There have been some good and insightful comments made here; I'll try to add a couple more.
Pedaller: I think we are on the same wavelength, so I hope I'm not misunderstanding. Your analogy to the skiier with poles is a good one, and is exactly what I was getting at when I said that the Pose method is probably really trying to reduce the deceleration forces of footstrike and thereby provide a boost to efficiency. Your discussion of the pole vault is also interesting. The difference between a pole vault pole and a runner's leg is that when the pole is jammed into the ground, it converts the vaulter's initial kinetic energy into potential energy and then reconverts it to kinetic energy with velocity in a new direction (up). The leg, when jammed into the ground, is not so efficient--much of the runner's kinetic energy will be dissipated as sound, heat, vibrating flesh, etc. Your comment that "you don't get something for nothing," is also right on the money--it's a practical way of stating the law of conservation of energy. In this case, it's important to remember that if there is no net vertical displacement of a runner's body (which we hope there won't be when we're running on flat ground), then gravity, being a force in the vertical direction, has done zero net work. In the cycle of a running stride, gravity does work to pull our center of mass down, and then we do an equal amount of work (i.e. negative work done by gravity) to push our body back up. If it was possible for us to glide along forward without bouncing up and down, then gravity would never do any work on us, and, by the same token, we would never do work against it--wouldn't that be nice! If we add up all the work we do to push ourselves up during a run, that is the total energy expended to "fight" gravity. And, to bring the focus back to the claim by Pose that we should let gravity do the work in moving us forward, we can see since gravity in fact does no net work that this claim carries no weight! ;)
Dre: You are absolutely right about the moon. If a giant hand was to suddenly stop it in its orbit, it would then fall toward the Earth (and indeed the Earth would "fall" toward it a bit too). As the moon orbits the Earth, the only force exerted on it is gravity pulling it down (or radially inward); so, it is always undergoing a resulting "radial" acceleration toward the Earth. But, there is no force on it in the tangential direction, so it goes along with no change in its tangential velocity. As with the hypothetical runner, since there is no change in the vertical (radial) position of the moon, gravity does no work on it as it orbits. The moon's energy doesn't change at all--rather, in this case, gravity is simply continuously steering the moon in a new direction.
Meg: I think you've made a really good analysis too. If we were riding on the moon, we would indeed experience the centrifugal "force". This "force" is only a perceived effect (and for this reason it's called a "pseudoforce") due to the fact that the moon is being steered out from under us by the constant redirecting effect of the Earth's gravity. It is indeed what you feel pressing you toward the outside of a curve when you go around it on a bike or in a car, and it is directed radially outward, not tangentially. You also make a great point about there being no net help to be gotten from gravity--it's only on our side for half of a stride. Your discussion of how we can provide the horizontal force needed to sustain forward progress leads me to think about one idealized example, which perhaps captures the essence of what Pose is trying to attain: if we push forward (horizontal friction force between shoe and ground), we will accelerate to a certain forward velocity. That velocity will remain unchanged (Newton's first or second law--take your pick) until a new horizontal force acts on us. Ignoring the drag force of the air, which is probably relatively unimportant at running speeds (at least at my running speeds!), such a new force can only come from the next interaction of shoe and ground. If there was no such interaction, we would glide happily along at our forward speed indefinitely! So the whole trick is to make sure that each footfall does as little as possible to decelerate us. Any deceleration that does occur, due to shoe-ground force in the backward direction, will have to be compensated for by a subsequent application of shoe-ground force in the forward direction which accelerates us back up to our desired forward velocity. This acceleration requires work to be done (i.e. energy to be expended), because, as mentioned in the pole vault comparison, our bodies can't recover the kinetic energy that is lost in the deceleration part of the footfall. It's my feeling that the teachings of Pose are in large part an effort to minimize the decelerative effect of footstrike. For there to be no deceleration upon footstrike, the foot must be traveling backward with respect to the body at the same speed as the body is moving forward with respect to the ground--that is, the foot must be stationary with respect to the ground when it comes in contact with it. I can see how the Pose foot position and turnover might lend itself to that.
christopher: I hope all of these comments made by others and myself have helped to clarify why gravity can be of no help to us in running (except for the important role of providing a means for there to be friction between shoe and ground). Gravity is at best a neutral party and at worst an energy sink that we pay into each time we push upward in a stride. You might also want to look at that link I posted above (if you haven't already done so), if you want to see an answer from Dr. Romanov himself. Thanks for your patience to you and to anyone else who bothered to read this long ramble! Maybe Dr. R was right after all when he suggested that it's best to "try not to think of it now, just enjoy your running." :) And one final comment now that I see your most recent post: Gravity accelerates us up and down, shoe-ground force accelerates us forward and backward, "deflection" is an irrelevant, complicating term, and Newton would have been appalled by the claim that gravity helps us move forward when we run!
