Petter Andre Husevåg Jølstad

• Linløkken, Mai-Sissel; Meyer, Frederic; Högström, Sven Erik Claes; Jølstad, Petter Andre; Spieker, Helge & Guillaume, Sebastien [Vis alle 9 forfattere av denne artikkelen] (2025). Equivalent Fall Height and Aerial Maneuver Difficulty Both Influence Landing Stability on World Cup Slopestyle Rollover Jumps For Skiers and Snowboarders. Scandinavian Journal of Medicine & Science in Sports. ISSN 0905-7188. 35(4). doi: 10.1111/sms.70053. Fulltekst i vitenarkiv Vis sammendrag

  This study investigates how landing stability on slopestyle jumps is affected by jump design and the athletes' aerial maneuvers, in World Cup skiers and snowboarders. The data were recorded on rollover jumps from a World Cup Slopestyle competition using a geodetic video method, allowing for a reconstruction of the athletes' center of mass trajectories in 3D-space and calculation of equivalent fall height (EFH). Aerial maneuvers and landing stability were assessed by human raters. A generalized estimating equations method with binary logistic regression was performed to investigate how aerial maneuvers and EFH impact landing stability (surrogate measure of potential injury risk). EFH increased the log odds for unstable landings for both skiers and snowboarders. Although five aerial maneuver factors affected landing stability for snowboarders (angular velocity, rotational axis, number of rotations, with interaction effects between multiaxial maneuvers and frontside rotation or switch landing), skiers landing stability was only affected by the number of rotations. This, along with the way skiers and snowboarders are attached to their equipment and their ability to compensate for instability in the landing, may explain why snowboarders show unstable landings more often than skiers. On this study's rollover jumps with generally low EFH, landing stability was regulated by both EFH and aerial maneuvers. As maneuver complexity and EFH have an influence on both performance and landing stability, it appears important that course builders emphasize the construction of safe jumps and athletes generate a good understanding of potential injury risk and performance reward when jumping.

• Luteberget, Live Steinnes; Jølstad, Petter Andre & Gilgien, Matthias (2023). Methods to assess validity of positioning systems in team sports: Can we do better? BMJ Open sport & exercise medicine. 9(1), s. 1–9. doi: 10.1136/bmjsem-2022-001496. Fulltekst i vitenarkiv Vis sammendrag

  Objectives: There is previously reported a large variety of criterion measures and reference systems applied to validate position tracking systems in sports. This study aims to investigate the effect of different criterion measures and reference systems on the outcome of accuracy assessments of tracking systems in sports. Methods: Data from a commercially available standalone global navigation satellite system (GNSS) were compared with two different reference systems: a high-end differential GNSS and a tape measure. Differences in accuracy outcomes of position (static and dynamic), distance and speed (mean and instantaneous) were investigated in team sport imitation courses. Results: The mean horizontal position error was larger when athletes were in motion (dynamic position; 1.53±0.82 m) compared with static measurements (1.10±0.60 m). Measured distances of the courses were markedly different (+6% to −17%) between the two reference systems, causing differences in error. Differences in error were also found between mean speed and instantaneous speed (0.10 vs 0.28 m). Errors in mean speed were highly affected by the time over which speed was averaged. Conclusion: Choice of criterion measure and reference system has a substantial impact on the accuracy assessments of tracking systems. Specifically, assessing static position is not a substitute for dynamic position, and mean speed is not a substitute for instantaneous speed. Therefore, the outcomes of validation studies should always be interpreted in light of the reference methods that were used.

