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We investigated the effects of adding heavy strength training to a high volume of endurance training on performance and related physiological determinants in junior female cross-country skiers. Sixteen well-trained athletes (17 ± 1 years, 60 ± 6 kg, 169 ± 6 cm, VO2max running: 60 ± 5 mL/kg/min) were assigned either to an intervention group ( INT; n = 9) or a control group ( CON; n = 7). INT completed two weekly sessions of upper body heavy strength training in a linear periodized fashion for 10 weeks. Both groups continued their normal aerobic endurance and muscular endurance training. One repetition maximum in seated pull-down increased significantly more in INT than in CON, with a group difference of 15 ± 8% ( P < 0.01). Performance, expressed as average power output on a double poling ergometer over 20 s and as 3 min with maximal effort in both rested (sprint-test) and fatigued states (finishing-test), showed similar changes in both groups. Submaximal O2- cost and VO2peak in double poling showed similar changes or were unchanged in both groups. In conclusion, 10 weeks of heavy strength training increased upper body strength but had trivial effects on performance in a double poling ergometer in junior female cross-country skiers. [ABSTRACT FROM AUTHOR]

Background: Skeletal muscle mitochondria and capillaries are crucial for aerobic fitness, and suppressed levels are associated with chronic and age-related diseases. Currently, evidence-based exercise training recommendations to enhance these characteristics are limited. It is essential to explore how factors, such as fitness level, age, sex, and disease affect mitochondrial and capillary adaptations to different exercise stimuli., Objectives: The main aim of this study was to compare the effects of low- or moderate intensity continuous endurance training (ET), high-intensity interval or continuous training (HIT), and sprint interval training (SIT) on changes in skeletal muscle mitochondrial content and capillarization. Secondarily, the effects on maximal oxygen consumption (VO 2 max), muscle fiber cross-sectional area, and fiber type proportion were investigated., Methods: A systematic literature search was conducted in PubMed, Web of Science, and SPORTDiscus databases, with no data restrictions, up to 2 February 2022. Exercise training intervention studies of ET, HIT, and SIT were included if they had baseline and follow-up measures of at least one marker of mitochondrial content or capillarization. In total, data from 5973 participants in 353 and 131 research articles were included for the mitochondrial and capillary quantitative synthesis of this review, respectively. Additionally, measures of VO 2 max, muscle fiber cross-sectional area, and fiber type proportion were extracted from these studies., Results: After adjusting for relevant covariates, such as training frequency, number of intervention weeks, and initial fitness level, percentage increases in mitochondrial content in response to exercise training increased to a similar extent with ET (23 ± 5%), HIT (27 ± 5%), and SIT (27 ± 7%) (P > 0.138), and were not influenced by age, sex, menopause, disease, or the amount of muscle mass engaged. Higher training frequencies (6 > 4 > 2 sessions/week) were associated with larger increases in mitochondrial content. Per total hour of exercise, SIT was ~ 2.3 times more efficient in increasing mitochondrial content than HIT and ~ 3.9 times more efficient than ET, while HIT was ~ 1.7 times more efficient than ET. Capillaries per fiber increased similarly with ET (15 ± 3%), HIT (13 ± 4%) and SIT (10 ± 11%) (P = 0.556) after adjustments for number of intervention weeks and initial fitness level. Capillaries per mm 2 only increased after ET (13 ± 3%) and HIT (7 ± 4%), with increases being larger after ET compared with HIT and SIT (P < 0.05). This difference coincided with increases in fiber cross-sectional area after ET (6.5 ± 3.5%), HIT (8.9 ± 4.9%), and SIT (11.9 ± 15.1%). Gains in capillarization occurred primarily in the early stages of training (< 4 weeks) and were only observed in untrained to moderately trained participants. The proportion of type I muscle fibers remained unaltered by exercise training (P > 0.116), but ET and SIT exhibited opposing effects (P = 0.041). VO 2 max increased similarly with ET, HIT, and SIT, although HIT showed a tendency for greater improvement compared with both ET and SIT (P = 0.082), while SIT displayed the largest increase per hour of exercise. Higher training frequencies (6 > 4 > 2 sessions/week) were associated with larger increases in VO 2 max. Women displayed greater percentage gains in VO 2 max compared with men (P = 0.008). Generally, lower initial fitness levels were associated with greater percentage improvements in mitochondrial content, capillarization, and VO 2 max. SIT was particularly effective in improving mitochondrial content and VO 2 max in the early stages of training, while ET and HIT showed slower but steady improvements over a greater number of training weeks., Conclusions: The magnitude of change in mitochondrial content, capillarization, and VO 2 max to exercise training is largely determined by the initial fitness level, with greater changes observed in individuals with lower initial fitness. The ability to adapt to exercise training is maintained throughout life, irrespective of sex and presence of disease. While training load (volume × intensity) is a suitable predictor of changes in mitochondrial content and VO 2 max, this relationship is less clear for capillary adaptations., (© 2024. The Author(s).)

