Mid Sweden University

BACKGROUND: This 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.

METHODS: Twenty-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.

RESULTS: Blood 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.

CONCLUSION: Metabolic 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.

Objective Few long-term prospective studies have investigated health problems in elite competitive cross-country (XC) skiers. Hence, our objective was to compare the prevalence of health problems in national team XC skiers over a competitive season.

Methods Forty national team XC skiers participated in this prospective, observational study. Two groups were characterized according to performance level: senior (n=18, ~26 years old, 9 women) and development (n=22, ~21 years old, 9 women). The skiers reported all and substantial injuries and illnesses weekly for 17 consecutive weeks throughout the 2019/2020 competitive season using the Oslo Sports Trauma Research Center Questionnaire on Health Problems.

Results The average weekly prevalence of all and substantial health problems was 19% (95% CI: 16% to 22%) and 12% (95% CI: 9% to 15%), respectively, and was similar between senior and development level skiers (p>0.05). The injury prevalence was higher in senior versus development level skiers (12%, 95% CI: 9% to 15% vs 5%, 95% CI: 3% to 7%; p<0.001), while illnesses were less common (8%, 95% CI: 3% to 13% vs 13%, 95% CI: 9% to 17%, respectively; p=0.031). Illnesses accounted for 72% of all problems. The prevalence of all health problems was higher in female than in male skiers (23%, 95% CI: 19% to 27% vs 15%, 95% CI: 11% to 19%; p<0.003).

Conclusions Health problems, especially illnesses, were relatively common, with approximately one in five skiers (19%) reporting at least one problem in any given week. Both performance level and sex influenced the prevalence of different types of health problems.

Objective: To monitor the daily variations and time course of changes in selected variables during a 17–21-day altitude training camp at 1,800 m in a group of elite cross-country skiers (9 women, 12 men) and biathletes (7 women, 4 men).

Methods: Among other variables, resting peripheral oxygen saturation (SpO2rest), resting heart rate (HRrest) and urine specific gravity (USG) were monitored daily at altitude, while illness symptoms were monitored weekly. Before and after the camp, body composition (i.e., lean and fat mass) and body mass were assessed in all athletes, while roller-skiing speed at a blood lactate concentration of 4 mmol·L−1 (Speed@4mmol) was assessed in the biathletes only.

Results: Neither SpO2rest, HRrest nor USG changed systematically during the camp (p > 0.05), although some daily time points differed from day one for the latter two variables (p < 0.05). In addition, body composition and body mass were unchanged from before to after the camp (p > 0.05). Eleven out of 15 illness episodes were reported within 4 days of the outbound or homebound flight. The five biathletes who remained free of illness increased their Speed@4mmol by ~ 4% from before to after the camp (p = 0.031).

Conclusions: The present results show that measures typically recommended to monitor acclimatization and responses to altitude in athletes (e.g., SpO2rest and HRrest) did not change systematically over time. Further research is needed to explore the utility of these and other measures in elite endurance athletes at altitudes typical of competition environments.

Competitive cross-country (XC) ski athletes (defined hereafter as XC skiers and biathletes combined) are vulnerable to developing various health-related symptoms and conditions due to several factors, such as high physiological and psychological demands, extreme competition and training environments, high training loads, demanding competition schedules, and frequent travel. On initiating this work, we (the author and supervisory team) were approached by the Swedish Ski Association (SSF) and the Swedish Biathlon Federation (SSSF) to investigate the relationships between training, racing, and health problems, with a specific focus on illnesses (rather than injuries), and an ultimate goal of improving future support practices and athletic performance. The project coincided with the teams’ Olympic-cycle preparations for the 2022 Beijing Olympic Winter Games, which were held at an altitude of ~ 1700 m. Therefore, optimizing preparation to competitions at altitude was also a key concern for the two sports organizations.

The project comprised four studies (Study I–IV). In Study I we examined the endurance training, performance, and illnesses characteristic in a group of highly-trained XC skiers throughout their transition from junior to senior level. In Study II we investigated the prevalence of injuries and illnesses in national team XC skiers over a competitive XC ski season. In Study III we monitored the daily variations and time course of changes in selected subjective and objective variables during an altitude training camp at ~ 1800 m in national team XC skiers and biathletes. Finally, in Study IV we explored whether the resting metabolic profile or changes in the metabolic profile in response to an exercise test can discriminate between athlete groups with different physiological, performance, and illness characteristics.

The skiers in Study I progressively increased their endurance training volume in a linear fashion from age 16 to 22 years old by ~ 50 h per year from ~ 470 h at age 16 to ~ 730 h at age 22 years old. The increase in endurance training volume was primarily achieved through an increase in low-intensity training and sport-specific training, rather than high-intensity and non-specific training. Furthermore, the skiers in Study I reported an average of three illness episodes per year, each typically lasting four days, which is comparable to senior elite-level athletes and the general population. During the competitive season health problems, especially illnesses, were relatively common, with approximately one in five skiers (19%) reporting at least one problem in any given week (Study II). Moreover, while the prevalence of all health problems was similar between performance levels, illnesses were less prevalent and overuse injuries were more prevalent in senior compared with development level skiers. Health problems, especially illnesses, were also more prevalent among female than male XC skiers.

