Validation of a Sensor-Based Dynamic Ski Deflection Measurement in the Lab and Proof-of-Concept Field Investigation.

Introduction: Ski deflection is a performance-relevant factor in alpine skiing and the segmental and temporal curvature characteristics (m−1) along the ski have lately received particular attention. Recently, we introduced a PyzoFlex® ski deflection measurement prototype that demonstrated high reliability and validity in a quasi-static setting. The aim of the present work is to test the performance of an enhanced version of the prototype in a dynamic setting both in a skiing-like bending simulation as well as in a field proof-of-concept measurement. Material and methods: A total of twelve sensor foils were implemented on the upper surface of the ski. The ski sensors were calibrated with an empirical curvature model and then deformed on a programmable bending robot with the following program: 20 times at three different deformation velocities (vslow, vmedium, vfast) with (1) central bending, (2) front bending, (3) back bending, (4) edging left, and (5) edging right. For reliability assessment, pairs of bending cycles (cycle 1 vs. cycle 10 and cycle 10 vs. cycle 20) at vslow, vmedium, and vfast and between pairs of velocity (vslow vs. vmedium and vslow vs. vfast) were evaluated by calculating the change in the mean (CIM), coefficient of variation (CV) and intraclass correlation coefficient (ICC 3.1) with a 95% confidence interval. For validity assessment, the calculated segment-wise mean signals were compared with the values that were determined by 36 infrared markers that were attached to the ski using an optoelectrical measuring system (Qualisys). Results: High reliability was found for pairs of bending cycles (CIM −0.69−0.24%, max CV 0.28%, ICC 3.1 > 0.999) and pairs of velocities (max CIM = 3.03%, max CV = 3.05%, ICC 3.1 = 0.997). The criterion validity based on the Pearson correlation coefficient was r = 0.98. The accuracy (systematic bias) and precision (standard deviation), were −0.003 m−1 and 0.047 m−1, respectively. Conclusions: The proof-of-concept field measurement has shown that the prototype is stable, robust, and waterproof and provides characteristic curvature progressions with plausible values. Combined with the high laboratory-based reliability and validity of the PyzoFlex® prototype, this is a potential candidate for smart ski equipment.

Isokinetic Leg-Press Power-Force-Velocity Profiles Are Reliable in Male and Female Elite Athletes but Not Interchangeable With Vertical Jump Profiles.

PURPOSE: To evaluate the test-retest reliability of isokinetic leg-press power-force-velocity profile (P-F-v) parameters in male and female elite athletes. In addition, we determined the concurrent validity of leg-press against squat-jump (SJ) P-F-v parameters in task-experienced athletes. METHODS: For test-retest reliability, 22 female and 23 male elite athletes (22.3 [4.1] y) with different sporting backgrounds conducted 3 isokinetic leg-press test sessions over 3 consecutive weeks. The testing consisted of bilateral leg extensions at isokinetic velocities of 0.1, 0.3, 0.7, and 1.2 m·s-1. For concurrent validity, 13 ski jumpers (20.3 [3.3] y) were recruited to perform the isokinetic leg-press and SJ P-F-v profile tests using 5 predefined loading conditions of 0%, +20%, +40%, +60%, and +80% of body mass. RESULTS: Relative and absolute reliability were acceptable for female (intraclass correlation coefficient ≥.87 and coefficient of variation ≤6.5%) and male (intraclass correlation coefficient ≥.89 and coefficient of variation ≤5.7%) elite athletes. In contrast, concurrent validity was insufficient, with correlations ranging from -.26 to .69 between isokinetic and SJ P-F-v parameters. CONCLUSION: Irrespective of sex, isokinetic leg-press P-F-v profiles provide reliable parameters. However, leg-press P-F-v profiles do not serve as a valid substitute for SJ P-F-v profiles. P-F-v parameter magnitudes are likely dependent on the constraints of the tested movement and testing device.

Simple foot strike angle calculation from three-dimensional kinematics: A methodological comparison.

