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Runners do not push off the ground but fall forwards via a gravitational torque

Discussion in 'Biomechanics, Sports and Foot orthoses' started by NewsBot, Oct 16, 2007.

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  1. NewsBot

    NewsBot The Admin that posts the news.

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    Runners do not push off the ground but fall forwards via a gravitational torque.
    Romanov N, Fletcher G.
    Poses Tech Corp, Coral Gables, Florida, USA.
    Sports Biomech. 2007 Sep;6(3):434-52.
     
  2. Admin2

    Admin2 Administrator Staff Member

  3. Smells just like another illogical argument that is presented for the sole purpose of selling a certain style of running by the style's creator, Romanov.:bang::bash::wacko:
     
  4. Bruce Williams

    Bruce Williams Well-Known Member

    Kevin;
    Dr. Romanov's position may be illogical, but the science could be quite logical.

    Howard Dananberg has talked for many years on the effects of gravity and the pendulum effect of the swing limb pulling us through our gait cycle. Why is it so hard to believe that gravity could not have the exact same effect, or nearly so, during a running type gait?

    Let the science speak for itself, if it exists within the paper.

    :drinks
    Bruce

    PS: anyone have a full copy of this one too! I need my fix man...
     
  5. Bruce:

    The science says Dr. Romanov's position is not logical. The science says that, during running, the center of mass of the body is accelerating upward from the middle of the support phase to the middle of the forward recovery phase of running.....against the acceleration of gravity. In fact, walking and running are exactly opposite each other in their use of potential energy (PE) and kinetic energy (KE). In walking, PE and KE are out of phase. However, in running, PE and KE are in phase (Novacheck, Tom F.: The biomechanics of running. Gait and Posture, 7:77-95, 1998). In other words, walking is energetically more like an inverted pendulum and running is more like a bouncing ball.

    Therefore, how can gravity be assisting the mechanics of running during this time of the running gait cycle when the movement of the center of mass of the body is upward, exactly opposite the effects of gravity?! Is this the same logic as saying that gravity makes the bouncing ball go upward because it first accelerated the ball downward to allow the ball to store elastic strain energy when it was then compressed against the ground due to effects of gravity only to be accelerated upward again when it released its elastic strain energy?!:wacko::bang:

    Also, Bruce, do you really want to go around the stump again of why I disagree with Howard's claim that the swing limb "pulls the body forward" and the stance phase limb "does not push the body forward", as I have heard Howard state in numerous lectures?? If while suspended in the air during the apex of a jump off of a trampoline, could a person somehow move their center of mass forward by moving their lower extremity anteriorly? No. That is because as the lower extremity accelerated forward in space (i.e. not touching the ground), this acceleration of the lower extremity forward would actually move the rest of the body posteriorly, not anteriorly, since the center of mass of the body cannot accelerate forward without an externally applied force acting on it (Newton's Second Law of Motion: a = F/m). I proposed a similar argument with my "walking on ice" analogy on the Podiatry Mailbase years ago when discussing this same topic with Howard. Since by the trampoline example and walking on ice example, we know that moving the swing limb forward can not move the body forward solely by its actions alone, then the only way to accelerate the body forward is by having an externally applied force acting from the ground on the body, pushing it forward.....and this doesn't come from the swing phase limb, swinging in space. It, instead comes from the reaction force from the stance foot pushing posteriorly against the ground.
     
  6. Interesting though in regards to the 'swing leg pulling the body forward', while the stance phase limb doesn't push the body forward. Looking from a sprinters perspective, and viewing the quickest flat speed runners in the world, i.e. Asafa Powell, I could safely claim it would be asinine to suggest that the stance foot DOES NOT push posteriorly against the ground, not to mention the minimal hip extension through the 46 steps over a 100m sprint.

    If this is not the case, I guess the best sprinters in the world may have to change their thoughts in terms of training, less power/strength development in the gym and focus more on " falling forwards via a gravitational torque while pulling the support foot rapidly from the ground using the hamstring muscles", thus causing horizontal displacement? Maybe not?
     
  7. Michael:

    Good one! Romanov's "Pose technique" along with the other forefoot striking technique the "ChiRunning method" is currently being touted as the most efficient, non-injury producing running method. In addition, Newton running shoes are the latest very expensive running shoes in the States that "promote natural forefoot striking" by having a large forefoot cushion, longitudinal forefoot outersole bars that supposedly promotes forefoot striking. This is all the latest fad in the running community and it is almost accepted now by some runners that if you aren't forefoot striking, then you are not running most efficiently.

