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The aim of this study was to simulate the activity pattern of rink hockey by designing a specific skate test (ST) to study the energy expenditure and metabolic responses to this intermittent high-intensity exercise and extrapolate the results from the test to competition. Six rink hockey players performed, in three phases, the 20-metre multi-stage shuttle roller skate test, a tournament match and the ST. Heart rate was monitored in all three phases. Blood lactate, oxygen consumption, ventilation and respiratory exchange ratio were also recorded during the ST. Peak HR was 190.7±7.2 beats · min-1. There were no differences in peak HR between the three tests. Mean HR was similar between the ST and the match (86% and 87% of HRmax, respectively). Peak and mean ventilation averaged 111.0±8.8 L · min-1 and 70.3±14.0 L · min-1 (60% of VEmax), respectively. VO2max was 56.3±8.4 mL · kg-1 · min-1, and mean oxygen consumption was 40.9±7.9 mL · kg-1 · min-1 (70% of VO2max). Maximum blood lactate concentration was 7.2±1.3 mmol · L-1. ST yielded an energy expenditure of 899.1±232.9 kJ, and energy power was 59.9±15.5 kJ · min-1. These findings suggest that the ST is suitable for estimating the physiological demands of competitive rink hockey, which places a heavy demand on the aerobic and anaerobic systems, and requires high energy consumption. [ABSTRACT FROM AUTHOR]

The dropout rate in the Finnish military service has increased during the past two decades. At the same time, the physical fitness level of young Finnish males has decreased, possibly leading to overtraining in new conscripts. The purpose of the present study was to examine whether body composition would influence neuromuscular function during the 8-week basic training (BT) period. Eighteen healthy male subjects (19 +/- 1 years) were divided into three different groups according to their body fat %. Group 1 (<10%), group 2 (10-13%) and group 3 (>13%). The soleus H-reflex response was measured in the standing position. In the seated position (knee 160 degrees and hip 110 degrees), the V-wave response was measured during maximal voluntary contraction, and the single twitch response was measured in passive conditions. In body composition (fat-free mass and fat mass) was observed small but not significant changes during 8-week period. H-reflex activity increased in groups 2 (10.9% not significant [ns]) and 3 (2.8% ns) but decreased in group 1 (-34.8%, p < 0.05) during the 8-week period. V-wave values decreased in all groups, and the biggest decrement was observed in group 2 (-34.7%, p < 0.05), whereas in group 1 and group 3 no significance was observed. For each group the single twitch torque (G1 ns, G2 and G3 p < 0.05) increased during the 8-week period. The major finding of the study was that the BT period did not cause overtraining in conscripts. Increased activity of the H-reflex and single twitch torque supports this finding. V-wave activity was decreased in all groups, which may also indicate that the training did not stimulate neural activity. In general, the observed changes in neuromuscular system supports the main finding. [ABSTRACT FROM AUTHOR]

Motor unit activation patterns were studied during four different force levels of concentric and eccentric actions. Eight male subjects performed concentric and eccentric forearm flexions with the movement range from 100° to 60° in concentric and from 100° to 140° elbow angle in eccentric actions. The movements were started either from zero preactivation or with isometric preactivation of the force levels of 20, 40, 60 and 80% MVC. The subjects were then instructed to maintain the corresponding relative force levels during the dynamic actions. Intramuscular and surface EMG was recorded from biceps brachii muscle. Altogether 28 motoneuron pools were analyzed using the intramuscular spike-amplitude frequency (ISAF) analysis technique of Moritani et al. . The mean spike amplitude was lower and the mean spike frequency higher in the isometric preactivation phase than in the consequent concentric and eccentric actions. When the movements started with isometric preactivation the mean spike amplitude increased significantly (P<0.001) up to 80% in isometric and concentric actions but in eccentric actions the increase continued only up to 60% (P<0.01). The mean spike frequency in isometric preactivation and in concentric action with preactivation was lower only at the 20% force level (P<0.01) as compared to the other force levels while in eccentric action with preactivation the increase between the force levels was significant (P<0.01) up to 60%. When the movement was started without preactivation the mean spike amplitude at 20% and at 40% force level was higher (P<0.01) in eccentric action than in concentric actions. It was concluded that the recruitment threshold may be lower in dynamic as compared to isometric actions. The recruitment of fast motor units may continue to higher force levels in isometric and in concentric as in eccentric actions which, on the other hand, seems to achieve the higher forces by increasing the firing rate of the active units. At the lower force levels mean spike amplitude was higher in eccentric than in concentric actions which might indicate selective activation of fast motor units. This was, however, the case only when the movements were started without isometric preactivation. [Copyright &y& Elsevier]

An abstract of the article "Effect of Physical Activity to the Motor Control in Preschool Children," by J. A. Salmi, M. Vähä and V. Linnamo is presented.

