Cross-country Skiers Research Articles

Running, walking, and cross-country skiing: how to shape adolescents’ personalities through physical activity?

Adolescence is crucial for personality development, and sports play a significant role. This study investigates the impact of various sports on the personality traits of junior high and high school students in Shandong Province, focusing on neuroticism, extraversion, openness, agreeableness, and conscientiousness. Utilizing data from the “Database of Youth Health,” we employed Seemingly Unrelated Regression (SUR) and Generalized Structural Equation Modeling (GSEM) to analyze the effects of physical activity on personality development. Findings reveal that walking significantly enhances openness and decreased neuroticism, while jogging/running substantially improves extraversion, agreeableness, and conscientiousness. Cross-country skiing, however, negatively impacts all assessed personality traits. In addition, the importance of gender differences in the relationship between physical activity and personality development was revealed. The results offer insights for promoting adolescent personality development through targeted sports activities.

The Electroencephalogram (EEG) Study for Estimating Endurance Sports Performance Base on Eigenvalues Extraction Method

Objectives. Brain–behavior connections are a new means to evaluate sports performance. This electroencephalogram (EEG) study aims to estimate endurance exercise performance by investigating eigenvalue trends and comparing their sensitivity and linearity. Methods. Twenty-three cross-country skiers completed endurance cycling tasks. Twenty-four-channel full-brain EEG signals were recorded in the motor phase and recovery phase continuously. Eighteen EEG eigenvalues calculation methods were collected, commonly used in previous research. Time-frequency, band power, and nonlinear analyses were used to calculate the EEG eigenvalues. Their regression coefficients and correlation coefficients were calculated and compared, with the linear regression method. Results. The time-frequency eigenvalues shift slightly throughout the test. The power eigenvalues changed significantly before and after motor and recovery, but the linearity was not satisfactory. The sensitivity and linearity of the nonlinear eigenvalues were stronger than the other eigenvalues. Of all eigenvalues, Shannon entropy showed completely non-overlapping distribution intervals in the regression coefficients of the two phases, which were −0.1474 ± 0.0806 s−1 in the motor phase and 0.2560 ± 0.1365 s−1 in the recovery phase. Shannon entropy amplitude decreased more in the F region of the brain than in the other regions. Additionally, the higher the level of sport, the slower the decline in Shannon entropy of the athlete. Conclusions. The Shannon entropy method provided more accurate estimations for endurance exercise performance compared to other eigenvalues.

Coaching by doing: communities of practice at Swedish sport schools in XC skiing since the 1970s

Since the introduction of a national system for upper-secondary sport schools in Sweden in the 1970s, these institutions have been an important environment for developments in training and coaching. This is particularly true for cross-country skiing, where these schools quickly became an obligatory passage point. Coaches at the sport schools, often formally employed as PE teachers, were among the first professionalized endurance sport coaches in Sweden. This article examines how communities of practice have influenced the professionalization process of XC ski coaches at Swedish sport schools. The results show how being part of this community is conditioned on personal experience of active learning, historically as a skier yourself and currently as a coach who participates in the everyday work. The strong communities of practice have enabled coaches to maintain a high degree of self-­governance and ensured that experiential knowledge remain important in relation to scientific knowledge.

The Relationship between Inflammatory Factors, Hemoglobin, and VO2 Max in Male Amateur Long-Distance Cross-Country Skiers in the Preparation Period

