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Peter Frick-Wright: From ���ϳԹ��� Magazine, this is The ���ϳԹ��� Podcast. The first time I ever talked to Paddy O’Connell—on the phone, a few weeks before I returned as the host of this show—we realized that we were both in possession of human bodies of roughly the same size.

I don’t remember how it came up, exactly. We talked about a whole bunch of stuff that day, but it was kind of a big deal. We are two people who don’t often encounter our own kind. We are both very tall, 6’5”, and neither one of us ever gets described as “bird-like” or “sinewy.” My wife says I have the body of a Lego man. And, it’s a very good burn.

Burns aside, those bodies came in handy for both Paddy and I, playing sports in college—basketball, and lacrosse—like, for the college’s team. Sports where height and bulk give you an advantage.

And there’s a thing that happens when you play sports pretty seriously as a kid and move up through the ranks. The thing that happens is that everyone starts to look the same. Or at least they kind of start to all have the same body. All the big guys play football, all the tall guys play basketball, swimmers are thin and long and shave their heads for the big meets, hockey players all have the same accent, and their haircuts are even worse.

Whatever your sport is, you get used to everyone looking sorta like you.

And then, one day, if you follow the same trajectory as a lot of people—from ball sport athlete to outdoor athlete—they don’t anymore.

And that’s where Paddy and I bonded the most. Because after college, we both found sports like mountain biking, ultrarunning, and backcountry skiing. Stuff where height and bulk just means that you can’t find gear that fits. Our people had stayed on the basketball courts and lacrosse fields. We hadn’t. It was like running into a long lost relative at the airport.

When I sign up for a trail race and look around the start line, there usually aren’t any other Lego men. If there are, we usually meet again in the middle of the pack. The back of the middle, if I’m honest. There just aren’t any tall or big athletes on the podium. Ever. Bike races even have a whole separate category for people over 200 lbs, like me and Paddy, the Clydesdale division. Depending on the race, women over 140 or 150 lbs are called Athenas.

I'm not talking about being over or underweight, which seems like an easy misconception given the prevalence of eating disorders among runners. I'm talking about people who are built big. Tall. Like a stereotypical lumberjack.

Lots of professional athletes fit this description, from the NFL to the WNBA. Turn on the TV, and you'll see these huge bodies moving so fast, for so long. There doesn’t seem to be a limit on how agile or explosive, how athletic, a Clydesdale can be. You’d think someone, at some point, would find their way to the podium of some kind of endurance race.

But they don’t. At least, not very often.

And so, Paddy and I started to wonder, Why is that? Sure, we might weigh more than other runners, but also, our muscles are bigger and longer than a small person’s. Shouldn’t that scale up with, like, training? Big muscles use more oxygen, but our lungs are bigger, too. I recently had a chest X-ray and my lungs didn’t even fit in one picture. The tech had to put the machine in the X-ray equivalent of “panorama” mode.

As we started looking into this, it quickly became clear that the reasons we would never be above-average endurance runners were both different, and more interesting than we expected. But also, maybe cause of our size, there wasn’t room for both of us in the story.

So, Paddy O is going to take it from here.

Paddy O’Connell: It's a beaut. Good job, Pats. Good job, Bodhi.

You're hearing me doing something I do a lot: trail running with my two dogs, Patsy and Bodhi.

Stay with me, bud. Good boy.

Me on the other hand? I find it challenging. If you’re ever on trail and hear an asthmatic elk bumping into trees, don’t worry. It’s just me jogging.

Holy shit. Now it’s getting hot. Okay. Oh god. Running is so fun.

Truth be told, I have a love-hate relationship with running. I love being outside with my pups, my wife, and our friends. I love when I'm done with a run, that sense of accomplishment, those guilt-free donuts and pizza, and like, you know, exercise or whatever. But I hate no matter how fit I feel, my wife and her friends always leave me in the dust and my dogs always seem ready for more when I want to throw in the towel.

And recently I've noticed that I never see anyone who comes even close to my size on trail or at the start of the races I've signed up for. It’s all David and no Goliath. Why exactly am I the only 6'5", 250 pound giant out there. What do all the other giants out there know that I don’t? And who could I ask about this?

Alex Hutchinson: My name is Alex Hutchinson. I'm a sports science journalist with ���ϳԹ��� Magazine. It's been a good 15 years that I've been writing about, not just sports science, but more specifically the science of endurance.

