Matthias Felix Gilgien

• Jølstad, Petter Andre; Gilgien, Matthias & Elfmark, Ola (2023). Investigation of individual strategies in the aerial phase in ski jumping. Scientific Reports. ISSN 2045-2322. 13. doi: 10.1038/s41598-023-49683-0. Full text in Research Archive
• Soligard, Torbjørn; Palmer, Debbie; Steffen, Kathrin; Lopes, Alexandre Dias; Grek, Natalia & He, Xuan [Show all 12 contributors for this article] (2023). Olympic Games during nationwide lockdown: Sports injuries and illnesses, including COVID-19, at the Beijing 2022 Winter Olympics. British Journal of Sports Medicine. ISSN 0306-3674. doi: 10.1136/bjsports-2023-107412. Full text in Research Archive Show summary

  Objective: The objective of this study is to describe the incidence of injuries and illnesses sustained during the Beijing Winter Olympic Games from 4 February 2022 to 20 February 2022. Methods: We recorded the daily number of athlete injuries and illnesses (1) through the reporting of all National Olympic Committee (NOC) medical teams and (2) in the polyclinic and medical venues by the Beijing 2022 medical staff. Results: In total, 2848 athletes (1276 women, 45%; 1572 men, 55%) from 91 NOCs were followed prospectively for the occurrence of injury and illness. NOC and Beijing 2022 medical staff reported 289 injuries and 109 illnesses, equalling 10.1 injuries and 3.8 illnesses per 100 athletes over the 17-day period. The injury incidence was highest in ski halfpipe (30%), ski big air (28%), snowboard slopestyle (23%) and ski slopestyle (22%), and lowest (1%–2%) in curling, alpine mixed team parallel slalom, Nordic combined and alpine super-G. The illness incidence was highest in ski aerials (10%), skeleton (8%), cross-country skiing (8%) and Nordic combined (7%). In the study period, COVID-19 affected 32 athletes, accounting for 29% of all illnesses affecting 1.1% of all athletes. Conclusion: Overall, 10% of the athletes incurred an injury and 4% an illness during the Beijing Winter Olympic Games. The incidence of illnesses overall, which was the lowest yet recorded in the Winter Olympic Games, and COVID-19 was mitigated through comprehensive countermeasures.

• 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. ISSN 2055-7647. 9(1), p. 1–9. doi: 10.1136/bmjsem-2022-001496. Full text in Research Archive Show summary

  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.

• Ogul, Burcin Buket; Gilgien, Matthias & Özdemir, Suat (2022). Ranking surgical skills using an attention-enhanced Siamese network with piecewise aggregated kinematic data. International Journal of Computer Assisted Radiology and Surgery. ISSN 1861-6410. doi: 10.1007/s11548-022-02581-8. Show summary

  Surgical skill assessment using computerized methods is considered to be a promising direction in objective performance evaluation and expert training. In a typical architecture for computerized skill assessment, a classification system is asked to assign a query action to a predefined category that determines the surgical skill level. Since such systems are still trained by manual, potentially inconsistent annotations, an attempt to categorize the skill level can be biased by potentially scarce or skew training data.

• Gilgien, Matthias & Özdemir, Suat (2022). Ranking surgical skills using an attention-enhanced Siamese network with piecewise aggregated kinematic data. International Journal of Computer Assisted Radiology and Surgery. ISSN 1861-6410. doi: 10.1007/s11548-022-02581-8.
• Magelssen, Christian; Haugen, Per; Reid, Robert Cortas & Gilgien, Matthias (2022). Is there a contextual interference effect for sub-elite alpine ski racers learning complex skills? Frontiers in Bioengineering and Biotechnology. ISSN 2296-4185. 10. doi: 10.3389/fbioe.2022.966041. Show summary

  Scientific understanding of the contextual interference effect stems mainly from studies on unskilled participants learning artificial laboratory tasks. Although one goal of such studies is to extrapolate the findings to include real-world learning situations such as sports, this generalization is not straightforward. This study tested the contextual interference effect with 66 sub-elite, competitive alpine ski racers who learned a new movement pattern−the pumping technique to increase velocity in slalom−by practicing this skill in three different slalom courses over a 3-day training period. The interleaved group practiced all three courses each day in a semi-random order. In contrast, the blocked group practiced only one course each day, which was randomized and counterbalanced across the participants in this group. A retention test was delivered 72 h after the last practice day. In contrast to our hypothesis, the interleaved group did not display significantly better retention than the blocked group. The interleaved group’s performance was also not significantly attenuated during skill learning compared to the blocked group. Our results underscore the importance of conducting motor learning experiments in natural environments to understand the conditions that facilitate learning beyond the laboratory environment.

• Elfmark, Ola; Ettema, Gertjan & Gilgien, Matthias (2022). Assessment of the steady glide phase in ski jumping. Journal of Biomechanics. ISSN 0021-9290. 139, p. 1–8. doi: 10.1016/j.jbiomech.2022.111139. Full text in Research Archive
• Elfmark, Ola; Ettema, Gertjan; Jølstad, Petter Andre & Gilgien, Matthias (2022). Kinematic Determination of the Aerial Phase in Ski Jumping. Sensors. ISSN 1424-8220. 22(2). doi: 10.3390/s22020540. Full text in Research Archive Show summary

  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.

• Oğul, Burçin Buket; Gilgien, Matthias & Özdemir, Suat (2022). Ranking surgical skills using an attention-enhanced Siamese network with piecewise aggregated kinematic data. International Journal of Computer Assisted Radiology and Surgery. ISSN 1861-6410. 17(6), p. 1039–1048. doi: 10.1007/s11548-022-02581-8. Full text in Research Archive Show summary

  Purpose: Surgical skill assessment using computerized methods is considered to be a promising direction in objective performance evaluation and expert training. In a typical architecture for computerized skill assessment, a classification system is asked to assign a query action to a predefined category that determines the surgical skill level. Since such systems are still trained by manual, potentially inconsistent annotations, an attempt to categorize the skill level can be biased by potentially scarce or skew training data. Methods: We approach the skill assessment problem as a pairwise ranking task where we compare two input actions to identify better surgical performance. We propose a model that takes two kinematic motion data acquired from robot-assisted surgery sensors and report the probability of a query sample having a better skill than a reference one. The model is an attention-enhanced Siamese Long Short-Term Memory Network fed by piecewise aggregate approximation of kinematic data. Results: The proposed model can achieve higher accuracy than existing models for pairwise ranking in a common dataset. It can also outperform existing regression models when applied in their experimental setup. The model is further shown to be accurate in individual progress monitoring with a new dataset, which will serve as a strong baseline. Conclusion: This relative assessment approach may overcome the limitations of having consistent annotations to define skill levels and provide a more interpretable means for objective skill assessment. Moreover, the model allows monitoring the skill development of individuals by comparing two activities at different time points.

• Jølstad, Petter Andre; Reid, Robert Cortas; Omholt Gjevestad, Jon Glenn & Gilgien, Matthias (2021). Validity of the AdMos, Advanced Sport Instruments, GNSS Sensor for Use in Alpine Skiing. Remote Sensing. ISSN 2072-4292. 14(1). doi: 10.3390/rs14010022. Full text in Research Archive Show summary

  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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