Tag Archives: gravity

The role of downforce in forward motion.

There are two main camps in the argument of exactly how we manage to move forward as we run. The traditional camp says that the body uses the muscles to “push against the ground.” The other—constituted almost solely by Dr. Nicholas Romanov’s Pose Method—proposes that we move forward thanks to the action of gravity on our bodies.

This second camp suggests that what the muscles do—their primary function—is to convert the downward force of gravity into net forward movement.

But how is it possible that the body can convert a downward force into horizontal movement?

Part of the answer lies in the fact that the running movement isn’t really horizontal. It consists of a wave-like movement of the hips and torso—an oscillation—that only seems to be a straight line if we’ve zoomed out far enough. If your model (incorrectly) assumes that the body is trying to convert a downward force into a force that travels on a horizontal linear vector, you’ll end up quite confused.

(But that’s a discussion for a different post.)

Let’s get to the issue I want to talk about: Proponents of the idea that runners “push off” often understand Dr. Romanov’s argument—that gravity is the “driving force”—as claiming that gravity provides “free” or “additional” energy (a.k.a. net energy) if we adopt a certain technique.

I believe that’s a rather shallow misrepresentation of what Dr. Romanov’s Pose Method has  actually suggested. Pose’s main message regarding the action of gravity in running is quite a bit more profound. To explain why this is—and what I believe the main message of Pose is—let’s abstract away from mentions of “gravity” for a second and talk about a more general concept: downforce.

Instead of runners, let’s look at race cars. What are the necessary factors in making them go?

First and foremost, a race car needs a powerful engine. Without an engine, it’s going nowhere. But an engine is not enough. As any connoisseur of modern racing will tell you, there came a point in the evolution of car racing in which the engine’s ability to turn the wheels exceeded the ability of the best tires to grip the best track.

Why? Engine power eventually exceeded the car’s weight (defined as “how much force is generated as gravity accelerates its mass towards the ground”), and the capacity of the tires and the track to covert that weight into friction.

This reveals an important truth about the car: the engine actually isn’t for moving the car forward. The function of the engine is to spin the wheels. (While this results in driving the car forward, actual forward motion only occurs insofar as the power with which the engine spins the wheels coincides with the extent to which gravity keeps the car on the track.)

At this point, the only way to achieve greater speed was for engineers to somehow find a way to add to the downward force that gravity exerts on the car. How did they solve this dilemma? By adding the ugly inverted wings we now see on the back of every Formula 1 and drag racer: spoilers.

By redirecting the flow of air upwards at the tail end of the car, spoilers create another significant downforce. This reveals that strictly speaking, it isn’t gravity that allows race cars to move forward. It’s downforce. (Gravity just happens to be the quintessential downforce on Earth.)  But the point is this: no downforce, no movement.

Let me spell out the implications in the strongest possible terms. Muscle power is NOT the driving force. It is the intermediary force. It converts a downforce into a quasi-horizontal oscillation. The driving force—the thing that ends up as movement—is gravity. Muscle power (a.k.a. metabolic energy expenditure through muscle use) is what lets gravity end up as movement. Gravity could provide zero net energy (zip, nada) and still it makes sense to call it the “driving force.”

The important question to ask about running isn’t really whether one running technique “uses” gravity to run—all running necessarily does so. Let me be even more specific: all overground movement is a result of expending energy in order to convert some downforce into a quasi-horizontal movement. The degree to which movement occurs is commensurate to the degree to which the organism/machine is harnessing downforce in real time.

Running according to the tenets of The Pose Method gets you “free energy” from gravity in the same sense that a car that never fishtails also gets “free energy.” In other words, Pose offers the cheapest way, all things considered—speed, agility, endurance, resilience, performance consistency, performance frequency, metabolic flexibility, recovery, longevity, etc.—to convert as much downforce as possible into overground movement. The critical observation offered by The Pose Method, then, is about how the body’s “engine”—its musculature and various systems—work best to harness the force of gravity to produce forward motion.

