Tag Archives: the human body

In defense of the endurance running hypothesis, part 1: how we think about evolution.

The endurance running hypothesis is the idea that humans evolved primarily as endurance runners. The argument goes that the human physique evolved and took its shape and function from the primary adaptive pressure of persistence huntingthat of chasing down our prey until its body shuts down.

However, this hypothesis is not without its detractors. A significant amount of scientists provide an array of counterevidence to the endurance running hypothesis. (And the debate continues.)

Take for example the case of the human gluteus maximus (butt muscle). Lieberman et. al. (2006) claim that the human gluteus maximus evolved its shape and size due to endurance running.

However, another article in the Journal of Comparative Human Biology finds that the gluteus maximus grows much more in high-force sports (weightlifting) and high-impact sports (such as soccer), than it does in endurance running. In fact, they also show that the butt muscle in endurance runners is no larger than in the non-athlete population.

What I disagree with is their conclusion, which is paraphrased in the “What does this mean?” section in the image below:

“The human gluteus maximus likely did NOT evolve through endurance running, but through varied explosive and forceful activities.”


My disagreements with the article (and the image) are primarily about how and why we interpret the science to mean a certain thing.

At first blush, the fact that endurance running doesn’t enlarge the gluteus maximus as much as other sports seems to detract from the idea that the muscle takes its shape from endurance running. But I think it actually adds to it.

By my analysis, these findings show that the basic, untrained shape and size of the gluteus maximus—it’s “factory specifications,” if you will—assume that it’s going to do the amounts of cutting, jumping, weightlifting, and sprinting that a habitual endurance runner might need to do. But it requires aftermarket modification to meet the (literally) outsize power and stability requirements of soccer or weightlifting.

Let’s say that a muscle evolved under a particular adaptive pressure. This means that its shape and size literally evolved to do that thing. If you take a muscle that usually doesn’t do a thing for which it evolved to do, and you ask it to do that thing, you are asking it to do something that it has prepared to do for millions of years of evolution.

In order to fit a function that it has been designed to do, the changes in shape and size that the muscle should have to undergo should be smaller, not larger. You would expect a muscle to change far more if you ask it to do something that is less aligned with its evolutionary job description.

Let’s illustrate this by looking at the arm and hand.

We probably all agree that one of the things that specifically sets us apart from our hominid cousins is the ability to coordinate the thumb with the rest of the fingers in order to grasp and manipulate objects to a high degree of dexterity. In its simplest form, this is the capability to oppose the thumb and the fingers—to make an “OK” sign with the thumb and each of the fingers of each hand.

Now let’s take a snapshot of the people who take this unique human ability to its very pinnacle: string musicians, graphic artists, etc. Their livelihood depends on the degree to which they can explore the potential of one of the major evolutionary functions of the human hand.

Compare the forearm muscles of a violinist or painter with that of a weightlifter. The weightlifter’s arms, hands, and shoulders will be much larger and more powerful. (I trust I need not cite a scientific, randomly-controlled study on the matter.) Why? Quite simple: weightlifters engage in activities that develop the body to phenomenal proportions.

But if we go by the conclusions of the article, the fact that the arm and hand get bigger through weightlifting would mean that it didn’t evolve for the kind of fine motor control that you produce in the arts. (Or that lifting heavy objects is its primary evolutionary role). A particularly ambitious version of this argument would be to suggest that one of the core functions of opposition is to become better able to lift heavy objects. But all these suppositions break down when you realize that our primate cousins were not only quite able to grasp branches and use them ably, but that opposition emerges at the same time that hominid arms were becoming smaller (and less powerful), not larger (and more powerful).

Of course, the human hand (and upper extremity in general) still needs to be able to grow and develop in order to be able to lift heavy objects—and can indeed grow to a huge degree to exhibit that function. But its core evolutionary function is to produce the unparalleled dexterity of the human being.

Furthermore, the fact that the non-painter’s hand remains relatively unchanged in size compared to the painter’s hand means that the non-painter’s hand is already relatively set up to perform that kind of dextrous function—because that’s what it presumably evolved to do. This should serve as evidence (not counterevidence) that the hand is primarily for painting (and other fine motor tasks), not for weightlifting.

We should think the same of the gluteus maximus.

Let me conclude by saying that nothing I’ve written here means that the gluteus maximus evolved exclusively for endurance running. Indeed, there is ample evidence suggesting that the architecture of the gluteus maximus is uniquely multifunction as far as muscles go. (In future posts, I’ll delve more into the nuanced view of the gluteus maximus that I proposed above: that it owes its shape and size to the fact that it is a muscle designed for the kinds of “varied explosive and forceful activities” that a bipedal, primarily endurance running animal expects to have to do.)

