Thursday, 9 July 2009

Humans, the runners

I won't complain about the weather today, or talk about Sarah's resignation. Instead, I want to talk about something Sarah Palin does. So does Obama. So does Justin Gatlin and... wait, who?

Running! When you think about animals that are good at running, we tend to think about cheetahs, gazelles, antelope and other things of that nature. Horses, definitely. But what about jackrabbits, and snowshoe hares? Sure! Jackrabbits actually have skulls that deform as they run, and contrary to popular belief, their ears are more used as levers to un-squish their skulls. That's rather neat, but not what I'm about to go on about.

Over the years, we've got a good grasp on what makes good runners, from
  • spinal flection - the bending of the spine with each stride to shorten and lenghten the torso.
  • reduced distal portions of limbs - since limbs are levers, and the lighter the end of limbs, the less mass that needs whipped around.
  • ligified limbs - absorbing and re-releasing energy from each trot.
  • generally long limbs - speed is a function of stride length times stride rate.
And there's a variety of other adaptations that appear evident between most running animals. We tend to call animals that run a lot "Cursorial animals." And the back of sugary cereals boxes are full of facts about how cheetahs can go XYZ fast, eat ABC gazelles per hour, and so on. As as side note, I hate that. I call it ADD biology - just little snippets without any depth that they throw at you one after another, before you get distracted by something new and shiny! Ooh! A tricycle!

One thing you don't find on the back of Admiral Crunch boxes, Arch-Duke Chocula, or Cookie crud, are humans as some pretty phenomenal runners. And why should we? After all how many humans do you see going 100 km/hr without being on a snowmachine or something else. First, we need to know not all running is equal. There are various types of movement, including trotting, or endurance running, and galloping, or sprinting.

The difference between them is one of oxygen consumption. In endurance running, oxygen consumption increases with speed. In sprinting, oxygen consumption no longer increases, and the body begins to enter into an oxygen deficit. If you think back (or forward!) to your highschool biology, you understand that endurance running is aerobic, while sprinting is anaerobic. Many species that can engage in other gaits have separate gaits for walking, trotting and galloping, but humans really only have separate gaits for walking and trotting, and our galloping is a modification of our trot.

Clearly, our sprint is nothing spectacular, but what about the rest of our running range? In our aerobic portion of our running range - the thing that we could quite plausably do all day, we find this:
This is a figure from Bramble and Lieberman 2004, and I'd draw your attention to the left half of it. You see that the human endurance running range far exceeds that of your typical quadruped of the same size. Even the average human 'light jogging' speed is close to an average four legged critter's trot-gallop transition. Even when you look at ponies, which are undboubtably good runners, a human trot can easily outpace their own, forcing them to enter into oxygen debt while the human is still doing quite nicely.

Adam Summers summed up the finding quite nicely when he said,
Where we excel is endurance running. Moreover, we run long distances at fast speeds: many joggers do a mile in seven-and-a-half minutes, and top male marathoners can string five-minute miles together for more than two hours. A quadruped of similar weight, about 150 pounds, prefers to run a mile at a trot, which takes nine-and-a-half minutes, and would have to break into a gallop to keep pace with a good recreational jogger. That same recreational jogger could keep up with the preferred trotting speed of a thousand-pound horse.
"But!" people protested, "What are the adaptations to running? Can you really just prove humans are cursorial mammals, and this isn't just some by-product of us being good bipedal walkers?" Yes, we can! But that will come in a later post. Now, I'll just let you all get comfortable with the idea that while a cheetah can break off into a sprint and go fast, you could probably keep running long after it had collapsed from exhaustion. Take that, cheetahs.


Cited:
Bramble, D. M. and D. E. Lieberman (2004) Endurance running and the evolution of Homo. Nature 432: 345-352.
Cheetah image from Wikimedia, rights reserved.

3 comments:

Alaskan Dave Down Under said...

Good analysis. Us humans are pretty darned good at endurance running, but only the those who practice it.

OT: you don't really drink PBR, do you?

TwoYaks said...

Not entirely true. Even those who aren't terribly fit could probably run distances that would cause other animals we consider `fast` to enter major oxygen debt. It's interesting, because Dennis Bramble (the guy who pioneered the analysis of human running) said he had good data set, and aside from the obvious (the disabled, the obese, etc.) even average humans are dang good runners (comparatively) with two exceptions: the old, and women late in their pregnancy. I wish I had copies of the graphs he had...

I sometimes do drink PBR. I don't like it, but when I'm with a couple of friends who really like it, I might have one or two myself. Who am I to say they're not allowed to enjoy something? Right now, I'm working through a case that I bought to celebrate a now-ex-gradstudent's completion of his Ph.D. - he was so exhaused he barely touched any beer that night. So it's up to me, I guess! It's been 2 weeks, and I haven't made much of a dent.

Alaskan Dave Down Under said...

It's been 2 weeks, and I haven't made much of a dent

Too right mate.