In Study III, we observed that measures typically recommended to monitor acclimatization and responses to altitude in athletes, such as resting peripheral oxygen saturation (SpO_2rest) and resting heart rate (HR_rest), did not follow the patterns suggested in the literature (e.g., an increase in SpO_2rest and a decrease in HRrest over time at altitude). We also observed that 11 out of 15 illness episodes were reported within four days of the outbound or homebound flight. In addition, the biathletes who remained free of illness improved submaximal endurance performance from before to after the camp by ~ 4%.

Study IV showed that acute changes in the metabolic profile in response to a standardized exercise testing session could distinguish athletes based on performance level in sprint skiing competitions, and illness susceptibility in the subsequent 33 weeks. This information is particularly valuable for susceptible athletes and their coaches, as preventive measures, such as vaccination, hygiene education, and social distancing, can be implemented to reduce the risk of illness.

Overall, this thesis expands upon previous knowledge about the health and training of competitive XC ski athletes and provides insights that can improve the support practices and athletic performance within the sports of XC skiing and biathlon.

Längdskidåkare och skidskyttar är sårbara för olika negativa hälsorelaterade tillstånd som en konsekvens av till exempel höga fysiologiska och psykologiska krav, extrema tävlings- och träningsmiljöer, hög träningsbelastning, krävande tävlingsscheman och frekventa resor. Denna avhandling ämnar undersöka sambanden mellan träning, prestation och hälsoproblem, med ett särskilt fokus på sjukdomar, och syftet att förbättra det stöd som ges till de aktiva och slutligen öka deras prestationsförmåga.

Avhandlingen består av fyra separata studier (Studie I–IV). I Studie I undersökte vi uthållighetsträningen, prestationsförmågan och sjukdomstillfällen i en grupp vältränade längdskidåkare under deras övergång från junior- till seniornivå. I Studie II undersökte vi förekomsten av skador och sjukdomar i en grupp längdskidåkare på landslagsnivå över en tävlingssäsong. I Studie III övervakade vi de dagliga variationerna och tidsförloppet för förändringar i utvalda subjektiva och objektiva variabler under ett höjdträningsläger på ~ 1800 m i en grupp längdskidåkare och skidskyttar på landslagsnivå. Slutligen, i Studie IV undersökte vi huruvida den metaboliska profilen i vila och efter ett standardiserat träningstest skiljer mellan skidåkare med olika fysiologiska egenskaper och prestations- och sjukdomshistorik.

Skidåkarna i Studie I ökade sin uthållighetsträningsvolym linjärt från 16 till 22 års ålder med ~ 50 timmar per år, från ~ 470 timmar vid 16 års ålder till ~ 730 timmar vid 22 års ålder. Ökningen uppnåddes främst genom en ökning av lågintensiv och sportspecifik träning, snarare än högintensiv och ospecifik träning. Dessutom rapporterade skidåkarna i Studie I i genomsnitt tre sjukdomsepisoder per år med en genomsnittlig duration på fyra dagar, vilket är jämförbart med idrottare på elitseniornivå och den allmänna befolkningen. Under tävlingssäsongen var hälsoproblem, särskilt sjukdomar, relativt vanliga. I genomsnitt rapporterade en av fem (19%) av skidåkarna i Studie II minst ett hälsoproblem varje vecka. Medans förekomsten av alla typer av hälsoproblem var likartad mellan prestationsnivåerna, var sjukdomar mindre vanliga och överbelastningsskador vanligare bland aktiva på en elitnivå jämfört med aktiva på en utvecklingsnivå. Dessutom var hälsoproblem, särskilt sjukdomar, vanligare bland de kvinnliga jämfört med manliga skidåkarna.

I Studie III observerade vi att vanligt förekommande variabler för att monitorera acklimatisering på höjd hos idrottare, såsom blodets syremättnad under vila och vilopuls, inte följde de mönster som tidigare har beskrivits i litteraturen (till exempel en ökning i syremättnad och en reduktion i vilopuls över tid på höjd). Vi observerade också att 11 av 15 sjukdomstillfällen rapporterades inom fyra dagar efter ut- eller hemresan. Dessutom förbättrade skidskyttar som inte blev sjuka under träningslägret sin submaximala prestationsförmåga från före till efter lägret med ~ 4%.

Studie IV visade att akuta förändringar i den metaboliska profilen efter det standardiserade träningstestet kunde särskilja idrottare baserat på prestationsnivå i sprintskidåkningstävlingar och sjukdomskänslighet under de efterföljande 33 veckorna. Denna information är särskilt värdefull för idrottare som ofta blir sjuka eftersom förebyggande åtgärder, såsom vaccination, hygienutbildning och social distansering, kan implementeras för att minska risken för sjukdom.

