| 1. |
- Andersson, Erik, et al.
(författare)
-
Analysis of sprint cross-country skiing using a differential global navigation satellite system
- 2010
-
Ingår i: European Journal of Applied Physiology. - : Springer Science and Business Media LLC. - 1439-6319 .- 1439-6327. ; 110:3, s. 585-595
-
Tidskriftsartikel (refereegranskat)abstract
- The purpose was to examine skiing velocities, gear choice (G2-7) and cycle rates during a skating sprint time trial (STT) and their relationships to performance, as well as to examine relationships between aerobic power, body composition and maximal skiing velocity versus STT performance. Nine male elite cross-country skiers performed three tests on snow: (1) Maximum velocity test (Vmax) performed using G3 skating, (2) Vmax test performed using double poling (DP) technique and (3) a STT over 1,425 m. Additional measurements of VO2max during roller skiing and body composition using iDXA were made. Differential global navigation satellite system data were used for position and velocity and synchronized with video during STT. The STT encompassed a large velocity range (2.9-12.9 m s-1) and multiple transitions (21-34) between skiing gears. Skiing velocity in the uphill sections was related to gear selection between G2 and G3. STT performance was most strongly correlated to uphill time (r = 0.92, P < 0.05), the percentage use of G2 (r = -0.72, P < 0.05), and DP Vmax (r = -0.71, P < 0.05). The velocity decrease in the uphills from lap 1 to lap 2 was correlated with VO2max (r = -0.78, P < 0.05). Vmax in DP and G3 were related to percent of racing time using G3. In conclusion, the sprint skiing performance was mainly related to uphill performance, greater use of the G3 technique, and higher DP and G3 maximum velocities. Additionally, VO2max was related to the ability to maintain racing velocity in the uphills and lean body mass was related to starting velocity and DP maximal speed.
|
|
| 2. |
- Andersson, Erik, 1984-, et al.
(författare)
-
Biomechanical analysis of the herringbone technique as employed by elite cross-country skiers
- 2014
-
Ingår i: Scandinavian Journal of Medicine and Science in Sports. - : Wiley-Blackwell. - 0905-7188 .- 1600-0838. ; 24:3, s. 542-552
-
Tidskriftsartikel (refereegranskat)abstract
- This investigation was designed to analyse the kinematics and kinetics of cross-country skiing at different velocities with the herringbone technique on a steep incline. Eleven elite male cross-country skiers performed this technique at maximal, high, and moderate velocities on a snow-covered 15° incline. They positioned their skis laterally (25 to 30°) with a slight inside tilt and planted their poles laterally (8 to 12°) with most leg thrust force exerted on the inside forefoot. Although 77% of the total propulsive force was generated by the legs, the ratio between propulsive and total force was approximately fourfold higher for the poles. The cycle rate increased with velocity (1.20 to 1.60 Hz), whereas the cycle length increased from moderate up to high velocity, but then remained the same at maximal velocity (2.0 to 2.3 m). In conclusion, with the herringbone technique, the skis were angled laterally without gliding, with the forces distributed mainly on the inside forefoot to enable grip for propulsion. The skiers utilized high cycle rates with major propulsion by the legs, highlighting the importance of high peak and rapid generation of leg forces.
|
|
| 3. |
- Andersson, Erik, 1984-, et al.
(författare)
-
Energy system contributions and determinants of performance in sprint cross-country skiing
- 2017
-
Ingår i: Scandinavian Journal of Medicine and Science in Sports. - : Wiley. - 0905-7188 .- 1600-0838. ; 27:4, s. 385-398
-
Tidskriftsartikel (refereegranskat)abstract
- To improve current understanding of energy contributions and determinants of sprint-skiing performance, 11 well-trained male cross-country skiers were tested in the laboratory for VO2max , submaximal gross efficiency (GE), maximal roller skiing velocity, and sprint time-trial (STT) performance. The STT was repeated four times on a 1300-m simulated sprint course including three flat (1°) double poling (DP) sections interspersed with two uphill (7°) diagonal stride (DS) sections. Treadmill velocity and VO2 were monitored continuously during the four STTs and data were averaged. Supramaximal GE during the STT was predicted from the submaximal relationships for GE against velocity and incline, allowing computation of metabolic rate and O2 deficit. The skiers completed the STT in 232 ± 10 s (distributed as 55 ± 3% DP and 45 ± 3% DS) with a mean power output of 324 ± 26 W. The anaerobic energy contribution was 18 ± 5%, with an accumulated O2 deficit of 45 ± 13 mL/kg. Block-wise multiple regression revealed that VO2 , O2 deficit, and GE explained 30%, 15%, and 53% of the variance in STT time, respectively (all P < 0.05). This novel GE-based method of estimating the O2 deficit in simulated sprint-skiing has demonstrated an anaerobic energy contribution of 18%, with GE being the strongest predictor of performance.
|
|
| 4. |
- Andersson, Erik, et al.
