Kinematic Determination of the Aerial Phase in Ski Jumping

The purpose of this study was to find a generic method to determine the aerial phase of ski jumping in which the athlete is in a steady gliding condition, commonly known as the ‘stable flight’ phase. The aerial phase of ski jumping was investigated from a physical point mass, rather than an athlete–action-centered perspective. An extensive data collection using a differential Global Navigation Satellite System (dGNSS) was carried out in four different hill sizes. A total of 93 jumps performed by 19 athletes of performance level, ranging from junior to World Cup, were measured. Based on our analysis, we propose a generic algorithm that identifies the stable flight based on steady glide aerodynamic conditions, independent of hill size and the performance level of the athletes. The steady gliding is defined as the condition in which the rate-of-change in the lift-to-drag-ratio (LD-ratio) varies within a narrow band-width described by a threshold τ. For this study using dGNSS, τ amounted to 0.01s−1, regardless of hill size and performance level. While the absolute value of τ may vary when measuring with other sensors, we argue that the methodology and algorithm proposed to find the start and end of a steady glide (stable flight) could be used in future studies as a generic definition and help clarify the communication of results and enable more precise comparisons between studies.

Injuries in elite women’s ski jumping: a cohort study following three International Ski Federation (FIS) World Cup seasons from 2017–2018 to 2019–2020

ObjectivesTo define incidence and injury patterns of International Ski Federation (FIS) World Cup (WC) women ski jumpers over three seasons.MethodsSki jump athletes competing in the Women’s FIS WC were recruited for prospective injury surveillance from 2017–2018 to 2019–2020. Team representatives recruited the athletes annually and prospectively recorded all injuries requiring medical attention. Retrospective end-of-season interviews corroborated injury surveillance. Medical doctors collected and processed the data. The 4-month competitive season was used to calculate the annual incidence of injuries per 100 athletes per season. Injury type, location, severity and aetiology were reported.ResultsAthletes from 19 nations were enrolled equalling 205 athlete-seasons. Mean age was 21.2 years (SD=3.8). Thirty-nine injury events resulted in 54 total injuries (26.3 injuries/100 athletes/season). Injuries were mostly acute (83%) and occurred on the ski jump hill (78%). The most common injury location was the knee (n=18, 33%). Crash landings were the most common cause of injury events (70%). Nearly half of the acute ski jump injury events occurred in snowy, windy or cloudy conditions (44%) and/or during telemark landings (46%), and most jumps (96%) were shorter than hill size. One third of the injuries were severe, and 78% of severe injuries involved the knee.ConclusionAcute injury events occur relatively frequently in elite women ski jumpers, most resulting in time-loss from sport and a significant proportion involving serious knee injuries. Crash landing was the leading cause of injury. This baseline information can be used to guide and evaluate future efforts at injury prevention.

Experimental Validation of Real-Time Ski Jumping Tracking System Based on Wearable Sensors

For sports scientists and coaches, its crucial to have reliable tracking systems to improve athletes. Therefore, this study aimed to examine the validity of a wearable real-time tracking system (WRRTS) for the quantification of ski jumping. The tracking system consists of wearable trackers attached to the ski bindings of the athletes and fixed antennas next to the jumping hill. To determine the accuracy and precision of the WRRTS, four athletes of the German A or B National Team performed 35 measured ski jumps. The WRRTS was used to measure the 3D positions and ski angles during the jump. The measurements are compared with camera measurements for the in-flight parameters and the official video distance for the jumping distance to assess their accuracy. We statistically evaluated the different methods using Bland–Altman plots. We thereby find a mean absolute error of 0.46 m for the jumping distance, 0.12 m for the in-flight positions, and 0.8°, and 3.4° for the camera projected pitch and V-style opening angle, respectively. We show the validity of the presented WRRTS to measure the investigated parameters. Thus, the system can be used as a tracking system during training and competitions for coaches and sports scientists. The real-time feature of the tracking system enables usage during live TV broadcasting.

Performance Analysis in Ski Jumping with a Differential Global Navigation Satellite System and Video-Based Pose Estimation

This study investigated the explanatory power of a sensor fusion of two complementary methods to explain performance and its underlying mechanisms in ski jumping. A differential Global Navigation Satellite System (dGNSS) and a markerless video-based pose estimation system (PosEst) were used to measure the kinematics and kinetics from the start of the in-run to the landing. The study had two aims; firstly, the agreement between the two methods was assessed using 16 jumps by athletes of national level from 5 m before the take-off to 20 m after, where the methods had spatial overlap. The comparison revealed a good agreement from 5 m after the take-off, within the uncertainty of the dGNSS (±0.05m). The second part of the study served as a proof of concept of the sensor fusion application, by showcasing the type of performance analysis the systems allows. Two ski jumps by the same ski jumper, with comparable external conditions, were chosen for the case study. The dGNSS was used to analyse the in-run and flight phase, while the PosEst system was used to analyse the take-off and the early flight phase. The proof-of-concept study showed that the methods are suitable to track the kinematic and kinetic characteristics that determine performance in ski jumping and their usability in both research and practice.