The Running Form Thread

[DayRunner]

Hi guys, if I can add my 2 cents worth on the subject of gravity (I've forgotten most of my Physics degree but still remember a bit of mechanics). Whilst I don't think gravity offers a magic source of energy, it does indirectly assist us when running by using a bit of lean. There's 2 reasons for this, neither of which are unique to running as they apply when we are on a Segway too; the first applies just when when we have net forward acceleration and the second applies increasingly the faster we go (air resistance).

When setting off, to accelerate yourself forward there needs to be a net forward force on your body, which is applied via friction where your feet (or wheels if on a Segway) touch the ground. As this net force does not resolve through your centre of mass, a net torque is applied to your body, tending to rotate you (=make you fall) backwards. You can counteract this by leaning forwards, so the normal reaction force with the ground (equal and opposite to the force of gravity on our body) is no longer in line with your centre of mass, creating an opposing torque. To illustrate this consider what would happen if the Segway didn't require you to lean forward before accelerating (it would leave a big lump on the back of the head and sales would plummet).

This is why sprinters are leant forwards at the start of races (consider what position they start in the blocks in, centre of mass is well ahead of feet). Of course once up to speed then no net accelerating force is required, although air resistance now applies an increasingly decelerating force the faster we go. This force is applied across our body, and needs to be countered at the feet by a net force in the opposite direction (so a force analagous to the one above needed to accelerate). This creates the same problem of torque, and hence the solution of a bit of forward lean to counter.

Net position of our centre of mass relative to feet (aka "net lean") is therefore is something which is dictated to us if we don't want to end up on our a$$es. However how we make up that net lean (eg with body and legs in a single line, or leaning body and straight legs, or straight legs and leaning body) is the space in which different running forms may exist. Net lean required is biggest for sprinters, due to both greater acceleration and greater speed (and therefore air resistance). For ultra runners less net lean is required, which is ironic as they are usually much leaner than sprinters.

 

[Curb Ivanic]

G'day DayRunner, glad someone else is chiming in. I'm with you on the air resistance but I have a question regarding your statements on gravity's effect. Why is a runner's center of mass moving in an upward arc as they move from stance phase into flight phase? (There is always a vertical component in running gait). Gravity can only have one direction of pull and that is down. So we would expect as gravity pulled on COM for it to travel in a downward arc from stance phase, which it clearly doesn't based on gait studies.

The second issue I have with the gravity pulling theory is that biological organisms capable of locomotion do not like to be off balance. Suppose there's a tree in a forest that has been blown off balance by a wind storm. Once the storm stops, if the tree has been uprooted enough and leans off balance for long enough, gravity will pull it down. It can't fight this force.

But a human body doesn't like to be off balance. It will reflexively resist getting pulled down (i.e. a true fall). So though you may be leaning while running you are still in balance. And for the speeds most runners run (8 - 10 min/mile) they really aren't leaning that much (if running with good form); certainly not to the degree that they are off-balance. The lean simply allows for optimal position of the hips to facilitate good extension, good body position to load the kinetic chain for maximal recoil and to counter any wind resistance.

Regarding the sprinter scenario, yes COM is well ahead of feet but the starting block position also allows the hips to extend powerfully into the blocks providing horizontal thrust. Within a few steps the runner is upright in a balanced position yet still continues to accelerate for some time. Why? Powerful hip extension and strong ground reaction forces. If they truly were falling at the start, the sprinter's body would resist and they would slow down not speed up.

If a sprinter is really falling at any point in the race it's at the end when they lean forward to cross the finish line ahead of a competitor. By trying to get their body over the line first they put themselves out of balance and fall. But they quickly correct this by braking with the legs.

I'm not saying gravity doesn't have an effect on running - we couldn't run without it; we need something to keep us grounded. But it cannot be a propulsive force while you run. Maybe it's just the terminology I have an issue with? Falling to me implies being out of balance and thus out of control.

 

[SillyC]

Stupid Facebook.

I think it would also be useful to mention that there's a wide range of opinions on the matter, and none are backed up by significant research. Almost all of the biomechanical studies I've come across either have serious methodological flaws, don't address the issue directly, or study gait as if the overstriding heel strike is the norm. To the best of my knowledge, there is no good research on "natural" running gait.

Would the rest agree?

Hi Jason,

I haven't read the whole thread, but I wanted to let you know that a year and a half ago, I ran on Lieberman's treadmill with a bunch of sensors duct taped to all my joints. They took pics of me with a high-speed camera. So, it may be coming!

