Health problems in national team cross-country skiers over a competitive season: a 17-week prospective cohort study.

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 characterised 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.

Monitoring Acclimatization and Training Responses Over 17-21 Days at 1,800 m in Elite Cross-Country Skiers and Biathletes.

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.

Performance and Micro-Pacing Strategies in a Freestyle Cross-Country Skiing Distance Race.

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.

Anthropometric, Physiological, and Performance Developments in Cross-country Skiers.

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.

An observational study of sleep characteristics in elite endurance athletes during an altitude training camp at 1800 m.

OBJECTIVES: To observe changes in sleep from baseline and during an altitude training camp in elite endurance athletes. DESIGN: Prospective, observational. SETTING: Baseline monitoring at <500 m for 2 weeks and altitude monitoring at 1800 m for 17-22 days. PARTICIPANTS: Thirty-three senior national-team endurance athletes (mean age 25.8 ± S.D. 2.8 years, 16 women). MEASUREMENTS: Daily measurements of sleep (using a microwave Doppler radar at baseline and altitude), oxygen saturation (SpO2), training load and subjective recovery (at altitude). RESULTS: At 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. CONCLUSION: This 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.

Enhanced splenic volume and contraction in elite endurance athletes.

Splenic contraction, which leads to ejection of stored erythrocytes, is greater in athletes involved in regular freediving or high-altitude activities. As this response facilitates oxygen-carrying capacity, similar characteristics may be expected of elite endurance athletes. Therefore, our aims were to compare resting and apnea-induced splenic volume in endurance athletes and untrained individuals, and to assess the athletes' exercise-induced splenic volume. Twelve elite biathletes (7 women) and 12 controls (6 women) performed a maximal effort apnea in a seated position. In addition, the biathletes completed a maximal roller-skiing time trial. Splenic dimensions were measured by ultrasonic imaging for subsequent volume calculations, whereas Hb was analyzed from capillary blood samples and cardiorespiratory variables were monitored continuously. Baseline splenic volume was larger in the biathletes (214 ± 56 mL) compared with controls (157 ± 39 mL, P = 0.008) and apnea-induced splenic contraction was also greater in the biathletes (46 ± 20 mL vs. 30 ± 16 mL, P = 0.035). Hb increased immediately after apnea in the biathletes (4.5 ± 4.8%, P = 0.029) but not in the controls (-0.7 ± 3.1%, P = 0.999). Increases in exercise-induced splenic contraction (P = 0.008) and Hb (P = 0.001) were greater compared with the apnea-induced responses among the athletes. Baseline splenic volume tended to be correlated with V̇o2max (r = 0.584, P = 0.059). We conclude that elite biathletes have greater splenic volume with a greater ability to contract and elevate Hb compared with untrained individuals. These characteristics may transiently enhance O2-carrying capacity and possibly increase O2 uptake, thereby helping biathletes to cope with high intermittent O2 demands and severe O2 deficits that occur during biathlon training and competition.NEW & NOTEWORTHY This study demonstrates that elite biathletes have larger splenic volume, apnea-induced splenic contraction, and Hb elevation compared with untrained individuals, which is likely functional to cope with high O2 demands and substantial O2 deficits. We believe that enhanced splenic contraction may be of importance during competitions involving cross-country skiing, to regulate circulating Hb and enhance O2-carrying capacity, which may protect [Formula: see text] and increase O2 uptake.

Training and illness characteristics of cross-country skiers transitioning from junior to senior level.

OBJECTIVE: This study aimed to describe the endurance training and incidence of illnesses reported by a group of well-trained cross-country (XC) skiers throughout their transition from junior to senior level. METHODS: Changes in self-reported training and performance, from 31 well-trained XC skiers, were analyzed from the start of the season they turned 16 y until the end of the season they turned 22 y, using linear mixed-effects models. Differences in the incidence of self-reported illness episodes were analyzed using incidence rate ratios, and the relationships between self-reported illness and training volumes were analyzed using linear mixed-effects models in a sub-group of 23 of the skiers. RESULTS: In total, 145 seasons of training data (including 85,846 h of endurance training) and 109 person-years of illness data (including 380 self-reported illness episodes) were analyzed. The athletes progressively increased their annual endurance training volume from age 16 to 22 y in a linear fashion, from ~ 470 to 730 h. Low- and high-intensity training volumes increased by 51.4 ± 2.4 h·y-1 (p < .001) and 4.9 ± 0.6 h·y-1 (p < .001), respectively. Sport-specific and non-specific training increased by 50.0 ± 2.2 h·y-1 (p < .001) and 4.6 ± 2.0 h·y-1 (p < .001), respectively. The athletes reported a median (range) of 3 (0-8) illness episodes and 17 (0-80) days of illness per year, and there was an inverse relationship between self-reported illness days and annual training volume (-0.046 ± 0.013 d·h-1; p < .001). CONCLUSIONS: This group of well-trained XC skiers increased their endurance training volume in a linear fashion by ~ 55 h annually. This was primarily achieved through an increase in low-intensity and sport-specific training. Furthermore, higher training volumes were associated with a lower number of self-reported illness days.

The effects of high altitude ascent on splenic contraction and the diving response during voluntary apnoea.

