Research on postural balance responses show that quote, "in response to a moving platform, normal subjects use three general “strategies” depending on perturbation magnitude and direction and the area of the support surface under the feet. The ankle strategy is used when the platform moves backward under the feet or rotates downward under the toes. Subjects extend their feet to move the center of pressure (cp) forward and to drive the center of mass backwards under the feet; there is little rotation at other joints (Horak and Nashner 1986; Nashner 1977). A hip strategy is employed when the base of support is so narrow that little force can be exerted with the toes and when large platform perturbations occur."
The ankle strategy is obvious in skiing to me, the hip strategy would seem to happen when we need a greater range of motion to deal with terrain or forces. Another situation would be if our range of motion in the ankle is artificially reduced by the boot we are wearing imposing a reduced base of support at our feet. For me, understanding the general response strategies gives me better insight into my movement analysis of other skiers. Correcting boot issues is a tough one to deal with as an instructor. Later, RicB.
be careful when quoting Nashner, esp. if this is going to be used for further articles & reseach. While the ankle, knee, & hip strategies he described are excell. for furthering our understanding of static / dynamic balance there have been several flaws in the work. Specifically the difficulty reproducing the results... most subjects will immedately go towards an avoidance of the 3 stategies & perform a stepping strategy when perturbed. In researching the original work, many of the original subjects were cued to stay on the platform & therefore not step to save balance.....with a little imagination we see stepping occuring in skiing: wide base, huge divergense, inside ski lead
I guess we must be cued to stay on the platform too!!!! good luck
I've been advised my editor to put more photos and less verbiage in this article, so I won't be going into a deep discussion about this. However, when you suggest an exercise for a TPS article, they want to know why you are working that specific muscle. A one sentence explanation is suitable.
On the other hand, this is a fascinating discussion for the forum.
Bob's graphic is absolutely awesome! what a great visual and myth disspeller! love it.
I tend to take skiers with limited flexion of this nature and lift under the heel inside the boot so as to open the ankle and maximize the range they do have. Most importantly align them so that the knee is in a good position over the toe of the boot so as to maximize static alignment and balance.
I think Bob's stick person demonstrates that properly aligned the skier does not need much in the way of ankle flexion to ski well.
Not sure but I believe that ankle flexion related to balance outside the ski boot & dynamic balance while sliding down a slope with the foot and ankle encased in a plastic ski boot are different?