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Why not consider a sex factor within the ISO 11088 ski binding setting standard?
  1. Gerhard Ruedl,
  2. Martin Burtscher
  1. Department of Sport Science, University of Innsbruck, Innsbruck, Austria
  1. Correspondence to Dr Gerhard Ruedl, Department of Sport Science, University of Innsbruck, Fürstenweg 185, 6020 Innsbruck, Austria; gerhard.ruedl{at}uibk.ac.at

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In recreational alpine skiing, about one-third of all injuries are related to the knee joint.1 However, female recreational skiers have twice the knee injury incidence of male skiers and the ACL injury risk is even three times higher in female skiers.1 A total of 60%–80% of knee injuries after a self-inflicted fall seem to be associated with a failure of binding release and again with decisive sex differences.1 Female skiers reported about 20% more often failure of binding release than men.1 In an epidemiological study including more than 1300 injured recreational skiers, self-reported failure of binding release was significantly higher in women when compared with men (51% vs 32%), irrespective of the injured body part.2 Noteworthy, among uninjured skiers, three times more women were unable to release their ski bindings during a self-release test even though their bindings were currently adjusted according to the official ski standards (International Organization for Standardization (ISO) 11088) for binding setting values.3

Strong thigh muscles seem to be a prerequisite for the ability to self-release the ski binding especially when set at a high level. Werner and Willis4 convincingly demonstrated a close relationship between thigh muscle torques and the ability to self-release the ski binding. Whereas the quadriceps torque was more important in men this was true for the hamstring torque in women.4 In addition, self-release seems to be rather possible when using the dominant leg.4

Current ski bindings are typically designed to release during a simple forward fall (upward release function of the heel piece) or during a forward fall with body rotation (side release function of the toe piece of the ski binding). Therefore, one may speculate that the higher number of binding release failure among women with knee injury results from backward falls where most ski bindings do not release. However, Ruedl et al 1 demonstrated an equal distribution of forward and backward falls among a cohort of 160 male and 337 female skiers with an ACL injury. Solutions can be seen in future standards to measure the relative dynamic forward retention function of ski bindings and the development of mechanical three-mode bindings with additional lateral heel release that can release below the ACL rupture limit or the development of mechatronic ski bindings containing both mechanical parts and electronic components which should be able to correct the individual release level according to the individual skiing style and skiing speed.5 6

According to the ISO 11088 standard, skiers’ body mass, height, age category, ski boot sole length and self-estimated skier type but not sex are considered for binding setting. That means, a male and a female skier of comparable age, height and body mass with a similar ski boot sole length, both classifying themselves as the same skier type, would get the same binding setting (z-)values. This would also be true for a woman with a body mass of 67 kg and a height of 167 cm and a man with 78 kg and 178 cm, as the ISO 11088 table allows such a broad range for the same category of release values. In addition, the body mass-to-strength ratio is negatively influenced by the higher fat mass in women7 and there are other sex differences associated with knee/ACL injury risk, mostly to the disadvantages of women, for example, hormonal fluctuations during a woman’s menstrual cycle, higher q-angle, lower relative strength of the lower limbs, lower hamstrings-to-quadriceps ratio, lower stiffness of the knee joint, worse tensile properties of the ACL and lower centre of mass displacement.8–10

Regarding the description of the three skier types according to the ISO 11088 standard, skiers have to differentiate between skiing speed (slow to moderate vs fast), terrain (gentle to moderate vs steep) and skiing style (cautious vs aggressive). Brunner et al 11 found that the perception of skiing speed (as fast, moderate or slow) depends on sex, skill level and risk-taking behaviour. From the same data, sex differences have been calculated with regard to skiing speed according to self-reported risk-taking behaviour and skill level (presented at the 22nd Conference of the International Society of Skiing Safety in April 2017 in Innsbruck, Austria). When compared with their male counterparts, female cautious skiers (50.2±13.9 vs 40.5±12.6 km/hour, P<0.001) and female risky skiers (56.4±13.6 vs 48.4±9.6 km/hour, P<0.001) showed a significantly lower (14%–19%) mean skiing speed. In addition, with respect to skill level, female beginner/intermediate skiers (46.6±11.5 vs 38.7±12.5 km/hour, P=0.001) and female advanced/expert skiers (53.7±14.5 vs 44.3±12.0 km/hour, P<0.001) showed a significantly lower mean skiing speed (17%–18%) compared with their male counterparts.

In conclusion, according to the ISO 11088 standard both a female and a male skier of the same skier type can have the same binding setting (z-)value although they differ significantly with regard to body mass and height, relative strength, knee stability and mean skiing speed. Noteworthy, the ISO 11088 standard accepts a 15% reduction of binding setting value on skiers’ request and there exists evidence that this reduction could decrease the injury risk of lower extremities, mainly knee injuries, without increasing the number of inadvertent binding release.12 However, this fact is largely unknown among skiers. Thus, implementing a correction factor (release torque reduction by 15%) for women within the ISO 11088 ski binding setting standard will likely be associated with a lower knee injury risk in female recreational skiers. In addition, an adequately performed self-release test (with both the dominant and the non-dominant legs) seems to be a valuable complementary control test of the ability to release the bindings, regardless of algorithm’s.

References

Footnotes

  • Competing interests None declared.

  • Provenance and peer review Not commissioned; externally peer reviewed.