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.

Athletes use hypoxic living and training to increase hemoglobin mass (Hb mass ), but Hb mass 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 Hb mass , and if changes in Hb mass were transferred to changes in maximal oxygen uptake (V̇o 2max ) and exercise performance. Hb mass 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 returning to sea level, 22 athletes included IHE (2 h rest) + CHT (1 h training) in their training every third day for 1 mo (HYP IHE + CHT ), whereas the other 22 HYP athletes were not exposed to IHE or CHT (HYP SL ). Hb mass increased from PRE to POST1 in both HYP IHE + CHT (4.4 ± 0.7%, means ± SE) and HYP SL (4.1 ± 0.6%) (both P < 0.001). Compared with PRE, Hb mass at POST2 remained 4.2 ± 0.8% higher in HYP IHE + CHT ( P < 0.001) and 1.9 ± 0.5% higher in HYP SL ( P = 0.023), indicating a significant difference between the groups ( P = 0.002). In SL, no significant changes were observed in Hb mass with mean alterations between -0.5% and 0.4%. V̇o 2max and time to exhaustion during an incremental treadmill test ( n = 35) were elevated from PRE to POST2 only in HYP IHE + 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 Hb mass commonly observed during the initial weeks after return to sea level. NEW & NOTEWORTHY Sets of 2-h intermittent hypoxic exposure + 1-h continuous hypoxic training, every third day, possess the potential to mitigate the typical decline in Hb mass that is commonly observed during the initial weeks after return to sea level from an altitude camp. Inclusion of IHE + CHT in the training regimen was also accompanied by improvements in V̇o 2max and exercise performance in most but not all Tier 3-Tier 5 level endurance athletes during the training season.

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.

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.

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 (VO 2max ), oxygen uptake (VO 2 ) 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, M 1 ) and end of the study (August 2021, M 2 ). 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 VO 2max ( r  = 0.61, p  = 0.005; r  = 0.54, p  = 0.014), VO 2 at OBLA ( r  = 0.63, p  = 0.003; r  = 0.62, p  = 0.003), and DP performance at M 2 ( 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 M 2 was explained by higher training volume (R 2  = 0.24, p  = 0.033) and higher relative VO 2max and VO 2 at OBLA at M 2 by lower F% (R 2  = 0.44, p  = 0.004; R 2  = 0.47, p  = 0.003). Increase from M 1 to M 2 in DP performance was explained by a decrease in F% (R 2  = 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.

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 (Hb mass ) was assessed using a carbon monoxide rebreathing method. Time to exhaustion (TTE) and maximal oxygen uptake (VO 2max ) 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: Hb mass 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). VO 2max 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 Hb mass but did not support the short-term development of maximal endurance performance and VO 2max when compared to the athletes who lived and trained in normoxia., (© 2023 The Authors. Scandinavian Journal of Medicine & Science In Sports published by John Wiley & Sons Ltd.)

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 ( R 2  = 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., Competing Interests: The authors declare that the research was conducted in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest., (© 2023 Kettunen, Mikkonen, Mursu, Linnamo and Ihalainen.)

Introduction: Although maximal oxygen uptake (VO 2 max) 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 VO 2 max for performance in comparison to other factors such as power production. Here, we examined the influence of endurance training on the VO 2 max, 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 VO 2 max 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 VO 2 max, jumping power or the levels of certain blood parameters, the improvement observed probably reflected better upper-body performance., Competing Interests: The authors declare that the research was conducted in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest., (© 2023 Mishica, Kyröläinen, Valtonen, Holmberg and Linnamo.)

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., Competing Interests: The authors declare that the research was conducted in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest., (© 2023 Zhao, Lindinger, Ohtonen and Linnamo.)

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.