STRATEGIES IN ALPINE SNOWBOARD PARALLEL GIANT SLALOM - A GNSS FIELD STUDY WITH THE SWISS NATIONAL TEAM

INTRODUCTION: Many factors influence performance in alpine snowboarding. Until now, only very few have been scientifically researched. The aim of this study was to investigate the influence of known factors on performance from alpine skiing in alpine snowboarding. For example, the curve phase distribution and the turn radius were examined. METHODS: Using global navigation satellite systems (GNSS), 212 training runs with a total of 3716 turns were recorded in trainings of the Swiss Snowboard World Cup team in the 2020/2021 season (♀ = 5; ♂ = 3). The course setting characteristic was measured in each training session using RTK GNSS sensors. RESULTS: Concerning the influence of the turn phases, no significant difference were found. In flat and medium slopes, the larger the smallest radius of the turn was, the better (lower) the time for this section was. This difference has occurred in the female group. The speed of the athletes was lowest in steep terrain and became higher the flatter the slope was. While speed was increasing on average in toe-edge curves (M = 0.92 km/h, SD = 2.73, n = 1898), a loss of speed resulted on average in heeledge turns (M = -1.26 km/h, SD = 2.71, n = 1814), t(3710) = 24.372, p < .001. DISCUSSION/CONCLUSION: In contrast to alpine skiing, it seems that under certain circumstances, maintaining speed with a larger minimum turn radius is more important for a good performance (short run time), than aiming for a long gliding phase. The differences found between toe and heel edge turns are very clear. This knowledge can serve as a basis for developing technique, strategies as well as equipment in the sport

A cross-sectional observation on maximal eccentric hamstring strength in 7-to 15-year-old competitive alpine skiers

Severe knee injuries are common in alpine skiing and the hamstring muscles are known to counteract the anterior tibial displacement that typically accompanies major injury mechanisms. This study aimed to assess the Maximal Eccentric Hamstring Strength (MEHS) of youth competitive alpine skiers during Nordic Hamstring Exercise (NHE) in terms of dependence of sex, age and biological maturation. A total of 246 7- to 15-year-old skiers were tested with respect to their MEHS using an NHE-based measurement device (Vald Performance, Newstead, Australia). Significantly greater absolute MEHS was observed in skiers of the under 15 years (U15) category compared to skiers under 10 years old (U10) (227.9 ± 61.1 N vs. 142.6 ± 28.9 N; p < 0.001), also when grouped by sex. Absolute MEHS was revealed to be lower in U15 females compared to males (213.5 ± 49.0 N vs. 241.9 ± 68.4 N; p = 0.001); in U10 skiers there was no sex difference. For all age groups and sexes, absolute MEHS values were significantly correlated with age and biological maturation (p < 0.001). However, when normalized to body weight such associations disappeared, which is why this is strongly recommended when testing around their growth spurt. Overall, this study established sport-specific normative reference data that may be of interest to researchers and sport practitioners alike

Deadbug Bridging Performance in 6- to 15-Year-Old Competitive Alpine Skiers—A Cross-Sectional Study

In competitive alpine skiing, a superior antirotation and rear-chain stabilization capacity is essential to constantly remain in dynamic equilibrium while skiing and to counteract the ski-specific adverse loading patterns of the back. As such, skiers' trunk stabilization performance during deadbug bridging (DBB) exercises has been shown to be associated with both skiing performance and overuse complaints of the lower back in skiers under 16 years of age (U16). However, to date, little is known about the corresponding stabilization abilities in younger skiers, i.e., 6- to 15-year-old skiers. As part of a biomechanical field experiment during a national off-snow fitness competition, a total of 101 youth competitive alpine skiers were tested with respect to their trunk stabilization performance during DDB exercise. The maximum contralateral displacement of the pelvic drop during leg lift (DBBdisplacement) was quantified using reflective markers and a motion capture system (Vicon, Oxford, UK). Potential age group and sex differences in DBBdisplacement were assessed using analysis of variance (ANOVA) at p < 0.05. Within each subgroup, the associations of DBBdisplacement with age, anthropometrics and maturity offset were analysed using Pearson's correlation (p < 0.05). Female skiers under 15 years of age (U15) showed better DBB performance than male U15 skiers, while there was no sex difference at the under 10-year (U10) level. In female U10 skiers, DBBdisplacement was moderately associated with body height, while in all other subgroups, no confounding associations with anthropometrics or biological maturation were found. Biomechanically quantifying DBB performance may be considered a feasible and nonconfounded screening test approach in young skiers older than 6 years. Body height may represent a confounding bias in exclusively the U10 female skier cohort and, therefore, should be considered when interpreting the test results. In summary, this study provided sport-specific normative reference data that may be of equal interest to both researchers and sport practitioners. Keywords: athletes; biological maturation; core stability; injury prevention; physical conditioning; physical fitness; skiing; testin

