I am a huge fan of Mikaela Shiffrin, not because I view her as a goddess with mystical powers but because I admire her intelligence.
At the beginning of the 2014-2015 World Cup season, Shiffrin was in serious trouble. It was obvious to me that she had made some significant changes to her equipment prior to the start of competition. Although it may sound harsh, I believe this is the best thing that could happened. The problems caused by these changes forced her to think about her equipment and especially her technique and how equipment affects it. The speed with which she turned around a bad situation is remarkable. Her winning margin of 1.68 seconds in the Snow Queen Slalom in Croatia, the biggest winning margin in the 10-year history of the event and an eternity for any World Cup race, should silence critics who claimed that she had lost her edge (she had lost the feel for her edge) or was suffering from a mental block.
Shiffrin’s comments in a Team USA.org story, Shiffrin Dominates Field To Win Snow Queen Trophy ( http://www.teamusa.org/News/2015/January/05/Shiffrin-Dominates-Field-To-Win-Snow-Queen-Trophy) provide valuable clues as to her sudden quantum leap in performance. After changing her boots and skis during a 10 day training camp in Italy Shiffrin commented, ”
I feel really comfortable on my feet right now after a lot of testing in Santa Caterina but also really great training.
With every single run that I take I get more confident…… My skiing is good right now, it’s kind of back on track and my equipment feels really good.
For the first time in my career, I just feel like I am in complete control of myself……… I feel like I am in a really great place right now.
Shiffrin’s accentuation of feel is significant as is the fact that she did, a lot of testing in Santa Catarina. These comments indicate to me that she has connected the feel in her feet with the alignment of W at ski flat with the proximate centre of the head of the first metatarsal of the new outside foot of a turn and and maintaining the alignment R and W with the proximate centre of the head of the metatarsal through the turn phase. If this is true, then she has a huge advantage over her competition because it is unlikely that they are able to feel what she feels.
So, why is Shiffrin suddenly not just skiing better than ever but far better than her competition? I believe an important factor is shear force. Seriously? Yes, seriously. While Shiffrin is clearly demonstrating sheer force in terms of the winning power of her skiing, I am actually referring to shear force in the context of a force acting in a direction parallel to a surface. Shear forces typically arise in the load points at the base of a truss under compression. The resulting tension in the unrestrained bearing points of the heel of the bottom chord (sole) of the truss cause the bearing points to spread away from the centre of the compression load. There is an important truss structure in the skier/ski equipment system. But I will save this for a future post.
The importance of shear forces in ski technique is that they creates fascial tension in the forefoot that potentiates small nerve proprioception, muscle power and, most important, act to stiffen the forefoot in a manner that enables rotation of the outside ski of a turn about a centre between the inner (medial) aspect of the head of the first metatarsal and the outer (lateral) aspect of the heel using whole leg, top-down, pelvis-driven, internal rotation. As I intend to demonstrate in future posts, this mechanism acts to extend the GRF acting along the inside edge out under the body of the ski thereby creating a source of GFR under the foot that the skier can use to balance on. This is the signature of the world’s best skiers. I will expand on this mechanism in a future post.
Other factors contributing to Shiffrin’s superior performance include:
Given the importance of her ski boots, it was appropriate that a cameras zeroed in on a close shot of her boots at the start of the second run. They appear to be an older Atomic model, most likely her old boots. Given the fact that Shiffrin did testing at Santa Catarina, I think it probable that she did some experiments with changes in her boots because she is skiing far better now than she did last year and will probably continue to improve.
The set up of her boots is a huge factor. The screen shot below is of Shiffrin skiing straight down the fall line out of the start. The configuration of the elements of her body in terms of creating tension in the arches of her feet is nearly perfect. The reason stance in the fall line is significant is that the pressure exerted by the shins on the front cuff of the boot is minimal. The COM of the racer has to be over the feet and supported by the muscles responsible for maintaining an erect stance.
This becomes obvious when her orientation is referenced to a level surface as shown in the graphic below. The red ball is my estimated location of her Centre of Mass. The force vector passes through the upper or proximal aspect of her tibia and continues through the proximate centre of the head of her first metatarsal. The key is the angle of the shank of her leg which must be achieved without applying significant force to the front of the cuff. This ensure that the triceps surae is in isometric contraction so that foot to core sequencing can occur. This issue will be the subject of a future post.
In watching the video of Shiffrin on course moving from turn to turn, her fluid pendulum action and rhythm resembles the action of a metronome.