Background: Identifying factors affecting heart health in amateur athletes can significantly impact their health and help them achieve high performance. The current knowledge of these predictors is insufficient. The purpose of this study was to identify the biochemical determinants of maximal oxygen uptake (VO2 max) in male amateur long-distance cross-country skiers (37.9 ± 6.58 years, 51.08 ± 4.61 VO2 max ml/kg/min) in the preparation period. Methods: In this cross-sectional study, a time trial test was used to determine VO2 max and venous blood via biochemical markers. Descriptive statistics and Pearson correlation were used to analyze the data. The regression model determined the predictors. Results: VO2 max was significantly correlated with nine moderate or weak variables. Two regression models (R2 = 0.94 and R2 = 0.9) each identified two determinants of VO2 max, hemoglobin (p < 0.001) and C-reactive protein (p < 0.001), as well as erythrocyte sedimentation (p < 0.001) and platelets (p = 0.03). Only hemoglobin positive affected VO2 max. Conclusions: The results may indicate, in addition to results regarding hemoglobin concentration and its changes, the necessity to monitor the immune system, which may affect the capacity for amateur exercise. Biochemical monitoring is an essential tool for evaluating the individual adaptation to exercise and developing an effective training plan. The application of this knowledge can facilitate the achievement of optimal individual performance capabilities among cross-country skiing amateurs.

The Effect of Four-Month Training on Biochemical Variables in Amateur Cross-Country Skiers.

Background/Objectives: Research on the effects of training on the health of amateur cross-country skiers remains limited, particularly on biochemical parameters. Therefore, this study aimed to assess such changes in response to four months of training for amateur cross-country skiers. Methods: Blood samples were collected after spring training in May (active rest) and in September at the end of the preparatory period. The Wilcoxon signed-rank test was used for comparison of both measurements (initial and final). Results: Training in a group of amateur cross-country skiers exerts a statistically significant influence on the decrease in leukocyte count (thousand/µL) (p = 0.045) and the decrease in mean corpuscular hemoglobin concentration (MCHC) (g/dL) (p = 0.021). The other parameters did not show statistically significant changes. Conclusions: The change in MCHC and WBC can be attributed to adaptation to prolonged exercise, with a simultaneous increase in VO2 max. It should not be identified with pathology. The decrease in MCHC was likely attributable to changes in hydration status and a slight reduction in hemoglobin concentration. Similarly, it is recommended that other biochemical parameters be within the reference ranges.

Wheat Peptides as Catalysts for Athletic Performance Improvement in Cross-Country Skiers: A Randomized Controlled Trial.

This study investigated the efficacy of wheat peptide supplementation compared to regular proteins in elite cross-country skiers, providing insights into the metabolic and performance effects of these supplements in order to guide athletes in selecting optimal energy sources for training and competition. Nineteen healthy male cross-country skiers were enrolled and assigned to either the peptide group (PEP, n = 9) or the protein group (PRO, n = 10). A four-week intervention study involving supplementation with wheat peptides/regular proteins was conducted, and pre- and post-intervention assessments were performed to evaluate exercise capacity and metabolic profiles. The study found that the PEP group and the PRO group showed distinct within-group effects on exercise performance. The PEP group demonstrated improved aerobic capacity, including better performance in 10 km roller skating, an increased lactate threshold, and reduced resting blood lactate levels. The PRO group enhanced anaerobic capacity, such as improved sprint time, hexagon test performance, and lactate clearance. Metabolomic analysis revealed specific metabolic pathways affected in each group, with the PEP group showing impacts on the α-linolenic acid pathway and the PRO group on ketone body synthesis and degradation as well as vitamin B6 metabolism. Our findings indicate that wheat oligopeptides and regular proteins have comparable effects on exercise performance. However, the wheat peptides may offer greater advantages in enhancing aerobic capacity. No significant variations were observed in blood metabolite profiles between the two groups, but distinct metabolic pathways exhibited different responses.

Gear Classification in Skating Cross-Country Skiing Using Inertial Sensors and Deep Learning.

The aim of this current work is to identify three different gears of cross-country skiing utilizing embedded inertial measurement units and a suitable deep learning model. The cross-country style studied was the skating style during the uphill, which involved three different gears: symmetric gear pushing with poles on both sides (G3) and two asymmetric gears pushing with poles on the right side (G2R) or to the left side (G2L). To monitor the technique, inertial measurement units (IMUs) were affixed to the skis, recording acceleration and Euler angle data during the uphill tests performed by two experienced skiers using the gears under study. The initiation and termination points of the tests were controlled via Bluetooth by a smartphone using a custom application developed with Android Studio. Data were collected on the smartphone and stored on the SD memory cards included in each IMU. Convolutional neural networks combined with long short-term memory were utilized to classify and extract spatio-temporal features. The performance of the model in cross-user evaluations demonstrated an overall accuracy of 90%, and it achieved an accuracy of 98% in the cross-scene evaluations for individual users. These results indicate a promising performance of the developed system in distinguishing between different ski gears within skating styles, providing a valuable tool to enhance ski training and analysis.

