By Gerhard Ruedl and Martin Burtscher

Department of Sport Science, University of Innsbruck, Austria

Take home message: Are women’s bindings set 15% too high – and increasing risk of knee injury?

Are you one of the over 200 million recreational skiers practicing this fascinating sport on snow covered ski slopes during the winter months? You might know that the injury risk among recreational skiers halved during the past 20 years.

It’s true that release bindings largely prevented tibia and ankle fractures, at least in adult skiers, knee injuries still represent the major injury type — about 1/3 of all ski injuries [1,2]. Female skiers have twice the knee injury risk and an about  three times the ACL rupture risk compared to males. Importanty, knee injured females still report an about 20 percent points higher failure of binding to release when compared to males [1,3].

According to the official ski standards (ISO 11088 standard) [4] for binding values, skiers have to differentiate between skiing speed (slow to moderate vs. fast), terrain (gentle to moderate vs. steep) and skiing style (cautious vs. aggressive) to classify themselves into one out of three skiing types without considering any sex-specific differences.[4]

Assume a male and a female skier of equal age, height, and weight and of equal ski shoe sole length, and both classifying themselves as type-3 skier (fast speed, steep terrain, aggressive style). They both would get the same binding setting values without considering any sex factor. However, there are at least two potential sources of error which could represent an explanation for the higher number of failure of binding release among female skiers.

First, a recent study by Brunner et al.[5] found that males, more skilled skiers, and risky skiers perceived their actual speed as fast, moderate and slow when skiing up to 10 km/h  faster compared to females, less skilled and cautious skiers. Therefore, one might suspect that compared to a ‘slow to moderate’ or ‘fast’ male skier the binding setting for a ‘slow to moderate’ or ‘fast’ skiing female is too high resulting in a higher number of failure of binding release as sexes seem not to differ neither with regard to the date of last binding adjustment,[6] nor with regard to not correctly adjusted bindings,[7] nor with regard to self-reported types of falling in the case of an ACL injury.[1,6]

Second, a study by Werner and Willis[8] found that muscle strength is highly correlated with the ability to release the ski binding in a self-release test. Due to the equal weight of the male and female skier in the aforementioned example it has to be considered that the weight-to-strength ratio is negatively influenced by the higher fat mass in females[9] maybe partly explaining the sex difference in the lack of binding release due to less muscular strength among females.

Although the ISO 11088 standard[4] does not consider female sex, it is important to know, especially for female recreational skiers, that according to ISO 11088 standard point B.4 the binding setting may be lowered by 15% upon request of the skier in the following cases:

1. a) Skiers who have satisfactory experience with lower settings regarding the manufacturer’s recommendations may request settings based on their experience;
2. b) Skiers who have skiing experience without inadvertent releases may request a setting up to 15% lower than recommended by the manufacturer, approximately achieved by moving one line up in the Table B 1;
3. c) Skiers having certain characteristics such as neutral skiing technique, defensive attitude, high degree of control, may request a setting up to 15% lower than recommended by the manufacturer, approximately achieved by moving one line up in the Table B 1.

Regarding point B.4 c), the terms “neutral skiing technique” and “defensive attitude” are very subjective and therefore may strongly vary between individuals and sex. When assuming that the terms “neutral skiing technique” and “defensive attitude” are – according to the ISO 11088 determination of skier type[4] – largely synonymous with a cautious (or smooth) skiing style in contrast to an aggressive (or risky) skiing style, our findings of an earlier study[10] that self-reported risk taking behaviour on ski slopes is independently associated with male sex (OR: 1.99) and a higher mean skiing speed (53 vs 45 km/h) are gaining in importance. In other words that means that a cautious behaviour on ski slopes is associated with female sex and a lower mean skiing speed.

