On-Field Ski Kinematic According to Leg and Discipline in Elite Alpine Skiers

Muscle-tendon unit length changes in knee extensors and flexors during alpine skiing

This study characterised the thigh muscle-tendon unit length variations (MTUv) in elite alpine skiing. MTUv were modelled for seven muscles from knee and hip angles in 17 national team skiers during 1602 cycles (546 Slalom (SL), 908 Giant-Slalom (GS), 136 Super-Giant (SG) and 12 Downhill (DH) cycles). The biarticular rectus femoris showed a dynamic pattern on both legs, especially in SL. On the other side, vastii displayed a stable length on the inside leg in all disciplines (37-46% of the cycle), contrasting with their dynamic behaviour on the outside leg being quasi-static for only 3% (SL) to 27% (DH) of the cycle. SL showed the largest amplitude of MTUv followed by GS, SG and DH. For vastus lateralis, MTUv was ~60%Lr.s-1 in SL but only ~12%Lr.s-1 in DH. In SL, a fine desynchronisation between both joints led to nearly constant MTUv (slow lengthening lasting ~45-51% of the cycle) for the biarticular hamstrings separated by faster variations during turn switch from outside to inside leg. In summary, biarticular MTUv were not characterised by single-joint behaviours, suggesting that extrapolating contraction regimen from knee joint only is not accurate in alpine skiing.

Bioimpedance Vector Analysis-Derived Body Composition Influences Strength and Power in Alpine Skiers

Purpose: Alpine ski racing is a complex sport where no single factor can exclusively account for performance. We assessed body composition, using bioelectrical impedance vector analysis (BIVA), and our purpose was to study its influence on the strength and power profile of young alpine skiers. Methods: Anthropometric measurements and advanced BIVA parameters were recorded on eighteen alpine ski racers (6 females/12 males; 17.0 ± 1.3 years; 172.2 ± 9.3 cm; 68.5 ± 9.8 kg). Dynamic force and power were assessed using countermovement jumps (CMJ), while maximal isometric strength was evaluated for hip flexion-extension and abduction-adduction movements. Stepwise regression models examined the relationship between BIVA-derived parameters and strength/power variables. Results: Body cellular mass (BCM) positively related to jump height (p = .021, R2 = 74%), jump momentum (p < .001, R2 = 89%), reactive strength index modified (p = .026, R2 = 75%) and peak concentric power (p < .001, R2 = 82%), while intracellular water (ICW) related to peak eccentric (p < .001, R2 = 76%) and concentric force (p < .001, R2 = 77%) as well as to concentric rate of force development together with the phase angle (PhA) (p = .008, R2 = 79% and R2 = 0.015). Regarding isometric assessment, ICW was a significant predictor for all four movement directions, and PhA contributed to hip adduction strength. Conclusions: Body composition, particularly BCM and ICW, significantly predict force- and power-related factors in young alpine skiers.

We know a lot about little and little about a lot: A contextualized scoping review on injury prevention in alpine ski racing

BACKGROUND

Our goal was to summarize and contextualize the available literature on alpine ski racing injury epidemiology, injury etiology, injury prevention measures, injury prevention context, and implementation issues.

MATERIALS AND METHODS

We searched four electronic databases using predetermined search terms. We included original studies that assessed injury, injury risk factors, and injury mechanisms, and assessed and reported the effect of an injury prevention measure in alpine ski racing. Two authors independently conducted title-abstract screening, and one performed the full-text review. For data synthesis and categorization, we used the Translating Research into the Injury Prevention Practice framework and a modified and adapted version of the Haddon matrix.

RESULTS

Of the 157 included studies, most corresponded to injury epidemiology and etiology, whereas few studies encompassed injury prevention measure development, implementation and evaluation. Preventive interventions targeting equipment, rules and regulations, course design and snow preparation were the most prevalent in the literature. Furthermore, various contextual factors in the current literature have been found, including gender, competition level, countries and federations, and time periods within a season.

CONCLUSIONS

We provided an in-depth and comprehensive overview of the current state-of-the-art in the alpine ski racing context. We know a lot about little and little about a lot across all the areas associated with injury prevention in such context. The limitations in the literature yield a road map for designing future injury prevention studies to address the key gaps identified. A more comprehensive context-driven approach throughout all stages of injury prevention would benefit the ultimate implementation of effective preventive strategies.