A simple and accurate method of determining foot strike angle (FSA) during running can simplify data collections and validations of wearable sensors. The purpose of this study was to determine the validity of two simplified methods for estimating FSA and foot angle (throughout the ground contact) from three-dimensional kinematics. Markers were placed on the heel and head of the second metatarsal (HEEL-TOE) or on the lateral side of the head of the fifth metatarsal (HEEL-MET5). When compared to the reference foot segment, the HEEL-TOE method performed similarly with a minimal mean difference (0.28° [0.19°,0.36°], p < 0.001), a high Pearson's r (r = 0.994; p < 0.001), and low bias (-0.20°±1.05°). Alternatively, the HEEL-MET5 method underestimated FSA: mean difference = 4.28° [4.07°,4.91°] (p < 0.001), Pearson's r = 0.968 (p < 0.001), and bias = -4.58°±2.61°. Throughout the contact phase, significant SPM cluster regions were identified, indicating that the HEEL-MET5 method underestimated the angle of the foot for all foot strike patterns in the first 23-34% of the stance (p < 0.025). This study supports the idea that the HEEL-TOE method can be used as a simplified method for determining FSA from 3D kinematics. Researchers should proceed with caution when employing the HEEL-MET5 method, as it is likely underestimating FSA due to foot inversion in the early stance phase.

Power-Force-Velocity Profiling as a Function of Used Loads and Task Experience.

PURPOSE: To evaluate cohort-specific reliability and concurrent validity of 3 different vertical power-force-velocity (P-F-v) profiles to determine force, velocity, maximal power, and the slope of the force-velocity relationship using squat jumps. METHODS: Fifteen male sport students and 15 elite ski jumping athletes (male = 11; female = 4) conducted 2 block-randomized test-retest sessions with 5-point-method or 2-point-method loading conditions. A third P-F-v profile was established by excluding the data point most declining the coefficient of determination (r2) of the 5-point method. RESULTS: Acceptable absolute and relative reliability were found across methods in ski jumping athletes (intraclass correlation coefficient [ICC] ≥ .79, coefficient of variation [CV] ≤ 6.2%). However, force values were significantly lower in the retest (≤2.1%, d ≤ 0.75). In contrast, no systematic differences (P ≥ .461), but unacceptable absolute and relative reliability, were found in sport students (ICC ≥ .63, CV ≤ 14.8%). The P-F-v parameters of the different collecting and evaluating approaches yielded high to excellent correlations (ski jumping athletes: r ≥ .64; sport students: r ≥ .61), but maximal power (≤4.6%) and velocity (<6.2%,) values of sport students revealed significant differences. CONCLUSION: The similarity of P-F-v testing and basic ski jumping training daily exercises seems to be more significant to obtain reliable force-velocity parameters than the methodological approach. Accordingly, P-F-v profiles seem to be reliable with the proposed methods only in highly task-experienced athletes but not in less task-experienced cohorts like sport students.

"When you're down, stay down": A lesson for all competitive alpine skiers supported by an ACL rupture measured in vivo.

BACKGROUND: During an experiment, a ski racer equipped with various measurement devices suffered an anterior cruciate ligament (ACL) rupture in his right knee. The aim of this study was to describe the underlying injury mechanism from a functional perspective. METHODS: Eight giant slalom turns (i.e., 4 left turns), followed by 1 left turn at which the ACL injury occurred, were recorded by 2 video cameras, electromyography of 4 relevant muscle groups, inertial measurement units to measure knee and hip angles, and pressure insoles to determine ground reaction forces. RESULTS: Due to a loss of balance, the ski racer began to slide sideways at the apex of a left turn. During sliding, his right (outside) leg was actively abducted upward without touching the ground. The ski racer then attempted to stand up again by dropping his leg back towards the snow surface. The end of this dropping was accompanied by a decrease in electromyographic activity in the knee stabilizing muscles. Once the inside edge of the outer ski caught the snow surface, a rapidly increasing peak force, knee flexion, and an aggressive sudden activation of the vastus medialis muscle were observed, while biceps femoris and rectus femoris further decreased their activation levels. This likely resulted in excessive anterior translation of the tibia relative to the femur, causing damage to the ACL. CONCLUSION: Our example emphasizes that ski racers should not get up until they stop sliding. Remember: "When you're down, stay down."

Perceptions of experts on key injury risk factors in alpine ski racing as a function of stakeholder role and associated level of competition.