 

[scedastic]

When I run barefoot for 20-30 miles, guess what is sore the next day. My core! Not my legs. But when running in shoes, my legs get sore. Why? The answer to me is simple, I can feel the difference when I run barefoot vs. shod in how much my core works. Core=glutes, obliques, TA etc.

As a relative noob, this is good to know. Makes me think I might be doing something right.
I run slowly, but after my long runs of 10miles+ or longer, or if I do more than one long run in a aweek,, lately (almost always in huaraches, rarely strictly bf due to running surfaces), my butt muscles get tight, my legs (down to my calves, including my hamstrings) also get tight, but it's more like an everything tired mode than a one part of the leg is sore. I'll take that as a sign of good form then, since running has never had an effect on my core and glutes back in thick shoe running past.

 

[DayRunner]

Hi Curb, just to clarify, I am not suggesting gravity propels us or that we should start falling over, but rather that with some lean then the normal reaction force (which counters gravity) helps us to maintain neutral torque, ie not fall over as we accelerate. To this end I don't see a conflict if our COM moves upwards from static, so long as it is remains an appropriate distance in front of the grounded foot. It just means the normal reaction force is greater than gravity (as we are using our body to exert some downward pressure) as we set off, sending our bodies on an upward arc which gravity then turns downwards, like a stone skimming across a lake. If gravity is always accelerating us downward then we periodically need to push/bounce off the ground if we wish to maintain sideways movement, otherwise we would eventually faceplant.

As for being off balance, as above I think I am in agreeance with you that the lean is only needed to achieve neutral torque on our bodies. Any more than this and we will start to rotationally accelerate (with the feet the pivot), which is not sustainable unless we can go really, really fast and achieve orbital velocity...

 

[Curb Ivanic]

Thanks for clarifying DR. Guess I misunderstood your previous comments and would agree with what you said. Thanks for adding your thoughts!

 

[damianstoy]

I'm confused. If a lot of lean helps us run really fast out of control, why wouldn't a little lean done correctly help us run efficiently?

Here's a partial video of how I teach the lean:

 

[DayRunner]

Hi Damian,

Whilst I was agreeing with Curb, I don't think I completely disagree with you either. I have been thinking futher about the mechanics of the situation and, over and above the need for lean I mentioned above to neutralise torque, I think I can see another reason why lean would be beneficial.

It can be difficult to factor in all the different components of running gait to say exactly what is happening and what is optimal, however I will start by prefacing/reiterating that gravity is not acting as a source of propulsion when we lean; however complicated our models are, the simple fact is that unless our COM has a net drop in height then there is no loss in gravitational potential energy, ie nothing to be converted into kinetic energy to propel us.

Now I will correct my previous comment that only one angle of lean (of the COM relative to the plant foot) is possible to achieve zero net torque. I was thinking about this further and my "Segway" model was in fact an oversimplifation as the Segway never leaves the ground (ie normal reaction force is equal and opposite to gravity, so no net vertical force). When running the normal reaction force can vary as we are "taking off" each stride (by an amount which can vary); we can in fact lean a little less and still achieve zero net torque, but it requires a greater normal reaction force with the ground (I won't get into debate whether this force results from a push-off or a bounce as I think that's a separate issue). This varying lean can be thought of in terms of levers: the closer the line of the force is to the COM, the larger it needs to be to effect the same leverage. This means that the less we lean, the greater normal reaction force required (to counter the torque from both acceleration and air resistance), and the more vertical oscillation in our running style. I think most will argue that this vertical oscillation is less efficient/desireable; if so then the ideal would be tending towards the angle of lean a Segway would need (a Segway has zero vertical oscillation). Incidentally less vertical oscillation goes hand in hand with a higher cadence - think of a skimming stone again: the higher the bounce (=vertical oscillation), the greater the time interval between bounces (=cadence).

Now if there is a range of angles of lean (AOL) available to us, apart from minimising vertical motion I believe there is another reason to favour maximum forward lean (particularly for barefoot runners) and that is because it increases the use of the foot as a spring lever. At maximum lean (within the range of AOL for which we can neutralise our net torque), gravity will effect the biggest leverage as its net effect (through our COM) will be the furthest from the pivot (ankle). I think things start to get more complicated from here, so there may be more complex reasons why we might not want absolute maximum lean but I don't think the optimal angle could be far off it.

 

[BFwillie_g]

I think it should be pretty easy to test this by monitoring the pulse.

