Study: Live to Run or Run to Live?

Long_Distance_RunningAs more and more of us face the cubicle world all day long, is it any wonder that we long for the freedom running down an open road or a wooded trail, with our thoughts wandering to a happy place instead of being terminally distracted by technology?  It’s about freedom, in a way.  Society and the workplace are becoming more restrictive, so it’s natural to seek freedom where we can.  But is it more than that?

Many in the running community will proudly say that they live to run.  They carefully plan their days and weeks around their training schedule, plan road trips around races, watch their diets and their sleep patterns, and do everything they can to make sure that their run time is as enjoyable and fulfilling as it can be.  It’s a way of life, and a healthy one at that.

But is that yearning to run a call from our distant past?  Some say that instead of living to run, that free feeling we get while running ties us to our earliest ancestors, who scientists suggest had to run to live.

The theory goes something like this:  roughly 2.5 million years ago, homo sapiens emerged from evolution with big brains, which require a much higher caloric intake to thrive.  At the same time, we faced major climate change, and had to change with the times.  As lush green forests gradually thinned out and became plains, our herbivore ancestors gradually became omnivores.

Bone studies dating back roughly two million years show a significant rise in proteins over their predecessors’ diets, backing up this theory.

Of course, that evidence begs a larger question:  If we as a species didn’t develop weapons until about 200,000 years ago, and didn’t develop the bow and arrow until 50,000 years ago, how did we catch enough food to fuel this collective rise in protein in our diets?

The most convincing argument I’ve seen was put forth by Harvard University’s Dr. Daniel Lieberman (of Born to Run fame).  He suggests that while humans are extraordinarily slow runners, we are ideally suited to running slowly for long periods of time.  We are unique in the animal world in that we can endure a higher work rate while efficiently regulating our body temperatures, while other species must stop periodically to regulate theirs.

running evolutionThis means simply that other animals can use a burst of energy to get away from us, but must eventually stop to pant.  We close the distance and make them run again, and continue the process until they go into heat stroke, and we have our protein.
It’s called persistence hunting, and Dr. Lieberman says it’s what we were born to do.

One of the competing theories suggests humans might have instead been strategic scavengers, able to discern opportunities to obtain that all-important protein.  Potential cues could have been scavenger birds circling above a fresh carcass, or blood stains in the grass, allowing us to track a wounded animal.

Either way, we’d have to run a long way to beat our competitors to the bounty.

While we are almost criminally slow compared to most other animals, our advantage lies in two areas:  kinesiology and physiology.

Kinesiology

While the creatures from George Orwell’s Animal Farm would say “four legs good, two legs bad”, they never had to run for a long period of time on a hot day.  Your typical four-legged animal suffers from one major disadvantage – the proximity of their legs to their lungs.  Since their lungs are wedged between their front and hind legs, they are constricted as the animal runs.  The body coils as the front legs complete their cycle, and expand as they reach forward to start the cycle.  That means that four-leggers have to breath once per cycle.

The problem is that increased speed demands increased oxygen, and the fact that quadrupeds increase speed by taking longer, more powerful strides means that they simply can’t pant fast enough to cool their bodies while running.  Even trotting at a relatively easy pace causes their bodies to overheat, forcing them to stop and pant to reduce their body temperature.

Contrast that with humans – our lungs sit above our load-bearing legs, and therefore aren’t tied to our locomotive cycle for breathing.  Since our running cycle doesn’t force our lungs to compress, we can inhale plenty of air to keep ourselves running at a steady pace.

Sure, sprinting for more than a short time would force us to stop and gasp for air, but hunting demands patience, not lightning speed.  Which leads us to our real advantage – a super-efficient cooling system.

Physiology

No one likes running on a hot, humid day.  We become a sweaty mess.  But it’s exactly that ability that gives us our greatest physical advantage over running quadrupeds.

We are covered in eccrine sweat glands – millions of them.  They secrete water and electrolytes, and also have the added benefit of helping our skin protect itself from bacteria.

tired-runner-cartoon-i0During physical activity, our body temperature rises, activating our eccrine sweat glands.  This secretes water to cover our skins.  That water evaporates, cooling our skin and releasing heat. As the water increases in temperature, the energy from the movement of the different water molecules also increases.  At a certain temperature, the fastest moving molecules of water will evaporate, taking their energy (read: heat) with them, leaving behind the cooler water, which cools our bodies.  Think of it as our own personal sprinkler system.

Our quadruped counterparts have no eccrine glands.  Instead, they have apocrine sweat glands, mainly in their armpit areas (we also have these).  These also secrete sweat, but are far less efficient than eccrine glands.

The Competition

The numbers don’t lie.  According to this 2012 article in Salon, the best distance-running quadrupeds are horses, dogs and wildebeests.

Dogs can gallop for only about 10 to 15 minutes before slowing to a trot, with their distance-running speed topping out at about 3.8 meters per second. Horses average about 5.8 meters per second, while wildebeests do 5.1 meters per second.

Top human runners can sustain speeds up to 6.5 meters per second. Most average joggers can typically do between 3.2 and 4.2 meters per second, which means they can outrun dogs at distances greater than two kilometers.

But the biggest difference occurs when you look at sustainable distance – the distance an animal can cover in a day.  African hunting dogs typically travel an average of 10 kilometers a day, and wolves and hyenas tend to go about 14 and 19 kilometers, respectively. Horses can cover about 20 kilometers a day. Contrast that with humans.  Increasing numbers of us routinely run 42.2-kilometer marathons in just a few hours, while tens of thousands more complete ultra-marathons  of 100 kilometers and longer.

The Bottom Line

When it comes to distance running, the maxim that success is ten percent inspiration and ninety percent perspiration have it right.  Our ability to cool our bodies makes all the difference, and is the reason we can outrun our competitors over long distances.

While the arguments over the theories of persistence hunting and strategic scavenging and the role they played in our evolution continue to rage, there is no denying that our bodies were built for endurance, rather than strength or speed.

It would be hard for me to believe that this unique ability is just coincidental.  Given the timeline of our development and all the things about us (see the graphic below), it simply makes too much sense to at least consider the persistence hunter theory, rather than discounting it outright.

Human_Running_Adaptations

 

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