OBJECTIVES: (1) To update experts' priorities of perceived key injury risk factors in alpine ski racing based on a framework and list derived 10 years ago, (2) to identify additionally emerging risk factors since then and (3) to compile a list with countermeasure suggestions. METHODS: A sample of 532 expert stakeholders (athletes, coaches, team medical staff, Ski Racing Suppliers (SRS) and International Ski Federation (FIS) representatives) from the World Cup (WC), European Cup (EC) and FIS-race level participated in a cross-sectional online survey. Experts were asked to name those risk factors with the highest believed impact on injury risk and rank them according to their current priority from a predefined list. In addition, experts were encouraged to name additional (not listed) risk factors and to suggest countermeasures. RESULTS: Regardless of stakeholder role and competition level, snow-related factors appeared to have the highest perceived priority. However, WC athletes' and coaches' perceptions were also related to equipment, while at the EC and FIS-race level fatigue and physical fitness-related factors were considered important. Athletes' perceptions were largely in agreement with SRS (ie, snow-related and equipment-related factors). At the same time, while coaches, team medical staff and FIS representatives additionally emphasised fatigue and physical fitness-related factors. CONCLUSION: Experts' perceptions on key injury risk factors in alpine ski racing depend on the stakeholder role and differ between the competition levels. Thus, to develop effective prevention measures and to successfully implement them, all relevant stakeholders should be given a voice, and prevention efforts should be targeted to the specific level.

Moving Beyond One-Size-Fits-All Approaches to Injury Prevention: Evaluating How Tailored Injury Prevention Programs Are Developed and Implemented in Academy Soccer.

OBJECTIVE: To evaluate the real-world development and implementation of tailored injury prevention exercise programs (IPEPs) in academy soccer players. DESIGN: A mixed-methods process evaluation employing the Consolidated Framework for Implementation Research. METHODS: The participants were 38 players and staff members (eg, coaches, physical therapists) from 4 male teams in 1 European soccer academy. The content and nature of the 4 teams' IPEPs and the degree of implementation across 1 playing season were evaluated. Additionally, participants took part in semi-structured interviews and focus groups, focusing on the development of tailored IPEPs and implementation barriers and facilitators. RESULTS: Teams employed multiple IPEPs, developed by the team physical therapists and strength and conditioning coaches. A range of sources, including scientific literature, guidelines, individual player screening data, and previous experience, influenced IPEP development. Across all teams, 76% of IPEP sessions were completed as originally planned and a further 11% were completed in modified form. The key barriers to implementation during the season were related to scheduling changes and managing player workload. Thematic coding of interviews and focus groups identified 25 IPEP implementation barriers (eg, time and scheduling, player workload) and 41 facilitators (eg, program adaptability, facilities and equipment). CONCLUSION: In a male soccer academy setting, physical therapists and strength and conditioning coaches played the key role in IPEP development. Teams employed a range of different, internally developed programs. The key implementation factors were related to time and scheduling and managing player workload. J Orthop Sports Phys Ther 2021;51(9):432-439. doi:10.2519/jospt.2021.10513.

A Novel Sensor Foil to Measure Ski Deflections: Development and Validation of a Curvature Model.

The ski deflection with the associated temporal and segmental curvature variation can be considered as a performance-relevant factor in alpine skiing. Although some work on recording ski deflection is available, the segmental curvature among the ski and temporal aspects have not yet been made an object of observation. Therefore, the goal of this study was to develop a novel ski demonstrator and to conceptualize and validate an empirical curvature model. Twenty-four PyzoFlex® technology-based sensor foils were attached to the upper surface of an alpine ski. A self-developed instrument simultaneously measuring sixteen sensors was used as a data acquisition device. After calibration with a standardized bending test, using an empirical curvature model, the sensors were applied to analyze the segmental curvature characteristic (m-1) of the ski in a quasi-static bending situation at five different load levels between 100 N and 230 N. The derived curvature data were compared with values obtained from a high-precision laser measurement system. For the reliability assessment, successive pairs of trials were evaluated at different load levels by calculating the change in mean (CIM), the coefficient of variation (CV) and the intraclass correlation coefficient (ICC 3.1) with a 95% confidence interval. A high reliability of CIM -1.41-0.50%, max CV 1.45%, and ICC 3.1 > 0.961 was found for the different load levels. Additionally, the criterion validity based on the Pearson correlation coefficient was R2 = 0.993 and the limits of agreement, expressed by the accuracy (systematic bias) and the precision (SD), was between +9.45 × 10-3 m-1 and -6.78 × 10-3 m-1 for all load levels. The new measuring system offers both good accuracy (1.33 × 10-3 m-1) and high precision (4.14 × 10-3 m-1). However, the results are based on quasi-static ski deformations, which means that a transfer into the field is only allowed to a limited extent since the scope of the curvature model has not yet been definitely determined. The high laboratory-related reliability and validity of our novel ski prototype featuring PyzoFlex® technology make it a potential candidate for on-snow application such as smart skiing equipment.