If the car weighs too much for the engine, it stays put. If engine power exceeds grip, it spins out. In other words, car’s absolute theoretical speed limit on Earth isn’t set by the power of the engine, the design and engineering of the transmission, or the materials it’s composed of. The maximum horizontal speed that any object can achieve is set by the theoretical limit to which it can harness the few downforces available to it on Earth. Once the car’s power and engineering causes it to reach speeds at which it is impossible to stop the air around it from supercavitating (creating a vacuum around the skin of the car), no aero kit will allow it to go faster, and no further improvements to the drivetrain will do it any good.

Of course, unlike race cars, the human body is not set up to use wind as a downforce—and we couldn’t run fast enough to make it matter anyway. Our running speed is a function of our ability to harness one downforce: gravity.

For a runner, improving efficiency by harnessing the force of gravity can mean 2 things:

  1. Removing power leaks and other muscle use that does not contribute to harnessing gravity. (The race car example would be to swap in better and better parts, and to make sure that you don’t throttle up enough to drift the car).
  2. Increasing top running speed: a runner with good form (a.k.a a runner whose movements and stances maximize the harnessing of downforce) can do so to a greater degree—in other words go faster—than an identical runner whose movements and postures do not effectively harness downforce.

Note that #2 is a hidden efficiency: it only reveals itself insofar as the runner goes faster. Both the inefficient runner and the efficient runner may be using a very similar amount of energy at lower speeds, but only the more efficient runner can get to a faster speed.

Pit my Toyota Tacoma against a Ferrari. Both would perform quite similarly at lower speeds and wide turning radii. If you ask both of us to make a wide sweeping turn at 60 miles an hour, we’d perform almost identically. You’d say “Whoa! Correcting for weight, they’re equally as efficient!”

But this observation only holds at lower speeds. If you increase the speed to 160 mph and tighten the curve, my Tacoma would start to spin out or come off the track, forcing me to reduce my speed. In other words, even if you doubled the horsepower on my Tacoma, I wouldn’t be able to match the Ferrari because of its stiffer suspension, better tires, lower profile, and aerodynamic design (in other words, it’s much better at harnessing downforce).

I believe that the discussion of “saving energy through the use of gravity” is meant to help us recognize—for starters—that we move forward only to the degree that friction and muscle power meet. It also has a few other implications (to put it mildly), but those are best left for another post.



UPDATE: Check out what I’ve written on The Pose Method:

About Pose theory of movement in running.

About Pose theory of movement in all sports.

About the “unweighing” principle of Pose theory.

The Running gait, Part 2: Movement logic and The Pose Method

It seems to me that nobody can quite agree on exactly what is happening during the running gait.

The running gait is characterized by an alternation of support: at one point, your body is supported on the ground by your left leg, then you’re suspended in the air, and then it’s supported by your right leg (and then subsequently back to your left leg). It’s how you get from these support phases—also called “stance phases”—to being suspended (and back again) that people vehemently disagree on.

Many in the running community say that the motive force of running is produced by a strong push of the leg muscles against the ground. But Dr. Nicholas Romanov of The Pose Method suggests a different—and in my opinion, far more parsimonious—interpretation of what happens: instead of “pushing,” the body accelerates its center of gravity by repositioning itself relative to the point of support (the foot on the ground).

UPDATE # 1: All repositioning occurs due to muscle activity, and the speed and effectiveness with which the body (or a specific body part) can reposition is commensurate to the power of the relevant muscles.

We typically think of “acceleration” as “the thing that makes cars go from 0 to 60.” But even a slight weight shift is an acceleration. When the slowest snail takes one tiny step, it’s accelerating it’s body (and then promptly decelerating it). Similarly, a slight weight shift constitutes an acceleration of the part of the body that moved. A greater weight shift is an even bigger acceleration. If you string together enough tiny weight shifts (or big ones) in a close enough sequence, you get a really big acceleration!

In this post, I’ll argue that the most logical way of producing a human movement (and that of any segmented organism) is by shifting the most easily-movable part first.