NEW FINDINGS: What is the central question of this study? What is the relative contribution of a putative tonic splenic contraction to the haematological acclimatization process during high altitude ascent in native lowlanders? What is the main finding and its importance? Spleen volume decreased by -14.3% (-15.2 ml) per 1000 m ascent, with an attenuated apnoea-induced [Hb] increase, attesting to a tonic splenic contraction during high altitude ascent. The [Hb]-enhancing function of splenic contraction may contribute to restoring oxygen content early in the acclimatization process at high altitude. ABSTRACT: Voluntary apnoea causes splenic contraction and reductions in heart rate (HR; bradycardia), and subsequent transient increases in haemoglobin concentration ([Hb]). Ascent to high altitude (HA) induces systemic hypoxia and reductions in oxygen saturation ( SpO2 ), which may cause tonic splenic contraction, which may contribute to haematological acclimatization associated with HA ascent. We measured resting cardiorespiratory variables (HR, SpO2 , [Hb]) and resting splenic volume (via ultrasound) during incremental ascent from 1400 m (day 0) to 3440 m (day 3), 4240 m (day 7) and 5160 m (day 10) in non-acclimatized native lowlanders during assent to HA in the Nepal Himalaya. In addition, apnoea-induced responses in HR, SpO2 and splenic volume were measured before and after two separate voluntary maximal apnoeas (A1-A2) at 1400, 3440 and 4240 m. Resting spleen volume decreased -14.3% (-15.2 ml) per 1000 m with ascent, from 140 ± 41 ml (1400 m) to 108 ± 28 ml (3440 m; P > 0.99), 94 ± 22 ml (4240 m; P = 0.009) and 84 ± 28 ml (5160 m; P = 0.029), with concomitant increases in [Hb] from 125 ± 18.3 g l-1 (1400 m) to 128 ± 10.4 g l-1 (3440 m), 138.8 ± 12.7 g l-1 (4240 m) and 157.5 ± 8 g l-1 (5160 m; P = 0.021). Apnoea-induced splenic contraction was 50 ± 15 ml (1400 m), 44 ± 17 ml (3440 m; P > 0.99) and 26 ± 8 ml (4240 m; P = 0.002), but was not consistently associated with increases in [Hb]. The apnoea-induced bradycardia was more pronounced at 3440 m (A1: P = 0.04; A2: P = 0.094) and at 4240 m (A1: P = 0.037 A2: P = 0.006) compared to values at 1400 m. We conclude that hypoxia-induced splenic contraction at rest (a) may contribute to restoring arterial oxygen content through its [Hb]-enhancing contractile function and (b) eliminates further apnoea-induced [Hb] increases in hypoxia. We suggest that tonic splenic contraction may contribute to haematological acclimatization early in HA ascent in humans.

Pole Length's Influence on Performance During Classic-Style Snow Skiing in Well-Trained Cross-Country Skiers.

PURPOSE: To investigate how self-selected pole length (PL) of ∼84% (PL84%) compared with ∼90% (PL90%) of body height influenced performance during a 700-m time trial with undulating terrain on snow. METHODS: Twenty-one cross-country skiers, 7 of whom were women, performed 4 trials at a maximal effort in a counterbalanced fashion with PL84% and PL90% separated by 20-minute breaks between trials. In trials I and II, only double poling was allowed, while in trials III and IV, skiers used self-selected classical subtechniques. Continuous speed, cyclic parameters, and heart rate were collected using microsensors in addition to a post-time-trial rating of perceived exertion (RPE). RESULTS: The 700-m times with only double poling were significantly shorter with PL90% than PL84% (mean ± 95% confidence limits -1.6% ± 1.0%). Segment analyses showed higher speed with PL90% in uphill sections than with PL84% (3.7% ± 2.1%), with the greatest difference found for the female skiers (5.6% ± 2.9%). In contrast, on flat terrain at high skiing speeds, speed was reduced with PL90% compared with PL84% (-1.5% ± 1.4%); this was only significant for the male skiers. During free choice of classical subtechniques, PL did not influence performance in any segments, choice of subtechnique, or cycle rate during the trials. No differences in rating of perceived exertion or heart rate between PLs were found. CONCLUSIONS: PL90% improved performance in uphills at low speeds when using double poling but hindered performance on flat terrain and at higher speeds compared with self-selected PLs. Choice of PL should, therefore, be based on racecourse topography, preferred subtechniques, and the skier's physiological and technical abilities.

Exercise Intensity During Cross-Country Skiing Described by Oxygen Demands in Flat and Uphill Terrain.

Purpose: In this study wearable global navigation satellite system units were used on athletes to investigate pacing patterns by describing exercise intensities in flat and uphill terrain during a simulated cross-country ski race. Methods: Eight well-trained male skiers (age: 23.0 ± 4.8 years, height: 183.8 ± 6.8 cm, weight: 77.1 ± 6.1 kg, VO2peak: 73 ± 5 mL⋅kg-1⋅min-1) completed a 13.5-km individual time trial outdoors and a standardized indoor treadmill protocol on roller skis. Positional data were recorded during the time trial using a differential global navigation satellite system to calculate external workloads in flat and uphill terrain. From treadmill tests, the individual relationships between oxygen consumption and external workload in flat (1°) and uphill (8°) terrain were determined, in addition to VO2peak and the maximal accumulated O2-deficit. To estimate the exercise intensity in the time trial, the O2-demand in two different flat and five different uphill sections was calculated by extrapolation of individual O2-consumption/workload ratios. Results: There was a significant interaction between section and average O2-demands, with higher O2-demands in the uphill sections (110-160% of VO2peak) than in the flat sections (≤100% of VO2peak) (p < 0.01). The maximal accumulated O2-deficit associated with uphill treadmill roller skiing was significantly higher compared to flat (6.2 ± 0.5 vs. 4.6 ± 0.5 L, p < 0.01), while no significant difference was found in VO2peak. Conclusion: Cross-country (XC) skiers repeatedly applied exercise intensities exceeding their maximal aerobic power. ΣO2-deficits were higher during uphill skiing compared to flat which has implications for the duration and magnitude of supramaximal work rates that can be applied in different types of terrain.