Cardiac output (Q̇ C ) and leg blood flow (Q̇ LEG ) can be measured simultaneously with high accuracy using transpulmonary and femoral vein thermodilution with a single-bolus injection. The invasive measure has offered important insight into leg hemodynamics and blood flow distribution during exercise. Despite being the natural modality of exercise in humans, there has been no direct measure of Q̇ LEG while running in humans. We sought to determine the feasibility of the thermodilution technique for measuring Q̇ LEG and conductance during high-intensity running, in an exploratory case study. A trained runner (30 years male) completed two maximal incremental tests on a cycle ergometer and motorized treadmill. Q̇ LEG and Q̇ C were determined using the single-bolus thermodilution technique. Arterial and venous blood were sampled throughout exercise, with continuous monitoring of metabolism, intra-arterial and venous pressure, and temperature. The participant reached a greater peak oxygen uptake (V̇O 2peak ) during running relative to cycling (74 vs. 68 mL/kg/min) with comparable Q̇ LEG (19.0 vs. 19.5 L/min) and Q̇ C (27.4 vs. 26.2 L/min). Leg vascular conductance was greater during high-intensity running relative to cycling (82 vs. 70 mL/min/mmHg @ ~80% V̇O 2peak ). The "beat phenomenon" was apparent in femoral flow while running, producing large gradients in conductance (62-90 mL/min/mmHg @ 70% V̇O 2peak ). In summary, we present the first direct measure of Q̇ LEG and conductance in a running human. Our findings corroborate several assumptions about Q̇ LEG during running compared with cycling. Importantly, we demonstrate that using thermodilution in running exercise can be completed effectively and safely., (© 2024 The Author(s). Scandinavian Journal of Medicine & Science In Sports published by John Wiley & Sons Ltd.)

Aim: To assess the impact of endurance training on skeletal muscle release of H + and K + ., Methods: Nine participants performed one-legged knee extension endurance training at moderate and high intensities (70%-85% of W peak ), three to four sessions·week -1 for 6 weeks. Post-training, the trained and untrained (control) leg performed two-legged knee extension at low, moderate, and high intensities (40%, 62%, and 83% of W peak ) in normoxia and hypoxia (~4000 m). The legs were exercised simultaneously to ensure identical arterial inflow concentrations of ions and metabolites, and identical power output was controlled by visual feedback. Leg blood flow was measured (ultrasound Doppler), and acid-base variables, lactate- and K + concentrations were assessed in arterial and femoral venous blood to study K + and H + release. Ion transporter abundances were assessed in muscle biopsies., Results: Lactate-dependent H + release was similar in hypoxia to normoxia (p = 0.168) and was lower in the trained than the control leg at low-moderate intensities (p = 0.060-0.006) but similar during high-intensity exercise. Lactate-independent and total H + releases were higher in hypoxia (p < 0.05) and increased more with power output in the trained leg (leg-by-power output interactions: p = 0.02). K + release was similar at low intensity but lower in the trained leg during high-intensity exercise in normoxia (p = 0.024) and hypoxia (p = 0.007). The trained leg had higher abundances of Na + /H + exchanger 1 (p = 0.047) and Na + /K + pump subunit α (p = 0.036)., Conclusion: Moderate- to high-intensity endurance training increases lactate-independent H + release and reduces K + release during high-intensity exercise, coinciding with increased Na + /H + exchanger 1 and Na + /K + pump subunit α muscle abundances., (© 2024 The Author(s). Scandinavian Journal of Medicine & Science In Sports published by John Wiley & Sons Ltd.)

Surviving long periods without food has shaped human evolution. In ancient and modern societies, prolonged fasting was/is practiced by billions of people globally for religious purposes, used to treat diseases such as epilepsy, and recently gained popularity as weight loss intervention, but we still have a very limited understanding of the systemic adaptions in humans to extreme caloric restriction of different durations. Here we show that a 7-day water-only fast leads to an average weight loss of 5.7 kg (±0.8 kg) among 12 volunteers (5 women, 7 men). We demonstrate nine distinct proteomic response profiles, with systemic changes evident only after 3 days of complete calorie restriction based on in-depth characterization of the temporal trajectories of ~3,000 plasma proteins measured before, daily during, and after fasting. The multi-organ response to complete caloric restriction shows distinct effects of fasting duration and weight loss and is remarkably conserved across volunteers with >1,000 significantly responding proteins. The fasting signature is strongly enriched for extracellular matrix proteins from various body sites, demonstrating profound non-metabolic adaptions, including extreme changes in the brain-specific extracellular matrix protein tenascin-R. Using proteogenomic approaches, we estimate the health consequences for 212 proteins that change during fasting across ~500 outcomes and identified putative beneficial (SWAP70 and rheumatoid arthritis or HYOU1 and heart disease), as well as adverse effects. Our results advance our understanding of prolonged fasting in humans beyond a merely energy-centric adaptions towards a systemic response that can inform targeted therapeutic modulation., (© 2024. The Author(s), under exclusive licence to Springer Nature Limited.)