Jumping with barbell load: Assessment of lower limb joint kinematics and kinetics during landing.

Loaded jumps are commonly used to improve leg muscle power. However, the additional load during jump-landing might increase the potential for overuse injury. Therefore, the aims of this study were to evaluate the effect that barbell load has on lower limb joint kinematics and kinetics during jump-landing and to evaluate the effect of arresting the barbell load at flight apex prior to landing on joint kinematic and kinetic variables. Barbell-loaded squat jumps (20, 40, and 60 kg) were investigated during two jump-landing conditions: 1) barbell-loaded (landing with barbell load) and 2) barbell-arrested (barbell load arrested at flight apex prior to jump-landing). Lower body kinematics and joint kinetics were assessed during jump-landing. In the barbell-loaded jump-landing condition, joint angles at initial contact decreased with increasing barbell load. Knee and hip peak power decreased (knee: -38%; hip: -46%), while ankle joint work increased with increasing barbell load. Joint moments, powers and work were decreased in the barbell-arrested condition compared to the barbell-loaded condition. Barbell-loaded jump-landings do not pose increased demands on the knee and the hip joint compared to bodyweight only jump-landings, due to the load-based reductions in jump height and joint kinematic adaptions. However, ankle joint contribution in energy dissipation is increased, possibly resulting in an increased overuse injury risk at this joint. Arresting the barbell load at flight apex prior to jump-landing substantially reduces the joint kinetics, hence serving as valuable training tool for athletes returning to sport after injuries.

Injury prevention in Super-G alpine ski racing through course design.

In Super-G alpine ski racing mean speed is nearly as high as in Downhill. Hence, the energy dissipated in typical impact accidents is similar. However, unlike Downhill, on Super-G courses no training runs are performed. Accordingly, speed control through course design is a challenging but important task to ensure safety in Super-G. In four male World Cup alpine Super-G races, terrain shape, course setting and the mechanics of a high-level athlete skiing the course were measured with differential global navigation satellite systems (dGNSS). The effects of course setting on skier mechanics were analysed using a linear mixed effects model. To reduce speed by 0.5 m/s throughout a turn, the gate offset needs to be increased by + 51%. This change simultaneously leads to a decrease in minimal turn radius (- 19%), an increase in impulse (+ 27%) and an increase in maximal ground reaction force (+ 6%). In contrast, the same reduction in speed can also be achieved by a - 13% change in vertical gate distance, which also leads to a small reduction in minimal turn radius (- 4%) impulse (- 2%), and no change in maximal ground reaction force; i.e. fewer adverse side effects in terms of safety. It appears that shortening the vertical gate distance is a better and safer way to reduce speed in Super-G than increasing the gate offset.

Curvature Detection with an Optoelectronic Measurement System Using a Self-Made Calibration Profile.