Per- and polyfluoroalkyl substances (PFAS) in Ski waxes and snow from cross-country skiing in Germany - Comparative study of sum parameter and target analysis

Per- and polyfluoroalkyl substances (PFAS) are often environmentally exposed via discharge through human consumer products, such as ski waxes. In our study we analyzed various ski waxes from the 1980s and 2020s, to determine both the sum parameter values total fluorine (TF), extractable organically bound fluorine (EOF), hydrolysable organically bound fluorine (HOF) as well as targeted PFAS analysis. This showed that modern high-performance waxes contain up to 6 % TF, but also PFAS-free labelled ski waxes contain traces of PFAS with EOF/HOF values in the low mg kg-1 range. With the ban of all fluorine-based waxes with the start of the 2023/2024 winter season this will probably change soon. Moreover, we applied our analysis methods to snow samples from a frequently used cross country ski trail (Kammloipe) in the Ore Mountain region in Germany, assessing the potential PFAS entry/discharge through ski waxes. Melted snow samples from different spots were analyzed by the adsorbable organically bound fluorine (AOF) sum parameter and PFAS target analysis and confirmed the abrasion of the ski waxes into the snow. Moreover, on a PFAS hotspot also soil samples were analyzed, which indicate that PFAS from the ski waxes adsorb after snow melting into the soil.

A-019 Unexpectedly High Cardiac Troponin Values in Healthy Athletes after SARS-CoV-2 Infection

Abstract Background Elevated levels of cardiac troponin I or T (cTnI, cTnT) in general have immediate clinical consequences including invasive cardiac imaging and rhythm monitoring. Macro-troponin is a complex of antitroponin autoantibodies and cTnI or cTnT and may result in falsely elevated values. In athletes, a reliable exclusion of cardiac disease is crucial to allow for intensive exercise. The prevalence and causes of falsely elevated cTn in professional athletes after SARS-CoV-2 infection are unknown. Methods These are preliminary results of an observational study including 35 professional athletes (16 -75 years old, median 24 years; 19 females, 16 males) who had post-Covid-19 check-ups at their practicing sports physician mostly in the year 2022 (6 athletes in 2023). One female athlete did not have a proven SARS-CoV-2 infection but vaccination. Divergences in high sensitivity (hs) cTn concentrations were investigated according to the sex-specific cut-off values of 4 different assays (hs-cTnI: Alinity/Abbott Diagnostics, Atellica/Siemens Healthineers, Access/Beckman Coulter and hs-cTnT: Cobas/Roche Diagnostics). All athletes were advised to stop training 48h before routine blood drawing and if required underwent electrocardiography (ECG), echocardiography and magnetic resonance imaging to exclude myocardial involvement, particularly when suspicious symptoms were present. Athletes with divergent hs-cTn assay results were further analyzed for the presence of macro-troponin using the reference method sucrose gradient ultracentrifugation. Results The two main professional sports were cycling (mountain biking or road biking) and soccer, further sports comprised curling, swimming, running including marathon, floorball, cross-country skiing or rhythmic gymnastics. Athletes mostly suffered from postviral exhaustion, mild infectious symptoms like headache, sore throat, dry cough, subfebrile temperature, or sniffles or had atypical thoracic pain. There were two males with known secondary diagnoses, one 25 years old with diabetes mellitus type 1 and one 75 years old with atherosclerosis and hypercholesterolemia. Eighteen (18/35) athletes had hs-cTn concentrations within the sex-specific cut-off values in all assays and did not undergo further investigation for macro-troponin by sucrose gradient ultracentrifugation. However, in 17 athletes (17/35) hs-cTn was increased in at least one assay method which was mostly a hs-cTnI method (for 2/17 all assays elevated). The sucrose-gradient ultracentrifugation method proved macro-troponin in 15/17 with original hs-cTn values for Abbott Alinity: 5 - 170 ng/L; Siemens Atellica: 9.6 - 376 ng/L; Beckman Access: 0.5 - 55 ng/L and Roche Cobas 4 - 77 ng/L. However, 2/17 had the free troponin form, one with only a minor hs-cTnT increase above the sex-specific cut-off and the other with increased values in all hs-cTn assays but normal values in a 2- and 4-days control follow-up measurement. Notably, there were no ECG or cardiac imaging findings including echocardiography or cardiac magnetic resonance imaging suggestive of myocarditis in the investigated athletes. Conclusions After SARS-CoV-2 infection, cTn might be increased in athletes without a correlate in ECG or imaging reports. This should prompt physicians to consider an assay interference by macro-troponin, particularly if a second troponin method such as hs-cTnT remains normal. AHL & CK share first and OH & CM share last authorship

