Combined intermittent hypoxic exposure at rest and continuous hypoxic training can maintain elevated hemoglobin mass after a hypoxic camp.

Athletes use hypoxic living and training to increase hemoglobin mass (Hbmass), but Hbmass declines rapidly upon return to sea level. We investigated whether Intermittent Hypoxic Exposure (IHE) + Continuous Hypoxic Training (CHT) after return to sea level maintained elevated Hbmass, and if changes in Hbmass were transferred to changes in maximal oxygen uptake (V̇O2max) and exercise performance. Hbmass was measured in 58 endurance athletes before (PRE), after (POST1), and 30 days after (POST2) a 27 ± 4-day training camp in hypoxia (n=44, HYP) or at sea level (n=14, SL). After return to sea level, 22 athletes included IHE (2 h rest) + CHT (1 h training) into their training every third day for one month (HYPIHE+CHT), whereas the other 22 HYP athletes were not exposed to IHE or CHT (HYPSL). Hbmass increased from PRE to POST1 in both HYPIHE+CHT (4.4 ± 0.7%, mean ± SEM) and HYPSL (4.1 ± 0.6%) (both p<0.001). Compared to PRE, Hbmass at POST2 remained 4.2 ± 0.8% higher in HYPIHE+CHT (p<0.001) and1.9 ± 0.5% higher in HYPSL (p=0.023), indicating a significant difference between the groups (p=0.002). In SL, no significant changes were observed in Hbmass with mean alterations between -0.5% and 0.4%. V̇O2max and time to exhaustion during an incremental treadmill test (n=35) were elevated from PRE to POST2 only in HYPIHE+CHT (5.8 ± 1.2% and 5.4 ± 1.4%, respectively, both p<0.001). IHE+CHT possesses the potential to mitigate the typical decline in Hbmass commonly observed during the initial weeks after return to sea level.

Evaluation of 3D Markerless Motion Capture System Accuracy during Skate Skiing on a Treadmill.

In this study, we developed a deep learning-based 3D markerless motion capture system for skate skiing on a treadmill and evaluated its accuracy against marker-based motion capture during G1 and G3 skating techniques. Participants performed roller skiing trials on a skiing treadmill. Trials were recorded with two synchronized video cameras (100 Hz). We then trained a custom model using DeepLabCut, and the skiing movements were analyzed using both DeepLabCut-based markerless motion capture and marker-based motion capture systems. We statistically compared joint centers and joint vector angles between the methods. The results demonstrated a high level of agreement for joint vector angles, with mean differences ranging from -2.47° to 3.69°. For joint center positions and toe placements, mean differences ranged from 24.0 to 40.8 mm. This level of accuracy suggests that our markerless approach could be useful as a skiing coaching tool. The method presents interesting opportunities for capturing and extracting value from large amounts of data without the need for markers attached to the skier and expensive cameras.

Associations between objective measures of performance-related characteristics and perceived stress in young cross-country skiers during pre-season training.

Monitoring performance-related characteristics of athletes can reveal changes that facilitate training adaptations. Here, we examine the relationships between submaximal running, maximal jump performance (CMJ), concentrations of blood lactate, sleep duration (SD) and latency (SL), and perceived stress (PSS) in junior cross-country skiers during pre-season training. These parameters were monitored in 15 male and 14 females (17 ± 1 years) for the 12-weeks prior to the competition season, and the data was analysed using linear and mixed-effect models. An increase in SD exerted a decrease in both PSS (B = -2.79, p ≤ 0.01) and blood lactate concentrations during submaximal running (B = -0.623, p ≤ 0.05). In addition, there was a negative relationship between SL and CMJ (B = -0.09, p = 0.08). Compared to males, females exhibited higher PSS scores and little or no change in performance-related tests. A significant interaction between time and sex was present in CMJ with males displaying an effect of time on CMJ performance. For all athletes, lower PSS appeared to be associated with longer overnight sleep. Since the females experienced higher levels of stress, monitoring of their PSS might be beneficial. These findings have implications for the preparation of young athletes' competition season.

Carbohydrate intake in young female cross-country skiers is lower than recommended and affects competition performance.