Introduction: Exercise with low carbohydrate availability increases protein degradation, which may reduce subsequent performance considerably. The present study aimed to investigate the effect of carbohydrate ingestion during standardized exercise with and without exhaustion on protein degradation and next-day performance., Methods: Seven trained male cyclists (V̇O 2max 66.8 ± 1.9 mL·kg -1 ·min -1 ; mean ± SEM) cycled to exhaustion (~2.5 h) at a power output eliciting 68% of V̇O 2max (W 68% ). This was followed by repeating 1-min work/1-min recovery intervals at 90% of V̇O 2max (W 90% ) until exhaustion. During W 68% , cyclists consumed a placebo water drink (PLA) the first time and a carbohydrate drink (CHO), 1 g carbohydrate·kg -1 ·h -1 , the second time. The participants performed the same amount of work under the two conditions, separated by at least 1 wk. A standardized diet was provided to the participants so that the two conditions were isoenergetic. To test the impact of carbohydrates on recovery, participants completed a time trial (TT) the next day., Results: Carbohydrate ingestion maintained carbohydrate availability during W 68% and W 90% : total carbohydrate oxidation was significantly higher in CHO ( P = 0.022), and plasma glucose concentration was maintained compared with PLA ( P = 0.025). Next-day performance during TT was better after CHO ingestion (CHO, 41:49 ± 1:38 min; PLA, 42:50 ± 1:46 min; P = 0.020; effect size d = 0.23, small), as was gross efficiency (CHO, 18.6% ± 0.3%; PLA, 17.9% ± 0.3%; P = 0.019). Urinary nitrogen excretion ( P = 0.897) and urinary 3-methylhistidine excretion ( P = 0.673) did not significantly differ during the study period. Finally, tyrosine and phenylalanine plasma concentrations increased in PLA but not in CHO ( P = 0.018)., Conclusions: Carbohydrate ingestion during exhaustive exercise reduced deterioration in next-day performance through reduced metabolic stress and development of fatigue. In addition, some parameters point toward less protein degradation, which would preserve muscle function., (Copyright © 2023 by the American College of Sports Medicine.)

Introduction: Previous studies have shown variable within-subject hemoglobin mass (Hb mass ) responses to altitude training. We investigated whether Hb mass responses depend on individual variations in pre-altitude Hb mass during repeated altitude sojourns., Methods: Nine elite endurance athletes carried out 3-5 altitude sojourns over 17 ± 10 months (mean ± 95% confidence interval), at an altitude of 1976 ± 62 m, for 21 ± 1 days, and a total hypoxic dose of 989 ± 46 km·h, with Hb mass assessed before and after each sojourn (carbon monoxide rebreathing). The individual mean baseline was calculated as the mean of all pre-altitude Hb mass values for an athlete, and it was investigated whether the percent deviation from the individual mean baseline affected the altitude-induced Hb mass response., Results: On average, Hb mass increased by 3.4 ± 1.1% (p < 0.001) from pre- to post-altitude. The intra-individual changes in Hb mass were highly inconsistent (coefficient of variation, CV: 88%), and we found no relationship between Hb mass changes in successive altitude sojourns (r = 0.01; p = 0.735). However, the percent increase in Hb mass was highly correlated with the pre-altitude Hb mass , expressed as the percent deviation from the individual mean baseline (y = -0.7x + 3.4; r = 0.75; p < 0.001). Linear mixed-model analysis confirmed a -0.6 ± 0.2% smaller increase in Hb mass for each 1% higher pre-altitude Hb mass than the individual mean baseline (p < 0.001) after adjusting for the covariates hypoxic dose (p = 0.032) and the relative Hb mass (g·kg -1 body weight; p = 0.031)., Conclusion: Individual variations in pre-altitude Hb mass significantly influence the athletes' Hb mass responses to repeated altitude sojourns, with a potentiated response after traveling to altitude with a low pre-altitude Hb mass ., (© 2022 John Wiley & Sons A/S. Published by John Wiley & Sons Ltd.)