 

[DayRunner]

Hi Willie, I'll have to take your word for that as I didn't study as much biology

An aside to the discussion on lean, I experienced the difference needed at different speeds first hand on Saturday when I entered a 60 and a 100 meter sprint race. I haven't sprinted for (18) years and have been doing purely distance/ultra running recently and it showed. I pitched out of the blocks much too vertically and felt like I came off the ground before I could find my feet and get some traction. Looking forward to having another go soon and coming up much more slowly to vertical.

 

[BFwillie_g]

Hi Willie, I'll have to take your word for that as I didn't study as much biology.

well, I meant over a longer period of time. If the lean from the ankles is indeed harvesting energy from gravity, getting a free boost as they say, then the effort level at a given pace should be lower. To my completely crude thinking, this should be reflected in the heartrate @ pace. And I'm only talking about the effort level; healthy biomechanics/injury prevention are a different can of worms.

 

[Last Place Jason]

well, I meant over a longer period of time. If the lean from the ankles is indeed harvesting energy from gravity, getting a free boost as they say, then the effort level at a given pace should be lower. To my completely crude thinking, this should be reflected in the heartrate @ pace. And I'm only talking about the effort level; healthy biomechanics/injury prevention are a different can of worms.

To the best of my knowledge, the only study that began to investigate the issue of efficiency looked at Pose. If I remember correctly Pose was less efficient. I'd attribute that to the unnecessary contraction of muscles, but I don't remember the authors' conclusion.

Role of a lean in running

Regarding a workable model of gait- The spring model works pretty well. Mark C. uses an pogo stick as an analogy. This is how he describes the need to lean- it changes the vector, which results in forward motion.

For example, if you bounce on a pogo stick and remain perfectly vertical, you go up and down. If you lean slightly forward (or any direction), you bounce that way.

Likewise, if you stand perfectly vertical and run, you run in place. If you lean slightly forward, you move slightly forward. The more you lean, the more horizontal movement is generated.

Role of muscles in running

This model only accounts for the energy return ("springiness") generated from the return of energy stored in soft tissues. It doesn't account for the other factor in forward propulsion- muscle contractions.

It is possible to run forward by standing perfectly vertical. You can run quite fast, in fact. Why? Muscles generate most of the energy required to run.

Role of gravity

Gravity does play a role in running, but not as a propulsive force. It's a force that must be overcome, along with drag. A simple diagram of pelvis position can explain what's going on:

This is the concept Curb and I have discussed. At mid-stance, the hips are at the lowest position of the gait cycle (note the black dot below the line). As we toe off (NOT a good term, IMHO), the hips move vertically to a high point during the aerial phase. The only "falling" that occurs is on the downward arc immediately before touch down.

If we were continually falling forward, mid-stance would be the point where our hips were at the highest point. The hips would then lower as we toe off (due to falling), would reach the lowest point at the middle of the aerial phase, then begin an upward arc at touch down.

The Unspoken Question

The Pose and Chi crowd seem to neglect a critical part of their theory. If you're falling, you need to expend energy to get back to a point where you can fall again. If we really were falling and we saw the movement pattern that would be the opposite of the above diagram, the point from touch down to mid-stance would require muscular energy to return to mid-stance so we could fall again.That energy expenditure would cancel out any possible gain from falling, plus more. To date, Ken S. is the only Pose coach that has addressed this issue... which is the reason I have so much respect for his ideas.

Why it's important to study gait

We don't necessarily need to study running gait to be able to teach people to run better. However, knowing all the underlying theories is a HUGE benefit to diagnosing problems or mastering a variety of teaching methods. I used to teach high school psychology. It was immensely helpful to have a strong background in the topic. I also taught history and didn't have a strong background. I was a great psychology teacher and a terrible history teacher.

It's also important to think critically about our own beliefs. Read the first edition of my book, then read some of my recent blog posts. I have different opinions on a TON of topics because I question my own beliefs regularly. While I really believe my above comments are the most accurate current model of running gait, I'm always looking for better models and will ditch this if something better comes along. I'm a science dork at heart, and that comes out in my inherent skepticism.

Folk knowledge versus science

Bare Lee made a comment awhile ago about the difference between folk wisdom and science. As barefoot runners, we tend to rely on folk wisdom, or tips and explanations that get us to more or less do the correct movements but have no basis in science. Examples would be:

• Lift your feet
• Bend your knees
• Pull your feet up
• lean forward at the ankles
• Run with a cadence of 180 or 180+
• land pancake flat
• feet land under the center of mass (gravity, hips... whatever)
• stand up straight

This also includes explanations of movement like "running is a controlled fall." It also includes claims like barefoot running reduces injuries, makes you faster, more efficient, etc. All of these ideas aren't grounded in empiricism or are obviously inaccurate, but are effective as teaching methods because they work for some people some of the time.