If you look at the body from a design perspective, you’ll see that it’s a stack of different parts (feet, calves, thighs, hips, etc.), all separated by joints. In the standing posture, each of these parts provides support for the part above it, much like a stack of bricks. But the difference is that the body’s joints let each brick move semi-independently of all the other bricks. The question, then, isn’t “how do we run?” It’s waaay more basic than that. The question is: to get from A to B (over and over again), how does a stack of things have to move?bricks.jpg

You could simply lift the bottom brick—along with all the bricks on top of it—and move it that way. That’s not particularly convenient, though: it requires a lot of energy in very little time. But there’s another way: start from the top brick. That way you only have to move one brick at a time, shifting bricks in quick succession.

This is the logic that your body (and the body of any segmented organism) uses to move. If you’re standing on two feet and want to lift your left foot, you don’t start by lifting your foot. You start by shifting your weight—starting by your shoulders, and moving down the body—onto your right leg, effectively removing all the weight off your left foot.

(This takes all the top “bricks” off the foot first.)

I’ve just described to you a process intrinsic to any human movement, which Dr. Romanov calls unweighing. This is the simplest process: if you want to move a limb, you first shift all the weight you can off it first, and then you move that limb. What makes Dr. Romanov’s theory parsimonious is that you need very few ideas to successfully describe human movement as a whole. Case in point: the movement of the entire body is simply a large-scale version of unweighing.

If you want to move, you create a forward weight shift in the direction you want to go. This effectively takes your weight off your feet and puts it in the space ahead of you.

Let’s talk running. During stance, one leg has the entire “stack of bricks” on top of it, and the other one is suspended in air (and already traveling forward), with nothing pulling it to the ground but its own weight. (UPDATE #2: In terminal swing, that leg actively reaches for the ground in order to provide new support). But when one leg is in early stance and midstance, which do you move? Do you push with the leg that has all the bricks on top of it, or do you move the foot with nothing holding it in place—the “topmost” brick?Running bricks

That’s the question Dr. Romanov answers with the Pull. The Pull describes the process of getting the back leg off the ground, and recycling it forward to produce the next step. But part of the hidden importance of the Pull is that it is also a weight shift: whereas in the previous weight shift you drifted your shoulders a few inches to one side, in the Pull, you aid the elastic recoil of your tendons in pulling your foot from the ground. This brings the mass of your entire leg ahead of the foot currently supporting you on the ground.

Galen Mo
Like this, but not as effectively (and with far less flair).

In a proper landing, your foot will touch the ground just ahead of your hips, torso, and head. There’s a slight deceleration due to the foot’s contact with the ground, but the body as a whole continues to travel forward, vaulting over the support leg. If the leg that just came off the ground—the “Pull” leg—moves forward fast enough, the body can add more of its mass ahead of the point of support.

We already know that a small weight shift—drifting the shoulder to one side—causes you to move (read: accelerate) slightly to that side. Now imagine how much more acceleration you can create by pulling the leg and moving its mass ahead of the body.

Mainstream thought questions whether this kind of weight shift can create enough momentum to offset wind resistance, plus the braking effect of landing, plus any power leaks that the person might have. The argument goes that if it can’t, the “pushing” argument is more likely the correct one.

But I hope I’ve convinced you that the best way to move a stack of things is by moving one part at a time in order to tip the stack in the direction you want (and then continue to move the parts in order to create more acceleration). Supposing that this—the best way to move a stack of things—somehow wasn’t enough to overcome wind resistance and the braking effect of landing, there’s no way that you could do it with pushing (a.k.a. moving from the bottom brick) because, well, it isn’t as effective.

So if the question of running is “what is the best way to offset wind resistance and braking?” the answer would still be to reposition the most easily movable limb in order to create a weight shift to move the body in the desired direction.

Read my initial take on the Pose Method here, and how the Pose Method applies to all other sports here.

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.

Gravity: The dilemma of the “slow runner.”

Some of us just want to run slowly. We don’t really want to get fast—we just don’t care.

