Systemic proteome adaptions to 7-day complete caloric restriction in humans.

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.

Carbohydrate Ingestion during Prolonged Cycling Improves Next-Day Time Trial Performance and Alters Amino Acid Concentrations.

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.

Individual variations in pre-altitude hemoglobin mass influence hemoglobin mass responses to repeated altitude sojourns.

INTRODUCTION: Previous studies have shown variable within-subject hemoglobin mass (Hbmass ) responses to altitude training. We investigated whether Hbmass responses depend on individual variations in pre-altitude Hbmass 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 Hbmass assessed before and after each sojourn (carbon monoxide rebreathing). The individual mean baseline was calculated as the mean of all pre-altitude Hbmass values for an athlete, and it was investigated whether the percent deviation from the individual mean baseline affected the altitude-induced Hbmass response. RESULTS: On average, Hbmass increased by 3.4 ± 1.1% (p < 0.001) from pre- to post-altitude. The intra-individual changes in Hbmass were highly inconsistent (coefficient of variation, CV: 88%), and we found no relationship between Hbmass changes in successive altitude sojourns (r = 0.01; p = 0.735). However, the percent increase in Hbmass was highly correlated with the pre-altitude Hbmass , 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 Hbmass for each 1% higher pre-altitude Hbmass than the individual mean baseline (p < 0.001) after adjusting for the covariates hypoxic dose (p = 0.032) and the relative Hbmass (g·kg-1 body weight; p = 0.031). CONCLUSION: Individual variations in pre-altitude Hbmass significantly influence the athletes' Hbmass responses to repeated altitude sojourns, with a potentiated response after traveling to altitude with a low pre-altitude Hbmass .

Increased Mass-Specific Maximal Fat Oxidation Rate with Small versus Large Muscle Mass Exercise.

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.

Effects of 150- and 450-mL Acute Blood Losses on Maximal Oxygen Uptake and Exercise Capacity.

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.

Impact of baseline serum ferritin and supplemental iron on altitude-induced hemoglobin mass response in elite athletes.

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.

Contribution of oxygen extraction fraction to maximal oxygen uptake in healthy young men.

We analysed the importance of systemic and peripheral arteriovenous O2 difference ( a-v¯O2 difference and a-vf O2 difference, respectively) and O2 extraction fraction for maximal oxygen uptake ( V˙O2max ). Fick law of diffusion and the Piiper and Scheid model were applied to investigate whether diffusion versus perfusion limitations vary with V˙O2max . Articles (n = 17) publishing individual data (n = 154) on V˙O2max , maximal cardiac output ( Q˙max ; indicator-dilution or the Fick method), a-v¯O2 difference (catheters or the Fick equation) and systemic O2 extraction fraction were identified. For the peripheral responses, group-mean data (articles: n = 27; subjects: n = 234) on leg blood flow (LBF; thermodilution), a-vf O2 difference and O2 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˙O2max (R2  = .73 and R2  = .67, respectively; both P < .001). The a-v¯O2 difference increased from 118-168 mL · L-1 from a V˙O2max of 2-4.5 L · min-1 followed by a reduction (second-order polynomial: R2  = .27). After accounting for a hypoxemia-induced decrease in arterial O2 content with increasing V˙O2max (R2  = .17; P < .001), systemic O2 extraction fraction increased up to ~90% ( V˙O2max : 4.5 L · min-1 ) with no further change (exponential decay model: R2  = .42). Likewise, leg O2 extraction fraction increased with V˙O2max to approach a maximal value of ~90-95% (R2  = .83). Muscle O2 diffusing capacity and the equilibration index Y increased linearly with V˙O2max (R2  = .77 and R2  = .31, respectively; both P < .01), reflecting decreasing O2 diffusional limitations and accentuating O2 delivery limitations. In conclusion, although O2 delivery is the main limiting factor to V˙O2max , enhanced O2 extraction fraction (≥90%) contributes to the remarkably high V˙O2max in endurance-trained individuals.

