A SEX COMPARISON OF RELEASE TORQUES DURING A SELF RELEASE TEST OF SKI BINDINGS ADJUSTED TO THE ISO 11088 STANDARD Markus Posch, Robert Eberle, Gerhard Ruedl ISSS 2015 San Vito
INTRODUCTION Female recreational skiers have twice the knee injury prevalence of male skiers and the ACL injury risk is 3 times greater in female skiers. Ekeland and Rodven, J. ASTM Int. 2012 LaPorte et al., J. ASTM Int. 2012 Male skiers with an ACL injury reported in 55-67% a non-release of bindings during accident compared to female skiers with 74-88%. Greenwald and Toelcke, J. ASTM Int. 1997 LaPorte et al., J. ASTM Int. 2008 Ruedl et al., Int. J Sports Med 2011 The ISO 11088 standard for binding setting values does not consider female sex despite existing sex differences, e.g. Hormonal, anatomical, and neuromuscular risk factors, Mean speed on slopes and speed perception. Hewett et al., Am J Sports Med 2006, 2007 Ruedl et al., Am J Sports Med 2012 + ISSS 2015
INTRODUCTION The most common type of fall among knee injured skiers seems a forward fall with body rotation ( valgus external rotation ) since the introduction of the short and shaped carving skis. Ruedl et al., Int. J Sports Med. 2011 Shea et al., The Orthop J Sports Medicine. 2014 (Natri et al. 1999) Males and females skiers did not differ regarding the self reported type of fall leading to an ACL injury. Ruedl et al., Int. J Sports Med. 2011 This type of fall corresponds well with the self release test of the ski binding which can be done By an inward twist of the foot and leg. Jorgensen et al., KSSTA 1998 (Jorgensen et al. 1998)
INTRODUCTION Aim of the study: to compare torques during a selfrelease test of ski bindings adjusted according to the ISO 11088 standard between sexes. Hypothesis: Considering the fact that the ISO 11088 standard for binding setting values does not contain any sex factor, we hypothesised that there are no sex differences a) within the frequency of binding releases, and b) in the amount of generated torques during binding nonrelease.
METHODS The day before: Ski binding adjustment according to the ISO 11088 standard with a Wintersteiger Speedtronic: Age Height Weight Ski shoe sole length Type of skier
METHODS Testday: 1) Bioelectrical Impedance Analysis for calculating relative Body Cell Mass (BCM). 3) Self release test on a Kistler force plate: each leg 3 times 2) Isometric leg strength test with a knee angle of 100. EMG dominant leg (6 males, 8 females): - Vast. Medialis - Vast. Lateralis - Biceps Femoris Relativized by MVC
METHODS/RESULTS Torques calculated via the force plate were relativized to torques calculated by the binding adjustment device (RRT: rel. release torque). Statistics: Chi-square tests, independent t-tests/mann-whitney-u-tests, Spearman/Pearson correlation coefficient. Subjects: Males (n=8) Females(n=9) P-value Age [yrs] 23.3±1.3 21.8±1.6 <.001 Height [m] 1.8±0.1 1.7±0.1 <.001 Weight[kg] 76.6±3.9 57.9±2.8 <.001 BMI [kg/m 2 ] 23.6±2.5 21.3±1.0 <.001 BCM [% BW] 47.1±3.0 44.4±3.2.068 Dominant leg strength[n/kg] 16.2±3.3 15.8±2.4.760
RESULTS 7/8 (87.5%) of males and 3/9 (33.3%) of females released their bindings at least once with both legs (p=.024). 37.5% of male trials (n=48) and 75.9% of female trials (n=54) showed a binding non release (p<.001). RRT [%] 120 100 80 60 40 * Binding released RRT [%] 100 80 60 40 20 0 92,1 72,9 20 0 71,2 59,3 male (n=48) female (n=54) male trials (n=18) female trials (n=41) Fig 1: Sex comparison of RRT of all trials (p<.001) Fig 2: Sex comparison of RRT of binding nonrelease trials (p=.065)
RESULTS Correlations between body weight, body cell mass (BCM) and isometric strength of the dominant leg: BCM [r (p)] Dominant leg strength [r (p)] Body weight BCM Total group (n=17) Males (n=8) Females (n=9) Total group (n=17) Males (n=8) Females (n=9).768 (<.001).663 (.004).549 (.159).892 (.003) -.141 (.718) -.237 (.539).685 (.002).786 (.021).050 (.898)
RESULTS 45 * 45 40 40 * * 35 35 30 30 EMG [% MVC] 25 20 15 EMG [% MVC] 25 20 15 10 10 5 5 0 m.biceps fem. m.vastus lat. m. vastus med. 0 m.biceps fem. m.vastus lat. m. vastus med. male trials (n=12) female trials (n=6) male trials (n=6) female trials (n=18) Fig. 3: Sex comparison of EMG activity of binding release trials Fig. 4: Sex comparison of EMG activity of binding non-release trials
Markus Posch Msc DISCUSSION Males released their bindings adjusted to the ISO 11088 standard significantly more often compared to females (88 vs. 33%), although no sex difference within isometric leg strength. no sex difference within BCM (% body weight). The ISO 11088 standard uses the weight method to determine leg strength for binding release values: No significant correlations between body weight, BCM, and leg strength were found among females! Weight-to-strength ratio is negatively influenced by the higher fat mass in females (Sinning 1985). How appropriate is the weight method for binding setting values among female skiers?
Markus Posch Msc DISCUSSION Mean RRT of binding non-release trials was about 17% lower among females compared to males (59 vs. 71%, p=.068). Lowering the binding settings according to the ISO 11088 standard by 15% for female skiers decrease the risk of knee injuries among females. LaPorte et al., J. ASTM Int. 2000, 2003, 2008 Future study: Measuring RRT of 15% lower binding settings among females.
Markus Posch Msc DISCUSSION EMG-acitivty during release trials was hamstring-dominated among males and quadriceps dominated among females: The medial hamstrings of a male skier were the most active muscles during an inward release twist of the ski binding. Werner and Willis, Int J Sports Med 2002 Females show a lower hamstring to quadriceps activation ratio during jumping or cutting activities. Urabe et al., Knee 2005 Bencke and Zebis, J Elektromygr Kinesiol.2011 Quadriceps dominance as a ACL risk factor: females appear to preferentially use the quadriceps more than males in order to stiffen and stabilize the knee joint. Hewett et al., N Am J Sports Phys Ther 2010
Markus Posch Msc DISCUSSION Limitations: Small number of participants will be increased in next months. Mean age of study cohort was clearly lower compared to ACL injured skiers male and female skiers with a higher mean age will be tested in the next winter season. Transferability of a self release test in the lab into binding releases during an accident while skiing? However, checking binding function by performing a self release test seems to decrease injury risk among alpine skiers (Ekeland et al. 1993, Jorgensen et al. 1998).
Markus Posch Msc Conclusion Males were significantly more often able to self release their binding compared to females, although sexes did not differ within relative leg strength and relative BCM, but did differ within EMGactivity. In contrast to males, no significant correlations between body weight, BCM and isometric leg strength were detected among females. These findings should be considered when discussing the introduction of a sex factor into the ISO 11088 standard (weight method) for setting binding release values. Thank you!