Mid Sweden University

Purpose: This study aimed to investigate how pole length, incline, and skiing intensity affect lower back muscle activation in elite cross-country skiers. This addressing a critical gap in understanding the biomechanical demands and risk of low back pain of double poling (DP). Method: Eleven elite cross-country skiers performed skiing trials on a treadmill, varying in incline (flat vs. 6 degrees), intensity (two self-selected speeds, training speed and racing speed), and pole lengths. Muscle activity was measured by surface electromyography on the erector spinae thoracic and lumbar muscles, on the left and right side. A motion capture system was used for kinematic analysis of the lower back-pole moment arm and the hip angle during the DP cycle. Results: Compared to men, female skiers had a significantly higher (p < 0.001), overall muscle activation for the m. erector spinae lumbar on both the left and right side (26% of MVC vs. 15% of MVC, and 28% of MVC vs. 22% of MVC, for the left and right side, respectively). No correlations were found, neither between muscle activation to the lower back-pole moment arm, or to the hip angle. Conclusion: The findings suggest that female skiers experience significantly higher lumbar erector spinae activation during DP, potentially indicating greater susceptibility to back-related issues. The results also highlight the need to tailor training and right adapted equipment to mitigate lower back stress, especially in flat terrain high-intensity conditions. The asymmetrical muscle activity and gender differences underscores the need for further investigation into biomechanical factors influencing back muscle engagement in cross-country skiing.

Purpose: This study aimed to differentiate external and internal training loads during on-snow biathlon training by adding an accelerometer-derived metric.

Methods: Eleven adolescent athletes were fitted with a combined heart rate (HR) and accelerometer to be worn during all training sessions. Duration, HR, training impulse (TRIMP), and average net force (AvFNetAvFNet) were used as training variables. All training was divided into either low-intensity training (LIT), or high-intensity training (HIT) based on reported intensity. The training was further categorized as training without any shooting practice (NS) or as a combination of skiing and shooting (COMB). Duration, HR, TRIMP, and AvFNetAvFNet were analyzed in a linear mixed model for the different training modalities.

Results: All training was similar in duration for LIT and HIT sessions (p = .0521) and NS and COMB sessions (p = .988). TRIMP did not differentiate between LIT or HIT training (p = .350) or for NS compared to COMB (p = .298). While AvFNetAvFNet decreased during COMB compared to NS during LIT sessions (p < .001) it remained similar during HIT training (p = 1.00).

Conclusion: The study’s findings indicated that there were no notable differences in internal training load (TRIMP) when comparing various training intensities and modes. However, the type of training had a significant impact on AvFNetAvFNet, especially leading to a decrease during COMB sessions under LIT conditions. Incorporating an external load metric could offer a fresh approach when prescribing and evaluating training, providing deeper insights into the training load.

Introduction: Officials are essential in terms of player safety and injury prevention, especially in contact team sports such as ice hockey, where numerous fast pace and high force contacts occur. If against the rules, these collisions can result in penalties. However, there is limited literature on the inter-rater reliability of the officials’ decisions. Hence, the purpose was to investigate the theoretical reliability agreement between professional ice hockey officials in the Swedish Hockey League (SHL).

Method: Fifty video clips with different match situations were shown to 33 professional ice hockey officials in the SHL. Each situation was shown three times and the officials had 20 s between each video clip to answer which offence and penalty they would judge. The answers were anonymously collected using an online questionnaire. Fleiss’ kappa was used to assess the reliability agreement between the referees, for each situation.

Results: The Fleiss’ kappa values for all officials were 0.63 and 0.35 for offences and penalties, respectively. Referees and linesmen had similar kappa values for offences (0.64 vs. 0.64), as well as for penalties (0.38 vs. 0.35).

Conclusion: The results show that the suggested methodology can be used to identify situations where officials agree and disagree. In ice hockey, poor agreement regarding penalties can depend on the chosen offence as the rulebook limits the availability of penalties, based on the chosen offence. This can create issues, as there are situations where different offences are equally correct but will result in different penalties.

