Hieronder de tekst weergegeven. Eerst het inleidende commentaar van Romanov, daarna de comments. De laatste 4 comments zijn van mij en antwoorden op mij.
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Errors in Running: Push Off
The extensor’s paradox highlights a very important point in running mechanics: there is no thigh (extensor muscles of the leg) activity after landing, therefore, there is no Push Off in Running. Dr. Romanov explains with examples why this is so.
All these demonstrations are nice off course but I see Debbie toppling over and that’s exactly what doesn’t happen in running or in the sprint start. If you topple over your COM loses height after the Pose stance, but in normal running your COM gains height after the Pose: completely different!! This movie is a demonstration of normal walking with a small jump incorporated. When you walk you change stance when the COM is at it’s lowest position, like in the demonstration. When running you change when the COM is at it’s maximum height. In running the COM accelerates upwards and forward after the Pose stance. The forward part has to be there to make up for the losses because of friction with the air and breaking in the first part of the ground contact.
Posted by pieter on 12/07 at 08:09 AM
First of all, Pieter, the concept of “topple over” doesn’t appear in our demostration, because Debbie, as you see, is progressing forward. This drill exactly shows the body leaving from the ground at the highest point of COM. The difference is only that forward progression is not as in a real run. In a drill there is certainly no momentum, so COM going down pretty much quickly. I do not know what you are trying to say.
Posted by DrRomanov on 12/13 at 09:17 PM
In the first part you see her topple over: The upper body changes angle with the ground. That does not happen in normal running; there the angle with the ground is constant.
In the last part of the movie you can very clearly (play the movie frame by frame) see that she pushes off before leaving the ground. She has to otherwise her COM would lose height immediatly after leaving the ground. In real running ( and also this demonstration) the COM is moving upward and forward at the moment of leaving the ground. The trajectory of the COM is a parabola.
In this demonstration it is suggested that the only thing you have to do to progress forward is lean and pull the foot from the ground. But there is a push off also that can be clearly seen!
You are right that there is a forward momentum when running normallly when you are in the Pose stance
Posted by Pieter on 12/16 at 09:47 AM
I’m talking what happens in reality here. The push off happens by itself and you should not try to do it deliberately off course. Again a difference between what happens and what makes it happen!?
Posted by Pieter on 12/16 at 09:51 AM
You said it exactly at the end of your statement. Dr. Romanov tries to focus on explaining things you should do in order to keep things simple. If his instructions were, okay, first you must be upright, then lean, then right before you pull, there is a slight push off, but don’t worry about that, it will happen, etc. etc. etc. It’s just too much. So Dr. Romanov tries to simplify his isntructions by ommiting certain commands that are involuntary actions and happen as a bi-factor of a command he is asking you to perform. It’s like telling someone to take down notes letter by letter. You have the right idea completely. Yes it happens, and no we don’t focus on it. Thanks for your attention to detail.
Posted by Pose vLog on 01/02 at 10:15 PM
I quote “there is no thigh (extensor muscles of the leg) activity after landing, therefore, there is no Push Off in Running.”
But: there IS thigh activity after landing, as numerous research articles tell. There IS push off as you ‘admit’ in other comments. I don’t see why you should hide that fact.
Posted by paul on 03/05 at 06:32 PM
I think you are misunderstanding what I am “admitting” to. I’ll try to make a clear distinction for you. If you look at the extensor muscle study, it clearly shows that the thighs are idle after the midstance of the landing. What this means: the thighs are not used for propulsion in order to “drive” the body forward. The push-off measured in studies is nothing more than ground reaction force. For every action there is an equal and opposite reaction.
Think of it this way, unless you are lifting one leg off the ground at a time, you will have to apply some kind of extra pressure in order to pull your leg from the ground. In running, after midstance your thighs go idle and the elastic component takes over. Remember that there is no benefit to actively pushing off when you do not have your body-weight to work with, which is only at midstance; at any point throughout the support phase after the body weight is off of support there is no pushing force you could create that you could derive any benefit from. This means that even if the athlete was artificially creating thigh muscle activity because he was taught to do so, there could be no benefit from doing so, just muscle expenditure.