Association of Gene Variants with Seasonal Variation in Muscle Strength and Aerobic Capacity in Elite Skiers

Background: The training of elite skiers follows a systematic seasonal periodization with a preparation period, when anaerobic muscle strength, aerobic capacity, and cardio-metabolic recovery are specifically conditioned to provide extra capacity for developing ski-specific physical fitness in the subsequent competition period. We hypothesized that periodization-induced alterations in muscle and metabolic performance demonstrate important variability, which in part is explained by gene-associated factors in association with sex and age. Methods: A total of 34 elite skiers (20.4 ± 3.1 years, 19 women, 15 men) underwent exhaustive cardiopulmonary exercise and isokinetic strength testing before and after the preparation and subsequent competition periods of the World Cup skiing seasons 2015-2018. Biometric data were recorded, and frequent polymorphisms in five fitness genes, ACE-I/D (rs1799752), TNC (rs2104772), ACTN3 (rs1815739), and PTK2 (rs7460, rs7843014), were determined with specific PCR reactions on collected DNA. Relative percentage changes of cardio-pulmonary and skeletal muscle metabolism and performance over the two seasonal periods were calculated for 160 data points and subjected to analysis of variance (ANOVA) to identify hypothesized and novel associations between performance alterations and the five respective genotypes and determine the influence of age × sex. A threshold of 0.1 for the effect size (h2) was deemed appropriate to identify relevant associations and motivate a post hoc test to localize effects. Results: The preparation and competition periods produced antidromic functional changes, the extent of which varied with increasing importance for anaerobic strength, aerobic performance, cardio-metabolic efficiency, and cardio-metabolic/muscle recovery. Only peak RER (-14%), but not anaerobic strength and peak aerobic performance, and parameters characterizing cardio-metabolic efficiency, differed between the first and last studied skiing seasons because improvements over the preparation period were mostly lost over the competition period. A number of functional parameters demonstrated associations of variability in periodic changes with a given genotype, and this was considerably influenced by athlete "age", but not "sex". This concerned age-dependent associations between periodic changes in muscle-related parameters, such as anaerobic strength for low and high angular velocities of extension and flexion and blood lactate concentration, with rs1799752 and rs2104772, whose gene products relate to sarcopenia. By contrast, the variance in period-dependent changes in body mass and peak VO2 with rs1799752 and rs2104772, respectively, was independent of age. Likely, the variance in periodic changes in the reliance of aerobic performance on lactate, oxygen uptake, and heart rate was associated with rs1815739 independent of age. These associations manifested at the post hoc level in genotype-associated differences in critical performance parameters. ACTN3 T-allele carriers demonstrated, compared to non-carriers, largely different periodic changes in the muscle-associated parameters of aerobic metabolism during exhaustive exercise, including blood lactate and respiration exchange ratio. The homozygous T-allele carriers of rs2104772 demonstrated the largest changes in extension strength at low angular velocity during the preparation period. Conclusions: Physiological characteristics of performance in skiing athletes undergo training period-dependent seasonal alterations the extent of which is largest for muscle metabolism-related parameters. Genotype associations for the variability in changes of aerobic metabolism-associated power output during exhaustive exercise and anaerobic peak power over the preparation and competition period motivate personalized training regimes. This may help to predict and maximize the benefit of physical conditioning of elite skiers based on chronological characteristics and the polymorphisms of the ACTN3, ACE, and TNC genes investigated here.

Repeated practice runs during on-snow training do not generate any measurable neuromuscular alterations in elite alpine skiers

Background

Alpine skiers typically train using repeated practice runs requiring high bursts of muscle activity but there is little field-based evidence characterizing neuromuscular function across successive runs.

Purpose

To examine the impact of repeated ski runs on electromyographic activity (EMG) of the knee extensors and flexors in elite alpine skiers.

Methods

Nineteen national team alpine skiers were tested during regular ski training [Slalom (SL), Giant Slalom (GS), Super Giant Slalom and Downhill (Speed)] for a total of 39 training sessions. The surface EMG of the vastus lateralis (VL), rectus femoris (RF), vastus medialis (VM), biceps femoris (BF) and semimembranosus/semitendinosus (SMST) muscles was continuously recorded along with right knee and hip angles. The EMG root mean square signal was normalized to a maximal voluntary contraction (%MVC). The first and fourth runs of the training session were compared.

