What is the optimal classical style sub-technique during uphill roller skiing in elite male cross-country skiers?

PURPOSE: To compare performance, physiological and biomechanical responses between double poling (DP) and diagonal stride (DIA) during treadmill roller skiing in elite male cross-country skiers. METHOD: Twelve skiers (VO2peak DIAup; 74.7 ± 3.7 ml kg-1 min-1) performed two DP conditions at 1° (DPflat) and 8° (DPup) incline, and one DIA condition, 8° (DIAup). Submaximal gross efficiency (GE) and maximal 3.5 min time-trial (TT) performance, including measurements of VO2peak and maximal accumulated O2-deficit (MAOD), were determined. Temporal patterns and kinematics were assessed using 2D video, while pole kinetics were obtained from pole force. RESULTS: DIAup induced (mean, [95% confidence interval]) 13% [4, 22] better 3.5-min TT performance, 7%, [5, 10]) higher VO2peak and 3% points [1, 5] higher GE compared to DPup (all P < 0.05). DPup induced 120% higher MAOD compared to DPflat, while no significant differences were observed for VO2peak or GE between DPflat and DPup. There was a large correlation between performance and GE in DP and a large correlation between performance and VO2peak for DIAup (all r = 0.7-0.8, P < 0.05). No correlations were found between performance and VO2peak for any of the DP conditions, nor between performance and GE for DIAup (r = 0.0-0.2, P > 0.1). CONCLUSION: At 8º uphill roller skiing, DIAup induce higher VO2peak, GE, and superior time-trial performance than DPup in elite male skiers. There was no difference between VO2peak or GE between DPflat and DPup. A large correlation was observed between DIAup performance and DIAup VO2peak, while DP performance was best correlated to submaximal GE.

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.

The influence of pole lengths on O2-cost, kinematics, and performance in double poling at high speeds before and after a training period with long poles.

PURPOSE: Previous studies have found an acute performance improvement with longer pole lengths in double poling (DP) at low-to-moderate speeds. We investigated the influence of pole lengths (PL) on O2-cost, 3D kinematics, and performance in DP at moderate-to-high speeds before (Pre) and after (Post) eight training sessions with long poles on a rollerski treadmill. METHODS: Seven male and four female skiers completed tests with two different PLs (84 and 90% of body height). Submaximal O2-cost (1º; 4.5 [females] or 6 m s-1 [males]) and a peak velocity test (1º; ∼ 7.3 m s-1) were assessed before and after a six week training period. The training sessions consisted of 50 min of low-moderate intensity training and 4 × 10 s maximal sprints with PL90%. RESULTS: On average for all tests, PL84% induced 1.0 ± 1.0% higher peak velocity compared to PL90% (mean ± CI) with no difference in vertical displacement of center of mass (COMz). From Pre to Post, peak velocity and cycle time were increased and the displacement of COMz were reduced similarly for both PLs. At moderate speed, PL90% induced less displacement of COMz with subsequent 1.1 ± 0.7% lower O2-cost compared to PL84%. From Pre to Post, the O2-cost and COMz were reduced similarly for both PLs. CONCLUSIONS: Longer PL than skiers self-selected lengths reduce O2-cost at moderate speeds, but induced lower peak velocity. Eight sessions of training with PL90% did not influence the difference between PL84% and PL90% on O2-cost, kinematics or peak velocity.

Pole lengths influence O2-cost during double poling in highly trained cross-country skiers.

