Are Ultramarathoners Just Built Different?

FLORA LICHTMAN: Hey, I’m Flora Lichtman, and you’re listening to Science Friday. It is the season for exercise resolutions. While many of us, myself included, are trying to figure out how to slowly jog a few miles each week or maybe squeeze in a couple sessions on a bike, other people are doing the absolute most. Ultramarathoners, people running 50 or 100 miles in a day, for example. I’m not sure why my feeds are overrun with these athletes, but I cannot look away. They seem superhuman and a little mysterious to me.

And at the same time, it makes me wonder, is there a limit to what our bodies can endure? Is there a cap on the number of calories you can burn without your body saying, I’m done? And what makes these athletes capable of pulling off these tremendous running feats?

Joining me to jog through the science of endurance are my guests Dr. Brandee Waite, Director of UC Davis Health Sports Medicine in Sacramento, California, and Dr. Andrew Best, Assistant Professor of Biology at the Massachusetts College of Liberal Arts. Welcome to you both to Science Friday.

BRANDEE WAITE: Thanks, Flora. Thanks for having us.

ANDREW BEST: Yeah, thank you. Nice to be here.

FLORA LICHTMAN: Let’s get this out of the way right at the top. I know you both study extreme endurance athletes. Are either of you practitioners yourselves?

BRANDEE WAITE: Well, I’m married to one, but my furthest distance run ever is a half marathon. That’s about as much as I ever have time to train for. But I have the crazy in my house with me every day.

FLORA LICHTMAN: OK. Drew?

ANDREW BEST: I would say I am probably the crazy in my house, but I’m not an ultra marathoner. I’m a reformed runner and trail runner who now mostly focuses on mountain biking. But I do have the obsession.

FLORA LICHTMAN: See, I’m so glad that you all talked about it this way because I do think for people who are, like me, very casual about exercise, seeing people do these ultramarathons seems superhuman. It seems insane to me. Is that how– how do you all view it?

BRANDEE WAITE: Well, I can jump in. And I shouldn’t be cavalier with the use of the term crazy. I think for a lot of people, this ultra running is really a challenge to themselves to see what they can train their body to do, and it takes an incredible amount of discipline and time, especially if you also work or take care of kids. People make a lot of sacrifices in order to properly train, so it is pretty amazing. I think it is accessible to more people than who do it, but it’s the desire to train that hard and go through that much discomfort that will wean people out or weed them out.

FLORA LICHTMAN: Drew.

ANDREW BEST: Yeah, I like to think that endurance sport, in general, is really a way of creating meaning. The daily grind is a way of distilling down, I don’t know, all the challenges of life into something where the work you put in directly leads to a result that you can feel good about in a way, that you can control.

FLORA LICHTMAN: There’s an output. Yes. You work hard, and you get a reward.

ANDREW BEST: Yeah, that’s really what it is.

FLORA LICHTMAN: Unlike regular life, where you just work hard.

[LAUGHTER]

OK, Brandee, I understand you just got back from a race in Greece where you were on the med team. Tell me about your role. And also, just tell us about what one of these races are like.

BRANDEE WAITE: Yeah, so I had the incredible pleasure of joining Racing the Planet Ultramarathon as they did a seven-day ultramarathon through the Peloponnese region in Greece, so kind of where the original marathon came from. And my role on the medical team is we had a team of, I think, six or eight physicians who took care of the athletes and the volunteers who work on the ultramarathon. That’s a whole separate show that we could do about the support staff that works at ultramarathons.

So from blisters to scalp lacerations to dehydration, we take care of whatever we can take care of there in our medical tent. So we’re on duty 24/7, and you cannot– individuals can go through a race like this and not need the medical team. But the roughly 200 people that we had at this race, you’re not going to get that many that go through the distance. And these athletes were running roughly a marathon a day for four days in a row, then a double marathon, and then about a 5K.

And so sometimes running through the night, sometimes there was a finish line each day. So ultramarathon has different flavors, if you will. There’s long, continuous races versus staged races. This was a staged race. And it was incredibly beautiful. We got to see culture. We got to see terrain. We got to see human nature and people overcoming difficulties. So it was all of the above. You can tell I love what I do.

FLORA LICHTMAN: I’m sorry we’re not– I can tell. And also, I wish listeners could see my face. My jaw is dropping. I mean, marathon after marathon after marathon, double marathon, and then a little bit more. Like, what are you asking your body to do when you take on a race like this?

BRANDEE WAITE: Your body goes through a lot. Drew, I’ll let you chime in. You’re the scientist. I’m the physician. Let’s see what you say and what I say.

[LAUGHTER]

ANDREW BEST: I think that you’ll probably be seeing what I’m about to describe in the flesh, but you’re basically asking your body to do two different things at once. When you’re exercising at all, you need to be getting way more oxygen to your muscle, glucose and fats into all the muscle tissue, or removing CO2 and hydrogen ions. And you have to do all of that while still maintaining homeostasis in the rest of the body. So you need to maintain a super narrow range of temperature, pH, oxygen concentration, all that stuff.