Effects Of Ischemic Preconditioning On Adaptations To An Altitude Training Camp In Well-trained Cross-country Skiers

Effects Of Ischemic Preconditioning On Adaptations To An Altitude Training Camp In Well-trained Cross-country Skiers

The Evolvement of Session Design From Junior Age to Senior Peak Performance in World-Class Cross-Country Skiers.

To compare designs of training sessions applied by world-class cross-countryskiers during their most successful junior and senior season. Retrospective analysis of self-reported training characteristics (ie,training form, intensity, and exercise mode) among 8 male and 7 female world-class cross-country skiers was conducted. Total number of sessions (441 [71] vs 519 [34], P < .001, large effect) and mean duration (1.5 [0.1]h vs 1.7 [0.1]h, P < .001, moderate effect) increased from junior to senior age. More double-session days were performed at senior age (124 [50] vs 197 [29]d, P < .001, large). The number (310 [64] vs 393 [64], P < .001, large effect) and duration (1.3 [0.1]h vs 1.5 [0.1]h, P < .001, moderate effect) of low-intensity training sessions increased from junior to senior age. Regarding intensive training, most emphasis was put on high-intensity training sessions lasting 20 to 39minutes with <5-minute intervals at junior age, while 40 to 59minutes ofmoderate-intensity training with 5- to 9-minute intervals was predominant at senior age. More MIXED (combined moderate- and high-intensity) sessions (9 [7] vs 14 [7], P = .023, moderate effect) and longer races (0.5 [0.1]h vs 0.6 [0.1]h, P = 0.29, moderate effect) compensated for fewer high-intensity training sessions at senior age (36 [17] vs 25 [10], P = .027, moderate effect). Duration of strength-training sessions increased significantly (0.6 [0.1] vs 0.8 [0.2]h, P = 0.30, moderate effect), while other training forms remained unchanged. World-class cross-country skiers increased their training volume from junior to senior age primarily by more and longer low-intensity training sessions and more often training twice per day. Concurrently, the most frequent intensive sessions were modified from high- to moderate-intensity training, lasted longer, and contained longer intervals.

Aerobic capacity and respiratory indices of junior cross-country skiers and biathletes during incremental exercise testing.

The present study compared the isocapnic buffering phase (ICB), hypocapnic hyperventilation phase, ventilatory threshold (VT), respiratory compensation point (RCP), and maximum oxygen uptake (VO2max) among biathlon and cross-country ski athletes during an incremental exercise test. 37 male and 33 female Turkish National Team athletes volunteered to participate in the research. Body fat percentage, lean mass, and fat mass values of athletes were measured using the bioelectrical impedance analysis method, and oxygen consumption (VO2) was measured with a portable cardiopulmonary exercise test system with a ramp protocol on the treadmill. In VT, RCP, and VO2max phases, male athletes had higher VO2 and speed values than female athletes (p < 0.05). In contrast, they had similar values across different categories of sports (biathlon and cross-country skiing) (p > 0.05). Additionally, XC skiers and males had higher absolute (Abs) VO2 and mass-normalized (Rel) VO2 values than biathletes and females in exhaustion times and ICBs (p < 0.05). In contrast, they had similar Abs VO2 and Rel VO2 values in hypocapnic hyperventilation phases (p > 0.05). In addition, XC skiers and males had higher absolute (Abs) VO2 and relative (Rel) VO2 values than biathletes and females in exhaustion times and ICBs (p < 0.05). In contrast, they had similar Abs VO2 and Rel VO2 values in hypocapnic hyperventilation phases (p > 0.05). These results indicate significant differences in physiological profiles between male and female athletes and between XC skiers and biathletes.

