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Terje Dalen,1 Ørjan Øverås,1 Roland van den Tillaar,1 Boye Welde,2 Erna Dianne von Heimburg1 1Department of Physical Education and Sport Science, Nord University, Levanger, Norway; 2UiT The Arctic University of Norway, School of Sport Sciences, Alta, Norway Background: The aim of this study was to compare the effect of different soccer-specific maximal actions (Continuous run, Sprint, Sprint with change of direction [Sprint COD], Jump and Shot) upon physiological (oxygen uptake and heart rate) and perceptual (rating of perceived exertion [RPE]) responses and accelerometer load. Materials and methods: Ten moderately to well-trained male soccer players volunteered to serve as subjects in this study. A repeated within-subject design was used in which each subject was tested on five occasions on different days, one test each day, during a period of 2 weeks. Each of the five tests had a distance of 900 m and lasted 5 minutes, thus the mean speed for all five tests was 3 m/s. During the test, oxygen uptake, heart rate and accelerometer load were measured. Immediately after each test, RPE was recorded, and after the test, oxygen uptake was measured for 5 minutes while the subject sat in an upright position on a chair. Results: In the comparison of different soccer-specific maximal actions upon physiological and perceptual responses and accelerometer load, this study found that the total accelerometer load was lowest in Sprint and Sprint COD conditions, although the physiological (oxygen uptake and heart rate) and perceptual (RPE) responses were highest in the respective conditions. The Jump condition experienced lower RPE than Sprint and Sprint COD but achieved the highest accelerometer load. Conclusion: Accelerometer load is not a valid measurement for energy costs or RPE but may function as a complementary tool to investigate the player loads during matches and training. Keywords: soccer, oxygen uptake, rate of perceived exhaustion, repeated sprint, jump, shot

PURPOSE: First, to measure the O(2) uptake ([OV0312]O(2)) and the blood lactate concentration during cross-country skiing at competition speed. Second, to compare these entities for the free technique and the classical technique. Further, to establish the subjects' [OV0312]O(2max) and the [OV0312]O(2) corresponding to the onset of blood lactate accumulation (OBLA, 4 mmol.L-1) during skiing, and finally to relate these entities to those of treadmill running. METHODS: Five high-level female junior cross-country skiers with a mean [OV0312]O(2max) of 63 mL.kg-1.min-1 served as subjects in five tests: examination of the [OV0312]O(2max) and the [OV0312]O(2) corresponding to the OBLA during up-hill cross-country skiing (both styles), inclined treadmill running, and a 6-km simulated cross-country ski race (both styles). RESULTS: The [OV0312]O(2max) obtained during up-hill cross-country skiing did not differ from that during treadmill running, nor did it differ between the two skiing styles. The peak heart rate was significantly lower during uphill cross-country skiing than during treadmill running. During the simulated competitions, the [OV0312]O(2) averaged 84% of the [OV0312]O(2max) or 95% of the [OV0312]O(2) at the OBLA found for uphill skiing. CONCLUSION: High-level female junior cross-country skiers are unable to ski at intensities close to their [OV0312]O(2max) or maintain an average intensity above that corresponding to their OBLA even during races lasting less than 25 min. Thus, training at intensities around the OBLA may be particularly relevant for cross-country skiers. [ABSTRACT FROM AUTHOR]

Purpose: This study aimed to investigate the effect of the MC and endogenous sex hormone concentrations on performance-determining variables in three distinct MC phases in endurance-trained females., Methods: Twenty-one eumenorrheic trained/highly trained endurance athletes completed a standardized test battery during the early follicular phase (EFP), ovulatory phase (OP), and midluteal phase (MLP) for either one ( n = 7) or two test cycles ( n = 14). MC phases were determined using calendar-based counting, urinary ovulation testing, and verified with serum hormone analysis. MCs were retrospectively classified as eumenorrheic or disturbed. Disturbed MCs were excluded from analysis. The test battery consisted of 4-6 × 5-min submaximal stages with stepwise speed increases, a 30-s all-out double-poling ski ergometer test, and a maximal incremental treadmill running test., Results: At a group level, there was no effect of MC phase or the serum concentrations of estrogen and progesterone on peak oxygen uptake (V̇O 2peak ), oxygen uptake at 4 mmol·L -1 blood lactate concentration, time to exhaustion, running economy, or mean 30-s power output (MPO 30s ). Serum testosterone concentration was positively associated with MPO 30s ( P = 0.016). Changes in V̇O 2peak from EFP to MLP were inconsistent between individuals and across cycles., Conclusions: None of the measured performance-determining variables were influenced by MC phase or serum estrogen or progesterone concentrations. Although some individual patterns could be observed, there was no indication that any single MC phase is consistently associated with improved or impaired V̇O 2peak on a group level., (Copyright © 2024 by the American College of Sports Medicine.)

Positive associations between physical activity and bone health have been found in population-based studies, however, mostly based on self-reported physical activity. Therefore, we investigated the association between accelerometer-measured physical activity, measured in steps per day and minutes of moderate to vigorous physical activity (MVPA) per day, and total hip areal BMD (aBMD) measured by DXA in a general population, utilizing multiple regression models. The study participants, 1560 women and 1177 men aged 40-84 yr, were part of the seventh survey of the Tromsø Study (2015-2016). In both genders, we found a positive association between the number of daily steps and aBMD adjusted for age, BMI, and smoking status ( P  < .001). In women, an increase of 1000 steps per day was associated with 0.005 g/cm 2 higher aBMD. For men, a polynomial curve indicated a positive association with aBMD up to 5000 steps per day, plateauing between 5000 and 14 000 steps, and then increasing again. Additionally, MVPA duration was positively associated with aBMD in both women ( P  < .001) and men ( P  = .004) when adjusted for age, BMI, and smoking status. Specifically, each 60-min increase in daily MVPA was associated with 0.028 and 0.023 g/cm 2 higher aBMD in women and men, respectively. Despite positive associations, the clinical impact of physical activity on aBMD in this general population of adults and older adults was relatively small, and a large increase in daily MVPA might not be achievable for most individuals. Therefore, further longitudinal population-based studies incorporating device-based measures of physical activity could add more clarity to these relationships., Competing Interests: None declared., (© The Author(s) 2024. Published by Oxford University Press on behalf of the American Society for Bone and Mineral Research.)