You can induce some small changes and some small debts in some of these things, like especially fuel. But for the most part, you’re now asking your body to sustain this muscular activity while still doing everything else it was already doing, really, except for digestion, which is really one of the only things that you’re going to really downregulate during an effort like this.

BRANDEE WAITE: When I talk to students about this, to tell them, I say it’s kind of like– or adults who are getting it– it’s kind of like you’ve got a bunch of children that you love, and you’ve got one unruly child. Those are your muscles. All of your energy is going towards that unruly child, but the others still need a little bit of care. And so your body is balancing, how do you take care of the unruly child and give them what they need and still show them love, but you don’t neglect the others? They still need to be fed. They still need to be cleaned. They still need to have their homework checked.

And so you’ve got the musculoskeletal system, which is kind of taking over. You’ve got to get enough oxygen to your muscles. And you also have to stay upright and moving. You’re not sleeping. You’re awake and alert. And so some of your other systems have to downregulate to give that energy to your muscles to work.

FLORA LICHTMAN: But do you hit a wall? Is there a limit to how much diverting of energy you can do to your unruly child muscles?

BRANDEE WAITE: Yes.

ANDREW BEST: Oh, yeah, absolutely.

BRANDEE WAITE: Well, runner’s gut is you’ve got to– you can’t run that far and not eat or drink anything, or else your body would shut down, just like the car– it has no gas, it has no oil, it’s not going to drive. And so you have to do that. But at a point in time, if you can’t digest the food that you’re going into because all the blood is shunted away from your gut, your intestines, and it can’t do its job of digesting, then you won’t get the nutrients that you need. And so other systems will just start to shut down eventually if you can’t digest, you can’t get food there, your muscles won’t work. Done.

ANDREW BEST: Yeah, to just to add some numbers to that from some research we’ve done and a paper that just came out on Kilian Jornet, who’s probably the greatest ultra athlete of all time, I would say. 40% to 50% is pretty much the limit of what we’re seeing athletes take in during the race.

FLORA LICHTMAN: Of the calories they burn?

ANDREW BEST: Exactly. Exactly. So athletes do need to be able to be replacing calories during these long events. And they’re mostly doing that now, many athletes, with a really high carbohydrate intake. Folks like Kilian are still taking in a lot of fat because fat’s a great fuel. But like Brandee was saying, if your stomach shuts down, because this is one of the only places in the body where blood flow is diverted from, is the intestines, it makes it harder to digest things, then you’re really at the mercy of your energy stores, which is about 2,000 to 2,500 calories worth of carbohydrates. That’s all you can store, which is really not going to get you that far. And all the fat under your skin, which might get you pretty far, but it’s kind of hard to access.

So you compound that challenge with the fact that you’re having a reduced blood flow to your intestines because you’re diverting blood from the intestines to the heart and the skin and the working muscle, and it’s harder to get those calories down. So really, the most we’re seeing that athletes are able to take in during a race like this is maybe 40% to 50% of the calories they’re burning. So there is a hard limit there. At a certain point, you’re just not going to be able to take in calories fast enough, and you’re depleted.

FLORA LICHTMAN: OK, so your body will shut down. But I mean, if you kept fueling your body– like, let’s say we come up with a super fuel and you can keep replenishing– or you could replenish at the rate that you are depleting, could you then go forever? Like, do we know what the wall is in terms of distance or time or something that we can measure outside of the body?

BRANDEE WAITE: Well, unofficially, Dean Karnazes, who’s from my neck of the woods in Northern California, has the longest continuous run. He went for 80 hours without sleeping and covered, I think, about 350 miles.

FLORA LICHTMAN: How?

BRANDEE WAITE: I know, it’s insane. For most people, it could be time. So officially, they’ll do like the furthest distance run in 24 hours. And that was almost 200 miles was the male record, like 198.6 miles.

FLORA LICHTMAN: In a day?

BRANDEE WAITE: In 24 hours measured time for a man. And I think for a woman, it was 167.99 miles run in 24 hours. So you can’t sleep. You are fueling. But eventually, you have to sleep, so you’ll have to stop. You can’t go forever because sleep would come in. Your muscles would break down. Many people get injured. Their Achilles goes out, or their quad tightens up, or their back flares. So your muscles also have a limit as to what they can do. You can train them, but there’s terrain, and there’s environment, and there’s heat, and there’s cold, and there’s your gear, your shoes, and your chafing from your shirt or your pants. So there are a lot of other factors that can bring you down other than your own body.

FLORA LICHTMAN: Drew.

ANDREW BEST: I think if we’re talking running, the limiting factors probably come in sooner. And that’s going to be muscle damage and tendon damage, the kinds of things you’re not going to get in a lower impact ultra sport like long-distance cycling or swimming. If we’re talking about an exercise competition in the heat, then we’re looking at fluid loss and maybe eventually salt loss. And it’s difficult to replace those things over multiple days without stopping. You might have some kidney problems, trying to concentrate urine when you’re that dehydrated. So the environmental factors come in.

