The physiology of running

What does running do to our bodies?
26 February 2019

Interview with 

Christof Schwiening, Cambridge University, Jenn Gaskell, University of Nottingham


a group of runners on a track


When any of us run, either to the bus stop or across an entire mountain range, our body goes through several changes. We've all felt them. But what are they? And why do they happen? A physiologist and keen runner Christof Schwiening from Cambridge University took Georgia Mills through what happens when you start at a gentle jog, after a word from Jenn Gaskell, Professor and Ultra Marathon runner, who discussed her love, of a good run...

Jenn- I always loved running around as a kid and I really liked being in the mountains and just ended up running lots of mountain races and increasing the distance every year. My favorite race is towards Tor des Géants in Italy. That's 340 kilometres long with three times the height of Everest, goes through some really beautiful mountains in the Italian Alps.

Georgia - Three hundred and forty! How long does that take?

Jenn - My best time is 115 hours, but I think I can do under 100 hours next time.

Georgia - When do you sleep?

Jenn - So they do have checkpoints down in the valleys and you pass some mountain refuges where you're allowed to stay for an hour or two. And sometimes just at the side of the trail in the sun if it's nice weather. I think in total I had about six hours the first time I did it.

Georgia - What made you want to go sort of beyond a marathon?

Jenn - I just really enjoyed the long adventures because you see so much and you see it at unique times of the day. So you might not go out for a hike in the Italian Alps at 3:00 a.m. in a storm, but if you're out running already you'll see this amazing lightning and things. And you cover quite a lot of ground, so one of the races I've done as well is the Ultra-Trail du Mont Blanc, where you run the 11 day hiking route around Mont Blanc where you can run it in one or two days. So you really see quite a lot of things doing this ultra running.

Georgia - And is the Mont Blanc trail the hardest ultra marathon there is or if you got an eye on a new challenge?

Jenn -  So there is a 450 kilometre version of Tor des Géants this year called Tor des Glacier, and that's got even more accent, probably four times the height of Everest. And next year I'll be running a 900 kilometre race across the Himalayas, but I think by then it becomes a bit easier because you actually do have to sleep every night.

Georgia - Now Jen has reached the extremes of long distance running but when any of us run, either to the bus stop or across an entire mountain range, our body goes through several changes. We've all felt them. But what are they? And why do they happen? A physiologist and keen runner Christof Schwiening from Cambridge University took me through what happens when you start at a gentle jog.

Christof - What we see are a set of changes that gradually develop over time and most of the time you won't be aware of what those changes are. They'll be occurring at the cellular level, the level of the microcirculation around the muscles. So when you first start this very gentle running your, muscles will be contracting more often. As a result, they'll be squeezing the blood vessels within them, and most importantly the veins, pushing blood gradually back towards the heart. So we call that an increase in venous return. So there'll be changes within your circulatory system, the control of your heart rate. Also as those muscles gradually become more active, they start to run down some of the early initial energy sources that you've got within the muscle and they'll gradually begin to build up metabolites which will lead to a dilatation of the blood vessels. Dilatation means simply the blood vessel swelling in size allowing more blood flow through the muscles. Even your breathing rate that will gradually start to increase and you won't even notice that the rate has begun to increase. Obviously the temperature will start to rise first of all in the active muscles it will creep up, by a tenth of a degree C gradually, maybe every minute or so, and you won't notice that your core body temperature will also gradually start to rise as well. Now as you start to run progressively faster, those changes begin to build up and the whole of your physiology begins to fight all of these changes to try and maintain the various parameters within your body within a range that is acceptable and compatible for life. So for instance as the blood flow increases through your muscles your heart will gradually have to work harder, will have to pump more blood to keep your blood pressure up and to keep your brain perfused with blood and that increase in rate will begin to put a stress upon the circulatory system. The consumption of oxygen and the buildup of CO2 will start to change the blood gases. And actually it's the buildup of CO2 which begins to be the first thing that you really notice. And that's because that CO2 enters the brain, a specific part of the brain, where it changes the pH. And that drives up your breathing frequency, so your respiration rate increases, and you actually breathe more deeply as well. So those changes then start to become obvious and gradually larger as you run you start to get hotter. And as you start to get hotter you begin to sweat and that becomes something that you will notice as well, you might even notice the slight pickling on the skin as the blood flow increases to the skin as well.In the end if you keep on running there is almost no system within the body that doesn't start to change.

Georgia -But what causes those horrible feelings when you push yourself further than you can really go?

Christof - If you're exercising very intensely and you don't have the adaptations at the level of the muscle to support the exercise intensity that you're doing, you can end up not burning fat and carbohydrates efficiently using oxygen, but actually relying on anaerobic metabolism. And the result of that is that you lose a lot of that energy from the muscle, it literally disappears out into the circulatory system as lactate, and you get alongside that an acidosis. So you can end up with the muscle becoming acidic, the result of that is that the muscle then becomes very inefficient and you also can get alongside that the painful feelings that some people refer to as a burn. The demand on the heart can end up being too high such that your blood pressure begins to fall and you begin to feel woozy or light headed. There are a whole set of problems that you can run up against. Another one is the gradual overheating. So as you're exercising your muscles are getting very hot. Now if your sweat glands are not adapted or they haven't started sweating early enough, then your temperature is going to rise higher than is compatible with normal processing in the brain. So the first thing that you find is it becomes much harder to think straight, as you get progressively hotter and indeed your motivation to continuing exercising decreases quite dramatically.

Georgia - All that being said I had to go on Christof's lab based treadmill measuring my heart rate and skin temperature to get a quantifiable measurement of quite how unfit I was. My heart rate was too high being too small and inefficient to get enough oxygen to the muscles, and I heated up like a lamp. Clearly an inefficient use of energy, so Christof gave me a challenge. Go on a 2k run, twice every single day, for a month to see what happens.

Christof - So what I'm hoping we're going to see is that one of the adaptations will be the training of your sweat glands that will have the effect of keeping your body a little bit cooler preventing the temperature rise. I'm expecting to see that your heart rate will be lower. The reason for that is you will have undergone a little bit of plasma volume expansion. You will have literally produced more blood. That more blood means that with each heartbeat you'll be pumping around a little bit more blood and therefore a little bit more oxygen as well. Now we're going to require you to get a bigger heart and unfortunately that's not gonna be a transplant. We can either stretch your heart a little bit...

Georgia - Sounds very painful!

Christof - Well you do that all the time. So when blood comes back to your heart, that stretches the heart a little bit so that stretching is going to become a little bit greater.


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