• Jølstad, Petter Andre; Gilgien, Matthias & Elfmark, Ola (2023). Investigation of individual strategies in the aerial phase in ski jumping. Scientific Reports. 13. doi: 10.1038/s41598-023-49683-0. Fulltekst i vitenarkiv Vis sammendrag

  The purpose of this investigation was to examine the performance strategy of three ski jumpers during the steady glide phase and explain how different strategical solutions can lead to jumps of roughly the same length. In this study, a total of 24 jumps performed by two World Cup (WC) athletes and one Continental Cup (COC) athlete were measured with a differential Global Navigation Satellite System (dGNSS) on a large ski jumping hill. For each athlete, the continuous position data, velocity, aerodynamic forces and lift-to-drag ratio (LD-ratio) were averaged and compared for the steady glide phase to examine individual jump strategies. The dGNSS yielded accurate measurements of trajectory, velocity and aerodynamic forces, revealing clear differences between the athletes. The largest differences were found between the WC athletes and the COC athlete. The WC athletes focused on maximizing horizontal velocity while the COC athlete minimized vertical velocity. This difference may be explained by the different hill sizes the athletes normally compete on. One of the WC athletes consistently increased their horizontal velocity during the end of the steady glide phase by maintaining a high LD-ratio, which highlights the effect of aerodynamics on the resulting velocity, trajectory and jump length.

• Elfmark, Ola; Ettema, Gertjan; Jølstad, Petter Andre & Gilgien, Matthias (2022). Kinematic Determination of the Aerial Phase in Ski Jumping. Sensors. 22(2). doi: 10.3390/s22020540. Fulltekst i vitenarkiv Vis sammendrag

  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.

• Jølstad, Petter Andre; Reid, Robert Cortas; Gjevestad, Jon Glenn Omholt & Gilgien, Matthias (2021). Validity of the AdMos, Advanced Sport Instruments, GNSS Sensor for Use in Alpine Skiing. Remote Sensing. 14(1). doi: 10.3390/rs14010022. Fulltekst i vitenarkiv Vis sammendrag

  The AdMos receiver from Advanced Sport Instruments is a global navigation satellite system (GNSS) frequently used in alpine ski racing, with users from national and professional teams. Therefore, a validation was conducted for use of the AdMos in alpine skiing, using data from both recreational and competitive skiers. Athletes skied a total of 60 km in different measurement and skiing conditions, while carrying both an AdMos and a differential GNSS, which was used as the gold standard. From the GNSS position data, speed, acceleration, turn radius, trajectory incline and impulse were calculated as instantaneous and turn average measures for both GNSS systems and errors between the systems were calculated. The median and interquartile range (IQR) for the instantaneous errors were below 3.5 (3.5) m for horizontal plane position and below 7.0 (4.3) m for the 3D position. The median and IQR for instantaneous errors and turn average errors, respectively, were below 0.04 (0.24)/0.04 (0.16) m/s for speed, below 0.23 (1.06)/0.35 (0.63) m/s2 for acceleration, below 0.47 (5.65)/0.73 (5.3) m for turn radius, and below 0.043 (1.96)/0.42 (1.42) degrees for trajectory incline. The median and IQR for turn average impulse were 0.025 (0.099) BWs. The position error changed gradually and randomly over time, with low noise levels causing smooth trajectories of similar shape but spatially shifted from the true trajectory that allowed the position–time derivation of the performance parameters, and detection of turns with 3% median and 5% IQR error. The accuracy assessment revealed that (1) the error levels were comparable to other consumer-grade standalone GNSS units designed for sport; (2) the trajectories closely resembled the true trajectories but with a random shift that changed over time and had a low noise level; (3) there was a very low instantaneous speed error that may allow the detection of many performance aspects of skiing and other sports; and (4) there were larger instantaneous errors for the remaining performance parameters, which decreased substantially when averaged over a turn.

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• Linløkken, Mai-Sissel; Vigane, Sondre; Högström, Claes; Jølstad, Petter; Spieker, Helge & Hoholm, Sindre [Vis alle 7 forfattere av denne artikkelen] (2024). A Biomechanical Analysis of how Athlete Behavior and Equivalent Fall Height Affect Landing Stability for Skiers and Snowboarders in a World Cup Big Air Competition. Fulltekst i vitenarkiv

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