Increased oxygen extraction and mitochondrial protein expression after small muscle mass endurance training.

When exercising with a small muscle mass, the mass-specific O2 delivery exceeds the muscle oxidative capacity resulting in a lower O2 extraction compared with whole-body exercise. We elevated the muscle oxidative capacity and tested its impact on O2 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 O2 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 O2 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 (O2 extraction: 3.2 ± 2.2% points; arteriovenous O2 difference: 7.1 ± 4.8 mL· L-1 ; P < .001). At 83% of W ˙ peak , muscle O2 conductance (DM O2 ; Fick law of diffusion) and the equilibration index Y were higher in TL (P < .01), indicating reduced diffusion limitations. The between-leg difference in O2 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 O2 extraction during small muscle mass exercise by elevating the muscle oxidative capacity and the recruitment of DM O2, especially evident during high-intensity exercise exploiting a larger fraction of the muscle oxidative capacity.

Blood volume expansion does not explain the increase in peak oxygen uptake induced by 10 weeks of endurance training.

PURPOSE: The endurance training (ET)-induced increases in peak oxygen uptake ([Formula: see text]O2peak) 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]O2peak and [Formula: see text]peak are preserved following phlebotomy of the BV gained with ET during supine but not during upright cycling. Arteriovenous O2 difference (a-[Formula: see text]O2diff; [Formula: see text]O2/[Formula: see text]), cardiac dimensions and muscle morphology were studied to assess their role for the [Formula: see text]O2peak improvement. METHODS: Twelve untrained subjects ([Formula: see text]O2peak: 44 ± 6 ml kg-1 min-1) completed 10 weeks of supervised ET (3 sessions/week). Echocardiography, muscle biopsies, haemoglobin mass (Hbmass) and BV were assessed pre- and post-ET. [Formula: see text]O2peak and [Formula: see text]peak during upright and supine cycling were measured pre-ET, post-ET and immediately after Hbmass was reversed to the individual pre-ET level by phlebotomy. RESULTS: ET increased the Hbmass (3.3 ± 2.9%; P = 0.005), BV (3.7 ± 5.6%; P = 0.044) and [Formula: see text]O2peak during upright and supine cycling (11 ± 6% and 10 ± 8%, respectively; P ≤ 0.003). After phlebotomy, improvements in [Formula: see text]O2peak 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]O2diff accounted for 70% and 30% of the [Formula: see text]O2peak 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]O2peak was preserved despite removing the increases in Hbmass and BV by phlebotomy, independent of posture. [Formula: see text]O2peak increased primarily through elevated [Formula: see text]peak but also through a widened a-[Formula: see text]O2diff, potentially mediated by cardiac remodelling and mitochondrial biogenesis.

Double-Poling Physiology and Kinematics of Elite Cross-Country Skiers: Specialized Long-Distance Versus All-Round Skiers.

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.

Cardiac output with modified cardio-impedance against inert gas rebreathing during sub-maximal and maximal cycling exercise in healthy and fit subjects.

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]O2 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.

Variability, Predictability, and Race Factors Affecting Performance in Elite Biathlon.

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).

The Influence of Pole Length on Performance, O2 Cost, and Kinematics in Double Poling.

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, O2 cost, and kinematics during treadmill roller skiing. METHODS: Nine male competitive cross-country skiers (24 ± 3 y, 180 ± 5 cm, 72 ± 5 kg, VO2max 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 O2 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 O2 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 O2 cost, and CoM vertical range of displacement were reduced in competitive cross-country skiers using poles 7.5 cm longer than self-selected ones.

Analysis of Classical Time-Trial Performance and Technique-Specific Physiological Determinants in Elite Female Cross-Country Skiers.

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.

An Analysis of the Pacing Strategies Adopted by Elite Cross-Country Skiers.

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 Physiological Capacity of the World's Highest Ranked Female Cross-country Skiers.

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.