Purpose: (1) To evaluate if energy availability (EA), macronutrient intake and body composition change over four training periods in young, highly trained, female cross-country skiers, and (2) to clarify if EA, macronutrient intake, body composition, and competition performance are associated with each other in this cohort. Methods: During a one-year observational study, 25 female skiers completed 3-day food and training logs during four training periods: preparation, specific preparation, competition, and transition periods. A body composition measurement (bioimpedance analyzer) was performed at the end of the preparation, specific preparation, and competition periods. Competition performance was determined by International Ski Federation (FIS) points gathered from youth national championships. Results: EA (36-40 kcal·kg FFM-1·d-1) and carbohydrate (CHO) intake (4.4-5.1 g·kg-1·d-1) remained similar, and at a suboptimal level, between training periods despite a decrease in exercise energy expenditure (p = 0.002) in the transition period. Higher EA (r = -0.47, p = 0.035) and CHO intake (r = -0.65, p = 0.002) as well as lower FM (r = 0.60, p = 0.006) and F% (r = 0.57, p = 0.011) were associated with lower (better) FIS-points. CHO intake was the best predictor of distance competition performance (R2 = 0.46, p = 0.004). Conclusions: Young female cross-country skiers had similar EA and CHO intake over four training periods. Both EA and CHO intake were at suboptimal levels for performance and recovery. CHO intake and body composition are important factors influencing competition performance in young female cross-country skiers.

Nutritional intake and anthropometric characteristics are associated with endurance performance and markers of low energy availability in young female cross-country skiers.

BACKGROUND: Low energy availability (LEA) can have negative performance consequences, but the relationships between LEA and performance are poorly understood especially in field conditions. In addition, little is known about the contribution of macronutrients to long-term performance. Therefore, the aim of this study was to evaluate if energy availability (EA) and macronutrient intake in a field-based situation were associated with laboratory-measured performance, anthropometric characteristics, blood markers, training volume, and/or questionnaire-assessed risk of LEA in young female cross-country (XC) skiers. In addition, the study aimed to clarify which factors explained performance. METHODS: During a one-year observational study, 23 highly trained female XC skiers and biathletes (age 17.1 ± 1.0 years) completed 3-day food and training logs on four occasions (September-October, February-March, April-May, July-August). Mean (±SD) EA and macronutrient intake from these 12 days were calculated to describe yearly overall practices. Laboratory measurements (body composition with bioimpedance, blood hormone concentrations, maximal oxygen uptake (VO2max), oxygen uptake (VO2) at 4 mmol·L-1 lactate threshold (OBLA), double poling (DP) performance (time to exhaustion), counter movement jump (height) and the Low Energy Availability in Females Questionnaire (LEAF-Q)) were completed at the beginning (August 2020, M1) and end of the study (August 2021, M2). Annual training volume between measurements was recorded using an online training diary. RESULTS: The 12-day mean EA (37.4 ± 9.1 kcal·kg FFM-1·d-1) and carbohydrate (CHO) intake (4.8 ± 0.8 g·kg-1·d-1) were suboptimal while intake of protein (1.8 ± 0.3 g·kg-1·d-1) and fat (31 ± 4 E%) were within recommended ranges. Lower EA and CHO intake were associated with a higher LEAF-Q score (r = 0.44, p = 0.042; r = 0.47, p = 0.026). Higher CHO and protein intake were associated with higher VO2max (r = 0.61, p = 0.005; r = 0.54, p = 0.014), VO2 at OBLA (r = 0.63, p = 0.003; r = 0.62, p = 0.003), and DP performance at M2 (r = 0.42, p = 0.051; r = 0.44, p = 0.039). Body fat percentage (F%) was negatively associated with CHO and protein intake (r = -0.50, p = 0.017; r = -0.66, p = 0.001). Better DP performance at M2 was explained by higher training volume (R2 = 0.24, p = 0.033) and higher relative VO2max and VO2 at OBLA at M2 by lower F% (R2 = 0.44, p = 0.004; R2 = 0.47, p = 0.003). Increase from M1 to M2 in DP performance was explained by a decrease in F% (R2 = 0.25, p = 0.029). CONCLUSIONS: F%, and training volume were the most important factors explaining performance in young female XC skiers. Notably, lower F% was associated with higher macronutrient intake, suggesting that restricting nutritional intake may not be a good strategy to modify body composition in young female athletes. In addition, lower overall CHO intake and EA increased risk of LEA determined by LEAF-Q. These findings highlight the importance of adequate nutritional intake to support performance and overall health.