In a second study[11] we demonstrated that mean skiing speed (measured with a radar speed gun) of more than 2100 skiers and snowboarders is significantly lower among female compared to male skiers and snowboarders (40 vs. 47 km/h).  In addition, we interviewed a subgroup of about 550 skiers and snowboarders and divided these persons into a faster (59 km/h mean speed) and slower skiing group (36 km/h mean speed).[11] The slower group was independently associated with female sex, higher age, lower skill level, snowboarding (vs. skiing) and cautious behaviour.[11] In a third study we evaluated whether self-reported risk taking behaviour on ski slopes was associated with the personality trait sensation seeking.[12] Again, self-reported cautious behaviour was associated with female sex, higher age, lower skill level, and less mean score of Sensation Seeking.[12]

Taken together, our results clearly highlight that female sex is associated with a more cautious behaviour and a less mean skiing speed on ski slopes indicating that the terms “neutral skiing technique” and “defensive attitude” may especially apply to female skiers.

Therefore, keeping in mind the clearly higher failure of binding to release among female skiers suffering from knee injuries, a 15% lower ski binding setting would likely be appropriate for the majority of female recreational skiers.

References

1. Ruedl G, Helle K, Tecklenburg K, et al. Factors associated with self-reported failure of binding release among ACL injured male and female recreational skiers: A catalyst to change ISO binding standards? Br J Sports Medicine (in press)
2. Burtscher M, Ruedl G. Favourable Changes of the Risk-Benefit Ratio in Alpine Skiing. Int. J. Environ. Res. Public Health 2015; 12 (86): 6092-6097. doi: 10.3390/ijerph12060000x
3. Greenwald RM, Toelcke T. Gender differences in alpine skiing injuries: a profile of the knee-injured skier. In: Johnson RJ, Mote CD, Ekeland E, eds. Skiing Trauma and Safety, 11^th J. ASTM Intl. 1997, Balitmore:111-21.
4. International Organization for Standardization. Assembly, adjustment and inspection of an alpine ski/binding/boot (S-B-B) system ISO 11088, Geneva, Switzerland, 2013
5. Brunner F, Ruedl G, Kopp M, et al. Factors associated with the perception of speeds among recreational skiers. PloS One. 2015 Jun 29; 10(6):e0132002. doi: 10.1371/journal.pone.0132002. eCollection 2015.
6. Ruedl G, Webhofer M, Linortner I, et al. ACL injury mechanisms and related factors in male and female carving skiers: a retrospective study. Int J Sports Med. 2011;32: 801-6.
7.  Ruedl G, Pocecco E, Sommersacher R, et al. Differences between actual and recommended binding z-values. In: Müller E, Lindinger S, Stöggl T, Pfusterschmied S, eds. 5th ICSS-Congress, 14.-19. Dec. 2010, St. Christoph, Austria. Book of abstracts: 141.
8. Werner S, Willis K. Self-release of ski-binding. Int J Sports Med. 2002;23:530-35.
9. Sinning WE. Body composition and athletic performance. In: Clarke DH, Eckert HM, eds. Limits of human performance. The academy papers. Champaign, 1985: 45-56.
10. Ruedl G, Pocecco E, Sommersacher R, et al. Factors associated with self reported risk taking behaviour on ski slopes. British Journal of Sports Medicine 2010, 44 (3): 204-206. 11.   Ruedl G, Sommersacher R, Woldrich T, et al. [Mean speed of winter sport participants depending on various factors]. Sportverletz Sportschaden. 2010;24:150-53.
11. Ruedl G, Abart M, Ledochowski L, et al. Self-reported risk taking and risk compensation in skiers and snowboarders are associated with sensation seeking. Accid Anal Prev. 2012;48:292-96.

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Gerhard Ruedl  is a Senior Assistant Professor, Department of Sport Science, University of Innsbruck, Austria. His research interests include: risk factors (e.g. risk-taking behavior) leading to injuries and use of protective equipment (e.g. helmets) among alpine skiers and development of motor performance and weight status among school children

Martin Burtscher is a Full Professor at the Department of Sport Science, University of Innsbruck, Austria. His research interests include: exercise physiology with emphasis on mountain sports activities; physiological and pathophysiological effects of altitude and hypoxia; epidemiology and prevention of accidents and emergencies in skiing and mountaineering; life-style interventions in health and disease mainly focusing on exercise, environmental and nutritional aspects.