The two University of Ottawa pressure studies used different groups of ski instructors with different qualifications for each study. One study used three highly skilled ski instructors (C.S.I.A. Level VI). The other study, the one presented at the Proceedings of the XVI International Symposium on Biomechanics in Sports (1998), used six internationally certified Canadian ski instructors. The pressure patterns seen in the two groups had some important differences.
“Of interest however is the short distance travelled by the cop during most of the turns.” (made by the six internationally certified Canadian ski instructors)
In the three C.S.I.A. Level IV instructors, the centre of pressure (COP) traveled from the head of the first metatarsal to the medial part of the heel as they made their way through a turn whereas COP in the six internationally certified Canadian ski instructors moved from the head of the first metatarsal at the beginning of all turns, except Giant Slalom turns, and progressively migrated towards the medial aspect of the longitudinal arch near the end of the turns. In all turns made by the internationally certified Canadian ski instructors, except GS turns, COP barely moved back from its position under the head of the first metatarsal.
It was only in the Giant Slalom turns for the internationally certified instructors that COP traveled from the head of the first metatarsal to the medial part of the heel in the last part of the turn. In no case did the pressure data find that COP was at the heel at the initiation of a turn for either group of instructors. While the studies might have inferred that high pressure COP was either under the head of the first metatarsal or the under the heel, but not both at the same time, this was not the case. When there is a well defined area of high pressure COP under the head of the first metatarsal or the medial part of the heel, there will always a secondary well defined area area of high, but lesser pressure COP, under the opposite area. The difference is in the degree or pressure differential between the two areas of high pressure COP.
When there is high pressure COP under the heel, there will be a poorly defined area of low pressure under the center of the forefoot as shown in the graphic below. The red circle over the heel with the black dot represents COP. COP creates a weak ‘sense’ of force along the center of the ski, in addition to a well defined sense of force acting perpendicular to center of the base of the ski. But a secondary area of a lesser high pressure COP cannot exist under the head of the first metatarsal in this configuration.
High pressure COP under the head of the first metatarsal is dependent on a secondary area of lesser high pressure COP under the heel as shown in the graphic below.
COM can only be guestimated when there is high pressure COP on the heel. But COM must be aligned with COP on the same axis and close to, but behind, COP when there is high pressure COP is on the head of the first metatarsal. The higher the pressure on the first metatarsal COP, the closer COM is to it. As I will explain in my next post, the position of COM creates high pressure COP; stance regulates the position of COM in relation to the outside foot of a turn. Therefor, stance creates high pressure COP. The ability to create these two areas of high pressure COP and control and especially manage the pressure differential between these two areas of high pressure COP, has long been the secret of the world’s greatest skiers. It is the ability to generate the combination of high pressure COPs on the head of the first metatarsal and heel and especially to manage the pressure differential between these two COPs, that seems to have eluded researchers. As I intend to explain in the next post, the small fore/aft movement in COP seen between the head of the first metatarsal and the medial arch, as turns progressed, is indicative of the degree of effectiveness of the management of the pressure differential by the skier between the high pressure COP on the head of the first metatarsal and high pressure COP on the heel. Increasing or decreasing pressure on one COP will result in a corresponding opposite change in pressure on the other COP.
“Historically, it has been quite complicated to perform biomechanics research on alpine skiing on-site. This fact is so because of the environment where the sport is practised which does not lend itself well to biomechanical measures using traditional equipment.”
Did I hear Birdcage? The researchers are correct when they say, “it has been quite complicated to perform biomechanics research on alpine skiing on-site”. Up until I designed the Birdcage 7 years earlier, in 1991, with Alex Sochaniwskyj, a brilliant biomedical engineer, it had been complicated to study biomechanics of alpine skiing during actual ski maneuvers. Sochaniwskyj not only contributed to the design of the Birdcage research vehicle, but also wrote the software and assembled the instrumentation package where none existed. For the studies done on Whistler’s summer glacier, Toshiba loaned Alex a prototype of a battery powered portable computer they were developing. This was in a day when the only computers commercially available were monsters that filled whole rooms or in kit form. The difference between Sochaniwskyj and I and the researchers who had to wait seven years for technologies to emerge before they could follow in our ‘footsteps’, was that we knew precisely what pressure patterns we were looking for in the feet of Olympic and World Cup Champions and neophyte skiers. And we knew what the pressure patterns meant before we did our studies. If we had been wrong, and we weren’t wrong, our very specific sensor placement would have recorded nothing of interest. Guess what we were studying?
In my next post I will talk about what the two high pressure COPs mean.
Wishing you all the best for the holiday season