PURPOSE: In elite cross-country skiing, double poling is used in different terrain. This study compared O2-cost and kinematics during double poling with four different pole lengths [self-selected (SS), SS - 5 cm, SS + 5 cm, SS + 10 cm] at Low versus Moderate incline. METHODS: Thirteen highly trained male cross-country skiers (mean ± SD 23 ± 3 years; 182 ± 4 cm; 77 ± 6 kg) completed eight submaximal trials with roller skis on a treadmill at two conditions: "Low incline" (1.7°; 4.5 m s-1) and "Moderate incline" (4.5°; 2.5 m s-1) with each of the four pole lengths. O2-cost and 3D body kinematics were assessed in each trial. RESULTS: In Low incline, SS + 10 cm induced a lower O2-cost than all the other pole lengths [P < 0.05; effect size (ES) 0.5-0.8], whereas no differences were found between the remaining pole lengths (P > 0.05; ES 0.2-0.4). In Moderate incline, significant differences between all pole lengths were found for O2-cost, with SS - 5 cm > SS > SS + 5 cm > SS + 10 cm (P < 0.05; ES 0.6-1.8). The relative differences in O2-cost between SS and the other pole lengths were greater in Moderate incline than Low incline (SS - 5 cm; 1.5%, ES 0.8, SS + 5 cm; 1.3%, ES 1.0, and SS + 10 cm; 1.9%, ES 1.0, all P < 0.05). No difference was found in cycle, poling or reposition times between pole lengths. However, at both conditions a smaller total vertical displacement of center of mass was observed with SS + 10 cm compared to the other pole lengths. CONCLUSION: Increasing pole length from SS - 5 cm to SS + 10 cm during double poling induced lower O2-cost and this advantage was greater in Moderate compared to Low incline.

The Effect of Resistance Exercise Priming in the Morning on Afternoon Sprint Cross-Country Skiing Performance.

PURPOSE: We tested whether a single session of heavy-load resistance priming conducted in the morning improved double-poling (DP) performance in the afternoon. METHODS: Eight national-level male cross-country skiers (mean [SD]: 23 [3] y, 184 [6] cm, 73 [7] kg, maximum oxygen consumption = 69 [6] mL·kg-1·min-1) carried out 2 days of afternoon performance tests. In the morning, 5 hours before tests, subjects were counterbalanced to either a session of 3 × 3 repetitions (approximately 85%-90% 1-repetition maximum) of squat and sitting pullover exercises or no exercise. The performance was evaluated in DP as time to exhaustion (TTE) (approximately 3 min) on a treadmill and 30-m indoor sprints before and after TTE (30-m DP pre/post). Furthermore, submaximal DP oxygen cost, countermovement jump, and isometric knee-extension force during electrical stimulation were conducted. Participants reported perceived readiness on test days. RESULTS: Resistance exercise session versus no exercise did not differ for TTE (approximately 3 min above) (mean ± 95% confidence interval = 3.6% ± 6.0%; P = .29; effect size [ES], Cohen d = 0.27), 30-m DP pre (-0.56% ± 0.80%; P = .21; ES = 0.20), 30-m DP post (-0.18% ± 1.13%; P = .76; ES = 0.03), countermovement jump (-2.0% ± 2.8%; P = .21; ES = 0.12), DP oxygen cost (-0.13% ± 2.04%; P = .91; ES = 0.02), or perceived readiness (P ≥ .11). Electrical stimulation force was not different in contraction or relaxation time but revealed low-frequency fatigue in the afternoon for the resistance exercise session only (-12% [7%]; P = .01; ES = 1.3). CONCLUSION: A single session of heavy-load, low-volume resistance exercise in the morning did not increase afternoon DP performance of short duration in high-level skiers. However, leg low-frequency fatigue after resistance priming, together with the presence of small positive effects in 2 out of 3 DP tests, may indicate that the preconditioning was too strenuous.

Morning Preconditioning Exercise Does Not Increase Afternoon Performance in Competitive Runners.

