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More efficient running style

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richh Dec 2013 3:32pm, 22 Dec 2013 653 posts	Quote Pin richh SPR, That definition is babble to me. I am not familiar with "parable" tangents. Why use the theoretical arc instead of the actual arc? And the foot makes an angle with the ground twice per stride, at the initiation and termination of contact - which is relevant to this definition? I wonder if this is just restating Dr. Romanov's famous exclamation, "Just pull goddam your foot from the ground!".
SPR Dec 2013 3:58pm, 22 Dec 2013 18,943 posts	Quote Pin SPR It was pretty much babble to me Rich. May I should have just quoted the last line: Essentially, it’s an interplay between how high your foot gets when it leaves the ground, and how far it travels." Can't see the actual study, so can't be sure that is true. last time I heard stride angle was to do with this: somaxsports.com
richh Dec 2013 5:17pm, 22 Dec 2013 654 posts	Quote Pin richh I wish the actual study were not hidden behind a pay wall!
jonp Dec 2013 5:29pm, 22 Dec 2013 4,488 posts	Quote Pin jonp Hi guys. Canute, quick question on this statement you made: "because the energy cost of repositioning the leg during swing increases with increasing cadence" Are you saying the energy cost overall are greater because the runner is basically repositioning the limbs more often? The reason I ask, is because a runner that leaves the foot/leg trailing for longer is likely to have more distance for the leg to recover and hence would have a higher energy cost for repositioning at faster speed. A runner with a more compact stride is likely to have less distance for the swing leg to recover surely - an also most likely a higher cadence?
Canute Dec 2013 8:33pm, 22 Dec 2013 833 posts	Quote Pin Canute SPR, Several things: First of all, stride angle is angle between the direction of motion of a marker on the foot at lift-off and the horizontal. Secondly, in that Spanish study, cadence was not related to efficiency, so cadence does not account for the observed effect of stride angle. (Of course, cadence does relate to efficiency within an individual but there is an optimum cadence for each runner at each speed. Therefore provided there was no systematic tendency for these well trained runners to be either above or below their optimum cadence, the differences in cadence between runners will not correlate with efficiency. In untrained runners, who usually tend to run at too low a cadence, you might expect increased cadence to relate to efficiency. But that is a different story.) Returning to the main point of this paper: the issue I had wanted to draw attention to is the trivial but often under-estimated fact that it is necessary to get airborne in order to run efficiently, and this requires a substantial upwards push. There is a trade-off between energy spent getting airborne and energy spent overcoming braking, so it is necessary to elevate the COG substantially in order to remain airborne long enough to avoid excessive braking. It is fairly easy to show this by application of Newton’s laws of motion. However maybe the interesting interpretation of the finding of this study is a bit more subtle. Flexing knee and hip immediately after take-off lifts the foot towards the torso, so the COG moves upwards relative to the hips. Thus a runner who produces a relatively large flexion of hip and knee will achieve the necessary elevation of the COG with somewhat less elevation of the upper body than would be required by a runner who produced less flexion of hip and knee. The upward motion of foot relative to torso will produce a large stride angle. Although as far as I am aware, the authors do not make this interpretation, but it seems to me that their finding might explain why elite athletes do not appear to produce a large up and down motion of their upper body despite a relatively long airborne time. Jonp, You are correct in assuming that the cost of repositioning the leg is the cost of accelerating the foot to catch up with the torso, but the crucial thing in the time available in which to do this. At higher cadence, there is a shorter period of time for the foot to catch up with the torso between lift-off and mid-fight, so the leg has to be accelerated more rapidly and that requires greater expenditure of energy. However, as you imply this repositioning cost will be less if the foot has not been left so far behind while on stance. This is another reason why short time on stance tends to be more efficient. However a precise calculation of repositioning cost is complex. I presented an approximate calculation in the calculations page of my Wordpress blog in April 2012
jonp Dec 2013 8:36pm, 22 Dec 2013 4,494 posts	Quote Pin jonp Cheers Canute. That makes sense.
SPR Dec 2013 9:26pm, 22 Dec 2013 18,944 posts	Quote Pin SPR Thank Canute. To your fourth paragraph, I think that was what Russ was suggesting, that the foot can move without independently of the torso.
richh Dec 2013 10:26pm, 22 Dec 2013 655 posts	Quote Pin richh "Flexing knee and hip immediately after take-off lifts the foot towards the torso" - Sounds like the point of the POSE foot tapping drill.
Canute Dec 2013 10:50pm, 22 Dec 2013 834 posts	Quote Pin Canute Yes, one of the good features of Pose is the emphasis on getting off stance quickly. Foot tapping probably helps this. I think that Change of Stance also helps develop a well coordinated lift-off. I am not a Pose enthusiast because the theory of Pose is questionable but I do practice COS.
jonp Dec 2013 9:46am, 23 Dec 2013 4,495 posts	Quote Pin jonp Canute, if you are practicing the COS drill, keep in mind that the movement starts at the hips, since (as I'm sure you appreciate :)) lifting the foot can't elevate your centre of mass. So focus on lifting the hips upwards, and following with pulling the foot up/under. The drill is really about timing the pull with the rising of the com. The lift of the hips is what Pose calls "unweighting". I demonstrate it here on this video along with a bunch of other elastic type drill (tapping, skipping, lunges etc): www.youtube.com/watch?v=6Pv-qCjYgjM