For those of you who don't have access to online Ski Racing magazine, let me copy a letter that David Dodge just send to the FIS. Dave is an engineer and a respected member of the ski industry and the ski racing community.
The following letter has been sent to FIS officials and others suggesting that the scientific logic behind the changing of ski regulations for safety reasons is flawed. It was sent by David Dodge and contains considerable research. Ski Racing urges all concerned to read it.
FIS President – Gian Franco Kasper
SRS President – Michael Schineis
FIS Alpine Executive Board - Bernhard Russi(SUI), Janez Flere(FIS), Niklas Carlsson(SWE), Herwig Demschar(USA), Reno Fleiss(CRO), Janka Gantnerova(SVK), Janne Leskinnen(FIN), Svein Mundal(NOR), Hans Pum(AUT), Ken Read(CAN), Fabien Saguez(FRA), Reinhard Schmalzl(ITA), Walter Vogel(GER), Toni Vogrinec(SLO)
FIS Legal and Safety Committee - Jose Luis Marco (ARG), Christopher Moore(CAN), Tsvetan Atanasov(BUL), Frits Avis(NED), Sortiris Babatzimopoulos(GRE), Marco Cozzi(ITA), Marco De Robles(SPA), Dean Gosper(AUS), David Howden(NZL), Klara Kaszo(HUN), Jerker Lofgren(SWE), Fransois-Kavier Manteaus(FRA), N.N(ISR), Alex Natt(USA), Naralia Ovchinnikova(RUS), Corinne Schmidhauser(SUI), Franz Steinle(GER), Robert Wallner(AUT), Sean Wilken(GBR), Katarina Zajc (SLO)
CC: Oslo Sports Trauma Research Center - Tone Bere, Tonje Wale Florenes, Trone Krosshaug, Lars Nordsletten, Roald Bahr; University of Salzburg - Erich Muller
The intention of this letter is to bring to the attention of the FIS that a large body of scientific evidence is at odds with the conclusions underlying the 2012-13 equipment regulations and that the studies used to develop the new 2012-13 equipment regulations do not constitute scientific proof.
The new skis were “scientifically proven to enhance athlete safety and reduce risk of injury,” F.I.S. said in a statement. “The meeting participants jointly agreed that the goal of the entire equipment review process is to only implement new rules that are scientifically proven to enhance athlete safety and reduce risk of injury” says an August 24th 2011 FIS press release. The studies referenced as “proof” were well conducted, the conclusions are disputable but not unreasonable and they are an important addition to the scientific body of evidence. However, the science as it exists now is not settled and the studies the FIS used to draw their conclusions certainly do not amount to proof.
I feel it is very probable that the unintended consequences of the FIS decisions will cause more injuries than will be prevented. I feel the FIS should reconsider their actions and take a slower more careful approach to equipment change that does not unnecessarily put at risk the health and safety of thousands of athletes.
The new skis might be safer, but I believe it much more likely they will be more dangerous. It can not be proven one way or the other, but the FIS decision forces thousands of athletes to accept this unknown risk to their health and safety in order to participate in their beloved sport. The ski industry will spend ten’s of millions of dollars developing and producing the new skis. If the FIS’s bet that the skis will be safer is wrong the liability is huge. Can the FIS survive if the new equipment decisions turn out to be wrong? The FIS can not say they were not warned.
I believe that increasing the length and increasing the sidecut radius for competition GS skis from the current 185cm minimum length and 27m minimum sidecut radius to 195cm minimum length and 35m minimum sidecut radius will have the following effects:
Non-linear control response – unstable leg geometry.
Higher probability of Phantom Foot ACL injury.
Non-linear control response
The Salzburg study shows that loads on the skier are reduced on longer, larger sidecut skis compared to the current 185cm, 27m sidecut skis. Their tests assume the load reduction is due to the ski differences but I believe it is more likely due to the fact that the comparison was made between a ski that was very familiar to the testers and several that were unfamiliar. I argue that the testers would have generated lower loads on any ski they were not familiar with and the ski design differences did not play a significant roll in reducing the measured loads. Athletes will find ways to use 100% of their strength no matter the equipment. This is what athletes do.