Purpose: To describe and compare the annual physical training characteristics between Norwegian female cross-country (XC) skiers and biathletes across competition levels and age categories., Methods: Daily training sessions for 1 year were recorded for 45 XC skiers and 26 biathletes, comprising international/national team (inter[national]) and nonnational/regional team members (nonnational) of both junior and senior age. Endurance, strength, flexibility, speed, and power training sessions were recorded. Data included exercise modality, intensity, and duration. Data were analyzed using linear mixed-effects models., Results: The total annual physical training volume consisted of ∼90% endurance training for both groups, although XC skiers had significantly higher total volumes (∼10%; P = .003; d = 0.78) than biathletes. Senior XC skiers performed more training hours of skiing and/or roller skiing compared with biathletes over the season. However, biathletes compensated for this lower volume by more skating and a higher proportion of endurance training as skiing (81% [17%]) compared with XC skiers (68% [16%]; P < .001; d = 0.94). Overall, (inter)national-level athletes completed a higher annual training volume than non-national-level athletes (740 [90] h vs 649 [95] h; P = .004;d = 0.81). Although juniors reported less endurance volume than seniors, they maintained a relatively stable level of endurance training across the preparatory and competition period, unlike senior athletes., Conclusions: The higher annual physical training volume by XC skiers compared with biathletes is likely caused by the different demands of the 2 sports; XC skiing necessitates training for 2 skiing styles, while biathlon requires additional shooting practice. However, biathletes compensate with a higher proportion of ski training, particularly in the skating technique.

Background: Current knowledge about the relationship between physical activity (PA) and cardiac remodeling is mainly derived from cross-sectional studies of athletes, and there is a knowledge gap of this association in the general adult and elderly population. Therefore, we aimed to explore the longitudinal association between cumulative PA and change in cardiac structure and function in a general adult and elderly population., Methods: This longitudinal study includes 594 participants from the sixth (Tromsø6, 2007-08) and seventh (Tromsø7, 2015-16) survey of the Tromsø Study. Cardiac structure and function were assessed by echocardiography at two time points, and PA was self-reported by questionnaire at both time points. PA volume was expressed as cumulative PA (Low, Moderate, and Hard) and the association with left atrial (LA) and left ventricular (LV) structure and function was assessed using ANCOVA., Results: Overall, LA diameter index (LADi) increased significantly more in Hard compared to Moderate PA (+0.08 cm/m 2 , 95% CI 0.01-0.15, p = 0.020) from Tromsø6 to Tromsø7. When stratified by sex or age, higher levels of cumulative PA were associated with increased LADi in males and in participants <65 years only. Indexed LV mass (LVMi) increased significantly more in Moderate than in Low PA (+3.9 g/m 2.7 , 95% CI 0.23-7.57, p = 0.037). When stratified by sex or age, these changes in LVMi and indexed LV diameter (LVDi) were only significant in females. No significant associations were observed between cumulative PA and change in relative wall thickness, E/e' ratio, e' velocity, LV ejection fraction, and LADi/LVDi ratio., Conclusion: Higher levels of cumulative PA were associated with increased LADi in males and participants <65 years, and with increased LVMi and LVDi in females. Despite cardiac chamber enlargement, the pump function of the heart did not change with higher levels of PA, and the atrioventricular ratio was unchanged. Our results indicate that cardiac chamber enlargement is a physiological response to PA., 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., (Copyright © 2022 Heitmann, Welde, Løchen, Stylidis, Schirmer and Morseth.)

Purpose: To investigate the prevalence of hormonal contraceptive (HC) use by female cross-country (XC) skiers and biathletes competing at a national and/or international level, their reasons for HC use, and to compare negative symptoms related to the HC-/menstrual cycle in HC users and non-HC users. Additionally, to characterize the self-perceived influence of HC use on training and performance., Methods: A total of 113 Norwegian competitive XC skiers and biathletes completed an online questionnaire including both closed and open-ended questions. The questions were designed to assess the type of HC, reasons for use, self-reported negative symptoms related to HC-/menstrual cycle, as well as athletes' experiences regarding how HC use affects training and performance., Results: In total, 68% of all the athletes used HC, with 64 and 36% of them using a progestin-only and combined type HC, respectively. Non-contraceptive reasons for HC use were reported by 51% of the progestin-only HC users vs. 75% of the combined HC users ( P = 0.039), with reduction of negative menstrual-related symptoms as the most common reason. Of the athletes reporting regular withdrawal bleedings in connection to HC use, 80% of the progestin-only and 86% of combined HC users experienced negative menstrual-related symptoms, which was comparable to the non-HC group (86%). The majority (81%) of HC users experienced solely positive, or no effect, of HC use on training and performance, with no differences between progestin-only and combined HC users ( P = 0.942)., Conclusions: In total, 68% of the XC skiers and biathletes used HC, with the highest proportion (64%) using a progestin-only HC. Many athletes used HC to manipulate their menstrual cycle due to perceived negative menstrual-related symptoms that interfered with their training sessions and/or competitions., 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., (Copyright © 2022 Engseth, Andersson, Solli, Morseth, Thomassen, Noordhof, Sandbakk and Welde.)

The aim of this study was to examine how relationships between exercise intensity and the rate of energy release established in different ways, affect the calculated O 2 deficit accumulated during strenuous exercise. Aerobic energy release is readily measured by the O 2 uptake, while anaerobic energy release is by definition independent of O 2 . The latter is not easily measured during strenuous exercise, but it can be estimated using the accumulated O 2 deficit principle. We have calculated it using nine different approaches. Thirteen moderately trained persons (three women) volunteered to serve as subjects for cycle ergometry. Their maximal O 2 uptake was 2.9 ± 0.6 mmol s -1 ( x̄ ± s ; 3.9 ± 0.8 L STPD min -1 ). Our reference method (M0) is based on measuring the steady state O 2 uptake at the end of at least ten bouts of 10 min of exercise at constant intensity, varying between 30 and 40% of that corresponding to the maximal O 2 uptake and up to a power >90% of the maximal O 2 uptake, which is a rather time-consuming method. The outcomes of eight different simpler approaches have been compared with those of the reference method. The main result is that the accumulated O 2 deficit calculated depends a great deal on the relationship used to calculate it. A protocol of stepwise increases in exercise intensity every 4 min appeared to work well. A gross efficiency method showed the poorest performance. Another important result is that at constant power the O 2 uptake continued to increase beyond 4 min of exercise at all powers examined, also at powers well-below those corresponding to the lactate threshold. Finally, the O 2 uptake during loadless pedaling was considerably higher than resting O 2 uptake, and it appeared to follow a cubic function of the pedaling frequency. In conclusion, to obtain reliable values of the anaerobic energy release using the accumulated O 2 deficit principle, reliable relationships between exercise intensity and O 2 demand must be established., 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., (Copyright © 2022 Medbø and Welde.)