Introduction: Skeletal muscle perfusion and oxygen (O2) delivery are restricted during whole-body exercise because of a limited cardiac output (Q˙). This study investigated the role of reducing central limitations to exercise on the maximal fat oxidation rate (MFO) by comparing mass-specific MFO (per kilogram of active lean mass) during one-legged (1L) and two-legged (2L) cycling. We hypothesized that the mass-specific MFO would be higher during 1L than 2L cycling., Methods: Twelve male subjects (V̇O2peak, 59.3 ± 8.4 mL·kg-1·min-1; mean ± SD) performed step-incremental 2L- (30%-80% of V̇O2peak) and 1L (50% of 2L power output, i.e., equal power output per leg) cycling (counterbalanced) while steady-state pulmonary gas exchanges, Q˙ (pulse-contour analysis), and skeletal muscle (vastus lateralis) oxygenation (near-infrared spectroscopy) were determined. MFO and the associated power output (FatMax) were calculated from pulmonary gas exchanges and stoichiometric equations. A counterweight (10.9 kg) was added to the contralateral pedal arm during 1L cycling. Leg lean mass was determined by DEXA., Results: The absolute MFO was 24% lower (0.31 ± 0.12 vs 0.44 ± 0.20 g·min-1, P = 0.018), whereas mass-specific MFO was 52% higher (28 ± 11 vs 20 ± 10 mg·min-1·kg-1, P = 0.009) during 1L than 2L cycling. FatMax was similar expressed as power output per leg (60 ± 28 vs 58 ± 22 W, P = 0.649). Q˙ increased more from rest to exercise during 1L than 2L cycling when expressed per active leg (ANOVA main effect: P = 0.003). Tissue oxygenation index and Δ[deoxy(Hb + Mb)] were not different between exercise modes (ANOVA main effects: P ≥ 0.587), indicating similar skeletal muscle fractional O2 extraction., Conclusions: Mass-specific MFO is increased by exercising a small muscle mass, potentially explained by increased perfusion and more favorable conditions for O2 delivery than during whole-body exercise., (Copyright © 2022 by the American College of Sports Medicine.)

The present study explored the impact of pre-altitude serum (s)-ferritin and iron supplementation on changes in hemoglobin mass (ΔHbmass) following altitude training. Measures of Hbmass and s-ferritin from 107 altitude sojourns (9-28 days at 1800-2500 m) with world-class endurance athletes (males n = 41, females n = 25) were analyzed together with iron supplementation and self-reported illness. Altitude sojourns with a hypoxic dose [median (range)] of 1169 (912) km·h increased Hbmass (mean ± SD) 36 ± 38 g (3.7 ± 3.7%, p < 0.001) and decreased s-ferritin -11 (190) µg·L -1 (p = 0.001). Iron supplements [27 (191) mg·day -1 ] were used at 45 sojourns (42%), while only 11 sojourns (10%) were commenced with s-ferritin <35 µg/L. Hbmass increased by 4.6 ± 3.7%, 3.4 ± 3.3%, 4.2 ± 4.3%, and 2.9 ± 3.4% with pre-altitude s-ferritin ≤35 µg·L -1 , 36-50 µg·L -1 , 51-100 µg·L -1 , and >100 µg·L -1 , respectively, with no group difference (p = 0.400). Hbmass increased by 4.1 ± 3.9%, 3.0 ± 3.0% and 3.7 ± 4.7% without, ≤50 mg·day -1 or >50 mg·day -1 supplemental iron, respectively (p = 0.399). Linear mixed model analysis revealed no interaction between pre-altitude s-ferritin and iron supplementation on ΔHbmass (p = 0.906). However, each 100 km·h increase in hypoxic dose augmented ΔHbmass by an additional 0.4% (95% CI: 0.1-0.7%; p = 0.012), while each 1 g·kg -1 higher pre-altitude Hbmass reduced ΔHbmass by -1% (-1.6 to -0.5; p < 0.001), and illness lowered ΔHbmass by -5.7% (-8.3 to -3.1%; p < 0.001). In conclusion, pre-altitude s-ferritin or iron supplementation were not related to the altitude-induced increase in Hbmass (3.7%) in world-class endurance athletes with clinically normal iron stores., (© 2021 John Wiley & Sons A/S. Published by John Wiley & Sons Ltd.)