Paddy: Before he was writer Alex Hutchinson, he was runner Alex Hutchinson. Alex got serious about running in high school, when he joined the cross country team. Then he ran in college and was a miler for the Canadian National Team. Today, at 47 years old, he is still very much a runner.

Alex: It started out as a hobby, but it's basically become my career. Not in the sense that I'm fast enough to run for money or anything like that, but I'm in the ancillary world of when I'm, Sitting around reading about running or watching races on TV, I feel like it's work adjacent. It's career adjacent. This is my life.

Paddy: I often joke that I'm a long jogger for the purpose of eating more snacks. What is it about running that first hooked you, and what keeps you like coming back?

Alex: The short answer is I have no idea. I don’t know why I like running so much.

Paddy: Yeah.

Alex: Look, when I started out, it was fairly simple. I was a kid who was fast, and so when I ran, I won races, and that felt good, and so it seemed pretty clear to me that as soon as I was out of school, I would stop running, because why would anyone continue running a, you know, when you weren't getting ribbons for it?

Maybe I've grown to like running and it was, it was definitely sort of like wasabi or, or, you know, sauerkraut or something. One of those things that I was doing because one does it and then after a while you're like, well, I guess I've done it enough that I actually like it for the sake of liking it.

Paddy: Even for Alex, running was an acquired taste. A sour, kinda spicy taste. But as he was learning to love it, he was helped along by something like the outdoorsy version of natural selection.

Alex has been the same height and weight - 6'1" and 140-pounds, tall with sinewy muscles - for 30-plus years. Suffice to say, the dude just looks like a runner. And me? Well, I look more like a refrigerator duct taped to a skateboard. It moves, sure. But, you better watch out.

Alex: One reason that there may be not so many 6 foot 5, 250 pound guys at the trail races is that they're all playing in the NFL, right? Like, they're, they're sleeping on huge piles of money. There just aren't that many people who are that tall and big. So let's start with the baseline.

You can look around the start line of a trail race, but you can also look around at the supermarket and you're not going to find many people who are bigger than you. So, so, so let's not, uh, you know, overlook the obvious factor that you are a special and unique person.

I want to offer some, further alternative hypotheses.

When you're 14 years old or you start high school and you have the choice like, Hey dude, do you want to be the captain of the football team and a big star, big man on campus? Or do you want to join cross country? There, there is a selection process where those who can aspire to be, you know, the big star of a contact sport often will select that option.

Let me just give it to you from my perspective. I go to a trail race and it's like, ah, these are my people, the other people who couldn't make the basketball team because we stopped growing at six feet and, and, and 140 pounds. So, as tongue in cheek as that may sound, there's a broader point, which is that human bodies are optimized for different activities.

And so, it's not just that you have an extra challenge as a big guy in a trail race. It's also that a lot of people with your body type may have discovered activities where their size is an advantage and, and they may have stuck to that. And I'm, I'm delighted that you, you know, didn't fall into that trap and still discovered the beauty and joy of trail running,

Paddy: That’s the beauty, joy, and pain of trail running, Alex. Pain that feels all the more pointless during a race, as opposed to a leisurely training run, cause in a race, the point is to finish quicker than the other people. And what I want to know is why aren’t I finishing quicker than I am?

And it turns out, there are a lot of reasons. But it starts with something very near and dear to my heart, and my center of gravity. Snacks.

Alex: The bigger you are, the, you know, the bigger the engine you're trying to fuel, the more fuel you need. There is some evidence that the maximum rate at which you can absorb nutrition is limited by the, basically, by the receptors on your intestinal wall and that it doesn't scale with size.

Paddy: At a certain point, Alex says, long endurance races come down to how much you can eat during the race. Your muscles store energy in the form of glycogen, and the fastest way to replace glycogen is eating as many carbs as possible. But that presents its own issue.

Alex: Traditionally people thought you could absorb about 60 grams of carbohydrate an hour and lately that's been pushed up to maybe, you know, 90 or even beyond that. But that's, people figure that's roughly true for small people and for big people. Just because you need more fuel doesn't mean your intestines can actually absorb more. And the, you know, if you try and take more than you can absorb, you'll just end up vomiting.

Paddy: So that’s a big problem. As the Ford F350 of athletes, I’ve got a bigger engine and a bigger fuel tank than the hatchbacks I’m racing against, but my gas pump runs at regular speed. And at the limits of endurance, how fast you refuel is a limiting factor.

Maybe the answer, then, is using less fuel. Could I, theoretically, increase my running efficiency to match a smaller runner?

Well, according to Alex, maybe.