But what we can say is that the fact that the gluteus maximus gets bigger through a particular stimulus has no bearing on its core evolutionary role, (or on the evolutionary story of the organism as a whole).

Runners: “Aerobic training” is not the same as “Endurance training.”

It’s common that training which develops the aerobic system is equated with training that increases the body’s endurance. It’s understandable: the aerobic system burns fats in the presence of oxygen in order to provide long-term energy for the body—exactly what it needs for endurance. But the problem is that a powerful aerobic system isn’t the only thing necessary for increase endurance.

The most important difference between “aerobic training” and “endurance training” is this: the former trains a critical supersystem of the human body (the aerobic system), while the latter improves the product of the successful interaction between the aerobic system and many other parts and functions of the body (endurance performance).

What runs isn’t the aerobic system—it’s the entire body. While the aerobic system can be powerful, it can’t perform on its own. Whenever we talk about “performance,” even when the subject is endurance performance, we’re talking about how (and how well) the body uses its aerobic power to create one particular kind of athletic movement.

Roughly, endurance means: “how long the body can produce a particular movement or action without falling below a minimum threshold of performance.”

Another way to say this is that the aerobic power is general, and endurance is specific. Geoffrey Mutai (elite marathoner) and Alberto Contador (Tour de France cyclist) both have extraordinary aerobic systems. In both athletes, all the parts that enable their muscles to be fueled for long periods of time are extremely developed.

It should be noted that in both athletes, we are talking about developing essentially the same parts, developed to comparable levels and talking to each other in very similar ways. Both these athletes also obtain fundamentally the same general physiological benefits—a greater ability to recover, better health, longer careers—all despite competing in wildly different sports.

However, their endurance in specific sports varies wildly. We can expect Mutai to be a proficient cyclist, and Contador to be an able runner, but we can expect neither to have world-class endurance in the other’s field. In other words, Mutai’s endurance is specific to running, and Contador’s is specific to cycling. This is because:

  • Both sports use different sets of muscles: runners use a larger set of muscles for stability than cyclists, since the latter have so many more points of support. Cyclists have the handlebars, pedals, and seat, whereas runners have at most 1 foot on the ground.
  • They load joints in different ways, and use very different ranges of motion: cyclists keep their waist and hips relatively flexed, while runners keep the same joints extended.
  • They use different neuromuscular mechanisms to facilitate endurance: running economy depends on a powerful stretch-shortening cycle, while cycling economy does not.

In my opinion, the stretch-shortening cycle is the most important piece of the running puzzle (and also one of the most overlooked). Running shares a lot of pieces with just about every sport—and developing them is very important if you want to become a good runner. But without an increasingly powerful stretch-shortening cycle, all the power that you develop in any other system (cardiovascular, respiratory, etc.) doesn’t translate into actual running performance increases.

As discussed above, the aerobic system is responsible for sustaining endurance. The best way to exclusively train the aerobic system is by running at a physiologically intensity (below the aerobic threshold).

This is a problem for less aerobically-developed runners: it takes a lot of juice to run the stretch-shortening cycle effectively. In previous posts I discussed how the minimum requirement for running properly is to be able to produce a (very fast) cadence of around 180 steps per minute (spm). This is because the muscles’ stretch-shortening cycle hits peak efficiency around that cadence.

So, these runners often need to run at a higher intensity: they’ll use the maximum output of the aerobic system at max and engage some of the anaerobic system in order to produce a cadence of 180 and properly activate their stretch-shortening cycle. If they fall below their aerobic threshold with the goal of doing “aerobic training,” their cadence falls and the stretch-shortening cycle will largely deactivate.

When I talk about hitting 180, I mean hitting 180 at an average step length: It’s possible for a weaker runner to shorten their stride to artificially increase their cadence without going above the aerobic threshold. But I consider this a rather useless hack, since in my experience it doesn’t really get runners the performance benefits expected of reaching “the magic 180 mark.” (More on this in a future post.)

For a workout to be “running performance training” (endurance or otherwise), it needs to train the key pieces necessary to improve running performance. So whenever you’re not actively training the stretch-shortening cycle, you’re not really doing “running performance training” in my book. “Running endurance training” would be about teaching the body how to run for longer, at a lower intensity, while maintaining a reasonable cadence.