Aims: The aim was to investigate the long-term association between leisure time physical activity and hip areal bone mineral density (aBMD), in addition to change in hip aBMD over time, in 32-86 years old women and men., Methods: Data were retrieved from the 2001, 2007-2008, and 2015-2016 surveys of the Tromsø Study, a longitudinal population study in Norway. Leisure time physical activity was assessed by the four-level Saltin-Grimby Physical Activity Level Scale which refers to physical exertion in the past twelve months. Hip aBMD was assessed by Dual-Energy X-ray Absorptiometry. Linear Mixed Model analysis was used to examine long-term associations between physical activity and hip aBMD (n = 6324). In addition, the annual change in hip aBMD was analyzed in a subsample of 3199 participants., Results: Physical activity was significantly and positively associated with total hip aBMD in the overall cohort (p<0.005). Participants who reported vigorous activity had 28.20 mg/cm2 higher aBMD than those who were inactive (95% CI 14.71; 41.69, controlled for confounders), and even light physical activity was associated with higher aBMD than inactivity (8.32 mg/cm2, 95% CI 4.89; 11.76). Associations between physical activity and femoral neck aBMD yielded similar results. Hip aBMD decreased with age in both sexes, although more prominently in women. From 2001 to 2007-2008, aBMD changed by -5.76 mg/cm2 per year (95% CI -6.08; -5.44) in women, and -2.31 mg/cm2 (95% CI -2.69; -1.93), in men. From 2007-2008 to 2015-2016, the change was -4.45 mg/cm2 per year (95% CI -4.84; -4.06) in women, and -1.45 mg/cm2 (95% CI -1.92; -0.98) in men., Conclusions: In this cohort of adult men and women, physical activity levels were positively associated with hip aBMD in a dose-response relationship. Hip aBMD decreased with age, although more pronounced in women than men., Competing Interests: The authors have declared that no competing interests exist.

Introduction: The COVID-19 outbreak with partial lockdown has inevitably led to an alteration in training routines for football players worldwide. Thus, coaches had to face with the novel challenge of minimizing the potential decline in fitness during this period of training disruption., Methods: In this observational pre- to posttest study involving Norwegian female football players (18.8 ± 1.9 years, height 1.68 ± 0.4 m, mass 61.3 ± 3.7 kg), we investigated the effects of a prescribed home-based and group-based intervention, implemented during the COVID-19 lockdown, on maximal muscular force production and high velocity variables. Specifically, maximal partial squat strength one repetition maximum (1RM), counter movement jump (CMJ) and 15 m sprint time were assessed 1 week prior to the lockdown and 12 weeks after the onset of lockdown. We also collected training content and volume from the prescribed training program and self-reported perceived training quality and motivation toward training., Results: We observed no change in 1RM [pretest: 104 ± 12 kg, posttest: 101 ± 11 kg ( P = 0.28)], CMJ height [pretest: 28.1 ± 2.3 cm, posttest: 26.8 ± 1.9 ( P = 0.09)], and 15 m sprint time [pretest: 2.60 ± 0.08 s, posttest: 2.61 ± 0.07 s ( P = 0.52)]., Conclusion: Our findings suggest that a prescribed home-based and group-based intervention with increased training time devoted to strength, jump, and sprint ability, and regulated to obtain a sufficient infection control level is feasible and effective to preserve strength, jumping, and sprinting abilities of high-level female football players during a ∼ 3-month period of a pandemic-induced lockdown., 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., (Copyright © 2021 Pedersen, Johansen, Casolo, Randers, Sagelv, Welde, Winther and Pettersen.)

Whereas left atrial (LA) enlargement is an independent predictor for adverse cardiovascular events and all-cause mortality, this is regarded a physiological adaption of exercise. Paradoxically, LA size in athletes may overlap the enlargement observed in patients with cardiac pathology. Current knowledge is mainly derived from studies of athletes, and little is known about cardiac adaptations to physical activity (PA) in the general population. We explored the association between objectively measured PA and LA volume index (LAVi), and between LAVi enlargement and indices of diastolic dysfunction stratified by PA-level. Our study included 1573 participants from the population-based Tromsø Study (2015-16). PA was assessed with an ActiGraph wGT3X-BT accelerometer. Echocardiography was performed according to current guidelines. The associations between PA and LAVi, and between LAVi enlargement and indices of diastolic dysfunction were estimated by univariable and multivariable linear regression analyses, adjusted for sex, age, and cardiovascular risk factors. Our multiple adjusted analyses showed significant linear associations between PA and LAVi in ages < 70 years, and between PA and LAVi in participants with normal diastolic function. No associations were seen in ages ≥ 70 years or for participants with abnormal diastolic function. In those 40-54 years, the most active participants had larger LAVi (4.45 mL/m 2 , p = 0.016) than the least active. LAVi enlargement was only associated with indices of diastolic dysfunction in the most inactive participants. In conclusion, higher levels of PA associate with greater LAVi in participants < 70 years with normal diastolic function. LAVi enlargement is only associated with diastolic dysfunction in the most inactive participants., Competing Interests: The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (© 2020 The Author(s).)

This study investigated the acute post-exercise hypotension (PEH) response in persons with elevated blood pressure or stage 1 hypertension following moderate and high-intensity isoenergetic endurance exercise. Twelve middle-aged persons (six females), with resting systolic and diastolic BP of 130±6 and 84±7 mmHg, participated in three bicycle ergometer bouts: 1) Testing of peak aerobic capacity (VO 2peak ), 2) Moderate intensity exercise (MOD) at 66% of VO 2peak , 3) High-intensity exercise (INT) at 80% of VO 2peak . All variables were recorded pre-exercise, during exercise and 0, 5, 10, and 30 minutes post-exercise. The total duration of exercise was 26% longer during MOD than INT ( p <0.001), while total energy expenditure (TEE) was similar between exercise conditions (359 ± 69 kcal). Oxygen consumption, heart rate, power output and ratings of perceived exertion was 21, 13, 21 and 26% higher during INT than MOD exercise, respectively (0.05 ≤ p ≤ 0.001). Compared to pre-exercise, systolic BP was significantly lower at 30 min post-exercise following both INT ( p < 0.05) and MOD ( p < 0.01) exercise, and there was no difference between INT and MOD conditions. Other variables were similar to pre-exercise values at 30 min post-exercise. Linear regression shows that the largest post-exercise reductions in systolic BP was found for the persons with the highest pre-exercise systolic BP (r = 0.58 r 2 = 0.33, p < 0.003). In conclusion, this study shows that endurance exercise with different intensities and durations, but similar TEE is equally effective in eliciting reductions in the post-exercise systolic BP. Furthermore, the magnitude of PEH response is partly dependent on the individuals' resting blood pressure.