I look like a washing machine that was pushed down the stairs when I run, is there something about running economy that helps smaller athletes.

Alex: That's a good question. I don't think there's any reason a priori that a bigger runner has to be less smooth or less poetic in motion than a smaller runner. And I can say, you know, I'm living proof of the fact that you can have a BMI of 18 and also run like a washing machine falling down the stairs.

Paddy: Really?

Alex: I have awful, awful looking form. It's just painful to watch me.

I'm not sure that, in terms of the biomechanics of a running stride, there's any inherent problem with being a big guy. The fact is, if every foot fall is landing with, You know 250 pounds on top of it. It may be harder to sort of leap it balletically from toe to toe than it is if you've got 120 pounds. On the other hand, your foot should be a lot bigger and, you know, have more muscles to absorb that landing.

Paddy: Turns out, running efficiency, on flat ground, is actually one place where bigger guys can hold their own. There’s nothing wrong with us. We’re not monsters.

Unfortunately, that all goes out the window as soon as the trail turns uphill. Add some elevation, and suddenly, we’re a human-sized wobbling Jenga tower that’s been lit on fire.

Alex: When I say there's a difference in like the body composition or the body structure, the body ratios between a small person and a big person, what we're effectively saying is that the big person wearing a backpack with some extra pieces of body that are not contributing in the same way. Not a dismembered corpse or anything like that. We're just talking. This isn't… this is notional.

Paddy: Yeah.

Alex: And so, that punishes them more as soon as they start trying to go uphill.

Paddy: In other words, the extra weight of my bigger bones matters more on an uphill climb than on flat ground. But there’s an even more fundamental problem.

Alex: Even though you can enlarge everything about the body, you can’t enlarge the fundamental properties of things like oxygen atoms.

Paddy: You were probably already thinking, “Hey, what about the fundamental properties of oxygen atoms?” Obviously. I’m right there with you. But just to give him something to do, I’ll let Alex explain it.

Alex: Okay, I'm claiming that if you're bigger you have more muscle and if you have more muscle you need more oxygen, but fortunately you have bigger airways and a bigger heart and everything's bigger. So everything is proportionally larger, but there's something that doesn't change between the two of us and that is the size of an oxygen molecule.

Paddy: Okay.

You don't have bigger oxygen molecules. So ultimately, if we go down to the level at which you're delivering oxygen, it's passing from your bloodstream into the muscle through these tiny little capillaries.

Paddy: In other words, I might be literally twice the size of an elite marathon runner. But we’re breathing the same air, and burning the same oxygen. So the blood vessels that transport oxygen have to be the same size in both of our bodies. Which means my body has to do more to get that oxygen to where it needs to go.

Alex: Our capillaries have to be roughly the same size because that is where the oxygen exchange is happening.

So if for me, I suck in oxygen through a big airpipe, and it goes into my bloodstream, and then that bloodstream, The passageways are going from big to smaller to smaller to smaller to smaller. And maybe it takes me, you know, 10 branchings to get down to the right size for oxygen diffusion.

If you start with bigger airways, it might take you 14 branchings to get down to the right size. And so there's a little more resistance to, passing oxygen from the air into your bloodstream and into your muscles.

If you take the best endurance athletes in the world, big people can use more oxygen, but they can use less oxygen per kilogram of body weight.

Paddy: When you’re fighting against gravity and going up hills, oxygen per kilogram of bodyweight—basically, your Vo2 max—is the gold standard metric for how fast you’re going to go. It’s especially apparent if you look at the best cyclists in the world.

Alex: The classic example of this is you look at cycle racing like Tour de France. Big guys can time trial really well. They've got huge engines, they can get rolling, and they can win flat stages and time trials. As soon as you get to the mountain stages, it's the tiny little guys who take over. And the simple answer to that is they have less weight to carry up the hill, right. So gravity is weaker. That simple answer is not actually very satisfying though, right? Because what defines your climbing ability as a cyclist is? Not your absolute power, but your power per kilogram.

How many watts can you put out per kilogram of body weight? If you can put out 300 watts and you weigh 50 kilograms, that's great. But if you weigh twice as much, your relative putting out 300 watts is half as good.

The scaling between how much bigger you get and how, you know, how much power you're able to produce and how much weight you're carrying around and how much of that weight is useful muscle versus, not so useful bone or fat, it varies. And all these things tend to come together in a way that means that bigger people have to work harder against gravity than smaller people. Their power doesn't increase as much as their weight.