Results

There was no meaningful main effect of run on EMG relative activation time or mean power frequency beyond the skier's intrinsic variability. However, EMG activity of the vastii increased from the first to the fourth run in SL [VM, ~+3%MVC for IL and outside leg (OL), p = 0.035)], speed (VL, IL:+6%/OL:+11%, p = 0.015), and GS (VM, IL:0/OL:+7%, p < 0.001); the later with an interaction with leg (p < 0.001) due to a localized increase on the OL. The run time and turn time did not change from the first to the fourth run. There were no meaningful changes in angular velocities, amplitude of movement, or maximal and minimal angles.

Conclusion

Neuromuscular activity remains highly stable in elite skiers with low variability across four runs.

Patellar Tendon Shear Wave Velocity Is Higher and has Different Regional Patterns in Elite Competitive Alpine Skiers than in Healthy Controls

Competitive alpine skiers are exposed to enormous forces acting on their bodies–particularly on the knee joint and hence the patellar tendon - during both the off-season preparation and in-season competition phases. However, factors influencing patellar tendon adaptation and regional pattern differences between alpine skiers and healthy controls are not yet fully understood, but are essential for deriving effective screening approaches and preventative countermeasures. Thirty elite competitive alpine skiers, all members of the Swiss Alpine Ski Team, and 38 healthy age-matched controls were recruited. A set of two-dimensional shear wave elastography measurements of the PT was acquired and projected into three-dimensional space yielding a volumetric representation of the shear wave velocity profile of the patellar tendon. Multivariate linear models served to quantify differences between the two cohorts and effects of other confounding variables with respect to regional shear wave velocity. A significant (p < 0.001) intergroup difference was found between skiers (mean ± SD = 10.4 ± 1.32 m/s) and controls (mean ± SD = 8.9 ± 1.59 m/s). A significant sex difference was found within skiers (p = 0.024), but no such difference was found in the control group (p = 0.842). Regional SWV pattern alterations between skiers and controls were found for the distal region when compared to the mid-portion (p = 0.023). Competitive alpine skiers exhibit higher SWV in all PT regions than healthy controls, potentially caused by long-term adaptations to heavy tendon loading. The presence of sex-specific differences in PT SWV in skiers but not in controls indicates that sex effects have load-dependent dimensions. Alterations in regional SWV patterns between skiers and controls suggest that patellar tendon adaptation is region specific. In addition to the implementation of 3D SWE, deeper insights into long-term tendon adaptation and normative values for the purpose of preventative screening are provided.

Altered regional 3D shear wave velocity patterns in youth competitive alpine skiers suffering from patellar tendon complaints - A prospective case-control study

AbstractPatellar tendon (PT) complaints are frequent throughout the population, with increased occurrence in athletes and, particularly, in youth competitive alpine skiers. Timely detection and treatment might improve prospects of recovery. Diagnostic modalities in clinical use to date rely on pain symptoms, manual palpation, and potentially, magnetic resonance imaging (MRI); however, MRI-based imaging yields limited sensitivity. Quantitatively measuring the morphological and mechanical properties of PTs by means of B-mode ultrasound and shear wave elastography (SWE), instead, may allow improved diagnosis or even early detection. We performed B-mode scans and three-dimensional ultrasound shear wave velocity (SWV) mapping and MRI of the PT in 106 youth skiers. A prospective one-year survey on health problems combined with clinical assessments served to categorize symptomatic and asymptomatic youth skiers. Skiers suffering from distal or proximal tendon complaints showed lower SWV in the respective tendon region than asymptomatic skiers (p = 0.035 and p = 0.019, respectively). Youth skiers with distal tendon complaints additionally exhibited decreased SWV in the proximal region compared to asymptomatic counterparts (p = 0.020). Cross-validated analysis of retrospective prediction indicated sensitivity and specificity in detecting tendon complaints in the range of 0.606-0.621 and 0.536-0.650, respectively. MRI detected distal tendon complaints with a sensitivity of 0.410 (12/29) but failed to detect any proximal cases. This study agrees with the most recent literature in that SWE holds promise as a valuable adjunct modality for the diagnosis of PT complaints or even the detection of subclinical prestages. However, to evaluate its prospective predictive value, long-term studies are warranted.