Background: High load (HL: > 85% of one repetition maximum (1RM)) squats with maximal intended velocity contractions (MIVC) combined with football sessions can be considered a relevant and time-efficient practice for maintaining and improving high velocity movements in football. Flywheel (FW) resistance exercise (RE) have recently emerged with promising results on physical parameters associated with football performance., Methods: In this randomized controlled trial over 6 weeks, 38 recreationally active male football players randomly performed RE with MIVCs two times per week as either 1) FW squats ( n  = 13) or 2) barbell free weight (BFW) HL squats ( n  = 13), where a third group served as controls ( n  = 12). All three groups conducted 2-3 football sessions and one friendly match a week during the intervention period. Pre- to post changes in 10-m sprint, countermovement jump (CMJ) and 1RM partial squat were assessed with univariate analyses of variance., Results: The FW and BFW group equally improved their 10-m sprint time (2 and 2%, respectively, within group: both p  < 0.001) and jump height (9 and 8%, respectively, within group: both p  < 0.001), which was superior to the control group's change (between groups: both p  < 0.001). The BFW group experienced a larger increase (46%) in maximal squat strength than the FW group (17%, between groups: p  < 0.001), which both were higher than the control group's change (both p  < 0.001)., Conclusion: Squats carried out with FWs or BFWs where both are performed with MIVCs and combined with football sessions, were equally effective in improving sprint time and jump height in football players. The BFW group experienced a more than two-fold larger increase in maximal partial squat strength than the FW group in maximal partial squat strength. This presents FW RE as an alternative to BFW HL RE for improving high velocity movements in football., Trial Registration: ClinicalTrials.gov Identifier: NCT04113031 (retrospectively registered, date: 02.10.2019)., Competing Interests: Competing interestsThe authors declare that they have no competing interests., (© The Author(s) 2020.)

The aim of this study was to investigate the effect of prolonged ski racing using skating style on technique choice in a transition section among female and male high-level skiers. Fifty three national-to-elite level skiers (20 females: 26.7 ± 4.8 years, 167.0 ± 6.5 m, 61.0 ± 5.1 kg, and 75.5 ± 68.8 FIS points; 33 males: 25.2 ± 3.5 years, 179.0 ± 5.2 cm, 73.1 ± 5.7 kg, and 73.7 ± 63.2 FIS points) were video recorded along a flat-to-uphill transition section of a course during the 30-km (females) and 50-km (males) races at the 2018 Norwegian National Championships. Across laps, section speeds decreased ( P < 0.001) in all skiers, with the best-ranked skiers faster than the lowest-ranked ( P < 0.001), and males faster than females in the first and middle laps. Section speed within each lap was associated with race performance ( r = 0.76-0.86, P < 0.001 in females and r = 0.87-0.89, P < 0.001 in males). The prevalence of Gear 2 (G2) increased, while Gear 3 (G3) use decreased (both P < 0.001) across the subsequent laps, with females preferring G2 more than males in lap one ( P = 0.027). In long-distance skate-style skiing, transition performance is representative of race performance and skiers decrease the use of the often-faster G3 technique while increasing the use of the slower G2 technique due to prolonged exercise. Especially female skiers should consider adding some flat-to-uphill G3 practice into established training, specifically early in the session before fatigue may occur., (Copyright © 2020 Ardigò, Stöggl, Thomassen, Winther, Sagelv, Pedersen, Hammer, Heitmann, Olsen and Welde.)

The aim was to describe longitudinal trends in peak oxygen uptake (VO 2peak ) among 14- to 19-year-old adolescents in Norway, and to examine effects of sex, body mass index (BMI), and physical activity (PA) level on VO 2peak during adolescence. Of 124 invited students from two lower secondary schools in Norway, 116 eighth-grade students (61 boys and 55 girls; 14 years old at baseline) volunteered to participate. The study has a longitudinal design with 6 yearly repeated measures of body height and mass, VO 2peak and PA level. VO 2peak allometrically scaled to body mass raised to the power of 0.67 was measured using a walking or running incremental test on a treadmill, whereas PA level was self-reported. Among 696 possible observations, 555 (79.7%) were valid. Multiple linear regression and linear mixed model analyses were used to examine the associations between age, sex, BMI, PA level and VO 2peak . VO 2peak showed a non-linear pattern from age 14 to 19, with a distinct increase for boys peaking at age 17, while the results provide a flatter and more stable curve for girls. Sex, BMI and PA level together explained 43-71% of the variance in VO 2peak at the different age levels. Sex and PA level contributed independently to explain a significant proportion of the variance in VO 2peak at all measurement occasions, while BMI did not. Adjusted sex differences in VO 2peak increased over time, from 26.5 ml·kg -0.67 ·min -1 at age 14 to 55.5 ml·kg -0.67 ·min -1 at age 19. The independent contribution from PA level to the variance in VO 2peak increased from age 14 to 16 and then decreased. While PA level explained 32.5% of the total variance in VO 2peak for 16-year-olds, this number was 14% in 19-year-olds. In conclusion, aerobic power showed a non-linear pattern during adolescence, peaking at age 17. Sex and PA level explained a large proportion of the variance in VO 2peak , each of them being an independent contributor to VO 2peak . Aerobic power is linked to improved health and seems to depend largely on sex and PA level in adolescents, emphasizing the importance of maintaining a sufficient PA level during adolescence., (Copyright © 2020 Welde, Morseth, Handegård and Lagestad.)

Introduction: Long-distance cross-country skiing (XCS) has gained increased popularity within the past decades. However, research about long-distance XCS is limited; therefore, the aim of this study was to analyze the intensity distribution, technique application, and pacing strategies during long-distance XCS racing., Methods: Heart rate (HR) and section skiing speeds of 9 elite (ranked 1-100) and 10 amateur skiers (ranked 101-1,500) during the 90-km Vasaloppet race were collected. In addition, during the first uphill, the first 1,000 skiers were video-recorded to analyze the applied skiing strategy (e.g. grip-waxed skis versus exclusive double poling)., Results: Mean race intensity was 82% of maximal HR and was not different between performance groups even though elite skiers skied ∼15% faster than amateurs. There was an interaction effect of section × group with a pronounced decrease in HR in amateurs compared with more even pacing in elite skiers (0.13 vs. 0.04% decrease/km) and skiing at higher percentage in the high-intensity zones in elite compared with amateurs (46 vs. 24%). Ninety-eight percent of the top 100 skiers and 59% of the first 1,000 skiers used exclusively double poling., Conclusion: Elite and amateur skiers ski at comparable mean race exercise intensity, but they have clear differences in skiing speed. The difference in the pacing profiles between elite and amateur skiers (more even vs. distinct positive pacing) demonstrate the greater capacity of the former with respect to physiological capacity and highlights that amateurs seem to start too fast according to their capacities. The exclusive application of the double poling technique is no longer a phenomenon of elite skiers but is widely used among the top 1,000 ranked skiers., (Copyright © 2020 Stöggl, Hertlein, Brunauer, Welde, Andersson and Swarén.)