Paddy: So, there it is. As you get bigger, you might get stronger in an absolute sense, but your strength per kilogram, your use of oxygen per kilogram, doesn’t scale up. Meanwhile, your ability to absorb calories and nutrients stays the same, even though you require more total calories to cover the same ground.

Physiologically, the deck is stacked against us. And learning all this sort of makes me ask the same question I ask myself every time I hit the wall on a run: Why the hell am out here? And why the hell am I out here with all these small super fast humans?

Dr. Joyner: In terms of your perceived exertion, or how hard you’re working relative to your package, I would guess, Paddy, that you may be working just a little bit harder than they are.

Paddy: So the argument could be made that I’m just more athletic?

Dr. Joyner: Yeah, mentally tougher, mentally tougher, but you could have a lot of fun with that one.

Paddy: I’m going slow because I'm more athletic than you are.

More on that, after the break.

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Paddy: Alex Hutchinson helped me get a better grasp on why trail running is so damn difficult for a guy my size, 6 foot 5 and 250 pounds. So much so that by the end of the conversation, I was close to wondering why even bother?

But Alex also suggested I talk to Dr. Michael Joyner, who has been studying the science of endurance at the Mayo Clinic since 1987.

Mike Joyner: My name is Mike Joyner and I'm a physiologist and anesthesiologist. I work at the Mayo Clinic where I've worked for a long time.

Paddy: I consider myself an intelligent person, but I'm hoping that you can explain everything we talk about today as if you were speaking to a kindergartner.

Dr. Joyner: I’ll do my best.

While I pulled up my carpet square and waited for snack time, Dr. Joyner explained—very patiently and very clearly—a lot of the same stuff Alex covered. I’m a big truck. Most runners are zippy little Miata’s. Size doesn’t matter so much on flat ground, but when you go uphill, it matters a lot. And bigger lungs don’t mean a bigger Vo2 max. It doesn’t scale.

Dr. Joyner: We typically think about a measurement called Vo2 max or maximal oxygen consumption, which is expressed as milliliters of oxygen consumed per minute per kilogram of body weight. So a lot of people who are pretty fit males can consume maybe four liters in a minute of oxygen or if they're really fit five and sometimes even six. Well, if you're dividing that four liters by 60 kilograms, you're gonna have a value in the 60s. If you're dividing that by 100 kilograms, you're going to have a value in the 40s.

Paddy: So, if you compare me at 6’5” to my wife, Carly, who’s 5’3”. She’s going to be more efficient at processing oxygen just because she’s smaller. Her ratios are better. And with the help of a clever little piece of science fiction from yours truly, Dr. Joyner was able to explain exactly why it doesn’t scale in a way that I was almost able to follow.

Paddy: Let's pretend, right, that I, that we had this magic ray, and it was able to shrink me down to, you know, 5 foot 3 or enlarge someone who was 5 foot 3 and, expand them to my size. What, what happens in the difference there?

Dr. Joyner: Let's think of a simple cube that is one meter, on each edge. So the volume of that cube would be one cubic meter.

Paddy: Okay.

Dr. Joyner: The surface area around that would be six, uh, square meters. So there's six, because there's six sides to a cube. And the linear dimension, each edge would be one, one across. So you have one, for a linear dimension, one for the volumetric dimension, and six for the surface area dimension, right? And that would be true as it, for, for the parts inside the body as well. Now let's make that two. So if we make it two, we've doubled the linear dimension, and we now have a surface area of 6 times 4, so now surface area is 24. So we've gone from 1 to 2 on the linear dimension. And from 6 to 24, we've increased at fourfold on the surface area dimension.

Now we've gone from 1 to 8 because the volumetric dimension is 2 by 2 by 2. You've doubled the length and increased the volume eightfold. You've only increased the surface area fourfold. So things are not going up in a linear way, just like as you go faster on your bike, the wind resistance is curvilinear. So the relationship between a body dimension and a volume is a cubic dimension, and a surface area is a squared dimension. So that's a little complicated geometry

Paddy: So in terms of endurance sports, you can think of our bodies as basically just squigly, slimy skin cubes of varying athleticism. And in this analogy, Carly is the little cube, 1 meter across, with a volume of 1 square meter. And I’m the big cube, 2 meters across, but with a volume of 8!

And when it comes to moving those cubes up a mountain, volume is bad. It’s dead weight that doesn’t help you go faster. Surface area, however, is good. That represents stuff like how much blood you can pump, and how well you can use oxygen.

