long it would take you to complete a marathon.

Could you run 1 kilometre every day? Yes you could.

Could you do it for the next 42 days? Yes you could?

You could run a marathon but it might take you 42 days to do it.

The question is how long does it take to train to get to be able to complete a marathon within the time limit that the marathon sets? The faster that you want to complete the marathon, the more training you have to do. And anybody can do it, you just simply have to do what gazelles do - they don’t go to running school. You rarely see them sitting around discussing running technique, they just run and really that’s all it is. It’s not rocket science, I’m afraid!


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