Performance-related physiological changes induced by one year of endurance training in young athletes.

Introduction: Although maximal oxygen uptake (VO2max) is generally recognized as the single best indicator of aerobic fitness in youth, interpretation of this parameter and the extent to which it can be improved by training remain controversial, as does the relative importance of VO2max for performance in comparison to other factors such as power production. Here, we examined the influence of endurance training on the VO2max, muscle power and sports-related performance of cross-country skiers attending a school specializing in sports, as well as potential relationships between any changes observed to one another and/or to perceived stress scale (Cohen) and certain blood parameters. Methods: On two separate occasions, prior to the competition season and separated by one year of endurance training, the 12 participants (5 males, 7 females, 17 ± 1 years) carried out tests for VO2max on a treadmill, explosive power utilizing countermovement jumps (CMJ) and ski-specific maximal double pole performance (DPP) employing roller skis on a treadmill. Blood levels of ferritin (Fer), vitamin D (VitD) and hemoglobin (Hg) were monitored, and stress assessed with a questionnaire. Results: DPP improved by 10 ± 8% (P < 0.001), but no other significant changes were observed. There were no significant correlations between the changes in DPP and any other variable. Discussion: Whereas one year of endurance training improved the cross-country ski-specific performance of young athletes significantly, the increase in their maximal oxygen uptake was minimal. Since DPP was not correlated with VO2max, jumping power or the levels of certain blood parameters, the improvement observed probably reflected better upper-body performance.

Hemoglobin mass and performance responses during 4 weeks of normobaric "live high-train low and high".

PURPOSE: To investigate whether 4 weeks of normobaric "live high-train low and high" (LHTLH) causes different hematological, cardiorespiratory, and sea-level performance changes compared to living and training in normoxia during a preparation season. METHODS: Nineteen (13 women, 6 men) cross-country skiers competing at the national or international level completed a 28-day period (∼18 h day-1 ) of LHTLH in normobaric hypoxia of ∼2400 m (LHTLH group) including two 1 h low-intensity training sessions per week in normobaric hypoxia of 2500 m while continuing their normal training program in normoxia. Hemoglobin mass (Hbmass ) was assessed using a carbon monoxide rebreathing method. Time to exhaustion (TTE) and maximal oxygen uptake (VO2max ) were measured using an incremental treadmill test. Measurements were completed at baseline and within 3 days after LHTLH. The control group skiers (CON) (seven women, eight men) performed the same tests while living and training in normoxia with ∼4 weeks between the tests. RESULTS: Hbmass in LHTLH increased 4.2 ± 1.7% from 772 ± 213 g (11.7 ± 1.4 g kg-1 ) to 805 ± 226 g (12.5 ± 1.6 g kg-1 ) (p < 0.001) while it was unchanged in CON (p = 0.21). TTE improved during the study regardless of the group (3.3 ± 3.4% in LHTLH; 4.3 ± 4.8% in CON, p < 0.001). VO2max did not increase in LHTLH (61.2 ± 8.7 mL kg-1 min-1 vs. 62.1 ± 7.6 mL kg-1 min-1 , p = 0.36) while a significant increase was detected in CON (61.3 ± 8.0-64.0 ± 8.1 mL kg-1 min-1 , p < 0.001). CONCLUSIONS: Four-week normobaric LHTLH was beneficial for increasing Hbmass but did not support the short-term development of maximal endurance performance and VO2max when compared to the athletes who lived and trained in normoxia.

Contribution and effectiveness of ski and pole forces in selected roller skiing techniques on treadmill at moderate inclines.