Purpose: This study investigated whether maximal oxygen uptake (V˙O2max) and exercise capacity are affected by small acute blood loss (150 mL) and elucidated compensatory mechanisms., Methods: Thirteen male subjects (V˙O2max, 63 ± 9 mL·kg-1·min-1; mean ± SD) performed incremental exercise to exhaustion on a cycle ergometer in three experimental conditions: in euvolemia (control; blood volume [BV], 6.0 ± 0.7 L) and immediately after acute BV reductions of 150 mL (BVR150mL) and 450 mL (BVR450mL). Changes in plasma volume (PV) and BV during exercise were calculated from hematocrit, hemoglobin concentration, and hemoglobin mass (carbon monoxide rebreathing)., Results: The reduction in V˙O2max per milliliter of BVR was 2.5-fold larger after BVR450mL compared with BVR150mL (-0.7 ± 0.3 vs -0.3 ± 0.6 mL·min-1·mL-1, P = 0.029). V˙O2max was not significantly changed after BVR150mL (-1% ± 2%, P = 0.124) but reduced by 7% ± 3% after BVR450mL (P < 0.001) compared with control. Peak power output only decreased after BVR450mL (P < 0.001). At maximal exercise, BV was restored after BVR150mL compared with control (-50 ± 185 mL, P = 0.375) attributed to PV restoration, which was, however, insufficient in restoring BV after BVR450mL (-281 ± 184 mL, P < 0.001). The peak heart rate tended to increase (3 ± 5 bpm, P = 0.062), whereas the O2 pulse (-2 ± 1 mL per beat, P < 0.001) and vastus lateralis tissue oxygenation index (-4% ± 8% points, P = 0.080) were reduced after BVR450mL, suggesting decreased stroke volume and increased leg O2 extraction., Conclusion: The deteriorations of V˙O2max and of maximal exercise capacity accelerate with the magnitude of acute blood loss, likely because of a rapid PV restoration sufficient to establish euvolemia after a small but not after a moderate blood loss., (Copyright © 2021 by the American College of Sports Medicine.)

We analysed the importance of systemic and peripheral arteriovenous O 2 difference ( a - v ¯ O 2 difference and a-v f O 2 difference, respectively) and O 2 extraction fraction for maximal oxygen uptake ( V ˙ O 2max ). Fick law of diffusion and the Piiper and Scheid model were applied to investigate whether diffusion versus perfusion limitations vary with V ˙ O 2max . Articles (n = 17) publishing individual data (n = 154) on V ˙ O 2max , maximal cardiac output ( Q ˙ max ; indicator-dilution or the Fick method), a - v ¯ O 2 difference (catheters or the Fick equation) and systemic O 2 extraction fraction were identified. For the peripheral responses, group-mean data (articles: n = 27; subjects: n = 234) on leg blood flow (LBF; thermodilution), a-v f O 2 difference and O 2 extraction fraction (arterial and femoral venous catheters) were obtained. Q ˙ max and two-LBF increased linearly by 4.9-6.0 L · min -1 per 1 L · min -1 increase in V ˙ O 2max (R 2  = .73 and R 2  = .67, respectively; both P < .001). The a - v ¯ O 2 difference increased from 118-168 mL · L -1 from a V ˙ O 2max of 2-4.5 L · min -1 followed by a reduction (second-order polynomial: R 2  = .27). After accounting for a hypoxemia-induced decrease in arterial O 2 content with increasing V ˙ O 2max (R 2  = .17; P < .001), systemic O 2 extraction fraction increased up to ~90% ( V ˙ O 2max : 4.5 L · min -1 ) with no further change (exponential decay model: R 2  = .42). Likewise, leg O 2 extraction fraction increased with V ˙ O 2max to approach a maximal value of ~90-95% (R 2  = .83). Muscle O 2 diffusing capacity and the equilibration index Y increased linearly with V ˙ O 2max (R 2  = .77 and R 2  = .31, respectively; both P < .01), reflecting decreasing O 2 diffusional limitations and accentuating O 2 delivery limitations. In conclusion, although O 2 delivery is the main limiting factor to V ˙ O 2max , enhanced O 2 extraction fraction (≥90%) contributes to the remarkably high V ˙ O 2max in endurance-trained individuals., (© 2020 The Authors. Acta Physiologica published by John Wiley & Sons Ltd on behalf of Scandinavian Physiological Society.)

When exercising with a small muscle mass, the mass-specific O 2 delivery exceeds the muscle oxidative capacity resulting in a lower O 2 extraction compared with whole-body exercise. We elevated the muscle oxidative capacity and tested its impact on O 2 extraction during small muscle mass exercise. Nine individuals conducted six weeks of one-legged knee extension (1L-KE) endurance training. After training, the trained leg (TL) displayed 45% higher citrate synthase and COX-IV protein content in vastus lateralis and 15%-22% higher pulmonary oxygen uptake ( V ˙ O 2 peak ) and peak power output ( W ˙ peak ) during 1L-KE than the control leg (CON; all P < .05). Leg O 2 extraction (catheters) and blood flow (ultrasound Doppler) were measured while both legs exercised simultaneously during 2L-KE at the same submaximal power outputs (real-time feedback-controlled). TL displayed higher O 2 extraction than CON (main effect: 1.7 ± 1.6% points; P = .010; 40%-83% of W ˙ peak ) with the largest between-leg difference at 83% of W ˙ peak (O 2 extraction: 3.2 ± 2.2% points; arteriovenous O 2 difference: 7.1 ± 4.8 mL· L -1 ; P < .001). At 83% of W ˙ peak , muscle O 2 conductance (D M O 2 ; Fick law of diffusion) and the equilibration index Y were higher in TL (P < .01), indicating reduced diffusion limitations. The between-leg difference in O 2 extraction correlated with the between-leg ratio of citrate synthase and COX-IV (r = .72-.73; P = .03), but not with the difference in the capillary-to-fiber ratio (P = .965). In conclusion, endurance training improves O 2 extraction during small muscle mass exercise by elevating the muscle oxidative capacity and the recruitment of D M O 2, especially evident during high-intensity exercise exploiting a larger fraction of the muscle oxidative capacity., (© 2020 John Wiley & Sons A/S. Published by John Wiley & Sons Ltd.)