Nordic walking – the healthiest sport ever? – A review

Nordic Walking (NW) is a widely practiced sport that was originally intended as a way for cross-country skiers to get a year-round workout. However, it quickly proved to be easy, enjoyable and undemanding, which led populations around the world to train NW. Today, the sport is used as rehabilitation in most medical specialties, as it is considered to be safe, not creating barriers, inexpensive and has no side effects. This article presents a literature review on the effects of NW on patients' mental and physical health.

Cross-Country Ski Skating Style Sub-Technique Detection and Skiing Characteristic Analysis on Snow Using High-Precision GNSS.

A comprehensive analysis of cross-country skiing races is a pivotal step in establishing effective training objectives and tactical strategies. This study aimed to develop a method of classifying sub-techniques and analyzing skiing characteristics during cross-country skiing skating style timed races on snow using high-precision kinematic GNSS devices. The study involved attaching GNSS devices to the heads of two athletes during skating style timed races on cross-country ski courses. These devices provided precise positional data and recorded vertical and horizontal head movements and velocity over ground (VOG). Based on these data, sub-techniques were classified by defining waveform patterns for G2, G3, G4, and G6P (G6 with poling action). The validity of the classification was verified by comparing the GNSS data with video analysis, a process that yielded classification accuracies ranging from 95.0% to 98.8% for G2, G3, G4, and G6P. Notably, G4 emerged as the fastest technique, with sub-technique selection varying among skiers and being influenced by skiing velocity and course inclination. The study's findings have practical implications for athletes and coaches as they demonstrate that high-precision kinematic GNSS devices can accurately classify sub-techniques and detect skiing characteristics during skating style cross-country skiing races, thereby providing valuable insights for training and strategy development.

Metabolic Phenotyping from Whole-Blood Responses to a Standardized Exercise Test May Discriminate for Physiological, Performance, and Illness Outcomes: A Pilot Study in Highly-Trained Cross-Country Skiers

BackgroundThis study used metabolic phenotyping to explore the responses of highly-trained cross-country skiers to a standardized exercise test, which was part of the athletes’ routine testing, and determine whether metabolic phenotyping could discriminate specific physiological, performance, and illness characteristics.MethodsTwenty-three highly-trained cross-country skiers (10 women and 13 men) participated in this study. Capillary whole-blood samples were collected before (at rest) and 2.5 min after (post-exercise) a roller-ski treadmill test consisting of 5–6 × 4-min submaximal stages followed by a self-paced time trial (~ 3 min) and analyzed using mass spectrometry. Performance level was defined by International Ski Federation distance and sprint rankings. Illness data were collected prospectively for 33 weeks using the Oslo Sports Trauma Research Center Questionnaire on Health Problems. Orthogonal partial least squares-discriminant analyses (OPLS-DA) followed by enrichment analyses were used to identify metabolic phenotypes of athlete groups with specific physiological, performance, and illness characteristics.ResultsBlood metabolite phenotypes were significantly different after the standardized exercise test compared to rest for metabolites involved in energy, purine, and nucleotide metabolism (all OPLS-DA p < 0.001). Acute changes in the metabolic phenotype from rest to post-exercise could discriminate athletes with: (1) higher vs. lower peak blood lactate concentrations; (2) superior vs. inferior performance levels in sprint skiing, and (3) ≥ 2 vs. ≤ 1 self-reported illness episodes in the 33-week study period (all p < 0.05). The most important metabolites contributing to the distinction of groups according to (1) post-exercise blood lactate concentrations, (2) sprint performance, and (3) illness frequency were: (1) inosine, hypoxanthine, and deoxycholic acid, (2) sorbitol, adenosine monophosphate, and 2-hydroxyleuroylcarnitine, and (3) glucose-6-phosphate, squalene, and deoxycholic acid, respectively.ConclusionMetabolic phenotyping discriminated between athlete groups with higher vs. lower post-exercise blood lactate concentrations, superior vs. inferior sprint skiing performance, and more vs. less self-reported illnesses. While the biological relevance of the identified biomarkers requires validation in future research, metabolic phenotyping shows promise as a tool for routine monitoring of highly-trained endurance athletes.