Background: Changes of direction (COD) repeated sprints (RSs) might have greater relevance to football than linear RSs. We aimed to compare the effects of linear and COD RSs on intermittent high intensity running (HIR) over an entire season., Methods: In total, 19 high-level male football players (16-19 years) randomly performed linear RSs or COD RSs twice a week during their competitive season over 22 weeks. Yo-Yo intermittent recovery test level 2 (Yo-Yo IR2), and 10- and 20-m sprint was assessed pre-, mid- (11 weeks), and post-intervention (22 weeks). Maximal oxygen uptake (VO 2max ) was assessed pre- and post-intervention., Results: There was no interaction effect (time x group) in Yo-Yo IR2 ( p = 0.36, p η 2 = 0.06) or sprint tests (10 m: p = 0.55, p η 2 = 0.04, 20 m: p = 0.28 p η 2 = 0.08), and no change differences between groups. There was a main effect of time for Yo-Yo IR2 ( p = 0.002, p η 2 = 0.31) but not in sprints or VO 2max ., Conclusion: Linear and COD RS exercise twice a week over 22 weeks equally improves intermittent HIR performance but does not improve sprint time or aerobic power in high-level junior football players. However, due to our two-armed intervention, we cannot exclude possible effects from other exercise components in the players' exercise program.

Biomechanical differences in double poling (DP) between sex and performance level were investigated in female and male cross-country skiers during a classical race (10/15 km). Skiers were divided into faster and slower on basis of race performance: females faster (n=20), females slower (n=20), males faster (n=20), and males slower (n=20). Based on video analysis while DP in a flat section of the track, joint and pole angles at pole plant (PP) and pole-off, cycle characteristics and the use and coordination pattern of heel-raise (raise of heels from the ground to have a higher body position at PP) were analysed. Faster females and males had 4.3% and 7.8% higher DP velocity than their slower counterparts (both P<0.001). Faster males had 6.5% longer cycles than slower males (P<0.001). Faster skiers stopped heel-raise later than slower skiers (females: 2.0±3.4% vs. -1.0±3.5%, P<0.05; males: 3.9±2.4% vs. 0.8±3.2% of cycle time in relation to PP, P<0.001). At PP, faster skiers and male skiers had a smaller pole angle and greater ankle to hip and ankle to shoulder angle with respect to vertical, resulting in a more distinct forward body lean. However, the majority of the differences are likely due to higher DP velocity.

The benefits of using longer than self-selected poles have been shown in double poling, but these potential benefits have not been examined in the gear 3 ski skating sub-technique (G3), during which the poling movement is very similar to double poling. The aim of this study was to examine the effect of longer than self-selected poles on physiological and perceptual responses in the G3 sub-technique. Ten cross-country skiers and biathletes (VO2max 72.4 ± 3.0 ml∙min-1∙kg-1, age 20.1 ± 2.8 years, height 1.81 ± 0.03 m and weight 73.1 ± 4.6 kg) completed two tests, each with three different submaximal intensities, during roller skiing using the G3 technique. The first test was carried out at a fixed speed (10 km∙h-1) and the skiers performed two intervals of 5 min at 7, 9 and 11% inclination on a roller ski treadmill with self-selected poles (SSP) and 7.5 cm longer poles (LP) at each step. The second test had a fixed inclination of 4% and speeds of 14, 17 and 20 km∙h-1, also performed with SSP and LP at each step. At fixed speed, the oxygen uptake was 2.7% lower (P = 0.005) and the gross efficiency (GE) 2.1% higher (P = 0.01) with LP than with SSP at the steepest inclination of 11%. At fixed inclination, the oxygen uptake was 2.1% lower (P = 0.01) and the GE was 4.1% higher (P = 0.03) with LP than with SSP at the highest speed of 20 km∙h-1. At 14 km∙h-1, the oxygen uptake was 3.0% lower (P = 0.05) and GE was 3.8% higher (P = 0.03) with LP than with SSP. Our novel findings show that longer poles in the G3 technique may enhance the efficiency of skiing., Competing Interests: The authors have declared that no competing interests exist.

Longer distance cross-country ski (14-220 km) races such as the Visma Ski Classics (VSC) has recently gained attention in addition to the traditional Olympic distances (5-50 km) associated with cross-country (XC) skiing. These long-distance races are characterized by extensive use of the upper body while double poling (DP). While there is a substantial amount of research on Olympic distance XC skiing, the physiological capacities of VSC skiers has not yet been explored. We recruited seven elite male VSC skiers and seven well-trained national level male XC skiers to undergo three tests in the laboratory: (1) a one repetition maximum (1RM) strength test in a cable pulldown; (2) roller skiing tests on a treadmill (10.5% inclination) for determination of gross efficiency (GE) at submaximal speeds (8 and 10 km·h -1 ) in DP and diagonal stride (DS); (3) two ramp protocols to exhaustion (15% inclination, starting speed 7 km·h -1 ) in DP and DS for the assessment of peak and maximal oxygen uptake ( V . O 2peak and V . O 2max ), respectively. Compared with the national level XC skiers, the VSC skiers performed similar in the 1RM cable pulldown, displayed 12.2% higher GE in DP at 8 km·h -1 but did not display any difference at 10 km·h -1 , and had lower blood lactate concentration and heart rate at both submaximal speeds. The VSC skiers had longer time to exhaustion compared with the national level XC skiers during the two ramp protocols in DS (18%) and in DP (29%). The V . O 2max was 10% higher in DS compared with DP, with no differences between the groups. The V . O 2peak / V . O 2max -ratio of 90% did not differ between the two groups. In conclusion, the main differences were lower cardiorespiratory and metabolic responses at submaximal speeds as well as longer time to exhaustion in VSC skiers compared with national level XC skiers. This suggest efficiency to be the main difference between VSC and national level XC skiers.

Here, female and male elite cross-country (XC) skiers were compared on varying terrain during an official 10-km (women) and 15-km (men) Norwegian championship race. On the basis of race performance, 82 skiers were classified as fast (FS) (20 women, 20 men) or slower (SS) (21, 21) skiers. All were video recorded on flat (0°), intermediate (3.5°), uphill (7.1°) and steep uphill (11°) terrain during the race at a distance of 0.8, 1.2, 2.1 and 7.1 km from the start, respectively. All skiers employed exclusively double-poling (DP) on the flat section and, except for the male winner, exclusively diagonal stride (DIA) on the uphill sections. On the intermediate section, more men than women utilized DP and fewer DIA (p = 0.001), with no difference in kick double-poling (DPK). More FS than SS utilized DPK and fewer DIA (p = 0.001), with similar usage of DP. Males skied with faster and longer cycles but lower cycle rate compared with females (p < 0.001), with largest absolute sex differences on flat terrain (p < 0.001) and largest relative differences for cycle velocity and length on intermediate and uphill terrain. External power output rose with increasing incline, being higher for men and FS (p < 0.001). Cycle velocity on flat terrain was the best predictor of mean race velocity for the men, while cycle velocity on steep uphill was the best predictor for the women (both p < 0.001). In conclusion, incline, sex and level of performance influenced cycle characteristics and power output. Greatest absolute sex gap was on flat terrain, whereas the relative difference was greatest on intermediate and steep uphill terrain. We recommend usage of more DP and/or DPK, and less DIA and fewer transitions between techniques on intermediate terrain. Predictors of race performance are sex specific with greatest potential for enhancing performance on flat terrain for men and on steep uphill terrain for women.