However, we can't confuse folk wisdom for science. Science is a controlled method of inquiry, and none of the above claims has been firmly confirmed via science. As such, it's important to figure out exactly how we run... or even if there's a right way to run. Many topics can be added to that list: what are the role of shoes? Is there a right way to teach people to run? If so, what is the most effective method? Is there a way to reduce injuries? If so, is it universal?

Folk wisdom is an adequate way to answer the questions in the absence of empirical research, but it shouldn't be a replacement.

 

[damianstoy]

Fantastic comments! Jason, I think everyone is on the same page that the lean changes pelvic position and therefore where the foot lands. This reduces impact and/or makes running more efficient.

Your use of Mark C.'s pogo stick analogy proves gravity plays a propulsive force when we run... to ME. I wonder if I'm missing something because I don't know much about physics. If you lean the pogo stick and it moves in that direction, isn't that gravity moving it forward? Isn't that the same with humans? (updated) Reread your post. You are saying it changes the vector, nevermind.

Also, I like you comment "If you're falling, you need to expend energy to get back to a point where you can fall again. " This may be symantecs. Is the pogo stick falling or leaning? We in the Chi Running world say falling and then we just pick up our feet. We aren't actually falling, we are moving horizontally just like the pogo stick.

Here are some pictures and description on my site that may help. The second video down may also for helpful for showing the reason why the lean works.

http://wholisticrunning.com/bozeman-chi-running/what-is-chi-running/

 

[damianstoy]

Ohhhhhh...further thought on Jason, Day and Curb's most recent comments. I now get what you are saying about the lean and you may be correct. Gravity isn't a propulsive force, it changes the vector....let me mull it over some.

 

[Last Place Jason]

Damian- falling, by definition, requires a change in vertical position. Otherwise it's not falling. If you're not falling, the gravity theory simply doesn't make sense. Furthermore, if the gait diagram from above is accurate and applies to Chi/Pose, too, a runner would be falling upward.Again, by definition, that's not falling. It's the opposite of falling. As such, the gravity/falling description is a terrible analogy for forward movement.

Regarding the pogo stick- it's leaning to redirect the springy return of energy to add a horizontal component. It only falls after it reaches the apex of the bounce.

 

[damianstoy]

Damian- falling, by definition, requires a change in vertical position. Otherwise it's not falling. If you're not falling, the gravity theory simply doesn't make sense. Furthermore, if the gait diagram from above is accurate and applies to Chi/Pose, too, a runner would be falling upward.Again, by definition, that's not falling. It's the opposite of falling. As such, the gravity/falling description is a terrible analogy for forward movement.

Regarding the pogo stick- it's leaning to redirect the springy return of energy to add a horizontal component. It only falls after it reaches the apex of the bounce.

This is why I enjoy these discussions. I can't say 100%, but I think I agree with you now about gravity and falling. You must be relieved...

I posted a few quick comments and pictures showing why teaching the lean is effective. I think the primary reason is changing the hip angle and where the feet land vs. gravity which is what I use to think.

http://wholisticrunning.com/2012/10/20/biomechanics/

The lean is a very effective teaching tool!

 

[Last Place Jason]

You must be relieved...

Yes, I can finally sleep.

I'm about to embark on a 30 hour drive, so I'll have to wait to comment on teaching the lean. A brief summary- it's valuable if you have time to work with someone for repeated sessions. It's dangerous to teach otherwise due to the "bending at the waist" tendency.

I stopped teaching a lean about a year ago when I realized people leaned an appropriate amount automatically if they had good posture and sped up their cadence/ reduced their stride length. I'd argue the lean is a symptom of better form, not a cause.

 

[damianstoy]

Now we are getting somewhere. I am finding the same thing: Teaching posture and cadence is more effective and students then automatically adjust the lean. However, we at CR now teach the lean slightly different and I can teach it in a way that is very effective. Some students still bend at the waist, but for about half of my students, it is an aha! moment.

Enjoy the drive!

 

[damianstoy]

Question for the group:

It seems like most here agree that elastic recoil is an important part of how we move. If this is true, how do we maximize elastic recoil? Stronger muscles? More flexible muscles? Relaxation? Spinal/hip rotation? General health of our soft tissues?

 

[BFwillie_g]

I think tendons are more important than muscles, but then I think a lot of things without being able to explain them satisfactorily, lol. Muscles don't "recoil" and they aren't "elastic" - tendons are/do both those things.