If you look at it from a larger scope, when the elastic component takes over, the only thing left to do is to pull your leg from the ground as soon as possible so that not to slow your momentum. When you jump in the air, or simply pull your feet under your body as quickly as possible you need to raise your GCM (general center of mass) in order to pull your feet under your body. In running, since your muscles are already contracting and expanding, the elastic component of your thighs along with other elastic elements helps in creating this slight raise in GCM, enough for you to be able to pull your leg back under your body. When you pull your leg off the ground, it creates a larger force on the ground in order to momentarily break free from gravity. If you are meassuring how much force is applied to the ground after midstance, the figures would read that the runner applies extra force during the latter part of the support phase in order to “propel” the body forward. That is simply an inaccurate interpretation of the data.
My final point is that, yes there are studies that show there is thigh activity after midstance, our position on this is that there is no benefit to gain from actively using thigh muscles to “push-off.” Finally, if measuring ground reaction force you could conclude that the runner is infact pushing off in order to “propel” himself forward; we however feel that that is a false interpretaion.
Posted by Pose vLog on 03/06 at 01:13 PM
Thanks for your elaborate answer, it makes discussion possible and makes things clearer for me.
(you say: …think of it this way, unless you are lifting one leg off the ground at a time, you will have to apply some kind of extra pressure in order to pull your leg from the ground)
my comment: this extra pressure is applied ‘at’ midstance which makes for a short effort, I call this ‘pushoff’ but maybe you call it ‘withstanding the ground reaction force’. It also seems that your definition of ‘pull’ is: ‘apply pressure to the ground in order to pull, then pull’. So, according to me AT midstance there is a (very short moment of) pushoff (or pressure to pull leg from ground).
I agree that after midstance the thighs go idle. I assume with elastic component you refer to elastic energy stored in tendons etc.
(you say: if you look at it from a larger scope, when the elastic component takes over, the only thing left to do is to pull your leg from the ground as soon as possible so that not to slow your momentum)
my comment: yes the momentum is very important, as you hit the ground with the other leg your pulled leg is already at/in front of the GCM and you are in what you call the Pose. You don’t have to wait for this leg and can immediately ‘in my terms’ bounce-move forward, in your terms ‘fall’ (but fall has some connotations that introduce technique errors in some people not very well in to running technique).
(you say: In running, since your muscles are already contracting and expanding, the elastic component of your thighs along with other elastic elements helps in creating this slight raise in GCM, enough for you to be able to pull your leg back under your body)
my comment: according to research there can be about 50% ‘elastic’ energy given back to you as you bounce. But the remainder is muscle activity: the muscles contract to withstand the pressure of landing and help move the GCM up and forward.
(you say: when you pull your leg off the ground, it creates a larger force on the ground in order to momentarily break free from gravity. If you are meassuring how much force is applied to the ground after midstance, the figures would read that the runner applies extra force during the latter part of the support phase in order to “propel” the body forward. That is simply an inaccurate interpretation of the data)
my comment: so can I say that this extra force after midstance is partly there because the runner doesn’t pull quickly enough after midstance? Or should the runner apply more force at midstance so he can quicker pull. (the command ‘pull’ then leads subconsciously to the command ‘push harder’).
Posted by paul on 03/07 at 04:41 PM
Thanks for the Reply Paul. Your interpretations are correct. It is absolutely true that Dr. Romanov and his instructions tend to me mis interpreted sometimes. I would agree that some of the way he describe things should be looked at and developed to be more of a complete answer so that not to confuse those individuals who have read many research studies on the subject. However, the mainstream market of runners probably wont care about half of the scientific data we can bring them. The bottom line for most runners is, does it work? Yes.
On a final note, if you have some suggestions as to what you believe is not clear in Pose explanation, do point it out to us, and we will be sure to include it on our website and our upcoming books. Thanks for your sincere interest. (you can email me @ email@example.com)
Posted by Pose vLog on 03/08 at 06:33 PM