Maximal Eccentric Hamstrings Strength in Competitive Alpine Skiers: Cross-Sectional Observations From Youth to Elite Level

Competitive alpine skiers are subject to substantial risks of injury, especially concerning the anterior cruciate ligament (ACL). During “landing back weighted” episodes, hamstrings may partially counteract the anterior shear force acting on the tibia by eccentrically resisting the boot-induced drawer of the tibia relative to the femur. The aim of the present study was to provide novel descriptive data and sport-specific reference values on maximal eccentric hamstrings strength (MEHS) in competitive alpine skiers from youth to elite level, and to explore potential relationships with sex, age and biological maturation. 170 competitive alpine skiers were investigated: 139 youth athletes (51 females, 88 males; age: 13.8 ± 0.59 years) and 31 elite athletes (19 females, 12 males; age: 21.7 ± 2.8 years). MEHS was assessed by the (Vald Performance, Newstead, Australia). U15 female skiers presented lower MEHS compared to female elite skiers for both limbs (R = 210 ± 44 N vs. 340 ± 48 N, respectively, p &lt; 0.001, and L = 207 ± 46 N vs. 303 ± 35 N, respectively, p &lt; 0.001). Similarly, lower MEHS was observed in U15 male skiers compared to male elite skiers for both limbs (R = 259 ± 51 N vs. 486 ± 62 N, respectively, p &lt; 0.001, and L = 258 ± 57 N vs. 427 ± 54 N, respectively, p &lt; 0.001). Correlations between MEHS and chronological age were modestly significant only for the U15 group (r = 0.37 and p &lt; 0.001). When the correlations for the U15 group were performed between MHES and maturity offset (obtained from the calculation of biological age, i.e., age at peak height velocity), statistical significance was reached by all the correlations run for 3 variables (Males &lt; 0: r = 0.59, p &lt; 0.0001; Males &gt; 0: r = 0.70, p &lt; 0.0001; and Females &gt; 0: r = 0.46, p &lt; 0.0001, start of maturity offset = 0). This cross-sectional description of MEHS in alpine skiers from youth to elite level highlights the importance of biological maturation for MEHS values in youth athletes and presents novel data that may offer insights into new approaches for injury prevention

Biological Maturity Status, Anthropometric Percentiles, and Core Flexion to Extension Strength Ratio as Possible Traumatic and Overuse Injury Risk Factors in Youth Alpine Ski Racers: A Four-Year Prospective Study

The aim of the present study was to investigate prospectively the role of biological maturity status, anthropometric percentiles, and core flexion to extension strength ratios in the context of traumatic and overuse injury risk identification in youth ski racing. In this study, 72 elite youth ski racers (45 males, 27 females) were prospectively observed from the age of 10 to 14 years. Anthropometric parameters, biological maturity status, and core flexion to extension strength ratios were assessed twice per year. Type and severity of traumatic and overuse injuries were prospectively recorded during the 4 years. Generalized estimating equations were used to model the binary outcome (0: no injury; 1: ≥1 injury). Factors tested on association with injury risk were sex, relative age quarter, age, maturity group, puberty status, core flexion to extension strength ratio, height percentile group, and weight percentile group. In total, 104 traumatic injuries and 39 overuse injuries were recorded. Age (odds ratio (OR) = 3.36) and weight percentile group (OR = 0.38) were significant risk factors for traumatic injuries (tendency: pubertal status). No significant risk factor for overuse injuries was identified (tendency: maturity group, puberty status, height percentile group). Future studies should focus on identifying risk factors for overuse injuries; growth rates might be of importance

Strength deficits of the hamstrings following surgery on the anterior cruciate ligament: a case-control ­study of elite alpine ski racers