This study compared the effects of long (4×4 min) and short intervals (4×8×20 s) of high-intensity interval exercise bouts (HIIT) on running performance, physiological and perceptual responses, and excess postexercise oxygen consumption (EPOC). Twelve healthy college students (8 men, 4 women; mean age=22±2 years) performed long (90-95% of peak heart rate) and short intervals (maximal intensity) of high-intensity training (running on a non-motorized treadmill) with the same total duration on separate days. The total volume of consumed oxygen during recovery was the same in both cases ( P =0.21), whereas the short intervals of high-intensity training were performed at a faster mean running velocity (3.5±0.18 vs. 2.95±0.07 m/s) and at a lower RPE breath compared with the long intervals of high-intensity training. The blood lactate concentration also tended to be lower during the short intervals of high-intensity training, indicating that short-interval training was perceived to be easier than long-interval training, even though the cardiovascular and metabolic responses are similar. Furthermore, EPOC lasted significantly longer (83.4±3.2 vs. 61.3±27.9 min, P =0.016) and tended to be higher (8.02±4.22=vs. 5.70±3.75 L O 2 , P =0.053) after short intervals than after long intervals of training.

In this study the pacing strategy, cycle characteristics and choice of technique of elite male cross-country (XC) skiers during a three-lap, 15-km classical race with interval start were measured. During the Norwegian Championships in 2016, fast (n = 18, age: 26±4 yr; height: 182±4 cm; body mass: 78±3 kg (means±SD)) and slow skiers (n = 18, age: 22±2 yr; height: 183±5 cm; body mass: 78±6 kg) were video recorded on flat (0°), intermediate (3.5°) and uphill sections (7.1°) of the first and final laps. All skiers adopted a positive pacing strategy, skiing more slowly (11.8%) with shorter cycles (11.7%) on the final than first lap (both p<0.001; pη2 = 0.93 and 0.87, respectively). The fast skiers were 7.0% faster overall (p<0.001, d = 4.20), and 6.1% (p<0.001, d = 3.32) and 7.0% (p<0.001, d = 3.68) faster on the first and final laps, respectively, compared to slower skiers. On all sections of both laps, the fast skiers exhibited 9.5% more rapid (pη2 = 0.74) and 8.9% (pη2 = 0.48) longer cycles (both p<0.001). On intermediate terrain, the fast skiers employed primarily double poling (DP, 38.9% on the first lap) and double poling with a kick (DPKICK, 50% on the final lap). In contrast, the slow skiers utilized for the most part DP alone (lap 1: 33.3%, lap 3: 38.9%) or in combination with other techniques (lap 1: 33.3%, lap 3: 38.9%) and decreased their usage of DPKICK from 27.8% on the first to 16.7% on the final lap. Skiing velocity on flat and intermediate terrain proved to be the best predictor of race performance (p<0.001). In conclusion, during a 15-km classical XC skiing race, velocity and cycle length decreased from the first to the final lap, most extensively on flat terrain and least uphill. Moreover, on the intermediate sections the fast and slow skiers chose to use different techniques.

This study compared the effects of adding upper-body sprint-intervals or continuous double poling endurance training to the normal training on maximal upper-body strength and endurance capacity in female cross-country skiers. In total, 17 female skiers (age: 18.1±0.8yr, body mass: 60±7 kg, maximal oxygen uptake (VO2max): 3.30±0.37 L.min-1) performed an 8-week training intervention. Here, either two weekly sessions of six to eight 30-s maximal upper-body double poling sprint-intervals (SIG, n = 8) or 45-75 min of continuous low-to-moderate intensity double poling on roller skis (CG, n = 9) were added to their training. Before and after the intervention, the participants were tested for physiological and kinematical responses during submaximal and maximal diagonal and double poling treadmill roller skiing. Additionally, we measured maximal upper-body strength (1RM) and average power at 40% 1RM in a poling-specific strength exercise. SIG improved absolute VO2max in diagonal skiing more than CG (8% vs 2%, p<0.05), and showed a tendency towards higher body-mass normalized VO2max (7% vs 2%, p = 0.07). Both groups had an overall improvement in double poling peak oxygen uptake (10% vs 6% for SIG and CG) (both p<0.01), but no group-difference was observed. SIG improved 1RM strength more than CG (18% vs 10%, p<0.05), while there was a tendency for difference in average power at 40% 1RM (20% vs 14%, p = 0.06). Oxygen cost and kinematics (cycle length and rate) in double poling and diagonal remained unchanged in both groups. In conclusion, our study demonstrates that adding upper-body sprint-interval training is more effective than continuous endurance training in improving upper-body maximal strength and VO2max.

Østerås, S, Welde, B, Danielsen, J, van den Tillaar, R, Ettema, G, and Sandbakk, Ø. Contribution of upper-body strength, body composition, and maximal oxygen uptake to predict double poling power and overall performance in female cross-country skiers. J Strength Cond Res 30(9): 2557-2564, 2016-Maximal oxygen uptake (V[Combining Dot Above]O2max) is regarded as the most performance-differentiating physiological measure in cross-country (XC) skiing. In addition, upper-body strength and lean mass have been associated with double poling (DP) power in XC skiers. In this study, we tested upper-body maximal strength, lean mass, and V[Combining Dot Above]O2max's contributions to predict DP power production of different durations and the overall XC skiing performance level of elite female XC skiers. Thirteen skiers (V[Combining Dot Above]O2max: 64.9 ± 4.2 ml·kg·min) performed one 30-second and one 3-minute DP performance test using a ski ergometer. The International Ski Federation's (FIS) ranking points determined their overall XC skiing performance. The skiers performed three 1-repetition maximal strength tests in poling-specific exercises that isolated the elbow extension, shoulder extension, and trunk flexion movements. Body composition was determined by a DXA scan, and V[Combining Dot Above]O2max was tested in an incremental running test. Multiple regressions were used to predict power production in the 30-second and 3-minute tests and FIS points. The 2 best predictions of 30-second DP power were lean upper-body mass and maximal upper-body strength (with the 3 strength tests normalized and pooled together as one variable) (R = 0.84 and 0.81, p < 0.001). Along with V[Combining Dot Above]O2max, the same 2 variables were the best predictions of both 3-minute DP power (R = 0.60 and 0.44, p ≤ 0.05) and overall XC skiing performance (R = 0.43 and 0.40, p ≤ 0.05). Although the importance of upper-body strength and lean mass to predict DP power production and the overall XC skiing performance declines with the performance duration in female XC skiers, the importance of V[Combining Dot Above]O2max shows an opposite relationship.