So, whenever an aerobically weak runner trains under the aerobic threshold, I consider it to be quality aerobic training but NOT “running performance training.”

It’s not that their running performance won’t increase—it will. Let me illustrate with a rather extreme example: If playing checkers is the only active thing someone does, playing checkers is better for their running performance than not doing so. But because it doesn’t train the critical systems for running, I don’t think of it as “running performance training.”

Of course, running at a low cadence shares a lot more with running at a high cadence than playing checkers does. But the idea here is to set the highest possible bar for what “running performance training” should mean: training the key systems that running performance rests on. And running without substantially activating the stretch-shortening cycle really doesn’t meet that criteria.

(We can say that running without the stretch-shortening cycle still helps you to improve your running—to a point. But you can’t hope to maximize your performance gains without it.)

For a competent runner (someone who can engage their stretch-shortening cycle at low physiological intensity), “aerobic training” and “running endurance training” become identical: just about all of their training provides all the benefits they need to maximize their running endurance.

What is a less-powerful runner to do with all this information? If I could say only one thing:

Jump rope! Jumping rope (on both feet, alternating feet, on one foot, spinning around, crossing the rope, etc.) is training primarily the stretch-shortening cycle up and down the body, almost identically to the way it’s used in running. IMO, if a runner does only one other thing besides running, it should be to explore and master the jump rope to its fullest potential.

UPDATE Nov 18, 2016: Another (great!) article on the mechanics of running, also touting the potential of jumping rope.

But there’s a lot more than this. Now that I’ve covered all the theoretical ground I absolutely need to cover for my following posts to have any real substance, I can begin to discuss concrete strategies that the runner can use.

Addendum (for the curious): Why do I focus so much on fleshing out the principles (and, more importantly, taking so long to get to the processes)?

Because the idea, of course, isn’t to “balance” aerobic training with performance training. (That’ll only increase endurance.) The idea is to potentiate aerobic training with performance training. (That’ll maximize endurance.) And to turn balance into potentiation, it’s necessary to already have understood the “why.”

Walking, jogging, running, and how gravity defines them.

What is the difference between walking and running? As runners, particularly runners who often stake their identity on running, this is a question that we should have thought deeply about. But the reality is that in the vast majority of cases, it remains ignored.

Say, the simplest and perhaps most important difference between walking and running—or at least the one with the most consequences—is that running includes a flight phase while walking does not. In other word, walking has a static interaction with gravity, while running has a dynamic one. But upon further consideration, there’s a lot more to be said:

Bounding (by which I mean jumping continuously) also has a flight phase. So does skipping. Of course, these are obviously different from running in that running alternates support, similarly to walking, whereas bounding does not (since both feet land together) and neither does skipping (since each foot repeats its support of the body before alternating to the other).

Running is somehow special when you compare it to bounding and jumping, at least as far as the body is concerned: when we need to travel faster than walking allows, neither bounding or skipping are our go-to methods of travel. Instead, we run. Although this may seem too obvious to be important, it’s important precisely because of that: What is it exactly that running offers us?

All the biomechanics junkies are way ahead of me at this point. Running offers us a way to contralaterally (read: using one leg and its opposing arm) maintain balance and support: when one leg pumps down, the other arm comes up, allowing the body to push on the ground alternately while not compromising balance.

And there’s another requirement: running uses the energy return capabilities of our tendon system (in particular the achilles tendon) to maximize running economy. This means that, by loading the achilles tendon like you would load a spring, the body manages to put the force that it arrives at the ground with into the next step, to make running more “economical” by reducing the amount of energy that the body puts into the next stride cycle: the achilles tendon stretches during the landing and stance phase, and then shortens explosively during pushoff, when the leg and foot, well, push off against the ground to begin the next stride cycle.

Neither bounding nor skipping allow us this increase in economy: to be able to bound successfully, we would have to be counterbalanced in the sagittal plane, (read: front to back) in order to put the hips at the midline of the body. Basically, we’d need a tail. But since we don’t, when we land from a bound (or squat), the hips are behind the center of gravity, and the knees are in front, in order to compress the body properly.

But if we had a tail like a kangaroo, the hips would remain under the center of gravity during the landing phase, because our weight would be more evenly distributed behind and forward of our hips. Without going too far into it, this means that the force put into each bound is primarily generated by muscle power for us, whereas for the kangaroo it is a product of tendon energy return. Skipping doesn’t increase economy either since energy is lost in that second step before alternating legs.