    To me it looks like some people are making a living on teaching runners who should be running heel first to be forefoot strikers. In my opinion, forefoot striking is simply not a natural way for most slower runners to train or race since research seems to indicate that experienced runners will self-select their kinematic pattern of running that is most energy efficient. I believe other research has shown that about 85% of runners are heel strikers. I was and still am a heel-striking runner, as were most of my mates on the cross-country team at UC Davis and the other high-level distance runners I competed against as a younger man. I was, during my prime, able to run a number of sub 2:35 marathons with a heel striking technique, even though, as the running pace increases, runners will naturally become more midfoot strikers and in sprinting will become forefoot strikers.

    In my clinic, I see more runners who have become injured with Achilles tendonitis, calf strains and other odd injuries trying Romanov's Pose method or the Chi method forefoot striking technique. Therefore, I am not convinced that runners should be converted from heel striking to forefoot striking for the simple reason that a few people may have benefited from the running style change. As far as I'm concerned, its just another fad in the running scene that will soon pass as more evidence shows that the ones benefitting the most from forefoot-striking running are those that are teaching, coaching or selling products promoted by each new running technique.
     
    Last edited: Oct 18, 2007
  8. efuller

    efuller MVP

    :pigs:

    Once you get up to speed, you don't need "motive" force. Momentum will keep you moving until something stops you. (Newton's first law) To get moving you could just fall forward, or you could push off of the ground to get moving faster. (F = Ma, Newton's second law) Think of sprinters starting blocks.

    One of the problems with the belief that the swing leg propels you forward is that it will also pull you backward. Right at toe off, the center of mass of the trailing limb is behind the base of support (the stance limb) and this will pull you backward. Some of the kinetic energy of the rest of the body is lost to the trailing limb to move the swing leg forward. This energy can be recovered before heel strike, but there is no net gain. Or some energy could added to the trailing limb with ankle push.
     
  9. Scorpio622

    Scorpio622 Active Member

    I feel that both mechanisms are in place (pulling of the swing leg and pushing off the stance) and the ratio of which is determined by extrinsic factors and the activity at hand. Why does it have to be one of the other ?? A few analogies ....

    First look at an individual with a BKA. They tend to limp more during the initial steps, but once they achieve a functional momentum, they display a surprisingly normal gait pattern. Aren't they pivoting over the prosthesis, more-so than generating force through it ???

    Next look at someone walking on slick ice. Although the gait pattern altered, they can still move their mass forward by NOT pushing off (otherwise they would slip).

    The sprinter analogy is a good one that illustrates the opposite effect. Perhaps as speed is increased, we rely more on propulsion of the stance limb.

    Kevin's trampoline analogy does illustrate that linear movement cannot be created with someone in midair- but can't they generate a rotational force (IE tumble)??? Doesn't the momentum of gait create rotational forces in the stance limb ???
     
  10. Nick:

    1. In the below-knee amputee (BKA), I would expect that there is a posteriorly-directed shearing force between the prosthetic foot and ground during latter stages of stance phase. We "pivot" over our own legs during walking, just as the BKA does also. I would expect the BKA also pushes off their "foot" but probably does so with magnitudes different from a non-amputee which will depend on the gait characteristics of the individual and the speed of walking selected by the individual.

    2. Ice is not a frictionless surface. Ice has reduced friction but is not frictionless. That is why you can walk on an ice....it does have friction. If ice was a truly frictionless surface, you could not walk on it since no posteriorly-directed shearing forces would be able to be exerted on it from the foot or shoe.

    3. As the speed of walking and running increase, the posteriorly-directed shearing forces do increase also.

    4. Accelerating a lower extremity anteriorly at the hip (i.e. hip flexion) while suspended in mid-air will cause an posterior rotation of the head-torso and a counter-rotation of the body within the transverse plane also. However, flexing the lower extremity anteriorly at the hip will not cause an alteration in the normal path of the center of mass (CoM) that would have otherwise occurred without the anterior leg acceleration.

    In order for the CoM to have an acceleration, an external force needs to first act on it. Therefore, the swing leg cannot possibly drive the CoM of the body forward during walking or running without a concomitant external force, such as that which occurs during walking and running with the anteriorly-directed shearing reaction force from the ground .
     
    Last edited: Oct 20, 2007
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