This study examined the effects of acute supplementation with L-arginine and nitrate on running economy, endurance and sprint performance in endurance-trained athletes. In a randomised cross-over, double-blinded design we compared the effects of combined supplementation with 6 g L-arginine and 614 mg nitrate against 614 mg nitrate alone and placebo in nine male elite cross-country skiers (age 18 ± 0 years, VO2max 69.3 ± 5.8 ml ⋅ min(-1) ⋅ kg(-1)). After a 48-hour standardisation of nutrition and exercise the athletes were tested for plasma nitrate and nitrite concentrations, blood pressure, submaximal running economy at 10 km ⋅ h(-1) and 14 km ⋅ h(-1) at 1% incline and 180 m as well as 5-km time-trial running performances. Plasma nitrite concentration following L-arginine + nitrate supplementation (319 ± 54 nmol ⋅ L(-1)) did not differ from nitrate alone (328 ± 107 nmol ⋅ L(-1)), and both were higher than placebo (149 ± 64 nmol ⋅ L(-1), p < 0.01). There were no differences in physiological responses during submaximal running or in 5-km performance between treatments. The plasma nitrite concentrations indicate greater nitric oxide availability both following acute supplementation of L-arginine + nitrate and with nitrate alone compared to placebo, but no additional effect was revealed when L-arginine was added to nitrate. Still, there were no effects of supplementation on exercise economy or endurance running performance in endurance-trained cross-country skiers., (Copyright © 2014 Elsevier Inc. All rights reserved.)

Purpose: To study performance, physiological and biomechanical responses during repeated upper-body sprint exercise., Methods: Twelve male elite cross-country skiers performed eight 8-s maximal poling sprints with a 22-s recovery while sitting on a modified SkiErg poling ergometer. Force, movement velocity, cycle rate, work per cycle, oxygen saturation in working muscles and pulmonary oxygen uptake were measured continuously. A 3-min all-out ergometer poling test determined VO2peak, and 1 repetition maximum (1RM) strength was determined in a movement-specific pull-down., Results: Average sprint power was 281 ± 48 W, with the highest power on the first sprint, a progressive decline in power output over the following four sprints, and a sprint decrement of 11.7 ± 4.1 %. Cycle rate remained unchanged, whereas work per cycle progressively decreased (P < 0.05). m. triceps brachii and m. latissimus dorsi were highly desaturated already after the first sprint (all P < 0.05), whereas the response was delayed for m. biceps brachii and m. vastus lateralis. Correspondingly, increases in VO2 mainly occurred over the first two sprints (P < 0.05) and plateaued at approximately 75 % of VO2peak. 1RM correlated with power during the first four sprints and with average sprint power (r = 0.71-0.80, all P < 0.05), whereas VO2peak correlated with power in the last three sprints (r = 0.60-0.71, all P < 0.05)., Conclusions: The main decrement in upper-body sprint performance was evident in the first five sprints, followed by highly desaturated muscles and a plateau in pulmonary oxygen uptake already after the first 2-3 sprints. While high maximal strength seems important for producing power, aerobic capacity correlates with power in the last sprints.

In the current study, we evaluated the impact of exercise intensity on gender differences in upper-body poling among cross-country skiers, as well as the associated differences in aerobic capacity, maximal strength, body composition, technique and extent of training. Eight male and eight female elite skiers, gender-matched for level of performance by FIS points, carried out a 4-min submaximal, and a 3-min and 30-sec maximal all-out test of isolated upper-body double poling on a Concept2 ski ergometer. Maximal upper-body power and strength (1RM) were determined with a pull-down exercise. In addition, body composition was assessed with a DXA scan and training during the previous six months quantified from diaries. Relative to the corresponding female values (defined as 100%), the power output produced by the men was 88%, 95% and 108% higher during the submaximal, 3-min and 30-sec tests, respectively, and peak power in the pull-down strength exercise was 118% higher (all P<0.001). During the ergometer tests the work performed per cycle by the men was 97%, 102% and 91% greater, respectively, and the men elevated their cycle rate to a greater extent at higher intensities (both P<0.01). Furthermore, men had a 61% higher VO2peak, 58% higher 1RM, relatively larger upper-body mass (61% vs 56%) and reported considerably more upper-body strength and endurance training (all P<0.05). In conclusion, gender differences in upper-body power among cross-country skiers augmented as the intensity of exercise increased. The gender differences observed here are greater than those reported previously for both lower- and whole-body sports and coincided with greater peak aerobic capacity and maximal upper-body strength, relatively more muscle mass in the upper-body, and more extensive training of upper-body strength and endurance among the male skiers.

Purpose: To investigate performance and the associated physiological and biomechanical responses during upper-body repeated-sprint work., Methods: Twelve male ice sledge hockey players from the Norwegian national team performed eight 30-m sprints with start every 30 s and an active recovery between sprints. Time was captured every 10 m by photocells, cycle length and rate were determined by video analyses, and heart rate and blood lactate concentration were measured by conventional methods., Results: The percentage sprint decrement was 7% over the 8 trials, with significant reductions in performance from the previous trial already on the second trial (all P < .05). Furthermore, cycle rate was reduced by 9% over the 8 trials (P < .05). Similar changes in performance and kinematic patterns were evident for all 10-m phases of the sprints. Heart rate gradually increased to 94% of maximal (178 ± 10 beats/min) over the 8 trials, and the mean reduction in heart rate was 7 ± 2 beats/min during the 22-24 s of active recovery for all trials (all P < .05). The blood lactate concentration increased to the athletes' maximal levels over the 8 sprints (P < .05)., Conclusions: This is the first study to investigate performance, physiological, and biomechanical aspects of self-propelled upper-body repeated-sprint work. The observed sprint decrement over the 8 trials was associated with reductions in cycle rates and high physiological demands. However, no kinematic and physiological characteristics were significantly correlated to repeated-sprint ability or the sprint decrement.

Ice sledge hockey is a popular paralympic team sport where players rely entirely on their upper body to propel themselves rapidly across the ice surface. The isolated and repetitive poling movements provide a good model for examining upper-body sprint ability and the related movement and strength characteristics. Therefore, the purpose of the present study was to investigate the relationship between upper-body maximal strength, power, and sprint performance in ice sledge hockey. Thirteen male ice sledge hockey players from the Norwegian national team performed three 30-m maximal sprint tests recorded by fixed light sensors. The best 30-m time for each subject was used for further analyses, and the sprint was analyzed more in detail for the first and last 10-m split times and kinematics (cycle length and rate) using photocells and 2-dimensional video analysis. One repetition maximum (1RM) strength and peak power were assessed in the bench press, bench pull, and pull-down exercises using a barbell and a linear encoder. Both 1RM strength and peak power for all the 3 strength exercises correlated significantly with the total sprint time (-0.75 < r < - 0.86, all p < 0.005), the first (0.60 < r < 0.72, all p < 0.05), and the last (0.74 < r < 0.83, all p < 0.05) 10-m split times in the 30-m sprint test. There were no significant relationships between sprint kinematics and 1RM strength and peak power. Overall, these results demonstrate that there are close relationships between upper-body strength, power, and sprint performance in highly trained athletes and that the ability to produce propulsion and high frequency in combination is important for the sprint abilities in ice sledge hockey.