Post-race reactions: The emotional paradox of high performance and anxiety – a conventional content analysis

BackgroundStudies examining post-race emotional experiences in the context of endurance races among recreational athletes are scarce. The purpose of this study was to describe how recreational athletes experience the time after completing an endurance race.MethodsIn this study, a qualitative study design was used, and data collection was carried out with semi-structured interviews. The selection of subjects was completed systematically through criterion selection. The selection criteria were men and women, aged 18 years or older, who had completed an endurance race, and finished, lasting at least 180 min within the past 12 months. The interviews were analyzed using conventional qualitative content analysis.ResultsSixteen recreational endurance athletes who, within six months, had completed an endurance race of running, cycling, cross-country skiing or Ironman, participated and were interviewed. Four overarching themes emerged from the analysis: “High on life”, “Loss of energy, Ambivalence and Melancholy”, “Activity-charged emotions”, and “Dimensions of emotions over time and new goals”, describing the content of the interviews.ConclusionsEndurance athletes experienced varied post-race emotions that were both physically and mentally challenging, suggesting a holistic approach to managing post-race emotions would be beneficial. From the athletes’ perspectives, post-race feelings were dependent on many factors, including time spent training for a specific race, and perceived inability to set new goals for an upcoming training period. Setting future goals prior to an event may be a tool for reducing the risk of negative post-race emotions, including post-race blues.

Nature-based winter sports and their ephemeral tracks: interspecies (non-)encounters in snow

Nature-based winter sports are often framed as a solution to the tension between people’s desire for pristine snowy landscapes and their effects on that environment. Low-impact activities such as ski touring and cross-country skiing allow outdoor enthusiasts to visit remote and mountainous locations without the need for hard infrastructure of ski resorts, leaving no permanent marks in the landscape. Yet their growing popularity raises a dilemma about negative effects, especially on wildlife conservation areas. We use the tracks and traces left behind by people as well as animals in Northern Europe and the Alps as a nexus through which to explore how humans and non-humans interact, ignore or avoid each other. Often imagined as ephemeral activities, we argue that the cumulative impacts of nature-based winter sports have significant consequences for wildlife and the way we aim to protect it long after its traces in the snow have disappeared.

A Smart Ski Pole for Skiing Pattern Recognition and Quantification Application.

In cross-country skiing, ski poles play a crucial role in technique, propulsion, and overall performance. The kinematic parameters of ski poles can provide valuable information about the skier's technique, which is of great significance for coaches and athletes seeking to improve their skiing performance. In this work, a new smart ski pole is proposed, which combines the uniaxial load cell and the inertial measurement unit (IMU), aiming to provide comprehensive data measurement functions more easily and to play an auxiliary role in training. The ski pole can collect data directly related to skiing technical actions, such as the skier's pole force, pole angle, inertia data, etc., and the system's design, based on wireless transmission, makes the system more convenient to provide comprehensive data acquisition functions, in order to achieve a more simple and efficient use experience. In this experiment, the characteristic data obtained from the ski poles during the Double Poling of three skiers were extracted and the sample t-test was conducted. The results showed that the three skiers had significant differences in pole force, pole angle, and pole time. Spearman correlation analysis was used to analyze the sports data of the people with good performance, and the results showed that the pole force and speed (r = 0.71) and pole support angle (r = 0.76) were significantly correlated. In addition, this study adopted the commonly used inertial sensor data for action recognition, combined with the load cell data as the input of the ski technical action recognition algorithm, and the recognition accuracy of five kinds of cross-country skiing technical actions (Diagonal Stride (DS), Double Poling (DP), Kick Double Poling (KDP), Two-stroke Glide (G2) and Five-stroke Glide (G5)) reached 99.5%, and the accuracy was significantly improved compared with similar recognition systems. Therefore, the equipment is expected to be a valuable training tool for coaches and athletes, helping them to better understand and improve their ski maneuver technique.