The geometric relationship between sidecut radius, edge angle and turning radius is well known to all ski designers. The theory shows that a 35m ski will have the same turning radius as a 27m ski if the ski is tipped on edge approximately 7 degrees more in a typical WC GS turn. The edge angle must be increased relative to the skiers COM (center of mass). In other words to ski the same line at the same speed the skier‘s COM must be in the same place, but the ski must be edged 7 degrees more. Thus more knee angulation. Athletes will discover that more knee angulation will allow them to ski the same line at the same speed as they are accustomed to skiing on their 27m sidecut skis vs. 35m sidecut skis. More knee angulation will cause an unstable leg geometry leading to uncontrollable, non-linear, generation of loads.
A typical WC GS skier on current skis will angulate in such a way that a line from the inside edge of their outside ski through the center of their knee will fall slightly outside their COM. This leg geometry is stable as a sudden increase in load will cause the edge angle to be reduced and the load to be reduced during the abrupt transition giving the athlete time to react appropriately.
The line from the ski edge through the knee of a skier using 7 degrees more knee angulation will fall well inside of the COM. This leg geometry is unstable as a sudden increase in load will cause an increase in the edge angle as the knee collapses inward leading to additional loading, leading to additional knee angulation, more loading, and so on until the skier can react. By the time the skier reacts this load generation can cause serious injury and/or loss of control. This is a non-linear reaction to natural control input and is to be avoided at all costs. Aggravating this problem is the likelihood that more knee angulation will make it more difficult for the inside ski to track parallel with the outside ski since adding more knee angulation on the inside leg is very difficult. This may encourage the skier to transfer weight from the inside ski to outside ski thus increasing the load on the now more vulnerable outside knee.
A supporting fact is that many of the best WC skiers choose skis with larger sidecut radii than the allowed minimum 27m and 23m for men and women respectively. For example Ted Ligety and Lindsey Vonn use 29m and 27m sidecut radii, respectively. It is reasonable to assume that Ted and Lindsey prefer these skis because they encourage postures that are stable, strong and safe. A less accomplished or weaker skier would need more sidecut to achieve the same postures. Too much sidecut for the skier’s ability and strength causes the line of force to fall too far outside the COM. Too little sidecut for the skier’s ability and strength cause the line of force to fall too far inside the COM. Both are undesirable, especially the latter.
The well known geometric relationship between sidecut radius, edge angle and turning radius shows that a 35m ski will fit the FIS description of a ski that is “too aggressive”. Of course it would take some training time on these 35m skis for the athletes to learn that they can ski faster using more knee angulation so it is unlikely to show up in short term tests.
Skiers should be allowed and encouraged to choose skis with sidecut radii that promote the most stable, strongest and safest postures. Coaching guides should be developed to help athletes achieve better postures through a better understanding of the relationship between ski design variables and skier postures.
The geometric relationships described above are well known and understood. The implications can not be responsibly dismissed or ignored.
Higher probability of Phantom Foot ACL injury
The Slip-Catch injury mechanism is identified in the Oslo3 study as the predominant cause of knee injuries on World Cup athletes. It is in my opinion a combination of the well known Phantom Foot and BIAD mechanisms. A review of the video and pictures included with the Oslo studies show a loss of edge grip on the downhill (outside) ski followed by a transfer of weight to the inside (uphill) ski. Prior to the loss of grip the skier’s center of mass (COM) was balanced between the skier’s feet. The sudden loss of grip on the outside ski caused an out-of-balance situation with the center of pressure suddenly moving uphill and forward causing the skier to start falling downhill and backwards. This backward rotation combined with the downhill rotation produces a precessional rotation on the third vertical axis that rotates the skiers mass away from the hill. Of course all these rotations are undesirable and the skier responds by retracting his uphill ski to reduce the forces throwing him out of balance. This allows the downhill ski to reengage. In order to arrest the unwanted rotations the skier naturally pressures the tail of the ski to correct the backwards and downhill rotation, but this creates an uphill rotation acting against the precessional downhill rotation of the skier’s COM (Center of Mass) causing the skier’s upper body to twist downhill, producing an internal-valgus rotation of the knee joint.
The skier is now in a position universally recognized as the final stage before a Phantom Foot ACL rupture except that his leg is relatively straight. Please note the ski sidecut had nothing to do with this scenario. All that is needed is a specific set of out of balance rotations and a lever extending backwards from the foot.