PURPOSE: Preconditioning exercise is a widely used strategy believed to enhance performance later the same day. The authors examined the influence of preconditioning exercises 6 hours prior to a time-to-exhaustion (TTE) test during treadmill running. METHODS: Ten male competitive runners (age = 26 [3] y, height = 184 [8] cm, weight = 73 [9] kg, maximum oxygen consumption = 72 [7] mL·kg-1·min-1) did a preconditioning session of running (RUN) or resistance exercise (RES) or no morning exercise (NoEx) in a randomized order, separated by >72 hours. The RUN consisted of 15 minutes of low-intensity running and 4 × 15 seconds at race pace (21-24 km·h-1) on a treadmill; RES involved 5 minutes of low-intensity running and 2 × 3 repetitions of isokinetic 1-leg shallow squats with maximal mobilization. Following a 6-hour break, electrically evoked force (m. vastus medialis), countermovement jump, running economy, and a TTE of approximately 2 minutes were examined. RESULTS: Relative to NoEx, no difference was seen for RUN or RES in TTE (mean ± 95% CI: -1.3% ± 3.4% and -0.5% ± 6.0%) or running economy (0.2% ± 1.6% and 1.9% ± 2.7%; all Ps > .05). Jump height was not different for the RUN condition (1.0% ± 2.7%]) but tended to be higher in RES than in the NoEx condition (1.5% ± 1.6%, P = .07). The electrically evoked force tended to reveal low-frequency fatigue (reduced 20:50-Hz peak force ratio) only after RES compared to NoEx (-4.5% ± 4.6%, P = .06). CONCLUSION: The RUN or RES 6 hours prior to approximately 2 minutes of TTE running test did not improve performance in competitive runners.

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.

Pole Length's Influence on Performance During Classic-Style Snow Skiing in Well-Trained Cross-Country Skiers.

PURPOSE: To investigate how self-selected pole length (PL) of ∼84% (PL84%) compared with ∼90% (PL90%) of body height influenced performance during a 700-m time trial with undulating terrain on snow. METHODS: Twenty-one cross-country skiers, 7 of whom were women, performed 4 trials at a maximal effort in a counterbalanced fashion with PL84% and PL90% separated by 20-minute breaks between trials. In trials I and II, only double poling was allowed, while in trials III and IV, skiers used self-selected classical subtechniques. Continuous speed, cyclic parameters, and heart rate were collected using microsensors in addition to a post-time-trial rating of perceived exertion (RPE). RESULTS: The 700-m times with only double poling were significantly shorter with PL90% than PL84% (mean ± 95% confidence limits -1.6% ± 1.0%). Segment analyses showed higher speed with PL90% in uphill sections than with PL84% (3.7% ± 2.1%), with the greatest difference found for the female skiers (5.6% ± 2.9%). In contrast, on flat terrain at high skiing speeds, speed was reduced with PL90% compared with PL84% (-1.5% ± 1.4%); this was only significant for the male skiers. During free choice of classical subtechniques, PL did not influence performance in any segments, choice of subtechnique, or cycle rate during the trials. No differences in rating of perceived exertion or heart rate between PLs were found. CONCLUSIONS: PL90% improved performance in uphills at low speeds when using double poling but hindered performance on flat terrain and at higher speeds compared with self-selected PLs. Choice of PL should, therefore, be based on racecourse topography, preferred subtechniques, and the skier's physiological and technical abilities.

Is the balance between skeletal muscular metabolic capacity and oxygen supply capacity the same in endurance trained and untrained subjects?

We attempted to test whether the balance between muscular metabolic capacity and oxygen supply capacity in endurance-trained athletes (ET) differs from that in a control group of normal physically active subjects by using exercises with different muscle masses. We compared maximal exercise in nine ET subjects [Maximal oxygen uptake (VO(2)max) 64 ml kg(-1) min(-1) +/- SD 4] and eight controls (VO(2)max 46 +/- 4 ml kg(-1) min(-1)) during one-legged knee extensions (1-KE), two-legged knee extensions (2-KE) and bicycling. Maximal values for power output (P), VO(2)max, concentration of blood lactate ([La(-)]), ventilation (VE), heart rate (HR), and arterial oxygen saturation of haemoglobin (SpO(2)) were registered. P was 43 (2), 89 (3) and 298 (7) W (mean +/- SE); and VO(2)max: 1,387 (80), 2,234 (113) and 4,115 (150) ml min(-1)) for controls in 1-KE, 2-KE and bicycling, respectively. The ET subjects achieved 126, 121 and 126% of the P of controls (p < 0.05) and 127, 124, and 117% of their VO(2)max (p < 0.05). HR and [La(-)] were similar for both groups during all modes of exercise, while VE in ET was 147 and 114% of controls during 1-KE and bicycling, respectively. For mass-specific VO(2)max (VO(2)max divided by the calculated active muscle mass) during the different exercises, ET achieved 148, 141, and 150% of the controls' values, respectively (p < 0.05). During bicycling, both groups achieved 37% of their mass-specific VO(2) during 1-KE. Finally we conclude that ET subjects have the same utilization of the muscular metabolic capacity during whole body exercise as active control subjects.