Nate
Pedaller: I think we are on the same wavelength, so I hope I'm not misunderstanding. Your analogy to the skiier with poles is a good one, and is exactly what I was getting at when I said that the Pose method is probably really trying to reduce the deceleration forces of footstrike and thereby provide a boost to efficiency. Your discussion of the pole vault is also interesting. The difference between a pole vault pole and a runner's leg is that when the pole is jammed into the ground, it converts the vaulter's initial kinetic energy into potential energy and then reconverts it to kinetic energy with velocity in a new direction (up). The leg, when jammed into the ground, is not so efficient--much of the runner's kinetic energy will be dissipated as sound, heat, vibrating flesh, etc. Your comment that "you don't get something for nothing," is also right on the money--it's a practical way of stating the law of conservation of energy. In this case, it's important to remember that if there is no net vertical displacement of a runner's body (which we hope there won't be when we're running on flat ground), then gravity, being a force in the vertical direction, has done zero net work. In the cycle of a running stride, gravity does work to pull our center of mass down, and then we do an equal amount of work (i.e. negative work done by gravity) to push our body back up. If it was possible for us to glide along forward without bouncing up and down, then gravity would never do any work on us, and, by the same token, we would never do work against it--wouldn't that be nice! If we add up all the work we do to push ourselves up during a run, that is the total energy expended to "fight" gravity. And, to bring the focus back to the claim by Pose that we should let gravity do the work in moving us forward, we can see since gravity in fact does no net work that this claim carries no weight! ;)
Dre: You are absolutely right about the moon. If a giant hand was to suddenly stop it in its orbit, it would then fall toward the Earth (and indeed the Earth would "fall" toward it a bit too). As the moon orbits the Earth, the only force exerted on it is gravity pulling it down (or radially inward); so, it is always undergoing a resulting "radial" acceleration toward the Earth. But, there is no force on it in the tangential direction, so it goes along with no change in its tangential velocity. As with the hypothetical runner, since there is no change in the vertical (radial) position of the moon, gravity does no work on it as it orbits. The moon's energy doesn't change at all--rather, in this case, gravity is simply continuously steering the moon in a new direction.
Meg: I think you've made a really good analysis too. If we were riding on the moon, we would indeed experience the centrifugal "force". This "force" is only a perceived effect (and for this reason it's called a "pseudoforce") due to the fact that the moon is being steered out from under us by the constant redirecting effect of the Earth's gravity. It is indeed what you feel pressing you toward the outside of a curve when you go around it on a bike or in a car, and it is directed radially outward, not tangentially. You also make a great point about there being no net help to be gotten from gravity--it's only on our side for half of a stride. Your discussion of how we can provide the horizontal force needed to sustain forward progress leads me to think about one idealized example, which perhaps captures the essence of what Pose is trying to attain: if we push forward (horizontal friction force between shoe and ground), we will accelerate to a certain forward velocity. That velocity will remain unchanged (Newton's first or second law--take your pick) until a new horizontal force acts on us. Ignoring the drag force of the air, which is probably relatively unimportant at running speeds (at least at my running speeds!), such a new force can only come from the next interaction of shoe and ground. If there was no such interaction, we would glide happily along at our forward speed indefinitely! So the whole trick is to make sure that each footfall does as little as possible to decelerate us. Any deceleration that does occur, due to shoe-ground force in the backward direction, will have to be compensated for by a subsequent application of shoe-ground force in the forward direction which accelerates us back up to our desired forward velocity. This acceleration requires work to be done (i.e. energy to be expended), because, as mentioned in the pole vault comparison, our bodies can't recover the kinetic energy that is lost in the deceleration part of the footfall. It's my feeling that the teachings of Pose are in large part an effort to minimize the decelerative effect of footstrike. For there to be no deceleration upon footstrike, the foot must be traveling backward with respect to the body at the same speed as the body is moving forward with respect to the ground--that is, the foot must be stationary with respect to the ground when it comes in contact with it. I can see how the Pose foot position and turnover might lend itself to that.
christopher: I hope all of these comments made by others and myself have helped to clarify why gravity can be of no help to us in running (except for the important role of providing a means for there to be friction between shoe and ground). Gravity is at best a neutral party and at worst an energy sink that we pay into each time we push upward in a stride. You might also want to look at that link I posted above (if you haven't already done so), if you want to see an answer from Dr. Romanov himself. Thanks for your patience to you and to anyone else who bothered to read this long ramble! Maybe Dr. R was right after all when he suggested that it's best to "try not to think of it now, just enjoy your running." :) And one final comment now that I see your most recent post: Gravity accelerates us up and down, shoe-ground force accelerates us forward and backward, "deflection" is an irrelevant, complicating term, and Newton would have been appalled by the claim that gravity helps us move forward when we run!
Nate