So, we can begin to lay down the differences between running and walking in this short list:

  1. A flight phase
  2. Contralateral stance and equilibrium
  3. A maximization of running economy

This is where we finally get to why “interaction with gravity” is so important: when running, the human body puts itself at risk of injury by taking off and then accelerating back to the ground, but it is counting on using that acceleration, generated by the force of gravity, to power its next step. This means that an important amount of the energy that is being put into each step is borrowed from the last, and doesn’t come from inside the body at all.

Running diverges from jogging in the following way: Jogging doesn’t really harness the energy return properties of the tendon system. It doesn’t allow for an improvement in running economy. Why not?

In order to create energy return, the relevant tendons (say, the achilles) have to remain taut during the landing phase, in order to stretch. This means that as the foot lands, the extensor muscles along the rear of the leg (hamstrings, gastrocnemius, glutes) begin contracting even as the frontal muscles (quads, tibialis anterior) take the majority of the load.

When the back and front muscles play together like that, a large amount of the energy that the body accelerated towards the ground with goes into the tendon system, and gets released as the foot leaves the ground.

During a jog, the leg muscles are working in a fundamentally different way. Because a jog is slower than a run, the forces being generated are a lot smaller, and so a the rear and the front muscles of the leg can work relatively independently of one another: the front muscles take the body’s load when the foot comes down, and the back muscles push off as the leg goes back. The tendons never become stretched, so they don’t get loaded that much at all.

This means that the jogging cadence is much slower than the running cadence: in order to maximize tendon load, the body is forced to increase the speed and rate at which the legs hit the ground: since the muscles at the back of the leg tense the tendon springs, this drives the leg down at a much greater speed than otherwise, resulting in a faster transition from landing to pushoff, resulting in a much faster stride rate.

However, this also separates jogging from actual running from a power standpoint: in order to run rather than jog, the muscles must be powerful enough that they can hold the tendons taut while the weight of the body comes down. (And of course, the tendons must be resistant enough to support this).

This is the minimum bar in order to run—developing enough leg power (and naturally, the aerobic power necessary to sustain it) that three interrelated capabilities emerge:

  1. The ability to hold the tendons taut throughout the stride cycle.
  2. Increasing the stride rate and successfully maintaining it.
  3. Equipping the body to successfully load tendons instead of absorbing power with muscle and bone tissue.

I believe it is these three capabilities that make someone a runner.

The Tales of Forgotten Subsystems, part III: aerobic respiration, a.k.a The Krebs Cycle.

What if I told you that by running at a lower intensity, you could boost your running efficiency by 600%?

You’d think I was lying.

Well, I’m not. That’s exactly what happens when we run at the right intensity. When we’re burning sugars anaerobically, the sugar only gets partially processed by the cell, and out comes lactate. But when we burn them aerobically, that lactate goes through another process: The Krebs Cycle.

Continue reading The Tales of Forgotten Subsystems, part III: aerobic respiration, a.k.a The Krebs Cycle.

The tales of forgotten subsystems, part I: The Fasciae

People typically think that becoming a stronger runner is all about training muscles, tendons and bones. It’s not.

It’s mainly about developing the connective tissue that holds them together.

Runners don’t dread getting injured by twisting their foot, or by becoming concussed, (even though those things do happen). Most “runner-specific” injuries are blown knees, torn ACLs, lower back pain, plantar fasciitis. All these injuries have one thing in common: they occur because the body was subjected to excess repetitive shock.

What do we typically say to this?

We say: let’s strengthen the muscles, tendons and bones (besides the usual “what did you expect? You went running”). But that advice is inaccurate, and largely useless.

That advice doesn’t take into account the existence of what is cumulatively one of the largest organs, whose main structural function besides connecting other tissues happens to be absorbing the mechanical stresses applied to the body.

Continue reading The tales of forgotten subsystems, part I: The Fasciae

Running in the heat (Part 1)

Here, I begin to answer a comment from this post, by Liliana Gutierrez Mariscal:

What makes running difficult for me?

Running in the heat

No matter what you do, it will be more difficult to run in the heat than in cool weather. But if you do take the time and trouble to run in the heat, it’ll really be worth your while.

I’ll devote another blog post to a very innovative idea that’s been put forth by a wealth of authors and scientists: the idea that we evolved into what we are now by chasing down four-legged animals in the heat of the african desert, (in other words, that we are desert endurance runners). But let’s not be tricked into thinking that achieving that level of expression will be an easy task.