The purpose of this study was to develop a method which uses positioning data to analyse player-specific skating characteristics and to investigate the possibility to use a cost function to generate new individual and game-specific training drills. Positioning data and video from a game for professional ice hockey team in the Swedish Hockey League were synchronized, and nine different skating characteristics were manually identified and tagged for two forward players. A cost function was developed to generate individual, continuous skating sequences and to create new individual and game-specific skating drills. Skating forward was the most commonly used skating characteristic for both player but the numbers of times the players used the different skating characteristics varied, (H(8) = 23.2, p = 0.003). The number of skating characteristics between the two players differed, (chi(2) (8, N = 688) = 3 4.0, p < 0.001). While the total average time spent in a skating characteristic was 2.01 +/- 1.13 s, time spent within each skating characteristic varied (p < 0.001). The presented method could generate individual skating drills with different attributes and shows promising results for creating individual and game-specific tests and training drills for ice hockey players, based on individual and game-specific skating characteristics.

The aim of this study was to determine the impact of runs 1 and 2 on overall rank in Giant Slalom. Data from 15 seasons (2005/2006–2019/2020) including and unique starts for women (n = 2,294) and men (n = 2,328) were analyzed. Skiers were grouped based on final ranks 1–3 (G3), 4–10 (G10), and 11–20 (G20) and separately analyzed for women and men. A Wilcoxon-signed rank test was used for comparisons between runs 1 and 2, while a multi-nominal logistic regression was used to identify odds ratios (OR) associated with group rank. Women had similar run times for runs 1 and 2 (p = 0.734), while men had faster times on run 2 (p < 0.001). The strongest association to G3 was during run 1 for run time (men: OR 1.06–1.12; women: OR 1.06–1.11, all p < 0.01) and gate-to-gate times (men: OR 33–475; women: OR 81–2,301, all p < 0.001). Overall, this study demonstrates the importance of a fast first run for improving the final ranking group and the need to increase the tempo going from the first to the second run for men.

This study examined the micro-pacing strategies during a distance freestyle cross-country (XC) skiing competition. Nine female and 10 male highly trained XC skiers wore a GNSS device during a FIS-sanctioned race. The course was ~4900 m; women completed two-laps; men completed three-laps. The course was divided into uphill (S1, S3, S5, S7), downhill (S2, S4, S6, S8), and flat (S9) sections for analyses. Statistical parametric mapping was used to determine the course positions (clusters) where total race time or section time was significantly associated with instantaneous skiing speed. Total race time was associated with instantaneous skiing speed during a cluster in S1 on lap 2 for both sexes (t ≥ 5.899, p ≤ 0.008). The two longest uphill sections (S1; S5) and the flat section (S9) contained clusters where section times were related to instantaneous skiing speed for both sexes (p < 0.05). The fastest woman gained 6.9 s on the slowest woman during a cluster in S1 on lap 1 and 7.3 s during a cluster in S9 on lap 1. The fastest man gained 51.7 s on the slowest man over all clusters in S5 over the 3 laps combined. Compared to skiers with longer total race times, skiers with shorter race times skied with faster instantaneous speeds in some clusters of the uphill sections, as well as on the flat section of the course. This study also identified different relative micro-pacing strategies for women and men during freestyle distance XC skiing races. Finally, statistical parametric mapping analyses can help to identify individual strengths and weaknesses for guiding training programs and optimise competition pacing strategies.