Dr. Joyner: It turns out many of the limiting factors in performance are related to cross sectional area. The cross sectional area of the skeletal muscle, the cross sectional area of the tubes in your lung, the cross sectional area of your blood vessels, right?

Paddy: Okay.

Dr. Joyner: So, those limit how much air you can get in and out and how much blood you can pump and how much force your muscles can generate, right? So even though your, the length has gone from 1 to 2, and you've had a 4 fold increase, a 4 fold increase in these surface areas, right?

You've had an 8 fold increase in weight, an 8 fold increase in volume or weight, right? So your absolute numbers are going up, but your numbers divided by what you're trying to move, your body weight, are relatively going down in terms of a relative power to weight ratio. So that explains why, if you take the weight out of it, put people in a boat and ask them to row, ask them to swim where weight is much, much less of a big thing. The rate at which you add power is greater than the rate at which you add resistance. So you end up going faster.

So part of it is, you know, Paddy, you've sort of picked the wrong sport.

Paddy: Yeah I was gonna say, shit doc, I’m in the wrong friggin sport.

Dr. Joyner: Yeah, well, as somebody who's 6'4” and when I was running competitively, 170, 175 pounds, I tell people one of the things I've learned in the last 40 plus years of exercise physiology research is I should have been a swimmer or a rower.

Paddy: It turns out that in addition to being a world-renowned exercise physiologist, Dr Michael Joyner is also, basically, a Clydesdale. Which means he knows the struggle. The futility. The heartbreak. Of wanting to be faster than you are. Faster than you’ll ever be.

Paddy: So I can, you know, when I'm getting like dusted on a trail run by my wife, I can say, “Well, this is a science problem, not a fitness problem.”

Dr. Joyner: Yeah, absolutely. Absolutely. And the reason it's going to be harder is because the determinants of aerobic capacity and muscle strength are related to, cross sectional area. And as you get taller, your cross sectional area goes up, but your body volume or body weight goes up even more.

Paddy: And this is where my conversation with Dr. Joyner turned from physiology to psychology.

If all this is stacked against me, why should I go?

Dr. Joyner: I think the main reason is… We always have to ask ourselves, why am I doing this? I mean, A, it's beautiful outside. B, the camaraderie, the community. But C, you know, to be able to meet that challenge. You know, all of us in endurance sports. I kind of had one this morning. I do regular interval training. And if you do it right, you can get into the zone a little bit and have somewhere between a mildly altered state and a really nice altered state if you’re able to kind of get with the rhythm, get with the flow and, and engage psychologically in what you're doing and, and really stay focused on pushing it and relaxing at the same time.

Paddy: At a certain point as a runner, no matter who you are, or what volume your gooey skin cube is, you gotta decide: science be damned, I’m gonna go for it. Because there’s always going to be someone a little faster, who finds running a little easier. Being bigger may be a slight disadvantage in a trail race, but it’s also a reminder that the real point of all this training, day after day, year after year, is not for a podium finish. Because after all, when you’re out there plodding along, you’re really only running against yourself.

Alex: Let's say you were much smaller. It's not like there's a million dollar prize waiting for you, if you were just a little bit farther ahead in the pack, we all do things for reasons that are sometimes hard to articulate.

My suspicion is that if you're to dig deep enough into your own motivations, your size doesn't really have a ton of bearing on what you get out of it.

I also think if you were to deploy your mind reading machine to learn what's going on in the heads of the people around you, or even the people half an hour ahead of you up the trail, you'd find that they're all wrestling with similar battles. They're wondering why the hell they're doing it. And they're all thinking, this is so hard, this is so unpleasant, the deck is stacked against me because of A, B, C, D, and E. We're all carrying different loads.

So I think, it's not to deny the reality of what you're feeling, but just to say that I don't think it actually changes the essence of what you or anyone else gets out of the sport. That we're looking for something beyond. It might be nice to go from 100th to 50th place, but the rewards are the same.

Peter: Paddy O’Connell is one of our regular contributors, and the host of PaddyO Sucks At, a very funny series where Paddy tries and sometimes succeeds at learning new skills and sports.

Alex Hutchinson is ���ϳԹ���’s Sweat Science columnist and the author of the book Endure: Mind, Body, and the Curiously Elastic Limits of Human Performance.

This episode was written and produced by Paddy O’Connell, with editing by me, Peter Frick-Wright. Music and sound design by Robbie Carver.

The ���ϳԹ��� Podcast is made possible by our ���ϳԹ��� Plus members. Learn more about all the benefits of membership at outsideonline.com/outsideplus/.