I ran, Tuesday night, probably the fastest 5K I have ever run. I don’t know how long it took. I didn’t time it. But I know that I started out at a good clip and thought “I’ll have to slow down to make 5K,” and then I didn’t slow down. I didn’t slow down, and I was at the top of the hill and running down the other side before I realized I had been climbing, and was a little disappointed when it came time to stop at the 5K point.
But stop I did, because it’s best not to over-train. That’s how you get the shin splints, the pronated ankles and blown-out knees, and I’m beginning again to think in the long term. The common advice is that when you’ve just started being able to run 5K, that each long run be followed by a day of rest.
So I only ran 2.5K on Wednesday afternoon. I ran a little slower, knees aching a bit at first, calves throbbing, and then — as usually happens when I’m not already distracted by work, or love, or heartache — my breathing rhythm filled my mind, and before long my legs felt loose and comfortable.
I time my breaths to my hoof beats. I start out at a measured pace, breathing in for four steps and out for four. When I feel a little bit of anoxia I move up to a three and three rhythm, IN (two three) OUT (two three), running and breathing in waltz time. These days I’m usually about a kilometer down the path when I again feel shortness of breath, and I move up to what has become my default, long-haul respiring rhythm, drawing deep breaths in for three steps and then exhaling forcefully in two. The hard exhalation raises the air pressure in my lungs, thus raising the partial pressure of oxygen, I tell myself, and I thus increase the efficiency with which my lungs extract that oxygen from the ambient air. I have no idea if that’s true, but it feels good. Heading uphill I will often find myself breathing faster still, a two-steps-in, two-steps-out rhythm, or even one and one if I am pushing myself too hard. As soon as the trail levels out I drop back to the three and two, usually without thinking about it.
It is often said, counterintuitively, that a man can outrun a horse. It seems stupid on the face of it, and in fact Olympic athletes have lost demonstration 100-yard dashes to near-senescent horses. But as PZ pointed out in a post about three years ago, that equine advantage dwindles when you lengthen the track. Quadrupeds are often excellent sprinters — I once, based on dead reckoning and guesswork, figured that the young Zeke’s “not really trying” fun sprints averaged around 25 mph — but not so good at the long haul endurance running thing. It is indeed quite possible for a well-conditioned human to outrun a horse in a race of ten miles or so.
The difference between sprinting and endurance running? Oxygen. In sprinting, you use up oxygen faster than you can breathe it in. It’s anaerobic exercise, and no animal can exercise anaerobically for very long. Endurance running is aerobic: you use only as much oxygen as you take in. Barring injury or hunger or stoplights, human endurance runners can keep going a very long way.
PZ’s post was spurred by a paper in Nature that postulated that much about the human body’s morphology could be attributed to selection for endurance running. He offers, in table form, a long list of human physical features that make endurance running easier, along with the service they offer the runner and the possible evolutionary points of origin for each feature. Of course, whether it was selection for running that sculpted each and every such feature is open to conjecture. It’s tempting to speculate as to the selective advantage of being able to run at moderate speeds for a very long time. It’s not much help when confronted by a jaguar 20 yards away intent on crunching on your temporal bone: the jaguar would find it fairly easy to outpace you, knowing it could relax and reoxygenate once it had made sure, by collapsing your trachea, that you couldn’t reoxygenate. But it’s easy to see advantages in running toward animals rather than from them (a.k.a. hunting), in warfare, perhaps in traversing bleak Miocene landscapes with miles of baboon-infested veldt between spots of suitable habitat.
Anyway, it’s a good post, and you ought to take the time to read it, perhaps ignoring the usual assortment of wise-ass Pharyngula commenters.
But I’ve been thinking, as I run, about one of PZ’s assertions in that post:
Just walking bipedally is a precarious exercise, and running amplifies the problem.
It’s true: compared to precarious bipeds, quadrupeds rarely find themselves doing face plants (though again, there are some Zeke anecdotes relevant here) and running makes the falling not only more likely but more spectacular. Some of the adaptations listed in PZ’s old post address the issue, such as our relatively larger inner ear organs.
But I wonder if our bipedalism might not be the reason we can run for such long distances relative to quadrupedal mammals.
This isn’t my insight, or it least it wasn’t until I borrowed it. In Peter D. Ward’s Out of Thin Air: Dinosaurs, Birds, And Earth’s Ancient Atmosphere, which I have been reading in between runs, Ward proposes that atmospheric oxygen levels throughout the history of earth have had dramatic effects on animal life. It’s a good read, so far, though it suffers a bit from the “one thing to rule them all and in the hypothesis bind them” syndrome. Ward proposes to explain a whole lot of stuff with atmospheric O2, enough to trip one’s inner skeptic.
