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F Force When The Foot Is In Front Of
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The two slides shown in Part 1: 6:00 and 7:00 show a couple of interesting attributes that Dr. Irene Davis does talk about but I believe are of interest in understanding changes to gaits and the attributes of different gaits.First up the slide at 6:00 “Impact Peaks and Loading rate reduced by 16-22%” does indeed illustrate how the runners on average reduced the impact You must be registered to view this link peak – as discussed by Irene.  What I’d like bring attention to is that isn’t the only change on interest.  The after retraining curve is shifted after – the position of the peak loads is later in stance, and the loads later on stance are higher relative to the before results.Why is this of particular interest? You must be registered to view this link  Well it shows after improving their gait they are running more balanced with much more even time on stance before and after the peak, and not front loading the stance, and… this means that they are landing with their Center of Gravity further back that they did before.  All too often we see it claimed that landing closer to the Center of Gravity is good thing, but here we have the exact opposite, those that land softly land with first contact point *further* ahead of their CoG as a measure of in time on stance.In terms You must be registered to view this link of balance this is exactly what one would expect, so this finding is just fine from a mechanics point of view.  It does run counter to the popular gait cue though so worth thinking about.The slide that follows this, at 7:00 shows the differences between different foot-strike type.  Here we see the differences in loading rates and the classic impact peak of the heel strikers, with the midfoot and forefoot strikers You must be registered to view this link close to illuminating this.  Irene highlights this aspect as again her for is on the first half of the stance. Looking further back to impact peak and we again see differences – the heel strikers have an impact peak that is earlier indicating that they are front loading their stance and landing nearing to their Center of Gravity as a ratio of time on stance.   The peaks for midfoot and forefoot strikers is later and much near to the center of time on stance – looking much more balanced either side of the peak.  What also jumps out is that the peak loads are substantially higher, and remain higher for the second half of time on stance.  From an efficiency standpoint a nice well balanced curve wins, but from a injury standpoint it’s an area one should look at for potential issues.  Given that Pete’s just published an article about stress fractures caused by loads after mid stance this may well be a significant finding.I’d like to come back to point about the distribution of loads across the stance, here we see data that tells as that You must be registered to view this link the heel strikers are landing closer to their Center of Gravity, an earlier peak and to me suggests that they will be trailing their leg further behind them on push off.  From a horizontal equilibrium point of view this is what you’d need to do to compensate for the high peak of force when the foot is in front of the Centre of Gravity(Mass). While the midfoot and forefoot runners are landing further in front of their You must be registered to view this link Center of Gravity but landing more softly so the horizontal forces won’t be higher, and with less backwards force their is less need to trail the leg, instead the foot comes off the ground earlier.  While the idea You must be registered to view this link that heel strikers might create more horizontal forces is often cited as a reason not to heel strike, it’s not at all because their are landing further in front of Center of Gravity than midfoot/forefoot strikers, they aren’t at all, the non heel strikers are actually landing further in front of their Centre of Gravity but don’t pay a big penalty because they land much more softly, with the big forces only arising nearer to when the center of mass is over the foot.  This is important point to take home, it’s the heel strikers that are landing closer to Center of Gravity, so using this as cue is when changing form to a You must be registered to view this link midfoot to forefoot strike is contrary to what actually happens with these gaits.I suspect what I’m saying here will be against the tide of runners that believe that landing close to the Center of Gravity will improve their gait.  They might even look back to You must be registered to view this link pictures of heel strikers and midfoot and forefoot runners and observer overstridding in the heel strikers and nice vertical shins on landing for the non heel strikers. So how does this fit with the above findings?
 



 
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