(författare)
-
The effects of skiing velocity on mechanical aspects of diagonal cross-country skiing
- 2014
-
Ingår i: Sports Biomechanics. - : Informa UK Limited. - 1476-3141 .- 1752-6116. ; 13:3, s. 267-284
-
Tidskriftsartikel (refereegranskat)abstract
- Cycle and force characteristics were examined in 11 elite male cross-country skiers using the diagonal stride technique while skiing uphill (7.5 degrees) on snow at moderate (3.5 +/- 0.3m/s), high (4.5 +/- 0.4m/s), and maximal (5.6 +/- 0.6m/s) velocities. Video analysis (50Hz) was combined with plantar (leg) force (100Hz), pole force (1,500Hz), and photocell measurements. Both cycle rate and cycle length increased from moderate to high velocity, while cycle rate increased and cycle length decreased at maximal compared to high velocity. The kick time decreased 26% from moderate to maximal velocity, reaching 0.14s at maximal. The relative kick and gliding times were only altered at maximal velocity, where these were longer and shorter, respectively. The rate of force development increased with higher velocity. At maximal velocity, sprint-specialists were 14% faster than distance-specialists due to greater cycle rate, peak leg force, and rate of leg force development. In conclusion, large peak leg forces were applied rapidly across all velocities and the shorter relative gliding and longer relative kick phases at maximal velocity allow maintenance of kick duration for force generation. These results emphasise the importance of rapid leg force generation in diagonal skiing.
|
|
| 5. |
- Fabré, Nicolas, et al.
(författare)
-
Alterations in aerobic energy expenditure and neuromuscular function during a simulated cross-country skiathlon with the skating technique
- 2015
-
Ingår i: Human Movement Science. - : Elsevier BV. - 0167-9457 .- 1872-7646. ; 40, s. 326-340
-
Tidskriftsartikel (refereegranskat)abstract
- Here, we tested the hypothesis that aerobic energy expenditure (AEE) is higher during a simulated 6-km (2 loops of 3-km each) "skiathlon" than during skating only on a treadmill and attempted to link any such increase to biomechanical and neuromuscular responses. Six elite male cross-country skiers performed two pretesting time-trials (TT) to determine their best performances and to choose an appropriate submaximal speed for collection of physiological, biomechanical and neuromuscular data during two experimental sessions ((exp)). Each skier used, in randomized order, either the classical (CL) or skating technique (SK) for the first 3-km loop, followed by transition to the skating technique for the second 3-km loop. Respiratory parameters were recorded continuously. The EMG activity of the triceps brachii (TBr and vastus lateralis (VLa) muscles during isometric contractions performed when the skiers were stationary (i.e., just before the first loop, during the transition, and after the second loop); their corresponding activity during dynamic contractions; and pole and plantar forces during the second loop were recorded. During the second 3-km of the 'IT, skating speed was significantly higher for the SK-SK than CL-SK. During this second loop, AEE was also higher (+1.5%) for CL-SKexp than SK-SKexp, in association with higher VLa EMG activity during both isometric and dynamic contractions, despite no differences in plantar or pole forces, poling times or cycle rates. Although the underlying mechanism remains unclear, during a skiathlon, the transition between the sections of classical skiing and skating alters skating performance (i.e., skiing speed), AEE and neuromuscular function. (C) 2015 Elsevier B.V. All rights reserved.
|
|
| 6. |
- Gejl, Kasper D., et al.
(författare)
-
Contractile Properties of MHC I and II Fibers From Highly Trained Arm and Leg Muscles of Cross-Country Skiers
- 2021
-
Ingår i: Frontiers in Physiology. - : Frontiers Media S.A.. - 1664-042X. ; 12
-
Tidskriftsartikel (refereegranskat)abstract
- Little is known about potential differences in contractile properties of muscle fibers of the same type in arms and legs. Accordingly, the present study was designed to compare the force-generating capacity and Ca2+ sensitivity of fibers from arm and leg muscles of highly trained cross-country skiers. Method: Single muscle fibers of m. vastus lateralis and m. triceps brachii of 8 highly trained cross-country skiers were analyzed with respect to maximal Ca2+-activated force, specific force and Ca2+ sensitivity. Result: The maximal Ca2+-activated force was greater for MHC II than MHC I fibers in both the arm (+62 %, P < 0.001) and leg muscle (+77 %, P < 0.001), with no differences between limbs for each MHC isoform. In addition, the specific force of MHC II fibers was higher than that of MHC I fibers in both arms (+41 %, P = 0.002) and legs (+95 %, P < 0.001). The specific force of MHC II fibers was the same in both limbs, whereas MHC I fibers from the m. triceps brachii were, on average, 39% stronger than fibers of the same type from the m. vastus lateralis (P = 0.003). pCa50 was not different between MHC I and II fibers in neither arms nor legs, but the MHC I fibers of m. triceps brachii demonstrated higher Ca2+ sensitivity than fibers of the same type from m. vastus lateralis (P = 0.007). Conclusion: Comparison of muscles in limbs equally well trained revealed that MHC I fibers in the arm muscle exhibited a higher specific force-generating capacity and greater Ca2+ sensitivity than the same type of fiber in the leg, with no such difference in the case of MHC II fibers. These distinct differences in the properties of fibers of the same type in equally well-trained muscles open new perspectives in muscle physiology.
|
|
| 7. |
- Gejl, Kasper Degn, et al.
