Assessment of performance, physiological responses, and movement technique in cross-country skiing using sensor data
Doctoral thesis
Permanent lenke
https://hdl.handle.net/11250/3097774Utgivelsesdato
2023Metadata
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Sammendrag
The main objective of this thesis was to investigate physiological responses, movement techniques, and their associations with training intensity and performance in cross-country skiing (XC) using sensor data, with a particular emphasis on mass-start competitions and the skating technique. The thesis followed a sequential approach, starting with two indoor studies conducted under standardized conditions. In these studies (Paper 1 and Paper 2), wearable sensors were used in conjunction with standard laboratory measurements to establish a foundation for interpreting data collected from sensors in outdoor settings. This approach allowed for the integration of highly accurate reference sensors and methodology, contributing to the development of expertise in analyzing outdoor sensor data.
Subsequently, two outdoor studies were conducted: one during an official mass-start competition (Paper 3) and one intervention study involving two time trials (Paper 4).
The impact of training intensity on physiological and biomechanical factors - Competitive XC skiing is a physiologically and technically demanding endurance sport in which speed, work rate, and energy expenditure fluctuate with the constantly changing terrain. However, despite XC skiing competitions being performed at high-intensity and high-intensity sessions being considered crucial for the development of XC skiers, the majority of training time is spent on low-intensity sessions. The specific physiological and biomechanical stimulus provided during low-intensity training, and its similarities with competition-specific demands, have not been adequately explored. Therefore, an indoor study was conducted under controlled environments to investigate the similarities and differences in the physiological and biomechanical responses to low- and high-intensity roller ski skating on varying terrain (Paper 1). Several similarities between low- and high-intensity training on varying terrain were observed. Both low- and high-intensity training induced significant terraindependent fluctuations in heart rate, oxygen uptake, and muscle oxygen saturation. Furthermore, the power distribution generated by poles and skis showed a similar pattern for both low- and highintensity, with a time-dependent shift towards increased power from the ski push-off from the start to the end of each session within all sub-techniques. Terrain-based fluctuations in oxygen uptake were also similar at both intensities. However, there were also differences between the two intensities. Heart rate exhibited less fluctuation at high- intensity and demonstrated a time-dependent increase known as cardiovascular drift. Additionally, gear 2 sub-technique was employed more frequently than gear 3 on the steepest uphill section during low- intensity compared to high-intensity, while cycle length increased 2–3 times more than cycle rate, and contact time for poles decreased more than contact time for skis when transitioning from low to high- intensity in the same terrain. The findings suggest that many of the demands that are important for XC skiing competitions can be adequately stimulated during low-intensity training, especially in less strenuous terrain. This may partially explain the benefits of low-intensity training, as it allows for a high volume of training while minimizing the accumulation of fatigue.
Mass-start events: an unexplored racing format in XC skiing - Different competition formats in XC skiing vary in distance, style (i.e., classic and/or skating), and type of starting procedure (i.e., individual time trials or mass-starts). Therefore, the impact of associated performance-determining factors can also differ considerably. Despite being the most common race format in XC skiing, massstart events have not been scientifically examined. Hence, we conducted two studies focusing on mass-start events: one describing race development and performance-determining factors in a massstart XC skiing competition (Paper 3) and one exploring physiological and biomechanical responses to a simulated mass-start race on a treadmill (Paper 2).
In Paper 2, it was found that mass-start competitions were influenced by many of the same performance-determining factors as individual time trials. Higher maximal oxygen uptake and gross efficiency were associated with better mass-performance, and uphill performance was identified as the most differentiating terrain. The top skiers utilized skiing sub-techniques suitable for higher speeds and adjusted the associated macro parameters accordingly in steep terrain. However, a novelty of this study was that higher maximal oxygen uptake and gross efficiency capacities appeared to have a different impact on mass-starts compared to time trials. Rather than using superior capacities to ski faster than lower-level peers throughout the entire race, as typically observed in time trials, our findings suggest that skiers with high scores in these performancedetermining variables could conserve energy and “utilize” their reserves better towards the end of the race and during the final sprint.
In Paper 3, we further revealed the importance of group dynamics and related factors in mass-start events. It was observed that skiers formed dynamic packs to benefit from drafting, and the majority of participants adopted the strategy of following the leader for as long as possible. This resulted in a more positive pacing pattern for lower-performing skiers, which may not have been optimal for their performance. The presence of a significant accordion effect in the first half of the competition led to additional decelerations, accelerations, and a higher risk of incidents that disadvantaged skiers positioned at the back of the pack. In summary, the key factors determining mass-start performance were found to be an adequate starting position (based on performance level), the ability to avoid incidents and disadvantages caused by the accordion effect, tolerance for intensity fluctuations, maintaining speed throughout the competition, and possessing well-developed final sprint abilities.
The performance impact of optimizing micro-pacing strategies - An essential factor in endurance competitions is optimizing the pacing strategy, which involves utilizing energetic resources as effectively as possible from start to finish. In XC skiing, skiers naturally employ a variable pacing pattern with higher metabolic rates and power production during uphill sections compared to flat and downhill terrain. Therefore, refining XC skiers micro-pacing strategy by adjusting speed and transitions between sub-techniques within or between terrain sections can be beneficial for performance improvement. Based on practical training with world-class skiers and findings in the literature, it was hypothesized that increasing speed over specific hilltops to save time in subsequent downhill sections, without reducing speed in other parts of the track, could enhance XC skiing performance. It was also hypothesized that this skill could be learned in a short-term competitionpreparation setting.