Purpose: The endurance training (ET)-induced increases in peak oxygen uptake ([Formula: see text]O 2peak ) and cardiac output ([Formula: see text] peak ) during upright cycling are reversed to pre-ET levels after removing the training-induced increase in blood volume (BV). We hypothesised that ET-induced improvements in [Formula: see text]O 2peak and [Formula: see text] peak are preserved following phlebotomy of the BV gained with ET during supine but not during upright cycling. Arteriovenous O 2 difference (a-[Formula: see text]O 2 diff; [Formula: see text]O 2 /[Formula: see text]), cardiac dimensions and muscle morphology were studied to assess their role for the [Formula: see text]O 2peak improvement., Methods: Twelve untrained subjects ([Formula: see text]O 2peak : 44 ± 6 ml kg -1  min -1 ) completed 10 weeks of supervised ET (3 sessions/week). Echocardiography, muscle biopsies, haemoglobin mass (Hb mass ) and BV were assessed pre- and post-ET. [Formula: see text]O 2peak and [Formula: see text] peak during upright and supine cycling were measured pre-ET, post-ET and immediately after Hb mass was reversed to the individual pre-ET level by phlebotomy., Results: ET increased the Hb mass (3.3 ± 2.9%; P = 0.005), BV (3.7 ± 5.6%; P = 0.044) and [Formula: see text]O 2peak during upright and supine cycling (11 ± 6% and 10 ± 8%, respectively; P ≤ 0.003). After phlebotomy, improvements in [Formula: see text]O 2peak compared with pre-ET were preserved in both postures (11 ± 4% and 11 ± 9%; P ≤ 0.005), as was [Formula: see text] peak (9 ± 14% and 9 ± 10%; P ≤ 0.081). The increased [Formula: see text] peak and a-[Formula: see text]O 2 diff accounted for 70% and 30% of the [Formula: see text]O 2peak improvements, respectively. Markers of mitochondrial density (CS and COX-IV; P ≤ 0.007) and left ventricular mass (P = 0.027) increased., Conclusion: The ET-induced increase in [Formula: see text]O 2peak was preserved despite removing the increases in Hb mass and BV by phlebotomy, independent of posture. [Formula: see text]O 2peak increased primarily through elevated [Formula: see text] peak but also through a widened a-[Formula: see text]O 2 diff, potentially mediated by cardiac remodelling and mitochondrial biogenesis.

Purpose: Long-distance cross-country skiers specialize to compete in races >50 km predominantly using double poling (DP). This emphasizes the need for highly developed upper-body endurance capacities and an efficient DP technique. The aim of this study was to investigate potential effects of specialization by comparing physiological capacities and kinematics in DP between long-distance skiers and skiers competing using both techniques (skating/classic) in several competition formats ("all-round skiers")., Methods: Seven male long-distance (32 [6] y, 183 [6] cm, 76 [5] kg) and 6 all-round (25 [3] y, 181 [5] cm, 75 [6] kg) skiers at high international levels conducted submaximal workloads and an incremental test to exhaustion for determination of peak oxygen uptake (VO2peak) and time to exhaustion (TTE) in DP and running., Results: In DP and running maximal tests, TTE showed no difference between groups. However, long-distance skiers had 5-6% lower VO2peak in running (81 [5] vs 85 [3] mL·kg-1·min-1; P = .07) and DP (73 [3] vs 78 [3] mL·kg-1·min-1; P < .01) than all-round skiers. In DP, long-distance skiers displayed lower submaximal O2 cost than all-round skiers (3.8 ± 3.6%; P < .05) without any major differences in cycle times or cyclic patterns of joint angles and center of mass. Lactate concentration over a wide range of speeds (45-85% of VO2peak) did not differ between groups, even though each workload corresponded to a slightly higher percentage of VO2peak for long-distance skiers (effect size: 0.30-0.68)., Conclusions: The long-distance skiers displayed lower VO2peak but compensated with lower O2 cost to perform equally with the all-round skiers on a short TTE test in DP. Furthermore, similar submaximal lactate concentration and reduced O2 cost could be beneficial in sustaining high skiing speeds in long-duration competitions.