Exercise Intensity During Cross-Country Skiing Described by Oxygen Demands in Flat and Uphill Terrain.

Purpose: In this study wearable global navigation satellite system units were used on athletes to investigate pacing patterns by describing exercise intensities in flat and uphill terrain during a simulated cross-country ski race. Methods: Eight well-trained male skiers (age: 23.0 ± 4.8 years, height: 183.8 ± 6.8 cm, weight: 77.1 ± 6.1 kg, VO2peak: 73 ± 5 mL⋅kg-1⋅min-1) completed a 13.5-km individual time trial outdoors and a standardized indoor treadmill protocol on roller skis. Positional data were recorded during the time trial using a differential global navigation satellite system to calculate external workloads in flat and uphill terrain. From treadmill tests, the individual relationships between oxygen consumption and external workload in flat (1°) and uphill (8°) terrain were determined, in addition to VO2peak and the maximal accumulated O2-deficit. To estimate the exercise intensity in the time trial, the O2-demand in two different flat and five different uphill sections was calculated by extrapolation of individual O2-consumption/workload ratios. Results: There was a significant interaction between section and average O2-demands, with higher O2-demands in the uphill sections (110-160% of VO2peak) than in the flat sections (≤100% of VO2peak) (p < 0.01). The maximal accumulated O2-deficit associated with uphill treadmill roller skiing was significantly higher compared to flat (6.2 ± 0.5 vs. 4.6 ± 0.5 L, p < 0.01), while no significant difference was found in VO2peak. Conclusion: Cross-country (XC) skiers repeatedly applied exercise intensities exceeding their maximal aerobic power. ΣO2-deficits were higher during uphill skiing compared to flat which has implications for the duration and magnitude of supramaximal work rates that can be applied in different types of terrain.

Upper-Body Muscular Endurance Training Improves Performance Following 50 min of Double Poling in Well-Trained Cross-Country Skiers.

This study investigated the effect of muscular endurance training on O2-cost and performance in double poling (DP) on a rollerski treadmill. Twenty-two well-trained cross-country skiers (31 ± 4 years, 77 ± 9 kg, 181 ± 8 cm, VO2max running: 64 ± 5 mL·kg-1·min-1) were counter-balanced to either a combined muscular endurance and running interval training group [MET; n = 11 (♂ = 9, ♀ = 2)], or an endurance running interval training group [ET; n = 11 (♂ = 9, ♀ = 2)]. Both groups continued their normal low-and moderate intensity training, but replaced 2 weekly high intensity-training sessions with two project-specific sessions for 6 weeks. In these sessions, MET combined upper-body muscular endurance training (4 × 30 repetitions, 90 s rest between sets) and running intervals (3 × 4 or 2 × 6 min, 3 min rest), while ET performed running intervals only (6 × 4 or 4 × 6 min, 3 min rest). The DP test-protocol consisted of 50 min submaximal poling for O2-cost measurement, followed by a self-paced 1,000-m performance test. In addition, subjects performed a VO2max test in running. MET increased muscular endurance (P < 0.05) and 1RM in simulated DP (P < 0.01) more than ET. Further, MET reduced the 1,000-m time and O2-cost compared to baseline values (P < 0.05), and tended to improve the 1,000-m time more than ET (P = 0.06). There were no changes in VO2max running or VO2peak DP in either MET or ET. In conclusion, 6 weeks of muscular endurance training increased both muscular endurance and 1RM in simulated DP. Further, specific upper-body muscular endurance training improved DP performance and thus, seems as a promising training model to optimize performance in well-trained cross-country skiers.