Hintergrund: Der Stand der Forschung zeigt auf, dass Kreuzbandverletzungen im alpinen Skirennsport häufig vorkommen. Der ischiocruralen Muskulatur wird eine wichtige Rolle zum Schutz des vorderen Kreuzbandes (VKB) attestiert. Dabei ist v.a. die exzentrische Muskelaktivität von grosser Bedeutung, da sie in Dauer und Intensität gegenüber der konzentrischen Muskelaktivität im alpinen Skirennsport vorherrschend ist. Ziel dieser Studie war herauszufinden, ob Elite Skirennfahrer nach einer VKB-Plastik exzentrische Kraftdefizite der ischiocruralen Muskulatur aufweisen. Methode: Es wurde eine Case-Control-Studie zwischen Skirennfahrer 49 ± 41 Monaten postoperativ nach einer VKB-Plastik und gesunden Skirennfahrer durchgeführt. Im Seitenvergleich wurde die exzentrische Gesamtkraft beider Beine der ischiocruralen Muskulatur der VKB- (n=18) mit der Kontrollgruppe (n=70), ferner die Kraft des operierten Beines einerseits mit der gesunden Seite und andererseits mit dem Mittelwert der gesunden Gruppe verglichen. Die exzentrische Kraft wurde während der Übung Nordic-Hamstrings auf dem NordBord gemessen. Gruppenvergleiche wurden mittels ANOVA mit Bonferroni Post-hoc Tests analysiert. Mittels multipler linearer Regressionsanalyse wurden zudem die relevanten unabhängigen Einflussvariablen zur Erklärung der exzentrischen Gesamtkraft und des Limb Symmetry Index ermittelt. Ergebnisse: Die relative exzentrische Gesamtkraft beider Beine der ischiocruralen Muskulatur der VKB-Gruppe war signifikant geringer als diejenige der Kontrollgruppe (p=0.031). Weiter war das operierte Bein bei der relativen exzentrischen Kraft signifikant schwächer als der Mittelwert der Kontrollgruppe (p=0.024). Auch der Limb Symmetry Index war bei den unilateral Operierten signifikant grösser (p=0.016) als bei den Gesunden und den bilateral Operierten. Die Unterschiede in der exzentrischen Gesamtkraft zwischen den Athleten liess sich zu 56% durch die drei unabhängigen Variablen Operation, Alter und Geschlecht erklären. Die Unterschiede im Limb Symmetry Index zwischen den Athleten konnte zu 18% durch die drei unabhängigen Variablen Operation, exzentrische Gesamtkraft beider Beine und Körpergrösse erklärt werden. Schlussfolgerung: Skirennfahrer haben auch mehrere Jahre nach einer VKB-Plastik persistierende Defizite in der exzentrischen Kraft der ischiocruralen Muskulatur verglichen mit gesunden Skirennfahrern. Daher sollte dem Training der exzentrischen Kraftfähigkeit der ischiocruralen Muskulatur während der Rehabilitation aus Sicht der Autoren mehr Aufmerksamkeit gewidmet werden. Die vorgestellte Messmethode ist einfach, praktikabel und kostengünstig. Um den Einfluss der Kraft der ischiocruralen Muskulatur auf Kreuzbandverletzungen besser verstehen zu können, sind weitere Studien nötig.Background: Research to date clearly shows that injuries to the cruciate ligaments are a frequent occurrence in alpine ski racing. The hamstrings play an important role in protecting the anterior cruciate ligament (ACL). Here eccentric muscle activity, in particular, is of great significance as it plays a more important role in terms of duration and intensity than concentric muscle activity in alpine ski racing. The aim of this study was to establish whether the hamstrings of alpine ski racers show eccentric strength deficits following surgery on the anterior cruciate ligament. Methods: A case-control study was performed with athletes who had undergone surgery on the anterior cruciate ligament 49 ± 41 months previously and healthy ski racers. The total eccentric strength of both legs measured in the hamstrings supporting the ACL (n=18) was compared with the healthy group (n=70); the strength of the operated leg was also compared with the healthy leg and with the mean for the healthy group. Eccentric strength was measured during the Nordic hamstrings exercise performed on the NordBord hamstring testing system. Group comparisons were performed using ANOVA and Bonferroni Post-hoc analyses. Multiple linear regressions were used to assess the relevant independent variables explaining total eccentric strength and Limb Symmetry Index. Results: The relative total eccentric strength of both legs in the hamstrings of the ACL group was significantly lower than in the healthy group (p=0.031). In addition, the relative eccentric strength of the operated leg was significantly lower compared to the healthy group (p=0.024). Leg asymmetry was also significantly greater in athletes who had undergone surgery on one leg (p=0.016) than in healthy subjects and athletes who had undergone surgery on both legs. 56% of the total eccentric strength of both legs could be explained by surgery, age and gender. 18% of the leg asymmetry was explained by the variables surgery, total eccentric strength of both legs and height. Conclusion: Several years after anterior cruciate ligament surgery, ski racers still have deficits in terms of the eccentric strength of their hamstrings compared with healthy ski racers. Therefore more attention should be paid during rehabilitation to the eccentric strength of the hamstrings with a view to strengthening and testing them. Measurement using the NordBord system is suitable for routine monitoring of eccentric strength. Further studies are needed to improve understanding of the influence of hamstrings strength on cruciate ligament injuries