Purpose: We measured cardiac output ([Formula: see text]) during sub-maximal and supra-maximal exercise with inert gas rebreathing ([Formula: see text]) and modified cardio-impedance ([Formula: see text]) and we evaluated the repeatability of the two methods., Methods: [Formula: see text]O 2 and [Formula: see text] were measured twice in parallel with the two methods at sub-maximal (50-250 W) and supra-maximal exercise in 7 young subjects (25 ± 1 years; 74.4 ± 5.2 kg; 1.84 ± 0.07 m)., Results: [Formula: see text] and [Formula: see text] increased by 3.4 L·min -1 and by 5.1 L·min -1 per 1 L·min -1 of increase in [Formula: see text], respectively. Mean [Formula: see text] (23.3 ± 2.5 L·min -1 ) was 9% lower than [Formula: see text] (25.8 ± 2.2 L·min -1 ) during supra-maximal exercise. Bland-Altman analysis showed that: (i) bias ([Formula: see text]-[Formula: see text]) was significantly different from zero (- 0.65 ± 2.61 L·min -1 ) and; (ii) the ratios [Formula: see text] ÷ [Formula: see text] were linearly related with [Formula: see text], indicating that [Formula: see text] tended to overestimate [Formula: see text] in comparison with [Formula: see text] for values ranging from 10.0 to 15.0 L·min -1 and to underestimate it for larger values. The coefficient of variation was similar for sub-maximal values (8.6% vs. 7.7%; 95% CL: ×/÷1.31), but lower for [Formula: see text] (7.6%; 95% CL: ×/÷ 2.05) than for [Formula: see text] (27.7%; 95% CL: ×/÷2.54) at supra-maximal intensity., Conclusions: [Formula: see text] seems to represent a valuable alternative to invasive methods for assessing [Formula: see text] during sub-maximal exercise. The [Formula: see text] underestimation with respect to [Formula: see text] during supra-maximal exercise suggests that [Formula: see text] might be less optimal for supra-maximal intensities.

Purpose: To investigate variability, predictability, and smallest worthwhile performance enhancement in elite biathlon sprint events. In addition, the effects of race factors on performance were assessed., Methods: Data from 2005 to 2015 including >10,000 and >1000 observations for each sex for all athletes and annual top-10 athletes, respectively, were included. Generalized linear mixed models were constructed based on total race time, skiing time, shooting time, and proportions of targets hit. Within-athlete race-to-race variability was expressed as coefficient of variation of performance times and standard deviation (SD) in proportion units (%) of targets hit. The models were adjusted for random and fixed effects of subject identity, season, event identity, and race factors., Results: The within-athlete variability was independent of sex and performance standard of athletes: 2.5-3.2% for total race time, 1.5-1.8% for skiing time, and 11-15% for shooting times. The SD of the proportion of hits was ∼10% in both shootings combined (meaning ±1 hit in 10 shots). The predictability in total race time was very high to extremely high for all athletes (ICC .78-.84) but trivial for top-10 athletes (ICC .05). Race times during World Championships and Olympics were ∼2-3% faster than in World Cups. Moreover, race time increased by ∼2% per 1000 m of altitude, by ∼5% per 1% of gradient, by 1-2% per 1 m/s of wind speed, and by ∼2-4% on soft vs hard tracks., Conclusions: Researchers and practitioners should focus on strategies that improve biathletes' performance by at least 0.8-0.9%, corresponding to the smallest worthwhile enhancement (0.3 × within-athlete variability).

Purpose: In the double-poling (DP) cross-country-skiing technique, propulsive forces are transferred solely through the poles. The aim of the current study was to investigate how pole length influences DP performance, O 2 cost, and kinematics during treadmill roller skiing., Methods: Nine male competitive cross-country skiers (24 ± 3 y, 180 ± 5 cm, 72 ± 5 kg, VO 2 max running 76 ± 6 mL · kg -1 · min -1 ) completed 2 identical test protocols using self-selected (84% ± 1% of body height) and long poles (self-selected + 7.5 cm; 88% ± 1% of body height) in a counterbalanced fashion. Each test protocol included a 5-min warm-up (2.5 m/s; 2.5°) and three 5-min submaximal sessions (3.0, 3.5, and 4.0 m/s; 2.5°) for assessment of O 2 cost, followed by a selfpaced 1000-m time trial (~3 min, >5.0 m/s; 2.5°). Temporal patterns and kinematics were assessed using accelerometers and 2D video., Results: Long poles reduced 1000-m time (mean ± 90% confidence interval; -1.0% ± 0.7%, P = .054) and submaximal O 2 cost (-2.7% ± 1.0%, P = .002) compared with self-selected poles. The center-of-mass (CoM) vertical range of displacement tended to be smaller for long than for self-selected poles (23.3 ± 3.0 vs 24.3 ± 3.0 cm, P = .07). Cycle and reposition time did not differ between pole lengths at any speeds tested, whereas poling time tended to be shorter for self-selected than for long poles at the lower speeds (≤3.5 m/s, P ≤ .10) but not at the higher speeds (≥4.0 m/s, P ≥ .23)., Conclusions: DP 1000-m time, submaximal O 2 cost, and CoM vertical range of displacement were reduced in competitive cross-country skiers using poles 7.5 cm longer than self-selected ones.