So far, no studies of material deformations (e.g., bending of sports equipment) have been performed to measure the curvature (w″) using an optoelectronic measurement system OMS. To test the accuracy of the w″ measurement with an OMS (Qualisys), a calibration profile which allowed to: (i) differentiates between three w″ (0.13˙ m-1, 0.2 m-1, and 0.4 m-1) and (ii) to explore the influence of the chosen infrared marker distances (50 mm, 110 mm, and 170 mm) was used. The profile was moved three-dimensional at three different mean velocities (vzero = 0 ms-1, vslow = 0.2 ms-1, vfast  = 0.4 ms-1) by an industrial robot. For the accuracy assessment, the average difference between the known w″ of the calibration profile and the detected w″ from the OMS system, the associated standard deviation (SD) and the measuring point with the largest difference compared to the defined w″ (=maximum error) were calculated. It was demonstrated that no valid w″ can be measured at marker distances of 50 mm and only to a limited extent at 110 mm. For the 170 mm marker distance, the average difference (±SD) between defined and detected w″ was less than 1.1 ± 0.1 mm-1 in the static and not greater than -3.8 ± 13.1 mm-1 in the dynamic situations. The maximum error in the static situation was small (4.0 mm-1), while in the dynamic situations there were single interfering peaks causing the maximum error to be larger (-30.2 mm-1 at a known w″ of 0.4 m-1). However, the Qualisys system measures sufficiently accurately to detect curvatures up to 0.13˙ m-1 at a marker distance of 170 mm, but signal fluctuations due to marker overlapping can occur depending on the direction of movement of the robot arm, which have to be taken into account.

Preventing injuries in alpine skiing giant slalom by shortening the vertical distance between the gates rather than increasing the horizontal gate offset to control speed.

BACKGROUND/AIM: To set a safe giant slalom course, speed needs to be controlled in certain sections. Speed may be reduced by adjusting how the gates are set on a course. We studied the effect of elements of course-setting, entrance speed and terrain incline on the mechanics of turning (ie, turn speed, turn radius, and ground reaction force and impulse). METHODS: During seven World Cup alpine giant slalom competitions, the course and terrain characteristics of the official racetracks and the mechanics of a professional-level athlete skiing the course immediately prior to competition were analysed with differential global navigation satellite system technology. Data were analysed using a linear mixed-effects model. RESULTS: Course-setting geometry (vertical gate distance and horizontal gate offset), entrance speed and terrain incline modulated the injury-relevant factor turn speed. Depending on the terrain, the speed throughout a turn can be reduced by 0.5 m/s either by shortening the vertical gate distance by 4.9-6.9 m (from -20% to -29%) or by increasing the horizontal gate offset by 2.8-3.2 m (from +33% to +55%). However, increasing the horizontal gate offset causes the skier to turn with a smaller minimal turn radius, increase maximal ground reaction force and also increase impulse. DISCUSSION: To reduce speed, we recommend decreasing the vertical gate distance rather than increasing the horizontal gate offset. Increasing horizontal gate offset would require the skiers to sharpen and prolong their turns (reducing turn radius), and this increases the acting ground reaction force and impulse and thus the athlete's fatigue.

Does enhanced footwear comfort affect oxygen consumption and running biomechanics?

Comfort as an essential parameter for running footwear is gaining importance in footwear research and development, and has also been proposed to decrease injury rate and improve metabolic demand in the paradigm of the comfort filter. The aims of this study were to determine differences in oxygen consumption and biomechanical variables associated with lower extremity injuries in response to running shoes of differing comfort. Fifteen male runners attended two testing sessions including an incremental lactate threshold test, a comfort assessment and treadmill running trials for the biomechanical and physiological measurements. Statistical analyses were performed on oxygen consumption, spatio-temporal variables including foot-ground angle and coupling angle variability of 12 couplings in five stride phases. No decrease in oxygen consumption was found in the most preferred shoe condition. Investigation of potential biomechanical contributors to changes in metabolic demands revealed differences in the stride rate between the most and least preferred condition. In coupling angle variability analyses, only one coupling (ankle dorsiflexion/plantarflexion to knee varus/valgus) yielded a significant difference between conditions in the phase including the touch down. Based on the findings of this study, previous suggestions regarding positive effects of enhanced footwear comfort during running cannot be supported - neither on economy nor on injury prevention perspective. However, a prospective study of lower extremity injury combined with measurements of biomechanical and physiological variables seems to be required for a definite support or contradiction of the comfort filter.

Familiarisation of novice and experienced treadmill users during a running session: Group specific evidence, time and individual patterns.