Design parameters and landing impacts of snow park jumps in Switzerland

Objectives: Design parameters and landing impacts for selected snow park jumps in Switzerland were compared with the parameters recommended to increase the jumps’ safety by the Swiss Council for Accident Prevention (BFU). High impact zones were identified to help snow park shapers optimize the design of their jumps. A rough estimate of the influence of snow hardness on landing impacts was also provided. Design: During the 2020/2021 winter season three-dimensional geometries of 23 jumps were captured using differential global navigation satellite system and terrestrial laser scanning. A point mass model was used to numerically calculate trajectories. The equivalent fall height (eFH) was used to quantify landing impacts and an empiric snow-deformation function was applied to take the effect of snow hardness into consideration. Workshops were held to discuss results and transfer findings. Methods: 2D-profiles of the jumps were estimated by projecting the captured 3D position data onto the longitudinal cross-section plane. Table and landing geometry were smoothed and interpolated to a spatial resolution of 0.1 ​m, while the kicker was fitted with a 2nd order polynomial. Trajectories were numerically calculated for take-off speeds from 6 to 17.6 ​m ​s−1 including aerodynamic forces using the Runge-Kutta method. The calculated eFH at the landing points were used to divide the landing into low-impact, medium-impact, and high-impact zones. Results: Medium sized jumps had a low-impact zone of sufficient length (>6 ​m) and eFH smaller than 1.5 ​m throughout the entire table meeting the BFU recommendations. Nevertheless, critical eFH larger than 1.5 ​m, were obtained when take-off speeds increased by only 1.14 ​m ​s−1. Large jumps had low-impact zone lengths in accord with the recommendations (>9 ​m), but high eFH (2.3–3.4 ​m) occurred for table landings. 10 of the 13 XL-jumps had long low-impact zones of approximately 12–15 ​m. Besides the risk of high impact landings towards the end of the landing area, as found similarly for the smaller jumps, portions of XL-jumps had very high eFH (2.6–4.6 ​m) for table landings. Conclusions: The study confirmed the existing BFU recommendations of size categories, design parameters and landing impacts limits as prevalent and practicable and provided knowledge for future safety recommendations. Modifying table geometries and taking measures to limit the in-run speeds would help reduce landing impacts, and the hazard due to hard snow conditions should also be considered

The effect of foot setting on kinematic and kinetic skiing parameters during giant slalom: A single subject study on a Paralympic gold medalist sit skier

Objectives: Aim was to study the effect of monoski foot adjustment on kinematic and kinetic skiing parameters expressing sit skier’s technique. Design: Independent variable was skier position with respect to bindings, acting on position of monoski foot sole clamp. Front (F), Mid (M) and Rear (R) settings changed with intervals of 20 mm. Course time, skiing speed, Ground Reaction Forces (GRFs) magnitude and point of application and damper stroke were dependent variables. Method: A Paralympic monoski was equipped with a dynamometric binding plate measuring GRFs, roll and pitch moments. A Paralympic gold medalist (LW10-1) was involved. Skier trajectory and gates location were measured by a differential global navigation satellite system (GNSS) in steep and medium steep slope portions. The athlete performed two giant slalom runs for each foot setting the same day. Results: GRFs, center of pressure (COP) and variations with foot settings were measured. Peaks values up to 3.36 times the total weight and damper speed of 675 mm/s in compression were found. Fastest runs, highest peak loads and best subjective ratings were recorded with F setting. COP mean values were influenced by foot adjustments. GRFs in left turns were 54% larger than in the right turns with F setting on steep slope. Conclusions: The monoski foot adjustment influenced kinematic and kinetic skiing, with F setting showing best results. A skier asymmetric behavior between right and left turning was discovered. Findings can support the design of monoskis for a wider dissemination of Paralympic alpine sit skiing