Losnegard, T, Kjeldsen, K, and Skattebo, Ø. An analysis of the pacing strategies adopted by elite cross-country skiers. J Strength Cond Res 30(11): 3256-3260, 2016-Understanding the pacing strategies used by the most successful skiers may provide insight into the most desirable pacing approach in cross-country (XC) skiing. This study examined the pacing strategies adopted by male and female XC skiers of different performance standards during 10 and 15 km races in World Cup, World Championships, and Olympic events. Analyses were performed on races involving 5 km laps in the men's 15 km (number of races = 22) and the women's 10 km (n = 14) individual start races (classic and freestyle) from season 2002/2003 to season 2013/2014. Final rank and lap times for the 40 top finishers in each race were analyzed. Both sexes demonstrated a positive pacing pattern shown by a decline in velocity from the first to the last lap (men: 6.76 ± 0.43 m·s vs. 6.47 ± 0.46 m·s; p < 0.001; women: 6.0 ± 0.47 m·s vs. 5.87 ± 0.53 m·s; p < 0.001). For the men, slower skiers (final ranking 21st-30th and 31st-40th) were characterized by a quick start relative to their average velocity, with a greater decrease during the race compared with the fastest skiers (1st-10th) (p = 0.007 and p < 0.001, respectively). For the women, no group differences in pacing strategy were found. In conclusion, this study shows that the pacing strategy indicates the standard of elite male XC skiers. Examining the pacing strategies of the best male performers suggests that lower-performing male skiers should consider a more even pacing strategy to improve their performance.

The present study investigated the contribution of performance on uphill, flat, and downhill sections to overall performance in an international 10-km classical time-trial in elite female cross-country skiers, as well as the relationships between performance on snow and laboratory-measured physiological variables in the double poling (DP) and diagonal (DIA) techniques. Ten elite female cross-country skiers were continuously measured by a global positioning system device during an international 10-km cross-country skiing time-trial in the classical technique. One month prior to the race, all skiers performed a 5-min submaximal and 3-min self-paced performance test while roller skiing on a treadmill, both in the DP and DIA techniques. The time spent on uphill (r = 0.98) and flat (r = 0.91) sections of the race correlated most strongly with the overall 10-km performance (both p < 0.05). Approximately 56% of the racing time was spent uphill, and stepwise multiple regression revealed that uphill time explained 95.5% of the variance in overall performance (p < 0.001). Distance covered during the 3-min roller-skiing test and body-mass normalized peak oxygen uptake (VO2peak) in both techniques showed the strongest correlations with overall time-trial performance (r = 0.66-0.78), with DP capacity tending to have greatest impact on the flat and DIA capacity on uphill terrain (all p < 0.05). Our present findings reveal that the time spent uphill most strongly determine classical time-trial performance, and that the major portion of the performance differences among elite female cross-country skiers can be explained by variations in technique-specific aerobic power.

Purpose: The objective of this study is to compare the physiological capacity and training characteristics of the world's six highest ranked female cross-country skiers (world class (WC)) with those of six competitors of national class (NC)., Methods: Immediately before the start of the competition season, all skiers performed three 5-min submaximal stages of roller skiing on a treadmill for measurement of oxygen cost, as well as a 3-min self-paced performance test using both the double poling (DP) and diagonal stride (DIA) techniques. During the 3-min performance tests, the total distance covered, peak oxygen uptake (V˙O2peak), and accumulated oxygen deficit were determined. Each skier documented the intensity and mode of their training during the preceding 6 months in a diary., Results: There were no differences between the groups with respect to oxygen cost or gross efficiency at the submaximal speeds. The WC skiers covered 6%-7% longer distances during the 3-min tests and exhibited average V˙O2peak values of ∼70 and ∼65 mL·min·kg with DIA and DP, respectively, which were 10% and 7% higher than the NC skiers (all P < 0.05). However, the accumulated oxygen deficit did not differ between groups. From May to October, the WC skiers trained a total of 532 ± 73 h (270 ± 26 sessions) versus 411 ± 62 h (240 ± 27 sessions) for the NC skiers. In addition, the WC skiers performed 26% more low-intensity and almost twice as much moderate-intensity endurance and speed training (all P < 0.05)., Conclusions: This study highlights the importance of a high oxygen uptake and the ability to use this while performing the different skiing techniques on varying terrains for female cross-country skiers to win international races. In addition, the training data documented here provide benchmark values for female endurance athletes aiming for medals.