[MUSIC]
In 490 BC a Greek messenger named Pheidippides ran from the Greek town of Marathon to the
capital Athens to deliver a message that the Greek army had
just beaten back the Persians, and the distance between those two towns is 26.2 miles, and
that’s the origin of the modern sporting event that we call the marathon. You might
know that story, but what they don’t always tell you is that when he got to Athens after
those 26.2 miles, Pheidippides died.
So why on Earth would anyone want to run one of those for fun? How are our bodies even
able to? I decided to find out, so I ran one. In the process, I
discovered a lot about what I’m made of, in more ways than one. You guys ready to run
the marathon? My training started millions of years before I ever got to the starting
line.
The first step to becoming a runner is, well, standing up, and bipedalism is only seen in
a handful of animals, except for a few species of birds walking on two legs is only uses
a temporary form of transportation. Our ancestors first stood up over three million years ago,
and well we were running probably not long after that, were made for
it. You could say that humans are built for long distance running but the truth is, long
distance running build us the most four on the floor quadrupeds could easily beat me
in a sprint, but humans are medal contenders in nature’s distance running events. Even
the cheetah, the most perfectly crafted running machine on Earth could only run for maybe
a mile and a half before it overheats. Today’s fastest Olympic marathoners, they would only
be beaten by a handful of Earth’s animals in that long
distance. One theory of human evolution says that our adaptations for distance running
work feast or hunting success like we talked about in my episode “Why Do We Cook?”,
bigger, richer meals mean that we could evolve, well, bigger, richer brains. There’s a whole
list of ways that we are made to run. In large tubes in our skulls help us balance while
we’re running, reflexes in our eyes keep our heads steady as we move up and down. It’s
short arms and thin ankles that take us less effort to swing. Wide shoulders, a thin waist,
and a pretty narrow pelvis help us counter the rotation of our moving legs. We have sweat
glands, and less body hair, and tall thin bodies that let us disperse more heat. Better
blood flow away from the brain to keep it cool, your big gluteus maximus muscles to
stabilize our upper body, high surface area knee, ankle, and hip joints for shock absorption,
and most importantly, our lower legs are built like rubber bands.
This is by far our coolest running adaptation. Every time my body hits the ground, it delivers
up to 8 times the force of my body weight. That’s over 1400 pounds! In order to keep
that up for 26.2 miles, my foot expands and spreads like a shock absorber. This is the
most important part of a running human: the Achilles tendon. Though my foot hits the ground,
my calf muscles flexed, but even then the muscles and tendons are still a little bit
elastic, and then my ankle joint acts as a lever, which transfers as much as 50 percent
of that energy into the next step. By using stored kinetic energy, instead of chemical
energy, we’re able to go farther with less work.
You can’t run a marathon with just rubber bands though. You need power that humans are
run on gasoline your car ATP. This is an image of a striated muscle, the same type we have
in our arms, in our legs, and basically everywhere that we move. Each row of stripes contains
a string of proteins called actin, next to another string of proteins called myosin.
And the head of that myosin protein, well, it acts like a ratchet, pulling along the
string of actin, shortening our contracting the muscle. That myosin machine is powered
by ATP. The thing is, our bodies only have a couple seconds worth of ATP stored up at
any moment, so instead, we’re constantly replenishing it, thanks to our mitochondria
and their little ATP factories. Just picture me as a giant ship with trillions of mitochondria
at the oars. My body cycled through something like 75 kilograms of ATP during the marathon.
That’s almost my entire body weight! It just shows you how good our bodies are at
recycling energy. Now that’s 75 kilograms of ATP broken down release the same amount
of free energy as a kilogram of TNT. My body gets ATP in a couple of different ways. If
I was running full speed the entire time, my cells would be forced to use an inefficient
process called glycolysis, but by running slightly slower for the whole race, I let
my mitochondria use a much more efficient method called the Krebs cycle and the electron
transport chain. I can burn lots of fuel and make that ATP, like fat or protein, but my
muscles prefer glucose, which is stored in long chains like glycogen for quick access,
but even they don’t keep that much just lying around. So instead, I topped off my
glycogen tank before the race by doing something called carb loading.
Look at all these waffles I have to eat. But even eating all that before the race, my body
can’t hold all the glycogen it needs to get through a marathon, so I had to eat and
drink more during the race, or else I would hit the dreaded wall.
Hitting the wall is just a big scary name for fatigue. And there’s lots of reasons
why it can happen. If you run out of glycogen, then your muscles can run out of ATP, and
that protein ratchet will get stuck in the lock position. It’s actually why something,
well, gets kinda stiff when it dies. If your cells don’t have enough salt, then your
nerves and muscles won’t have the sodium, potassium, and calcium that they need to pass
electrical signals. The main reason that people hit the wall is because of this. See, your
brain is competing with your muscles for blood sugar, and if those levels dip too low, well,
“I think I’m gonna die. I’m gonna die. ”
Your brain is actually preventing your muscles from firing goad for some emergency power
save mode. I’ve never run a marathon before and I discovered it’s not like any other
sporting event I’ve ever taken part in. You’re not battling an opponent; you’re
only battling yourself. All those feelings of joy, and fatigue, and pain, they only exist
in your mind. That mind is connected to the physical muscles and chemical power plants
and proteins doing work. I’ve never understood more about my body, or my biology, and when
I push them to the limit, and in the process, I discovered that it wasn’t a limit after
all. That was the most fun I’d never want to have again. Like halfway through, it was
like the hardest thing I’ve ever done, and the entire second half
was just pure willpower, like a competition against yourself, and I-I won. I beat- I beat
my own mind. That was awesome. Thank you, everybody.
We’re not the only social animals that sit down to eat together, but we are the only
ones who cook. Cultural anthropologist Claude Levi-Strauss is above all cooking establishes
the difference between animals and people, although I’d think he’d agree that pants
make a big difference, too.