Femoroacetabular Impingement in Elite Skiers and Snowboarders: Return to Sports and Outcomes After Hip Arthroscopy

BACKGROUND

Hip arthroscopy has been shown to be an effective treatment for femoroacetabular impingement (FAI) in high-level athletes; however, limited outcome and return-to-play data exist for hip arthroscopy in skiers and snowboarders.

PURPOSES

To determine the return-to-sports rate of elite skiers and snowboarders who have undergone hip arthroscopic surgery for FAI and to assess hip-related outcomes at a minimum 2-year follow-up.

STUDY DESIGN

Case series; Level of evidence, 4.

METHODS

Elite skiers and snowboarders who underwent hip arthroscopy for the treatment of FAI between 2005 and 2018 were identified via a retrospective review of prospectively collected data. Data were obtained from fis-ski.org, usskiandsnowboard.org, xgames.com, and wikipedia.org, including information on each player's career length, participation on a national team, and time between surgery and first competition after surgery. Patient-reported outcomes (PROs) were prospectively collected preoperatively and at minimum 2 years postoperatively.

RESULTS

In total, 26 elite skiers and snowboarders (34 hips) were included. The mean ± standard deviation age at surgery was 24.5 ± 6.7 years (range, 18.7-46.8 years). A total of 85% (22/26) returned to elite-level competition at 8.9 months (range, 2.9-23.7 months) with an average career length of 3.6 ± 2.7 years after surgery. Four athletes (5 hips) required revision arthroscopy, with adhesions being the most frequent indication. At a mean follow-up of 7.7 ± 3.2 years, significant improvement in PROs (P < .05) was demonstrated for the Hip Outcome Score (HOS)-Activities of Daily Living (from 76 ± 20 to 95 ± 6), HOS-Sport Specific Subscale (from 63 ± 28 to 92 ± 14), modified Harris Hip Score (from 70 ± 19 to 89 ± 12), and 12-Item Short Form Health Survey Physical Component Summary (from 45 ± 11 to 54 ± 8). Patient satisfaction had a mean of 8 ± 2 (range, 1-10) and median of 10.

CONCLUSION

The return-to-competition rate in elite skiers and snowboarders after hip arthroscopy for FAI was 85% at an average of 8.9 months and with a career length of 3.6 years after surgery. Significant improvement in PROs was demonstrated for the HOS-Activities of Daily Living, HOS-Sport Specific Subscale, modified Harris Hip Score, and 12-Item Short Form Health Survey Physical Component Summary, with a median patient satisfaction score of 10. These findings support hip arthroscopy as an effective procedure for the treatment of FAI in elite skiers and snowboarders with symptomatic activity-limiting hip pain, allowing them to return to their previous levels of competition at a high rate.

Swiss-Ski Power Test Results in Youth Competitive Alpine Skiers Are Associated With Biological Maturation and Skiing Performance

PURPOSE

To explore reasonable application purposes and potential confounders of the Swiss-Ski Power Test (SSPT) that is, since 2004, annually performed by all youth competitive alpine skiers of the under-16-years age category in Switzerland.

METHODS

Preseason SSPT results (8 individual tests on anaerobic and aerobic capacity, muscle strength, and speed and coordination) of 144 skiers (57 female and 87 male) age 14.5 (0.7) years were analyzed along with anthropometry and biological age. Skiing performance was quantified as the actual performance points according to the Swiss national ranking. After the SSPT tests, skiers were prospectively monitored over 12 months using the Oslo Trauma Research Center questionnaire. Data were analyzed using multivariate analysis of variance, Pearson correlations, and multiple linear/binary logistic regression models.

RESULTS

Biological maturation and SSPT results differed between sexes and age (P < .05). For males, SSPT results in the subdisciplines Swiss Cross, 1-leg 5-hop, and standing long jump were correlated to maturity offset, while for females only the obstacle run was related. High box jump and Swiss Cross scores were associated with skiing performance (P < .05). However, none of the SSPT subdisciplines was related to traumatic and overuse injuries (P < .05).