If the ski has less grip in the tail the skier will continue to fall backwards; the ski will skid and continue to rotate uphill due to the slope of the snow surface relative to the skier’s COM. If the skier fights these rotations with sufficient vigor he will most probably rupture the ACL on the downhill knee in a classic Phantom Foot posture. If he gives up the recovery attempt, pulls his body into a safer posture and lets the fall progress naturally he will almost certainly avoid an ACL injury. No WC racer is likely to do this without extensive training on how to avoid the Phantom Foot trap. Ettlinger et al5 have shown that such training can dramatically reduce the likelihood of Phantom Foot ACL injuries.
If the ski has aggressive grip in the tail the skier may be able to reverse the backward and downhill fall, re-center his for-aft balance, quickly enough that he is able to reengage the uphill ski in a way that arrests the downhill rotation without resorting to twisting his upper body in a way that applies the injury producing valgus-internal rotation of the downhill knee.
Supporting the above analysis is a large (34 year, 6,780,940 skier day) epidemiological injury study by Ettlinger et al4 showing that the knee injury rate has increased steadily from 1972 until approximately 1992-1993 unabated by all the equipment developments during that time period. Since 1992-1993 the trend has reversed. Shorter, shaped skis became popular in the 1992 -1993 time frame. Superior edge grip at the tail, stronger self steering effect and the shorter length are the differentiating features of these skis compared to the older skis they replaced. It is therefore reasonable to conclude that one or more of these features lead to the reduced knee injury rate.
It is clear that a less aggressive ski will reduce the forces that appear to contribute directly to the injury in the Slip-Catch scenario. However a less aggressive ski limits the skier’s ability to arrest the rotations that lead to Phantom Foot type injuries.
Equipment related solutions to the above scenarios are not very well understood, but my opinion that a longer ski with less sidecut will increase Phantom Foot injuries is reasonable. The implications can not be responsibly dismissed or ignored without further investigations.
I believe the FIS is recklessly endangering thousands of athletes participating in their sanctioned events by irresponsibly ignoring or dismissing large bodies of scientific evidence, the opinions of many experts and the gut instincts of the vast majority of coaches and athletes. I believe that the FIS is forcing the industry to spend ten’s of millions of dollars to develop and manufacture skis that may turn out to be too dangerous to use.
There are legal and moral consequences to the new equipment rules. The rushed imposition of the new rules should be carefully reconsidered.
David J. Dodge, BSME
1. Bere, Mechanism of ACL Injury in Skiers: Letter to the Editor, The American Journal of Sports Medicine
2. FIS ISS 2006-2011 SAFETY IN ALPINE SKI RACING
3. Bere, Mechanisms of Anterior Cruciate Ligament Injury in World Cup Alpine Skiing, The American Journal of Sports Medicine
4. Ettlinger CF, Johnson RJ, Shealy JE, The Prevention of Knee and Lower Leg Injuries Among Elite Alpine Skiers and Competitors.
5. Ettlinger CF, Johnson RJ, Shealy JE. A method to help reduce the risk of serious knee sprains incurred in alpine skiing. Am J Sports Med.
A discussion of biased assumptions.The quotes below represent some of the assumptions that are the foundation on which FIS built its “proof” that the new equipment rules will reduce injuries.
“In this out-of-balance position, it is reasonable to believe that carving skis may catch the edge more easily than older skis”.1
“Problems with current equipment in terms of safety according to expert opinions:
Equipment is too aggressive
Equipment is too direct in force transmission
Equipment has too strong self steering behavior
Equipment is difficult to control
Equipment is difficult to get from the edge
Equipment allows too high edge angles”.2
“This loading pattern is related to the carving ski’s self-steering effect”.3
“With aggressively carving skis and aggressive snow conditions, large forces are generated when the inside edge catches the snow surface”. 3
A set of less biased assumptions could be:
Without edge grip control is impossible – more control is good.
Without a self-steering effect control is impossible – more control is better.
Athletes will use the tail of the ski whether the ski has a large radius or a short radius - without a tail balance is impossible.
The athlete will find ways to use 100% of their strength to prevent a fall – this is what athletes do.
A predictable ski is a safe ski – the skier has control of all forces.
A more reasonable set of conclusions might be:
Safer skis should discourage skiers from taking body positions known to lead to injury.
Safer skis should have linear responses to control inputs
Aggressive skis = Skis that are too sensitive and/or have non-linear responses to control inputs.