Background: Most of the studies about the effects of incline on cross-country skiing are related to the metabolic efficiency. The effective skiing biomechanics has also been indicated to be among the key factors that may promote good performance. The aims of this study were to provide biomechanical characteristics and investigate the relative contribution and effectiveness of ski and pole forces in overcoming the total external resistance with double poling (DP) and Gear 3 (G3) techniques at varying moderate uphill inclines. Methods: 10 male cross-country skiers participated in this study. Custom-made force measurement bindings, pole force sensors, and an 8-camera Vicon system were used to collect force data and ski and pole kinematics at 3°, 4° and 5° with 10 km/h skiing speed. Results: The cycle length (CL) decreased by 10% and 7% with DP and G3 technique from 3° to 5° (p < 0.001, p < 0.001). The cycle rate (CR) increased by 13% and 9% from 3° to 5° with DP and G3 technique respectively. From 3° to 5°, the peak pole force increased by 25% (p < 0.001) and 32% (p < 0.001) with DP and G3 technique. With DP technique, the average cycle propulsive force (ACPF) increased by 46% (p < 0.001) from 3° to 5°and with G3 technique, the enhancement for ACPF was 50% (p < 0.001). In G3 technique, around 85% was contributed by poles in each incline. Conclusion: The higher power output in overcoming the total resistance was required to ski at a greater incline. With DP technique, the upper body demands, and technical effectiveness were increasing with incline. With G3 technique, the role of external pole work for propulsion is crucial over different terrains while role of legs may stay more in supporting the body against gravity and repositioning body segments.

Sensor Technology for Sports Monitoring.

Over the past decades, huge steps have been made in the development of sensor technology related to sports monitoring [...].

Validation of 2D Force Measurement Roller Ski and Practical Application.

Several methods could be used to measure the forces from skis or roller skis in cross-country skiing. Equipment that could measure medio-lateral forces may be of good help for investigating the relevant skating techniques. The aim of this study was to validate a pair of newly designed two-dimensional force measurement roller skis. The vertical and medio-lateral forces which were perpendicular to the body of the roller ski could be measured. Forces were resolved into the global coordinate system and compared with the force components measured by a force plate. A static and dynamic loading situation for the force measurement roller ski was performed to reveal the validity of the system. To demonstrate whether the force measurement roller ski would affect roller skiing performance on a treadmill, a maximum speed test with the V2 technique was performed by using both normal and force measurement roller skis. The force-time curves obtained by these two different force measurement systems were shown to have high similarity (coefficient of multiple correlations > 0.940). The absolute difference for the forces in the X and Z directions over one push-off cycle was 3.9−33.3 N. The extra weight (333 g) of the force measurement roller ski did not affect the performance of the skiers. Overall, the newly designed two-dimensional force measurement roller ski in this study is valid for use in future research during daily training for skate skiing techniques.

Propulsion Calculated by Force and Displacement of Center of Mass in Treadmill Cross-Country Skiing.

This study evaluated two approaches for estimating the total propulsive force on a skier's center of mass (COM) with double-poling (DP) and V2-skating (V2) skiing techniques. We also assessed the accuracy and the stability of each approach by changing the speed and the incline of the treadmill. A total of 10 cross-country skiers participated in this study. Force measurement bindings, pole force sensors, and an eight-camera Vicon system were used for data collection. The coefficient of multiple correlation (CMC) was calculated to evaluate the similarity between the force curves. Mean absolute force differences between the estimated values and the reference value were computed to evaluate the accuracy of each approach. In both DP and V2 techniques, the force-time curves of the forward component of the translational force were similar to the reference value (CMC: 0.832-0.936). The similarity between the force and time curves of the forward component of the ground reaction force (GRF) and the reference value was, however, greater (CMC: 0.879-0.955). Both approaches can estimate the trend of the force-time curve of the propulsive force properly. An approach by calculating the forward component of GRF is a more appropriate method due to a better accuracy.

The Effect of Paddle Stroke Variables Measured by Trainesense SmartPaddle® on the Velocity of the Kayak.

(1) Background: This study aimed to compare key variables of paddle stroke measured by a commercial Trainesense SmartPaddle® against the strain-gauge shaft and investigate how these variables are associated with the velocity of the boat among national-level canoe polo players. (2) Methods: This study involved 14 Finnish national-level canoe polo players. The measurement protocol consisted of three different paddling velocities, which were performed in indoor swimming pools. The velocity of the boat was calculated based on the performance time measured with the laser photocell gate. Canoe polo equipment was used in the study and a SmartPaddle sensor was attached to the paddle blade. A strain-gauge paddle shaft was used as a reference method to examine the validity of SmartPaddle. (3) Results: The stroke rate, force production time, mean and maximal force measured with the strain-gauge paddle shaft correlated strongly (r = 0.84-0.95, p < 0.01) with SmartPaddle. However, the SmartPaddle overestimated the maximum force compared to the strain-gauge shaft. Stroke rate (r = 0.86, p < 0.01), mean force (r = 0.79, p < 0.01), maximal force (r = 0.78, p < 0.01) and total absolute impulse (r = 0.70, p < 0.01) correlated positively and force production time negatively (r = -0.76, p < 0.01) with the velocity of the boat. (4) Conclusions: We conclude that the SmartPaddle provides promising information on stroke key variables when compared to the strain-gauge paddle shaft. The SmartPaddle is a new and interesting tool for biomechanical research and daily kayaking coaching in real open water conditions. However, more research and algorithm development are needed before the SmartPaddle can be used in everyday coaching sessions in kayaking.