Long-Term Incidence of Bradycardia and Pacemaker Implantations Among Cross-Country Skiers: A Cohort Study.

Bradycardia is more common among well-trained athletes than in the general population, but the association with pacemaker implantations is less known. We investigated associations of endurance training with incidence of bradycardia and pacemaker implantations, including sex differences and long-term outcome, in a cohort of endurance trained individuals. All Swedish skiers who completed >1 race in the cross-country skiing event Vasaloppet between 1989 and 2011 (n=209 108) and a sample of 532 290 nonskiers were followed until first event of bradycardia, pacemaker implantation, or death, depending on end point. The Swedish National Patient Register was used to obtain diagnoses. Cox regression was used to investigate associations of number of completed races and finishing time in Vasaloppet with incidence of bradycardia and pacemaker implantations. In addition, Cox regression was used to investigate associations of pacemaker implantations with death in skiers and nonskiers. Male skiers had a higher incidence of bradycardia (adjusted hazard ratio [aHR], 1.19 [95% CI, 1.05-1.34]) and pacemaker implantations (aHR, 1.17 [95% CI, 1.04-1.31]) compared with male nonskiers. Those who completed the most races and had the best performances exhibited the highest incidence. For female skiers in Vasaloppet, the incidence of bradycardia (aHR, 0.98 [95% CI, 0.75-1.30]) and pacemaker implantations (aHR, 0.98 [95% CI, 0.75-1.29]) was not different from that of female nonskiers. The indication for pacemaker differed between skiers and nonskiers, with sick sinus syndrome more common in the former and third-degree atrioventricular block in the latter. Skiers had lower overall mortality rates than nonskiers (aHR, 0.16 [95% CI, 0.15-0.17]). There were no differences in mortality rates by pacemaker status among skiers. In this study, male endurance skiers had a higher incidence of bradycardia and pacemaker implantations compared with nonskiers, a pattern not seen in women. Among male skiers, those who completed the most races and had the fastest finishing times had the highest incidence of bradycardia and pacemaker implantations. Within each group, mortality rates did not differ in relation to pacemaker status. These findings suggest that bradycardia associated with training leads to a higher risk for pacemaker implantation without a detrimental effect on mortality risk.

Design and development of a feedback system for automatic treadmill speed adaptation

Treadmills with automatic speed adjustment offer a unique advantage: they can mimic outdoor conditions for specific training or testing protocols. This versatility makes them highly applicable in both sports and rehabilitation settings. This study presents a novel framework based on a feedback control loop system, conceived to control a treadmill belt speed using a non-invasive and low-cost sensor (Microsoft Kinect) to detect the users’ position and avoid object obstruction issues. The speed of the treadmill belt is regulated according to the user’s speed, by means of a proportional-integrative-derivative (PID) controller and a parabolic gain function. By tuning the gain function parameters, the user can customize the response of the treadmill. Position data collected during exercise using the Microsoft Kinect sensor was compared with that collected with a stereophotogrammetric motion capture system, showing promising results in terms of accuracy in position assessment. The comparison highlighted a 0.9 degree of correlation between the two systems during the running and cross-country indoor skiing tests performed. In addition, upon considering the relationship between the differences and averages of the two measures, no systematic bias was identified. The system proved to be functional for running and cross-country skiing, and it can therefore re-create similar typical characteristics of outdoor environments (e.g., speed and slope) thanks to the non-invasive user’s position detection and the customizable gain function.