CONCLUSIONS

The SSPT is a broadly implementable and cost-effective field test providing a general fitness profile of youth skiers. Around the growth spurt, differences in biological maturation should be considered. While SSPT results showed association with skiing performance, the test in its current form is limited for identifying injury-relevant physical deficiencies. Consequently, more specific tests may be required.

Inline Skating as an Additional Activity for Alpine Skiing: The Role of the Outside Leg in Short Turn Performance

The complexity of skiing movements urges recreational alpine skiers and competitors to undertake many specific skill trainings not only during the season but also during the off-season using alternative sports. In AS, the role of the outside leg is crucial for successful turn performance. By measuring kinematic and kinetic parameters, we could define whether there is an objective similarity of the role and the movements of the outside leg while performing a turn in AS to those in the most used additional activity, IS. The sample consisted of ten female alpine ski instructors (age 31.6 ± 8.23, height 170.66 ± 7.32 cm, weight 60.16 ± 7.58 kg). Overall, 280 turns were analyzed (140 for AS and 140 for IS). For the purposes of this study, the variable sample consisted of 14 variables in total. For the detection of differences between short turn performance in AS and IS, MANOVA was used. The main findings of our study are defined similarities in pressure distribution during IS and AS and noticeable differences in the kinematic parameters of the outside leg between the mentioned activities. Based on the gathered results, recreational alpine skiers should be aware that IS cannot be used for the purpose of AS adoption, but rather as a dry-land additional activity for AS preparation.

The effect of countermovement on force production capacity depends on extension velocity: A study of alpine skiers and sprinters

In jumping, countermovement increases net propulsive force and improves performance. We aimed to test whether this countermovement effect is velocity specific and examine the degree to which this varies between athletes, sports or performance levels. Force-velocity profiles were compiled in high-level skiers (N= 23) and sprinters (N= 30), with their performance represented in their overall world ranking and season-best 100 m time, respectively. Different ratios between force-velocity variables were computed from squat and countermovement jumps (smaller = less effect): jump height (CR_h), maximum power (CR_P), force (CR_F), and velocity (CR_v). Countermovement effect differed per velocity (inverse relationship between CR_F and CR_v, r_s = -0.74, p< .001), and variation force-velocity profiles with countermovement. Skiers exhibited smaller CR_F (r_rb = -0.675, p< .001), sprinters smaller CR_v (r_rb = 0.426, p= .008), and "moderate" velocity conditions did not differentiate groups (CR_P or CR_h, p> .05). 33% of the variance in skiers' performance level was explained by greater maximum force and a lower CR_F (i.e., high explosiveness at low-velocities without countermovement), without an association for sprinters. Countermovement effect appears specific to movement velocity, sport and athlete level. Consequently, we advise sports-specific assessment, and potentially training to reduce the countermovement effect per the relevant velocity.

What Are Kinematic and Kinetic Differences between Short and Parallel Turn in Alpine Skiing?

There are numerous programs worldwide adapted for alpine ski beginners and they all share the same primary goal-inclusion of skiing beginners in alpine ski schools. The final elements of ski school taught in the parallel skiing technique are parallel turn and short turn. Synchronized analysis of kinetic and kinematic parameters of the parallel turn (PT) and short turn (ST) was conducted to determine the main biomechanical differences from a standpoint of foot pressure and lower limb angles. Both elements were performed by nine male ski instructors (age 33.4 ± 8.62, height 179.52 ± 5.98 cm, weight 78.6 ± 8.88 kg). Kinetic and kinematic analysis was conducted on 180 turns, 90 for each element. Differences in kinetic and kinematic parameters between parallel and short turns were tested by a paired t-test. The main findings of our study are determined differences in the ratio of pressure distribution on the inside and the outside foot and differences in kinematic parameters of the outside leg between elements. The mentioned analysis can provide an objective insight into the complexity of each element and provide guidelines for teaching process of those elements. This study determined the reasons for higher complexity of ST compared to PT based on the objective evaluation of biomechanical factors.