Suppose we truly did evolve for the purpose of being runners, and more importantly, thanks to that activity. That being the case, we can make the argument that, running in hot weather in particular constitutes a very important part of the physical and physiological (and no doubt cognitive and emotional) expression of a human being.

Perhaps one of our most natural forms of expression (if not the most natural) is to run in the heat.

This argument comes from an evolutionary-systemic point of view. If you use a particular system for the very activity that it was developed to do in the first place (by first making it capable of operating at that level), then that system is very likely to manifest functions (or an efficiency of function) that it can’t express by performing any other activity.

Ultrarunning—the sport of putting the body through an irresponsible amount of miles—may tap into that level of expression. We already know that people sign up to run across the Sahara Desert, Death Valley, or to do back-to-back marathons in the desert summer as is the case with the Comrades Marathon.

But you don’t need to look that far for some idea that running was not created equal to other sports: Answer in the comments if you’d ever heard of a “golfer’s high,” or a “cyclist’s high.” It’s not that these cognitive states don’t happen in those sports. But the associations between running and favorable cognitive states are that much higher. They are so high, in fact (or so I argue), that people still sign up by the hundreds of thousands to run 26.2 miles despite the near-certainty that they will end the day with a significant injury.

Why do we still do it? As Christopher McDougall argues: it’s because we were born for it.

Those are the ultimate reasons for why you should run in the heat.

But I’ll give you a more proximate reason: you can make bigger gains in performance. I’m going to paraphrase a chapter-long argument in Tim Noakes’ book Waterlogged: The Serious Problem of Overhydration in Endurance Sports.

There are two important numbers in this story: 98.6° Fahrenheit and 104° Fahrenheit.

The first number, 98.6°, is of course, our normal core temperature. 104° is the temperature at which the body’s functioning becomes compromised. (This is a severe emergency).

What this means is that there are still, say, 2½ degrees of “give” between normal core temperature and the temperature at which things start getting too close to the danger zone (which starts at around 101º).

Take your typical runner stepping out into 100º heat for the first time: the body feels the heat and decides that no way is it going to let core temperature rise. It’s not accustomed to that environment—and more importantly, it doesn’t have a sweating system powerful enough to bring core temperature down, in case it needs to.

The cooling system of this average runner is fighting the environment heroically, struggling for every single tenth of a degree. That has a huge metabolic cost: the cooling systems go into overdrive, and the runner experiences fatigue in order to force a reduction in activity. Maintaining core temperature at a level that the body is comfortable with has become the most important thing—far more important than athletic performance.

But as that runner continues to train in the heat, the body begins to adapt over time: its sweating mechanism becomes more powerful, its able to more effectively circulate blood from the core to the skin—and furthermore, it knows that it’s still got those 2½ degrees of “give” between normal core temperature and the 101°, where its really beginning to skirt close to the danger zone. The runner experiences incrementally less and less fatigue; running becomes easier and easier.

As sweating system becomes more powerful, the body gives itself a little bit of rope. It’s getting used to that heat, so it lets core temperature rise a tenth of a degree, then another, and another. This isn’t a problem—it’s still in the safe zone.

What’s happening? It no longer has to fight the environment to cool those three-tenths of a degree.

In other words, the body developed a more powerful cooling system, and yet, because it developed that system, it no longer needs to use it that much!

Becoming accustomed to the heat lets you increase your level of performance in two ways: you can keep exercising at a higher core temperature, and with a more powerful sweating system. Suppose you increase your metabolic rate to tax the sweating system (which has now become more powerful) just as much as you used to tax it when you had only just started running in the heat: now you’ll be running at a much greater speed—and none of this has to do with your muscle power.

This brings us back to the argument that I was making earlier: by running in the heat, you can manifest physiological functions (heat tolerance) and psychological functions (lessened fatigue) that can’t be manifested under any other conditions.

The argument I make in this post is very similar to the argument I made in yesterday’s blog post. Just like having stronger muscles makes you a faster and safer runner at the same time, having a stronger sweating system does two things, instead of just one.

All this said, training in the heat means that we’re going to be playing with dangerous forces. Too much heat really will kill us. If we do choose to train that way, let’s do so with humility and care.

This will become a recurring topic. Soon, I’ll post a few exercises and training ideas that we can use to safely develop our heat tolerance. Also, I’ll post about the physiological aspects of the human body, that make us such good heat runners.

Remember, even though running in the heat might be really difficult, in a very deep way, it is what you do. If you gain that ability, you probably won’t regret it.

Happy running!