But I mean, assuming everything else was perfect and we’re talking about something like cycling, then I think sleep really then would be the ultimate thing that stops you.

FLORA LICHTMAN: I mean, Drew, I know that you’ve done a recent study on looking at the metabolic limits for these ultra endurance athletes. Do we know how many calories someone’s burning when they’re doing one of these ultra marathons?

ANDREW BEST: Yeah, so you can estimate it fairly well just by saying, oh, a person of this body size probably burns x number of calories per mile, and you’ll be pretty close. But yeah, no, it’s 10,000 to 15,000 calories, something like that, for a 100-mile race. I mean, a paper just came out recently showing that Kilian Jornet burned 16,000 calories in his second-place finish at the Western States 100, which, if those numbers are right, is actually not that economical. He was burning 160 calories a mile for 14.5 hours.

So over those shorter durations, there seems to be a lot of variability in what people’s metabolic limit is. And that’s all intuitive. I mean, someone who can cover more distance or do more work in a certain time frame, yeah, they’re obviously burning more calories to do it, probably. But over longer time frames, that’s really what our recent study looked at. And it seems like that variability in maximal metabolic rate that we see over shorter time frames really gets a lot narrower when we’re looking at something like 30 to 52 weeks.

So when we look at how many calories people are burning in life and training, and it seems that– from the numbers we found, it seems to be 2.5, maybe up to 2.7 times your basal metabolic rate.

FLORA LICHTMAN: What’s a basal–

ANDREW BEST: Yeah, so basal metabolic rate is the calories it takes just to stay alive if you don’t move a muscle. So if you’re bedridden for 24 hours, you still burn, the average person, maybe 1,500 calories in those 24 hours just to keep your body functional.

FLORA LICHTMAN: Good to hear, for me.

ANDREW BEST: Yeah, it’s not nothing. It’s not nothing. And we don’t know if it’s a limit. But the biggest numbers we’re seeing are 2.5 to 2.7 times that basal rate is what people seem to be able to sustain over the course of, say, a year. And that would suggest that the mechanisms that limit that long-term endurance are probably very different from the mechanisms that limit short-term endurance. And we’re not entirely sure what they are.

FLORA LICHTMAN: That’s fascinating. Do we understand what is different about these folks who are performing at this level? Do their bodies work differently from mine?

BRANDEE WAITE: I’m going to say maybe a tiny bit, but the training effect is huge. You cannot say, I haven’t exercised in six months, but I’m going to run a marathon tomorrow. Most people, their bodies wouldn’t do it. It would break down. But given the proper training and nutrition and gear that supports your body the way that it needs to be supported, that’s one of the things actually I love about the staged ultramarathons I do with Racing the Planet is maybe the top 20% of the field, they’re competing. And the rest, the 80%, their goal is to finish and challenge themselves.

FLORA LICHTMAN: Persisting.

BRANDEE WAITE: They’re just trying to persist and do a personal challenge. So they may not be the fastest, but they’ve trained over time, and they can get their body to do it if they don’t get injured.

ANDREW BEST: Yeah, I just want to add to that that one thing that’s beautiful about especially a really long-distance sport, like ultramarathoning, is that it seems to be less about that inherent talent in the physiological parameters we can measure. So over a shorter distance race, it’s like, well, if we can measure someone’s maximal oxygen consumption, we’re going to have a pretty good idea of how they’re going to do in a 5K race. If we can measure how much lactate somebody’s muscles make and how quickly they’re able to clear that and use it as a fuel, we have a pretty good idea how well they can do in a one-hour event.

But there aren’t really any physiological measurements we can take that tell you who’s going to win a 100-mile race. There are definitely physiological factors, but most of them are developed through training. It’s really durability. It’s have you done the right things in training to train your gut? And the thing we haven’t talked about yet is psychology. One of the best things about the research I’ve been doing is I’m getting to know these people who are near the top of ultra endurance sport, and they just have a different relationship with pain and suffering.

FLORA LICHTMAN: Say more.

ANDREW BEST: Well, I don’t think anybody enjoys pain. I don’t how many true masochists there really are in the ultra world or in the endurance sport space. But I think that they and myself, to a much lesser extent, are able to reframe that suffering in a way that’s productive and that they enjoy in some sense. It’s the difference between type II and type III fun. Type II fun is fun afterwards when you’re thinking about it. And type III fun is just not fun. And I think that ultra athletes really find all this to be type II fun.

FLORA LICHTMAN: That makes a lot of sense. I want to thank you both for joining me to talk about this. It’s been absolutely fascinating.

BRANDEE WAITE: Thanks so much, Flora. This was great fun.

ANDREW BEST: Yeah, I love Science Friday, so thanks for having me.

FLORA LICHTMAN: Thank you. Dr. Brandee Waite, Director of UC Davis Health Sports Medicine in Sacramento, California, and Dr. Andrew Best, Assistant Professor of Biology at the Massachusetts College of Liberal Arts. That’s about all the time we have. Kathleen Davis produced this segment. Thank you for listening, and we’ll see you tomorrow.

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