Another thing that happens as we run is that we modify the stiffness of our lower limbs in order to maintain a relatively stable displacement of our center of mass (see Ferris et al., 1998 for an excellent summary). In this sense the mass of our body can be viewed as a weight, and our lower leg can be viewed as a spring that supports that weight – this is known as the mass-spring model of running. Moving the center of mass (COM) up and down is energetically costly, and the body seems to have an inherent desire to control the displacement of the COM in order to keep it as stable as possible regardless of what is happening underfoot. If viewing a runner from the side, this can be thought of as a relatively stable up-down position of the head and trunk regardless Adidas NMD Mujerof the type of surface the runner might be passing over at any given moment.To give you an extreme example of this, think about what would happen if you were to run across a hard gym floor and onto a trampoline. What would your legs do? Most probably, when you hit the trampoline your legs would remain extended to a much greater degree at each joint than they were while running over the hard floor – in other words, your legs would be straighter on the trampoline. The springiness of the leg is a function of its joints – the hip, knee, ankle, and in some cases the bones and connective tissues of the forefoot and arch. As a general rule, leg stiffness will increase on softer surfaces, and will decrease (i.e., the joints will bend more) on hard surfaces. It is possible, however, that there may be a cost to extremes of stiffness in Nike Air Max 90 Femme either direction. Too straight a leg could increase impact through the bones (think of the jolt you get when stepping unexpectedly off a curb)Nike Air Max 270 Herr , whereas a leg with extreme bending at the joints could work the muscles of the leg a lot harder (i.e., a wasteful, inefficient gait).The mechanism by which these stiffness adaptations are accomplished is not entirely understood (at least by me), but it seems to happen on the fly, and we are able to make the necessary changes prior to stepping on a new type of surface if we know that a change in surface properties is coming (e.g., see this paper by Ferris et al., 1999). Conversely, unexpected changes can cause trouble, and in his book Nigg tells an interesting story about how he was able to help reduce injury rates among Cirque du Soleil performers by advising them to redesign their stage www.goulvenbazire.fr from a compliant surface supported at regular intervals by hard beams (e.g., and unpredictable hard/soft surface) to a uniformly hard surface Nike Air Max 270 Femme (i.e., a predictable surface). He told the story in reference to muscle tuning, but it seems it could equally apply to stiffness adaptations.So how does all of the above relate back to my running shoe preferences?I suspect that each of us has a certain range of leg stiffness that is tolerable for us while we run, and that we each have slightly different natural frequencies for the soft tissues in our legs. Our individual tolerances are probably determined by our bony and muscular anatomy, body weight, training status, and a variety of other factors. Thus, what makes a given shoe comfortable for one individual and not for another may tie back to factors such as these.If I had to guess, I Nike Air Max 2017 Mens probably do very little forefoot running in the Saucony Kinvara – most of the time I’m probably landing either flat or slightly toward the Nike Air Max Classic BW Dames heel. What this does is largely remove the forefoot and ankle as springs in the chain to cushion impact (the ankle and arch will still likely play some role via pronation and subsequent arch compression), and replaces them with the soft, compressible midsole of the shoe and probably greater bending of the knee. Because the midsole of the Kinvara is soft, the exchange works for me, and I can run comfortably in the shoes. Interestingly, I have found that my Kinvaras are less comfortable now that I have put over 200 miles on them, and I think that this might be because the midsole has broken down and no longer has the same degree of softness that it once did. This probably leads me to adapt my leg Nike Air Max 2017 Mujer stiffness slightly when I run in them, leading to slightly greater flex at the joints. This in turn, might be sensed as a bit more effort Nike Air Max 95 Femme> required to run in them. Just speculation, but it makes logical sense.