The purpose of this study was to test whether a long duration of aerobic high-intensity interval training is more effective than shorter intervals at a higher intensity in highly trained endurance athletes. The sample comprised of 12 male and 9 female, national-level, junior cross-country skiers (age, 17.5 ± 0.4 years, maximal oxygen uptake (V[Combining Dot Above]O2max): 67.4 ± 7.7 ml min kg), who performed 8-week baseline and 8-week intervention training periods on dry land. During the intervention period, a short-interval group (SIG, n = 7) added 2 weekly sessions with short duration intervals (2- to 4-minute bouts, total duration of 15-20 minutes), a long-interval group (LIG; n = 7) added 2 weekly sessions with long duration intervals (5- to 10-minute bouts, total duration of 40-45 minutes). The interval sessions were performed with the athletes' maximal sustainable intensity. A control group (CG; n = 7) added 2 weekly sessions with low-intensity endurance training at 65-74% of maximal heart rate. Before and after the intervention period, the skiers were tested for time-trial performance on 12-km roller-ski skating and 7-km hill run. V[Combining Dot Above]O2max and oxygen uptake at the ventilatory threshold (V[Combining Dot Above]O2VT) were measured during treadmill running. After the intervention training period, the LIG-improved 12-km roller ski, 7-km hill run, V[Combining Dot Above]O2max, and V[Combining Dot Above]O2VT by 6.8 ± 4.0%, 4.8 ± 2.6%, 3.7 ± 1.6%, and 5.8 ± 3.3%, respectively, from pre- to posttesting, and improved both performance tests and V[Combining Dot Above]O2VT when compared with the SIG and the CG (all p < 0.05). The SIG improved V[Combining Dot Above]O2max by 3.5 ± 3.2% from pre- to posttesting (p < 0.05), whereas the CG remained unchanged. As hypothesized, a long duration of aerobic high-intensity interval training improved endurance performance and oxygen uptake at the ventilatory threshold more than shorter intervals at a higher intensity.

Purpose: The present study describes the distribution of cardiorespiratory fitness (VO2peak) in a large sample of healthy adolescents and the associations between VO2peak, self-reported physical activity, and a selection of conventional markers for future cardiovascular health., Methods: In a substudy of the Young-HUNT study in Norway, 570 adolescents (289 girls and 281 boys) 13–18 yr. old were tested for directly measured VO2peak. Blood pressure, resting heart rate, height, weight, and waist circumference was measured by standardized procedures. Data about physical activity and pubertal development were obtained using self-administered questionnaires. General linear modeling and ANOVA were used to examine the relationships between VO2peak and age, physical activity, and cardiovascular risk factors., Results: The mean T SD VO2peak was 183.9 +/- 24.6 mL x kg(-0.67) x min(-1) (49.2 mL x kg(-0.67) x min(-1)) in girls and 235.1 +/- 35.3 mL x kg(-0.67) x min(-1) (59.5 mL x kg(-0.67) x min(-1)) in boys. Absolute VO2peak (L x min(-1)) was consistently higher in older age groups in both sexes (P trend < 0.001). VO2peak allometrically scaled to body mass (mL x kg(-0.67) x min(-1)) was similar across the age groups in girls (i.e., difference between 13- to 14-yr-olds and 17- to 18-yr-olds = -3.2 mL x kg(-0.67) x min(-1), 95% confidence interval = 3.8 to -10.1) and slightly higher in the older age groups in boys (i.e., difference between 13- to 14-yr-olds and 15- to 16-yr-olds = -31.0 mL x kg(-0.67) x min(-1), 95% confidence interval = -22.0 to -40.1). Physical activity was positively associated with VO2peak in all sex and age groups. Quartiles of VO2peak were inversely associated with resting heart rate (P trend = 0.004) in both sexes and body mass index (P trend = 0.004) and waist circumference (P trend = 0.006) in boys., Conclusion: Although VO2peak was generally high across the age groups, VO2peak was higher in physically active adolescents of both sexes and physical activity in accordance with the recommended level may be sufficient to maintain or even increase VO2peak through adolescence.

Purpose: The objective of this study is to examine the effects of acute ingestion of dietary nitrate on endurance running performance in highly trained cross-country skiers. Dietary nitrate has been shown to reduce the oxygen cost of submaximal exercise and improve tolerance of high-intensity exercise, but it is not known if this holds true for highly trained endurance athletes., Methods: Ten male junior cross-country skiers (V˙O(2max)) ≈ 70 mL·kg·min) each completed two trials in a randomized, double-blind design. Participants ingested potassium nitrate (614-mg nitrate) or a nitrate-free placebo 2.5 h before two 5-min submaximal tests on a treadmill at 10 km·h (≈55% of V˙O(2max)) and 14 km·h (≈75% of V˙O(2max)), followed by a 5-km running time trial on an indoor track., Results: Plasma nitrite concentrations were higher after nitrate supplementation (325 ± 95 nmol·L) compared with placebo (143 ± 59 nmol·L, P < 0.001). There was no significant difference in 5-km time-trial performance between nitrate (1005 ± 53 s) and placebo treatments (996 ± 49 s, P = 0.12). The oxygen cost of submaximal running was not significantly different between placebo and nitrate trials at 10 km·h (both 2.84 ± 0.34 L·min) and 14 km·h (3.89 ± 0.39 vs. 3.77 ± 0.62 L·min)., Conclusions: Acute ingestion of dietary nitrate may not represent an effective strategy for reducing the oxygen cost of submaximal exercise or for enhancing endurance exercise performance in highly trained cross-country skiers.

The purpose of the present study was to investigate the relationship between aerobic characteristics and sprint skiing performance, and the effects of high-intensity endurance training on sprint skiing performance and aerobic characteristics. Ten male and 5 female elite junior cross-country skiers performed an 8-week intervention training period. The intervention group (IG, n = 7) increased the volume of high-intensity endurance training performed in level terrain, whereas the control group (CG, n = 8) continued their baseline training. Before and after the intervention period, the skiers were tested for 1.5-km time-trial performance on roller skis outdoors in the skating technique. Maximal oxygen uptake (VO₂max) and oxygen uptake at the ventilatory threshold (VO₂VT) were measured during treadmill running. VO₂max and VO₂VT were closely related to sprint performance (r = ~0.75, both p < 0.008). The IG improved sprint performance, VO₂max, and VO₂VT from pre to posttesting and improved sprint performance and VO₂VT when compared to the CG (all p < 0.01). This study shows a close relationship between aerobic power and sprint performance in cross-country skiing and highlights the positive effects of high-intensity endurance training in level terrain.