Sammantaget har denna avhandling bidraget till ökad kunskap om elitaktiva skidåkare och skidskyttars hälsa och träning och gett insikter som kan förbättra det stöd som ges de aktiva och därigenom öka deras förutsättningar för att prestera optimalt.

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.

Background A limited number of long-term prospective studies have investigated health problems in competitive cross-country skiers. Moreover, limited information exists regarding differences in the prevalence and severity of health problems between senior and development female and male cross-country skiers.

Objective To compare the prevalence and severity of health problems between senior and development female and male national team cross-country skiers.

Design Comparative, prospective, observational cohort study.

Setting Senior and development national cross-country ski teams.

Participants Eighteen (9 women, 9 men) senior and 22 (9 women, 13 men) development national team skiers.

Intervention Skiers self-reported their health problems weekly for 17 weeks throughout the 2019/2020 competitive cross-country ski season using the Oslo Sports Trauma Research Center Questionnaire on Health Problems (OSTRC-H2).

Main Outcome Measurements We calculated weekly prevalence and severity measures for illnesses, acute and overuse injuries, substantial health problems (i.e., health problems leading to moderate or severe reductions in training volume or sports performance, or a complete inability to participate) and all health problems combined.

Results Weekly response rate to the OSTRC-H2 was 90% (SD 7%). Average weekly prevalence of substantial (~12%) and all (~25%) health problems were similar between senior and development team skiers. However, illness prevalence was lower in senior vs. development skiers (8%, 95% CI [3%, 13%] vs. 13%, 95% CI [9%, 17%], respectively; p = .026) and injuries were higher (12%, 95% CI [9%, 15%] vs. 5%, 95% CI [3%, 7%]; p < .001). There were no differences in severity measures (all p > .05).

Conclusions Health problems were relatively common among the skiers, with one quarter affected by at least one problem at any given time. While the prevalence of all health problems was similar, illnesses were less prevalent in the senior compared to the development team skiers and injuries were more prevalent.

DesignProspective, observational.SettingBaseline monitoring at <500 m for 2 weeks and altitude monitoring at 1800 m for 17-22 days.

ParticipantsThirty-three senior national-team endurance athletes (mean age 25.8 ± S.D. 2.8 years, 16 women).

MeasurementsDaily measurements of sleep (using a microwave Doppler radar at baseline and altitude), oxygen saturation (SpO2), training load and subjective recovery (at altitude).

ResultsAt altitude vs. baseline, sleep duration (P = .036) and light sleep (P < .001) decreased, while deep sleep (P < .001) and respiration rate (P = .020) increased. During the first altitude week vs. baseline, deep sleep increased (P = .001). During the first vs. the second and third altitude weeks, time in bed (P = .005), sleep duration (P = .001), and light sleep (P < .001) decreased. Generally, increased SpO2 was associated with increased deep sleep while increased training load was associated with increased respiration rate.

ConclusionThis is the first study to document changes in sleep from near-sea-level baseline and during a training camp at 1800 m in elite endurance athletes. Ascending to altitude reduced total sleep time and light sleep, while deep sleep and respiration rate increased. SpO2 and training load at altitude were associated with these responses. This research informs our understanding of the changes in sleep occurring in elite endurance athletes attending training camps at competition altitudes.

Purpose This study aimed to describe changes in laboratory-assessed anthropometric and physiological characteristics, training volumes, and competitive performance in national development-team cross-country skiers over a 25-month period, and to analyze whether changes in competitive performance could be predicted by changes in laboratory-assessed qualities and training volumes.

Methods Data collected over 25 months from 30 national development-team cross-country skiers (14 women, 16 men; age, 18–23 yr) were analyzed retrospectively using multivariate statistics. Anthropometric and physiological characteristics were assessed via dual-energy x-ray absorptiometry and incremental roller-ski treadmill tests, respectively. Total training volumes and distributions of low- and high-intensity training were analyzed from online training diaries, and competitive performance was determined by International Ski Federation (FIS) distance and sprint points.

Results Whole- and upper-body lean mass increased in the full cohort of skiers (n = 30; both P < 0.05), whereas lower-body lean mass, whole-body fat mass, speed and oxygen uptake (V˙O2) at a blood lactate concentration (BLa) of 2 and 4 mmol·L−1, as well as time-trial completion time, power output, and peak V˙O2, improved in the women only (all P < 0.05). Valid predictive models were identified for female skiers’ best FIS distance points (R2 = 0.81/Q2 = 0.51) and changes in FIS distance points (R2 = 0.83/Q2 = 0.54), with body mass, fat mass, lean mass, V˙O2peak, and speed at a BLa of 4 mmol·L−1 identified as consistently important variables for projection.

Conclusions The valid prediction of competitive performance was achieved for women only in distance events. This study suggests that improvements in body composition and aerobic capacity may be more beneficial for elite female development-level skiers than for their male counterparts. These results have implications for athlete selection and performance development.