The elimination of familiarisation effects is a recurring topic in biomechanical testing during treadmill running among different experience levels. The two aims of this study were (i) to calculate familiarisation times of novice and experienced treadmill runners on a group level and (ii) to examine individual familiarisation patterns in order to classify those with similar characteristics. Twenty runners participated in this study by performing a treadmill running session with 3D motion capture. Familiarisation times for 9 kinematic variables among both groups (novices and experienced treadmill runners) were statistically analysed. Additionally a qualitative clustering process (supported by quantitative criteria) provided individual familiarisation patterns for all participants and variables. Group mean familiarisation times were inconsistent across variables (ranging from 3 to 14 min), with no general tendency for decreased familiarisation time in experienced compared to novice treadmill runners. The analysis of individual familiarisation patterns revealed that 30.5% were not stable after 15 min. Substantial changes compared to the initial state were observed in data sets with detected familiarisation pattern. Treadmill running experience does not affect familiarisation patterns since this process is highly individual and variable-specific. Consequently, no generalised familiarisation time can be provided and the elimination of familiarisation in biomechanical testing a priori does not seem to be possible in the first 15 min for approximately one third of the individual patterns studied. In conclusion, the common practice of collecting data subsequent to a pre-defined generalised familiarisation time ought to be replaced by measurements at several points in time during trials. This required procedure would allow for checking familiarisation patterns and fluctuations in order to exclude inappropriate data sets in future treadmill studies.

A Magnet-Based Timing Tystem to Detect Gate Crossings in Alpine Ski Racing.

In alpine skiing, intermediate times are usually measured with photocells. However, for practical reasons, the number of intermediate cells is limited to three⁻four, making a detailed timing analysis difficult. In this paper, we propose and validate a magnet-based timing system allowing for the measurement of intermediate times at each gate. Specially designed magnets were placed at each gate and the athletes wore small magnetometers on their lower back to measure the instantaneous magnetic field. The athlete's gate crossings caused peaks in the measured signal which could then be related to the precise instants of gate crossings. The system was validated against photocells placed at four gates of a slalom skiing course. Eight athletes skied the course twice and one run per athlete was included in the validation study. The 95% error intervals for gate-to-gate timing and section times were below 0.025 s. Each athlete's gate-to-gate times were compared to the group's average gate-to-gate times, revealing small performance differences that would otherwise be difficult to measure with a traditional photocell-based system. The system could be used to identify the effect of tactical choices and athlete specific skiing skills on performance and could allow a more efficient and athlete-specific performance analysis and feedback.

Comfort assessment of running footwear: Does assessment type affect inter-session reliability?

Assessing comfort of running footwear reliably is challenging. The purpose of this study was to compare the intra-rater reliability between different assessment types, to calculate intra-individual reliability scores and to evaluate the effect of rater selection based on individual reliability scores on group level reliability. Three assessment types: ranking, Visual Analogue Scale (VAS), and Likert Scale (LS) were provided twice in six separate sessions among 30 participants, who assessed comfort of five shoes after treadmill running. Spearman's rho provided an evaluation of inter-session relative reliability and typical error as a measure of absolute reliability for each assessment type. Ranking (r = 0.70, 95% confidence interval [CI] 0.61-0.78) yielded the highest relative reliability for overall comfort, followed by VAS (r = 0.67, 95% CI 0.56-0.75) and LS (r = 0.63, 95% CI 0.52-0.72), with large-scale overlaps of CIs between assessment types. The same order of assessment types was found for the percentage of reliable raters (r ≥ 0.7) with 60% in ranking scale, 47% in VAS and 37% in LS. Forming subgroups corresponding to the intra-individual reliability substantially increased group level reliabilities. Based on measures of relative reliability, an extreme reduction in resolution as provided by the ranking from pairwise comparisons seems to be a valuable tool in footwear comfort assessments if assessment time is of minor importance. No preference can be provided for the two investigated rating scales. Besides the assessment type, a selection of the best raters in additional reliability checks seems to be a prerequisite for further comfort-related studies.

Influence of body segment parameter estimation on calculated ground reaction forces in highly dynamic movements.