Effects of Aerodynamic Drag and Drafting on Propulsive Force and Oxygen Consumption in Double Poling Cross-Country Skiing.

PURPOSE: This study aimed to investigate the effects of aerodynamic drag and drafting on propulsive force (FPROP), drag area (CDA), oxygen cost (V˙O2), metabolic rate (E˙), and heart rate (HR) during roller skiing on a treadmill in a wind tunnel using the double poling technique. A secondary aim was to investigate the effects of wind versus no-wind test conditions on the same physiological parameters. METHODS: Ten subjects of each gender participated in the experiments. One pair of skiers of the same gender roller skied simultaneously in line with the air flow; the distance between the skiers was ~2.05 m. Each pair was tested as follows: I) with wind, leading; II) with wind, drafting; and III) without wind. The treadmill inclination was 0° throughout the tests. For the wind conditions, the air velocity was similar to the treadmill belt speed: 3 to 7 m·s-1 for men and 3 to 6 m·s-1 for women. RESULTS: Drafting resulted in significantly (P < 0.05) lower FPROP,CDA, V˙O2, and E˙, compared with leading, for both genders at racing speed but not at lower speeds, whereas HR was only affected for the male skiers at racing speed. The test without wind resulted in significantly lower FPROP, V˙O2, and E˙ at all tested speeds compared with the tests with wind present, whereas HR was lower only at higher speeds. CONCLUSIONS: At racing speed, but not at lower speeds, the positive effects of drafting behind a skier during double poling were obvious and resulted in a lower FPROP, CDA, V˙O2, E˙, and HR. Tests without wind present put even lower demands on the skiers' physiology, which was also evident at lower speeds.

Evaluation of nocturnal vs. morning measures of heart rate indices in young athletes.

PURPOSE: The purpose of this study was to compare heart rate (HR) and heart rate variability in young endurance athletes during nocturnal sleep and in the morning; and to assess whether changes in these values are associated with changes in submaximal running (SRT) and counter-movement jump (CMJ) performance. METHODS: During a three-week period of similar training, eleven athletes (16 ± 1 years) determined daily HR and heart rate variability (RMSSD) during sleep utilizing a ballistocardiographic device (Emfit QS), as well as in the morning with a HR monitor (Polar V800). Aerobic fitness and power production were assessed employing SRT and CMJ test. RESULTS: Comparison of the average values for week 1 and week 3 revealed no significant differences with respect to nocturnal RMSSD (6.8%, P = 0.344), morning RMSSD (13.4%, P = 0.151), morning HR (-3.9 bpm, P = 0.063), SRT HR (-0.7 bpm, P = 0.447), SRT blood lactate (4.9%, P = 0.781), CMJ (-4.2%, P = 0.122) or training volume (16%, P = 0.499). There was a strong correlation between morning and nocturnal HRs during week 1 (r = 0.800, P = 0.003) and week 3 (r = 0.815, P = 0.002), as well as between morning and nocturnal RMSSD values (for week 1, r = 0.895, P<0.001 and week 3, r = 0.878, P = 0.001). CONCLUSION: This study concluded that HR and RMSSD obtained during nocturnal sleep and in the morning did not differ significantly. In addition, weekly changes in training and performance were small indicating that fitness was similar throughout the 3-week period of observation. Consequently, daily measurement of HR indices during nocturnal sleep provide a potential tool for long-term monitoring of young endurance athletes.

Performance-determining factors in biathlon prone shooting without physical stress.