That’s okay. We’re all entitled to our own ways of running. But while we do that, we should recognize that there are some ways of running that observe the realities of the world (and some that don’t). Someone I met once said:

All models are wrong, and some are useful.

That goes for any and all of our ideas, including our body’s idea of what is the best way to run. No idea will ever be able to exactly model the world. But some are more useful than others—and the useful ones are useful because they account for such realities with a certain success.

We must stand in observation of the reality that, when we run, the most important force we will interact with is The Force of Gravity. The quality of our interactions with gravity will determine whether we become injured or not (among other things, like speed).

In systems thinking terms, we move and live within a particular physical system. Inside of that system, there are certain constant and variable forces which the body must be capable of interacting with. If it isn’t (yet) capable of interacting with those forces, and we push it to do so, we will compromise its integrity.

In that system, if we push off the ground, we will accelerate back to it at a rate of 9.78m/s² (32ft/s²). Which means two very important things: first, that the longer we are suspended in the air, the more we will accelerate. Second, in order to maintain bodily integrity, our muscles (but also our bones and connective tissue) must be strong enough to resist the stresses incurred by interacting with that magic number.

What this amounts to in athletic terms is that body must have (1) very strong muscles, capable of responding explosively in sustained activity, and (2), the ability to maintain the center of mass (the torso) relatively stable throughout the run. In other words, it must have the ability to make the torso rise and fall as little as possible. 

How does the body achieve this mechanically?

By moving the legs faster, i.e. increasing the stride rate (to somewhere around 180 steps per minute). If we can make our feet strike the ground 20 milliseconds (.02 seconds) faster than before, that would be .02 seconds less that we’d be accelerating towards the ground. Stronger and more powerful muscles (to move our legs faster) mean that we’re accelerating less towards the ground. But here’s the kicker:

It also means that they are more capable of withstanding the stress placed on them by gravity.

But wait: there’s more!

As Owen Anderson writes in Running Science, if we could make a 20 millisecond (ms) improvement between footfalls, that would constitute a time improvement of 756 seconds across the duration of a marathon—in other words, an improvement of 12 minutes and 36 seconds! As Anderson himself writes:

[That is] an almost infinitesimal change and therefore one that most runners can easily make.

In the interest of beating this point into the ground (pun intended), that’s 12 minutes and 36 seconds we’re not accelerating towards the ground. And remember the thing about acceleration: the first 20 milliseconds and the last 20 are not created equal.

If we’re running at 150 steps per minute, we might be in the air for 60% of the gait cycle. Doing the calculations for you, we’re accelerating towards the ground for 116 ms.

At the end of the first 20 ms of acceleration, we’d be going at a speed of .09 m/s second (.29 f/s).

At the end of the 116 ms of acceleration, we’d be going at .056 m/s, or 1.64 f/s.

But if we make a 20 ms improvement from 116 (in other words, 96), our maximum falling speed would be of 0.47 m/s, or 1.54 f/s.

Let’s reiterate: A 20 ms improvement from 116 ms means that the runner is going a tenth of a foot per second slower upon hitting the ground, and it’s only that way because of muscles that are stronger.

If take the time and energy to make our bodies more capable of interacting with gravity, we will inevitably end up being the faster version of ourselves.

Let’s internalize this, because it really does constitute the minimum passing grade of the “entry exam” for a runner:

Being strong enough to interact with gravity is the minimum power requirement for a human runner.

Although elite runners have muscles that are much more powerful than necessary to deal with the requisite 9.8 m/s², that number is where the laws of physics and the Earth’s mass have set the bar for human runners. That is our system. Those are its requirements. Let’s stand in observation of that fact.

There are two good ways that I know of, that can get us to meet those requirements. The first is by jumping rope as I’ve described, and the second one is an exercise in this video by Dr. Mark Cucuzella (at 6:09).

(By all means, look at the entire video—it’s very engaging and informative).

Now, go talk to gravity until you’ve gotten to know it like an old friend.

UPDATE: You can find a couple of good discussions on stride rate and running speed here and here.