The effect of body segment parameter estimation (BSP) on the inverse dynamics modelling results has not yet been demonstrated in specific groups during athletic movements with high segment accelerations. Therefore, the purpose of this study was to analyse this effect in ski-jumpers as representatives of a specific group (i.e. low body mass index) by comparing calculated and measured ground reaction forces during ski-jumping imitation jumps. Full body kinematics and vertical ground reaction forces were recorded of 9 ski-jumpers performing three imitation jumps each. BSP were estimated using three previously published, one individually optimized and one ski-jumper group specific model. Vertical ground reaction forces were calculated using the vertical acceleration of the segments as well as the BSP of the single models in a top-down approach. Statistical analysis revealed a main model effect concerning the root mean square error between the calculated and the measured ground reaction force with deviations between the models of 53%. Individual optimization and the application of the ski-jumper group specific model increased the accuracy of the calculated ground reaction forces by 11 and 7%, respectively, compared to the best performing published model. The results of inverse dynamics modelling are very sensitive to the BSP estimation for specific groups like ski-jumpers during movements incorporating high segment accelerations. This emphasizes the importance of selecting adequate BSP estimation models or methods when analysing specific groups in highly dynamic movements in order to increase the accuracy of the inverse dynamics analyses results.

Acute Effects of an Ergometer-Based Dryland Alpine Skiing Specific High Intensity Interval Training.

Introduction: To establish an alpine ski racing (ASR) specific dryland high intensity training protocol (HIT), we set out to analyze cardiorespiratory and metabolic responses of three ASR specific HIT modes using a ski ergometer compared with a running HIT. Methods: Ten healthy international FIS level subjects (18 ± 1 years) performed an incremental running VO2max test, three different ASR specific HIT modes [slalom (SL), giant slalom (GS), and SL/GS mix] and a running HIT with measurements of VO2, heart rate (HR), blood lactate, and rate of perceived exertion (RPE). The HIT protocols included 15 × 1-min intervals with >90% HRmax and 30 s active rest. Furthermore, one elite alpine skier performed an 8-week, 17 session HIT block using the SL/GS mixed mode. Results: Running HIT resulted in greater VO2peak and whole-body RPE compared with the three ASR-specific HIT modes. During all four exercise modes participants were able to reach exercise intensities high enough to be classified as HIT (>90% HRmax and >89% VO2max). Legs RPE was similar between the four HIT modes, while arms RPE was higher for the ski-specific HIT. For all studied parameters, similar results for the three skiing specific HIT modes were observed. The 8-week HIT block was feasible for the athlete and resulted in an 11% increase in VO2max at unchanged peak power output. Conclusion: Across all HIT protocols high cardiorespiratory and metabolic responses were achieved. Therefore, the ASR specific HIT was shown to be feasible, thus could offer new possibilities for endurance training in elite alpine skiers. It is suggested to use the SL/GS mixed mode in terms of movement variety. The reduced VO2 in the ski-specific modifications can be attributed to the concentric and eccentric muscle activity resulting in mechanical hindrance for O2 extraction. The long-term effectiveness of ASR specific HIT in elite alpine skiers needs to be proven in a future study.

The role of path length- and speed-related factors for the enhancement of section performance in alpine giant slalom.

Knowing how to enhance alpine skiing performance is essential for effective coaching. The purpose of this study was to explore the role of path length- and speed-related factors for performance enhancement, while skiing on a homogeneously set/constantly inclined giant slalom course section (average gate distance: 27 m; offset: 8 m; slope inclination: 26°). During a video-based three-dimensional kinematic field-experiment, the data of six athletes who skied a two-gate section on four different types of skis were collected. The performance parameter analysed was section time. The performance predictors analysed were centre of mass (CoM), path length and the change in specific mechanical energy per entrance speed along the analysed section. Furthermore, since the current study examined alpine skiing performance within short sections, the skier's entrance speed was also considered. Classified as a high-performance and a low-performance group based on section time, slow and fast trials significantly differed in CoM path length, the change in specific mechanical energy per entrance speed and entrance speed. The entrance speed of all trials analysed ranged between 15.25 and 17.66 m/s. In trials with both high and low entrance speed, the change in specific mechanical energy per entrance speed was found to be more relevant for the prediction of section time than CoM path length. However, further studies should investigate whether such a prioritization can be unrestrictedly generalized to other situations, such as entrance speeds, course sets, slope inclinations and competition disciplines different to those assessed in the current study.