This study investigated the most important factors determining biathlon prone shooting performance. Ten female and 16 male biathletes (age 19.9 ± 2.9 years) from the national teams of Finland and Vuokatti-Ruka Sports Academy performed 6 × 5 biathlon prone shooting shots without physical stress under laboratory conditions. Shooting performance and multiple aiming point trajectory variables were measured together with an analysis of triggering force. Based on the aiming point trajectory data principal component analysis, we identified four technical components in biathlon prone shooting: stability of hold, aiming accuracy, cleanness of triggering, and timing of triggering. Multiple regression analysis (MRA) further determined that cleanness of triggering, aiming accuracy, and timing of triggering accounted for 80% of mean shooting performance (p < 0.001). Better stability of hold, aiming accuracy and cleanness of triggering were directly associated with better shooting performance (0.62 ≤ |r| ≥0.79, all p < 0.001). Better stability of hold measures were also associated with better cleanness of triggering, and higher pre-shot trigger force levels were associated with better stability of hold and cleanness of triggering. These results indicate that with both direct and indirect effects on performance, stability of hold seems to be a general prerequisite for successful biathlon shooting. The results also highlight the importance of aiming accuracy, cleanness and timing of triggering, along with a high pre-shot trigger force level. The variables identified in this study could be used to assess biathletes' performance in the most relevant shooting technical aspects to guide the emphasis of their shooting training.

Unilateral Maximal Isometric Hex Bar Pull Test: Within-Session Reliability and Lower Body Force Production in Male and Female Freeski Athletes.

The aim of the study was to (1) assess the within-session reliability of a unilateral isometric hex bar pull (UIHBP) maximal voluntary contraction (MVC) test and, (2) determine unilateral isometric absolute peak force (PFabs) and relative peak force (PF) values in freeski athletes. Twenty-one male and eight female academy to national team freeskiers performed the novel UIHBP MVC task on a force plate and PFabs and relative PF were assessed (1000 Hz). Within-session measures of PFabs offered high reliability on left and right limbs for males (ICC = 0.91-0.94, CV = 2.6-2.2%) and females (ICC = 0.94-0.94, CV = 1.4-1.6%), while relative PF measures showed good to high reliability in both left and right limbs for males (ICC = 0.8-0.84, CV = 2.6-2.2%) and females (ICC = 0.92-0.90, CV = 1.4-1.7%). We observed significantly lower PFabs (p < 0.001) and relative PF (p < 0.001) in females compared to males. No statistical difference was found between left and right limbs in males and females in PFabs (p = 0.98) and relative PF measures (p = 0.93). The UIHBP MVC test appears to be a reliable method for assessing PFabs and relative PF in male and female freeski athletes.

Nutrition Knowledge Is Associated with Energy Availability and Carbohydrate Intake in Young Female Cross-Country Skiers.

The aim of this study was to provide information on energy availability (EA), macronutrient intake, nutritional periodization practices, and nutrition knowledge in young female cross-country skiers. A total of 19 skiers filled in weighted food and training logs before and during a training camp. Nutrition knowledge was assessed via a validated questionnaire. EA was optimal in 11% of athletes at home (mean 33.7 ± 9.6 kcal·kgFFM-1·d-1) and in 42% at camp (mean 40.3 ± 17.3 kcal·kgFFM-1·d-1). Most athletes (74%) failed to meet recommendations for carbohydrate intake at home (mean 5.0 ± 1.2 g·kg-1·d-1) and 63% failed to do so at camp (mean 7.1 ± 1.6 g·kg-1·d-1). The lower threshold of the pre-exercise carbohydrate recommendations was met by 58% and 89% of athletes while percentages were 26% and 89% within 1 h after exercise, at home and at camp, respectively. None of the athletes met the recommendations within 4 h after exercise. Nutrition knowledge was associated with EA at home (r = 0.52, p = 0.023), and with daily carbohydrate intake at home (r = 0.62, p = 0.005) and at camp (r = 0.52, p = 0.023). Carbohydrate intake within 1 and 4 h post-exercise at home was associated with better nutrition knowledge (r = 0.65, p = 0.003; r = 0.53, p = 0.019, respectively). In conclusion, young female cross-county skiers had difficulties meeting recommendations for optimal EA and carbohydrate intake. Better nutrition knowledge may help young athletes to meet these recommendations.

Relationships between Heart Rate Variability, Sleep Duration, Cortisol and Physical Training in Young Athletes.