But some of what Ward proposes seems fairly sensible. Take the early Triassic, for instance, and the astounding change in animal life that took place back then. Before the end-Permian extinction, the therapsids — once called “mammal-like reptiles,” but called that no longer since they were neither — dominated the land, with gorgonopsians as perhaps the top predator in the late Permian. Then whatever it was that caused the end-Permian extinction happened — three guesses what Ward suggests it was — and the gorgonopsians died out along with 95 percent of all the species on the planet, and with conditions pretty damn bleak for those who survived.
Atmospheric oxygen levels in the early Triassic were as low as they’d been since the invention of photosynthesis, Ward says, and the Triassic air at sea level might have offered as much oxygen as modern-day air at 11,000 feet. You and I can survive indefinitely at 11,000 feet: it just takes acclimation, a bit more lethargy relative to life at sea level, and if we’re lucky, coca leaf tea. But our lungs are much better at wresting oxygen from the atmosphere than were the standard-model surviving Triassic therapsids. It’s likely that therapsids spent much of their time breathing hard, eking out a living as herbivores and ambush predators in habitable pockets along the Triassic coasts. Elevations higher than about 3,000 feet would likely have been unpopulated, even by plants, which need sufficient oxygen to diffuse into the soil to keep root cells alive. This low-oxygen climate lasted for tens of millions of years.
And then the first dinosaurs showed up, and ruled the earth. Their lungs were likely far more efficient than the therapsids’. Their present-day descendants, the birds, can fly at altitudes far higher than those humans can reach without canned air. They could get enough O2 from the Triassic air, Ward suggests, that they could hunt cursorially — by running, like wolves and cheetahs, instead of by laying in wait to ambush like moray eels. Not only could they outrun their prey, they could run around all day looking for it. This gave them a huge advantage.
Part of this, Ward suggests, was due to those highly efficient, innovative lungs, which allow them still to dominate the earth to this day: with 10,000 known species, their bird descendants make up the most diverse group of terrestrial vertebrates.
But another part of the reason for the dinos’ advantage, offers Ward, was their good posture. The first dinosaurs were bipeds.
Horses are excellent runners indeed, for quadrupeds. They’ve evolved strong and sturdy streamlined legs, shock-absorbing and tough hooves, pretty flowing manes, the whole gamut. Here’s a famous set of photos of a horse running quite fast, taken by Eadweard Muybridge, collated into animated gif form. Enjoy it for a moment — it’s an important document in the history of visual representation of scientific information — and then we’ll continue.
OK. Now if you will, please watch the horse’s thoracic area for a bit. You’ve got the scapulae and associated muscles working to bring the forelegs forward and then to use them as levers against the earth for forward motion. You’ve got the hips and gluteal muscles doing the same thing in the posterior part of the horse with its rear legs. But there’s something else going on between those two ends. The horse’s trunk is extending, when the legs are at their furthest extension either front or back (which characterizes a gallop) and contracting when all four legs are tucked beneath the horse and off the ground.
It’s a good way to increase power to the legs. There’s just one problem with it. Another bodily function depends on extension and contraction of the trunk: breathing. Unless the rhythms of breathing and running are meshed, at least one of those functions is going to be performed at less than peak efficiency.
For sprints, that doesn’t matter, and horses cover a mile just fine at a gallop, and they can breathe hard later and catch up. It’s a great strategy for escaping predators. But if you need to run for very long distances at a somewhat more moderate pace, doesn’t it make sense to decouple the breathing motion from the locomotion?
I run using my gluteals and hips and legs, and I breathe by expanding and contracting thoracic muscles and ribs, and the two actions are related but not chained together. I can give breaths and paces strict one-to-one parity if I wish, and I do some nights when the jaguar eyes me a bit more intently than usual, but that’s not necessary or even usually advisable. I can run through the usual measured, distracting breathing routine I followed today. I can match my respiration rate to the music in my head.
Or I can let my autonomic nervous system take over and disengage breathing from pace entirely, using a complex and mysterious algorithm based on blood CO2 levels, engaging in a millions-of-years-old family tradition and a signal human talent, a trick we share with the oldest dinosaurs.
Which also frees my mind for the detached contemplation of jaguars. As long as you run toward the jaguars instead of from them, the advantage is yours.