The International Ski Federation (FIS) implemented new ski regulation prior to the 2012/2013 season for men and women and for the men again prior to the 2017/2018 season in an effort to increase skiers’ safety in the Giant Slalom (GS) event in the Alpine World Cup (WC). At present, no study has investigated how these changes impacted total race times, gate-to-gate times or number of gates per race. Hence, the purpose of this study was to investigate how the regulation changes have affected these parameters. Data were collected from the official result lists, by the FIS, for the GS event during 15 WC seasons (2005/2006-2019/2020), for men and women, respectively and grouped into Rule 1 (2005/2006-2011/2012), Rule 2 (2012/2013-2016/2017) and Rule 3 (2017/2018-2019/2020). Differences (for total race time, gate-to-gate times and number of gates) between rules were analyzed using Mann-Whitney tests and Kruskal-Wallis rank sum tests for women and men, respectively. For male skiers, the race time during Rule 2 was 152.51 (138.72-157.55) s, which was significantly slower (p < 0.01) than Rule 1, 147.42 (143.13-154.26) s and to Rule 3, 149.37 (135.63-158.32) s (p<0.05). For women, race times during Rule 1 was significant slower (p<0.001, r=0.23, df =455, U=939852.5, z = 12.079) than Rule 2, 141.3 (132.71-148.78) s vs. 137.12 (125.05-146.78) s. The men’s gate-to-gate times increased for Rule 2 compared to Rule 3, 1.49 (1.45-1.55) s vs. 1.48 (1.45-1.52) s, p<0.05), whereas the women’s gate-to-gate times decreased for Rule 2 compared to Rule 1, 1.53 (1.48-1.57) s, vs 1.57 (1.52-1.62) s, p<0.001. Changing the ski equipment regulations affected men and women differently as well the course setting and should not be considered as the sole effort to reduce skiing speed and risk of injury in GS in the alpine WC.

This study investigates the feasibility to use a passive marker motion capture system on ice to collect 3D kinematics of slap shots and one timers. Kinematic data were collected within a volume of 40x15x2 m by 20 motion capture cameras at 300 Hz, a resolution of 12 megapixels and a mean residual for all cameras of 3.4±2.5 mm, at a distance of 11.6 m. Puck velocity, blade velocity, ice contact time and distance to the puck were analysed for ten consecutive shots for each technique, for two professional ice hockey players. The total mean puck velocity was 38.0 ± 2.7 m/s vs. 36.4 ± 1.0 m/s. (p=0.053), for one timers and slap shots respectively. One player had higher puck velocity with one timers compared to slap shots 40.5 ± 1.0 m/s vs. 36.9 ± 1.0 m/s (p=0.001). Puck contact time was longer for slap shots than for one timers, 0.020 ± 0.002 s vs. 0.015 ± 0.002 s, (p<0.001). The motion capture system allowed continuous kinematic analyses of the puck and blade velocities, ice contact times and detailed stance information. The results demonstrate the possibilities to use motion capture systems to collect and analyse shooting kinematics on ice, in detail.

Purpose:

To 1) investigate the cardiorespiratory and metabolic response of trail running and 2) evaluate whether heart rate (HR) adequately reflects the exercise intensity or whether the tissue saturation index (TSI) could provide a more accurate measure when running in hilly terrain.

Methods:

Seventeen competitive runners (female: n=4, V’O_2max: 55±6 mL·kg⁻¹·min⁻¹; male: n=13, V’O_2max: 68±6 mL·kg⁻¹·min⁻¹) performed a time trial on an off-road trail course. The course was made up of two laps covering a total distance of 7 km and included six steep up- and downhill sections with an elevation gain of 486 m. All runners were equipped with a portable breath-by-breath gas analyzer, HR belt, global positioning system receiver and near-infrared spectroscopy (NIRS) device to measure the TSI.

Results:

During the trail run, the exercise intensity within the uphill and downhill sections was 94±2% and 91±3% of HR_max, 84±8% and 68±7% of V’O_2max, respectively. The oxygen uptake (V’O₂) increased within the uphill and decreased within the downhill sections (P< .01). While HR was unaffected by the altering slope conditions, the TSI was inversely correlated to the changes in V’O₂ (r = - .70, P< .05).

Conclusions:

The HR was unaffected by the continuously changing exercise intensity, however, the TSI reflected the alternations in V’O₂. Recently used exclusively for scientific purpose, this NIRS based variable may offer a more accurate alternative to HR to monitor running intensity in the future, especially for training and competition in hilly terrain.