Force output in giant-slalom skiing: A practical model of force application effectiveness

Alpine ski racers require diverse physical capabilities. While enhanced force production is considered key to high-level skiing, its relevance is convoluted. The aims of this study were to i) clarify the association between performance path length and velocity, ii) test the importance of radial force, and iii) explore the contribution of force magnitude and orientation to turn performance. Ski athletes (N = 15) were equipped with ski-mounted force plates and a global navigation satellite system to compute the following variables over 14 turns: path length (L), velocity normalized energy dissipation [Δemech/vin], radial force [Fr], total force (both limbs [Ftot], the outside limb, and the difference between limbs), and a ratio of force application (RF = Fr/Ftot). Data were course-averaged or separated into sectional turn groupings, averaged, and entered into stepped correlation and regression models. Our results support Δemech/vin as a discriminative performance factor (R2 = 0.50-0.74, p < .003), except in flat sections. Lower course times and better Δemech/vin were associated with greater Fr (R2 = 0.34-0.69 and 0.31-0.52, respectively, p < .032), which was related to both Ftot and RF (β = 0.92-1.00 and 0.63-0.81, respectively, p < .001) which varied in predictive order throughout the sections. Ftot was associated with increased outside limb force and a more balanced contribution of each limb (β = 1.04-1.18 and -0.65- -0.92, respectively, p < .001). Fr can be improved by either increasing total force output or by increasing technical effectiveness (i.e., proportionally more force radially) which should increase the trajectories available to the skier on the ski course.

Overuse injuries in the knee, back and hip of top elite female alpine skiers during the off-season preparation period: prevalence, severity and their association with traumatic preinjuries and training load

Objectives

To investigate knee, back and hip overuse injuries in top female elite alpine skiers during the off-season preparation, which has so far received little attention, and to assess their relationship with traumatic preinjuries and overall training load.

Methods

A cohort of 26 females of the Swiss Alpine Ski-Team were prospectively surveyed by the use of the Oslo Sports Trauma Research Centre questionnaire. Along with the surveys also total training loads were monitored. Data on preinjuries were assessed retrospectively by baseline questionnaires and were verified by team medical records.

Results

57.7% of the female skiers suffered from at least one severe traumatic knee injury during their preceding career. The average 2-weekly prevalence of overuse injuries was highest for the knee, followed by the back and hip. Technique specialists (major giant slalom and slalom) were more prone to back overuse injuries than speed specialists (major super-G and downhill). The occurrence of knee overuse complaints was directly associated to previous severe traumatic knee injuries and athletes' total training hours.

Conclusion

In top female elite alpine skiers, knee, back and hip overuse injuries are relatively frequent. Moreover, discipline preferences, previous traumatic injuries and the overall training load may play an important role for their manifestation.

Lower limb force-production capacities in alpine skiing disciplines

Specific force capacities might be a limiting factor for alpine skiing performance, yet there is little consensus on the capabilities in question, and whether they differ between disciplines. We aimed to test discipline (speed and technical) and performance (event-specific world standing) effects on lower limb force-production qualities. National-level skiers (N = 31) performed loaded squat jumps and isometric mid-thigh pulls to detect dynamic force output at extremely low and high velocities and maximum isometric force and rate of force development, respectively. Discipline differences were assessed via a general linear model including performance and allowing for interaction effects, with performance associations further characterized via distinct Pearson's correlations. Jump height did not differentiate disciplines, with absolute power slightly higher in speed athletes (F_(1,27)  = 4.42, P = .045, ω²  = 0.10), and neither variables were related to performance. Speed athletes possessed greater dynamic force at low velocities (F₀ ; F_(1,27)  = 13.8, P < .001, ω²  = 0.17), and greater relative and absolute maximum isometric force (F_(1,25)  = 11.19-20.70, ω²  = 0.16-0.22, P < .003). Overall, higher ranked athletes possessed more force-dominant profiles (F_(1,27)  = 16.28, ω²  = 0.34; r = 0.60 to 0.67, P < .001) and increased rate of force development characteristics (average and maximum, r = -0.50 to -0.82, P < .048). Very robust associations existed between maximum isometric force and speed performance (r = -0.88, P < .001), but only a trend for higher absolute isometric force in technical athletes (r = -0.49, P = .052). Alpine skiers display a preponderance for dynamic force output at low velocities, and isometric force for speed athletes, which highlights the interest in specific assessment and conditioning practices for ski athletes.