Science Friday - Are Ultramarathoners Just Built Different?

Episode Date: January 2, 2026

‘Tis the season for exercise resolutions. For a select few, an ultramarathon—a race of 50, 100, or even more miles—may be on the table for 2026. But is there a limit to what our bodies can endure? And what makes ultramarathoners capable of these tremendous feats? Joining Host Flora Lichtman are sports medicine expert Brandee Waite and biological anthropologist Andrew Best.Guests:Dr. Brandee Waite is the director of UC Davis Health Sports Medicine in Sacramento, California.Dr. Andrew Best is an assistant professor of biology at the Massachusetts College of Liberal Arts.Transcripts for each episode are available within 1-3 days at sciencefriday.com. Subscribe to this podcast. Plus, to stay updated on all things science, sign up for Science Friday's newsletters.

Hey, I'm Flora Lichtenen, 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, you know, a couple sessions on a bike, other people are doing the absolute most. Ultra marathoners. 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. Brandy 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. Thanks, Laura. Thanks for having us.

Yeah, thank you. Nice to be here. 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? 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. Okay. Drew?

I would say I am probably the crazy in my house, but I'm not an ultramarathoner. I'm a reformed runner and trail runner who now mostly focuses on mountain biking, but I do have the obsession. See, I'm so glad that you all talked about it this way because I do think for people who are, you know, like me, very casual, you know, about exercise. Seeing people do these ultramarathons seems superhuman. Like, it seems insane to me. Is that how, how do you all view it? 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. 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. True. Yeah, I like to think that endurance sport in general is really a way of

creating meaning. You know, the daily grind is a way of sort of, you know, distilling down like, 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. Yes. You work hard and you get a reward. Yeah. That's really what is. Unlike regular life where you just work Right. Okay, Brandy, 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. 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, 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.

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, you know, people overcoming difficulties. So it was all of the above. You can tell I love what I do. 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, you, you, you, you, take on a race like this. Your body goes through a lot. Drew, I'll let you chime in. You're the, you're the scientist. I'm the physician. Let's see what you say and what I say. 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, you know, into all the muscle tissue, you know, removing CO2 and hydrogen ions.

And you have to do all of that while still maintaining homeostasis in the whole rest of the body, right? 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 deaths 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. 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 can't, 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. But do you hit a wall? Is there a limit? to how much diverting of energy you can do to your unruly child muscles. Yes. Oh, yeah. Absolutely. Well, runners' gut is, you know, you've got to, right, 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, you have to do that. But at a point in time, you know, if you can't digest the food that you're going into because all the blood is shunted away from your gut, your intestine. 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 the food there, your muscles won't work, done. Now, just to sort of add some numbers to that from some research we've done and a paper that just came out on Killian Jorna, 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. So of the calories they burn. Exactly. Exactly.

So, you know, athletes do need to be able to be replacing calories during these long events. And they're mostly doing that now, you know, many athletes with a really high carbohydrate intake. Folks like Killian are still taking in a lot of fat because fat's a great fuel. But like Brandy was saying, if your stomach shuts down, because this is one of the only places in the body where blood, blood flow is diverted from, that's the intestines, makes it harder to digest things. Then you're really at the mercy of your energy stores, which is about two to two and a half thousand 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, you know, 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 percent 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. Okay. So your body will shut down. But I mean, if you kept fueling your body, like let's say, you know, we come up with a superfuel 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, the wall is in terms of distance or time or, you know, something that we can measure outside of the body? Well, unofficially, Dean Carnazis, 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. How? And so, 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 all almost 200 miles was the male record like a hundred and ninety eight point six miles in a day. In 24 hours measured time for a man. And I think for women 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 you'll have to stop. You can't go forever because sleep would come. them in. Your muscles would break down. Many people get injured, right? They, they, you know, their Achilles goes out or their quad tightens up or their back flares. So, you know, 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 or your shoes and you're chasing, you know, from your shirt or your or your pants. So there are a lot of other factors that can bring you down other than your own body. True. I think if we're talking running, um, you know, the limiting factors probably come in sooner, and that's going to be muscle damage and tendon damage, you know, the kinds of things you're not going to get in a lower impact all for sport, like long distance cycling or swimming.

If we're talking about, you know, 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. 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 ultramarathons?

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 to 15,000 calories, something like that for a 100 mile race. I mean, a paper just came out recently showing that Killian Jornay burns 16,000 calories in his second place finish at the Western States 100, which if those numbers are right, is actually not that economical. It was burning 160 calories a mile for 14 and a half 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 timeframes, that's really what our recent study looked at. And it seems like that variability in maximum 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've found, it seems to be two and a half, maybe up to 2.7 times your basal metabolic rate. That's about. What's a basal metabolic rate? Yeah. 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 if you're bed ridden for 24 hours, you still burn, you know, the average person, maybe 1,500 calories in those 24 hours just to keep your body functional. Good to hear. For me. It's not nothing, right? It's not nothing. And we don't know if it's a limit, right? But the biggest numbers we're seeing are two and a half 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. That's fascinating. I mean, do we understand what is different about these folks who are, you know, performing at this level? Like, do their bodies work differently from mine? 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.

You know, 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%, they're, their goal is to finish and challenge themselves. They're just trying to, you know, 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. Yeah, I just want to add to that that one thing that's beautiful about especially really long distance sport, like ultra-marathoning,

is that it seems to be less about that inherent talent in the physiological parameters we can measure. Right. So over a shorter distance race, it's like, well, if we can measure someone's maximum 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 the most of the 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. I mean, 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. And say more. Well, I mean, I don't think anybody enjoys pain. I don't know 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 that suffering in a way that's productive and that they enjoy in some sense. It's the difference between type two and type three fun. Type type two fun is fun afterwards when you're thinking about it and type three fun is just not fun.

And I think that ultra athletes really find all this to be type two fun. That makes a lot of sense. I want Thank you both for joining me to talk about this. It's been absolutely fascinating. Thanks so much, Flora. This was great fun. Yeah, I love Science Friday, so thanks for having me. Thank you. Dr. Brandy 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.