The aims of the current study were to examine the relationships between heart rate variability (HRV), salivary cortisol, sleep duration and training in young athletes. Eight athletes (16 ± 1 years) were monitored for 7 weeks during training and competition seasons. Subjects were training for endurance-based winter sports (cross-country skiing and biathlon). Training was divided into two zones (K1, easy training and K2, hard training). Heart rate and blood lactate during submaximal running tests (SRT), as well as cortisol, sleep duration and nocturnal HRV (RMSSD), were determined every other week. HRV and cortisol levels were correlated throughout the 7-week period (r = -0.552, P = 0.01), with the strongest correlation during week 7 (r = -0.879, P = 0.01). The relative changes in K1 and HRV showed a positive correlation from weeks 1-3 (r = 0.863, P = 0.006) and a negative correlation during weeks 3-5 (r = -0.760, P = 0.029). The relative change in sleep during weeks 1-3 were negatively correlated with cortisol (r = -0.762, P = 0.028) and K2 (r = -0.762, P = 0.028). In conclusion, HRV appears to reflect the recovery of young athletes during high loads of physical and/or physiological stress. Cortisol levels also reflected this recovery, but significant change required a longer period than HRV, suggesting that cortisol may be less sensitive to stress than HRV. Moreover, our results indicated that during the competition season, recovery for young endurance athletes increased in duration and additional sleep may be beneficial.

Aiming strategy affects performance-related factors in biathlon standing shooting.

This study focused on investigating differences in shooting performance and performance-related factors between two different aiming strategies (HOLD, low radial velocity during the approach 0.4-0.2 seconds before triggering, and TIMING, high radial velocity) in biathlon standing shooting. A total of 23 biathletes fired 8 × 5 standing shots at rest (REST) and 2 × 5 shots during a race simulation (RACE). Shooting performance (hit point distance from the center of the target), aiming point trajectory and postural balance were measured from each shot. Shooting performance was similar both at REST (HOLD 33 ± 5 mm vs TIMING 38 ± 8 mm, P = .111) and in RACE (40 ± 11 mm vs 47 ± 12 mm, P = .194). Better shooting performance was related to smaller distance of the aiming point mean location (REST r = 0.93, P < .001, RACE r = 0.72, P = .018) and higher time spent within ⅔ of the distance of the hit area edge from the center 0.6-0.0 seconds before triggering (REST r=-0.88, P = .001, RACE r=-0.73, P = .016) in HOLD, and to lower aiming point total velocity 0.6-0.0 seconds before triggering (REST r = 0.77, P = .009, RACE r = 0.88, P = .001) and less aiming point movement 0.2-0.0 seconds before triggering (REST r = 0.82, P = .003, RACE r = 0.72, P = .012) in TIMING. Postural balance was related to shooting performance at REST in both groups and in RACE in TIMING. Biathletes using the hold strategy should focus on stabilizing the aiming point before triggering and aiming at the center, whereas biathletes using the timing strategy benefit of decreasing the total velocity during the final approach as well as minimizing the aiming point movement right before triggering.

Effect of Sitting Posture on Sit-Skiing Economy in Non-disabled Athletes.

This study focused on resolving the differences in economy between two common sit-skiing postures used by disabled athletes, suspected to be the most and least effective. Ten experienced non-disabled male cross-country skiers went through an incremental testing protocol with an ergometer simulating double poling in two sitting postures "kneeing" and "knee-high." The protocol consisted of 3 × 4 min steady-state stages (13, 22, and 34% of maximal sprint power output). Subjects' respiratory gases and heart rate were measured and blood lactate concentrations were determined. In addition, pulling forces and motion capture recordings were collected. Oxygen consumption was 15.5% (p < 0.01) higher with "knee-high" compared to "kneeing" at stage three. At stage three cycle rate was 13.8% higher (p < 0.01) and impulse of force 13.0% (p < 0.05) and hip range of motion 46.6% lower (p < 0.01) with "knee-high" compared to "kneeing." "Kneeing" was found to be considerably more economical than "knee-high" especially at 34% of maximum sprint power output. This might have been due to higher cycle rate, lower impulse of force and smaller hip range of motion with "knee-high" compared to "kneeing." This indicates that sit-skiers should adopt, if possible, posture more resembling the "kneeing" than the "knee-high" posture. Combining such physiological and biomechanical measurements and to further develop them to integrated miniature wearable sensors could offer new possibilities for training and testing both in the laboratory and in the field conditions.