The intervention conducted in Paper 4 aimed to investigate the performance effects of video- and sensor-based feedback for implementing a terrain-specific micro-pacing strategy in preparation for an XC skiing competition. The results demonstrated that the intervention group significantly reduced the time spent in the targeted downhill segment and overall downhill and flat terrain, compared to matched controls who underwent similar training without any instructions or feedback. No significant effects of the intervention were observed in physiological responses, time spent in uphill terrain, or overall race performance. In conclusion, targeted training combined with video- and sensor-based feedback has the potential to successfully improve terrain-specific micro-pacing strategies in XC skiing.
Utilizing sensors in outdoor XC skiing - In relation to this thesis, the performance, physiological responses, and movement technique of national-level skiers were explored using multiple wearable sensors during training and competition. Global Navigation Satellite Systems (GNSS) sensors were employed to measure speed and position, providing a valuable tool for tracking performance and measuring speed profiles both in training and competition. Inertial Measurement Units (IMUs) were used to validly classify skate sub-techniques and assess the corresponding macro- and microparameters, both indoors and outdoors. IMUs also enabled the estimation of total variation of chest acceleration, which serves as a measure of biomechanical intensity. The exploration of physiological measurements presented several challenges. Simultaneous measurements of oxygen uptake (V̇ O2) and heart rate (HR) revealed that HR exhibited intensity-dependent drift and asymmetrical responses to terrain, which differed from the V̇ O2 response. Therefore, caution must be exercised when interpreting HR measurements as a surrogate for V̇ O2 in fluctuating terrain. Similar caution applies to near-infrared spectroscopy (NIRS) measurements, used to track variations in muscle oxygenation based on terrain and sub-techniques, as there is a significant individual variability that disqualifies its use as an absolute measure. In addition, this approach challenged the practical problem of measuring all parameters at the same time and successfully synchronizing them to a common timeline, which is required to provide complementary and integrative understanding. Lastly, Paper 4 demonstrated that sensor data can be utilized to drive behavioral changes. The methodology employed in this study is likely generalizable and transferable to other settings, offering an effective learning process to improve technical or tactical skills in various sports or during rehabilitation.
Taken together, the studies presented in this thesis provide novel insights into the physiological and biomechanical factors that underpin XC skiing performance. They highlight the significance of pacing strategy, group dynamics, technique, and other performance-determining factors in massstart competitions. The utilization of various sensor data, along with customized signal processing and intelligent classification and detection models, provides valuable new insights into the interconnected physiological and biomechanical demands of XC skiing. Moreover, these findings can be directly applied during training to enhance the quality of each session and effectively improve technical and tactical skills.
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Paper 1: Seeberg, Trine Margrethe; Kocbach, Jan; Danielsen, Jørgen; Noordhof, Dionne; Skovereng, Knut; Meyer, Frederic; Sandbakk, Øyvind Bucher. Physiological and Biomechanical Responses to Cross-Country Skiing in Varying Terrain: Low- vs. High-Intensity. Frontiers in Physiology 2021 ;Volum 12. s. - Copyright © 2021 Seeberg, Kocbach, Danielsen, Noordhof, Skovereng, Meyer and Sandbakk. This is an open-access article distributed under the terms of the Creative Commons Attribution License (CC BY).Paper 2: Seeberg, Trine Margrethe; Kocbach, Jan; Danielsen, Jørgen; Noordhof, Dionne; Skovereng, Knut; Hatling Haugnes, Pål; Tjønnås, Johannes; Sandbakk, Øyvind Bucher. Physiological and Biomechanical Determinants of Sprint Ability Following Variable Intensity Exercise When Roller Ski Skating. Frontiers in Physiology 2021 ;Volum 12. s. - Copyright © 2021 Seeberg, Kocbach, Danielsen, Noordhof, Skovereng, Haugnes, Tjønnås and Sandbakk. This is an open-access article distributed under the terms of the Creative Commons Attribution License (CC BY).
Paper 3: Seeberg, Trine Margrethe; Kocbach, Jan Martin; Wolf, Hanna; Talsnes, Rune Kjøsen; Sandbakk, Øyvind Bucher. Race development and performance-determining factors in a mass-start cross-country skiing competition. Frontiers in Sports and Active Living 2023 ;Volum 4. © 2023 Seeberg, Kocbach, Wolf, Talsnes and Sandbakk. This is an open-access article distributed under the terms of the Creative Commons Attribution License (CC BY).
Paper 4: Seeberg, Trine Margrethe; Kocbach, Jan; Talsnes, Rune Kjøsen; Meyer, Frederic; Losnegard, Thomas Johansen; Tjønnås, Johannes; Sandbakk, Øyvind; Solli, Guro Strøm. Performance Effects of Video- and Sensor-Based Feedback for Implementing a Terrain-Specific Micropacing Strategy in Cross-Country Skiing. International Journal of Sports Physiology and Performance (IJSPP) 2022 ;Volum 17.(12) s. 1672-1682. © 2022 The Authors. Published by Human Kinetics, Inc. This is an Open Access article distributed under the terms of the Creative Commons Attribution-Non Commercial 4.0 International License, CC BY-NC 4.0