(författare)
-
Effects of Acute Exercise and Training on the Sarcoplasmic Reticulum Ca(2+)Release and Uptake Rates in Highly Trained Endurance Athletes
- 2020
-
Ingår i: Frontiers in Physiology. - : Frontiers Media SA. - 1664-042X. ; 11
-
Tidskriftsartikel (refereegranskat)abstract
- Little is presently known about the effects of acute high-intensity exercise or training on release and uptake of Ca(2+)by the sarcoplasmic reticulum (SR). The aims here were to characterize this regulation in highly trained athletes following (1) repeated bouts of high-intensity exercise and (2) a period of endurance training including high-intensity sessions. Eleven cross-country skiers (25 +/- 4 years, 65 +/- 4 mL O-2.kg(-1).min(-1)) performed four self-paced sprint time-trials (STT 1-4) lasting approximate to 4 min each (STT 1-4) and separated by 45 min of recovery; while 19 triathletes and road cyclists (25 +/- 4 years, 65 +/- 5 mL O-2.kg(-1).min(-1)) completed 4 weeks of endurance training in combination with three sessions of high-intensity interval cycling per week. Release (mu mol.g(-1)prot.min(-1)) and uptake [tau (s)] of Ca(2+)by SR vesicles isolated from m.triceps brachiiand m.vastus lateraliswere determined before and after STT 1 and 4 in the skiers and in m.vastus lateralisbefore and after the 4 weeks of training in the endurance athletes. The Ca(2+)release rate was reduced by 17-18% in both limbs already after STT 1 (arms: 2.52 +/- 0.74 to 2.08 +/- 0.60; legs: 2.41 +/- 0.45 to 1.98 +/- 0.51,P< 0.0001) and attenuated further following STT 4 (arms: 2.24 +/- 0.67 to 1.95 +/- 0.45; legs: 2.13 +/- 0.51 to 1.83 +/- 0.36,P< 0.0001). Also, there was a tendency toward an impairment in the SR Ca(2+)uptake from pre STT1 to post STT4 in both arms and legs (arms: from 22.0 +/- 3.7 s to 25.3 +/- 6.0 s; legs: from 22.5 +/- 4.7 s to 25.5 +/- 7.7 s,P= 0.05). Endurance training combined with high-intensity exercise increased the Ca(2+)release rate by 9% (1.76 +/- 0.38 to 1.91 +/- 0.44,P= 0.009), without altering the Ca(2+)uptake (29.6 +/- 7.0 to 29.1 +/- 8.7 s;P= 0.98). In conclusion, the Ca(2+)release and uptake rates by SR in exercising limbs of highly trained athletes declines gradually by repetitive bouts of high-intensity exercise. We also demonstrate, for the first time, that the SR Ca(2+)release rate can be enhanced by a specific program of training in highly trained athletes, which may have important implications for performance parameters.
|
|
| 8. |
- Gejl, Kasper D., et al.
(författare)
-
Local depletion of glycogen with supra-maximal exercise in human skeletal muscle fibres
- 2017
-
Ingår i: Journal of Physiology. - 0022-3751 .- 1469-7793. ; 595:9, s. 2809-2821
-
Tidskriftsartikel (refereegranskat)abstract
- Skeletal muscle glycogen is heterogeneous distributed in three separated compartments (intramyofibrillar, intermyofibrillar and subsarcolemmal). Although only constituting 4-15% of the total glycogen volume, the availability of intramyofibrillar glycogen has been shown to be of particular importance to muscle function. The present study was designed to investigate the depletion of these three sub-cellular glycogen compartments during repeated supra-maximal exercise in elite athletes. Ten elite cross-country skiers (age: 25 +/- 4 yrs., VO2 max : 65 +/- 4 ml kg-1 min-1 , mean +/- SD) performed four approximately 4-minute supra-maximal sprint time trials (STT 1-4) with 45 min recovery. The sub-cellular glycogen volumes in m. triceps brachii were quantified from electron microscopy images before and after both STT 1 and STT 4. During STT 1, the depletion of intramyofibrillar glycogen was higher in type I fibres (-52% [-89:-15%]) than type 2 fibres (-15% [-52:22%]) (P = 0.02), while the depletion of intermyofibrillar glycogen (main effect: -19% [-33:0], P = 0.006) and subsarcolemmal glycogen (main effect: -35% [-66:0%], P = 0.03) was similar between fibre types. In contrast, only intermyofibrillar glycogen volume was significantly reduced during STT 4, in both fibre types (main effect: -31% [-50:-11%], P = 0.002). Furthermore, for each of the sub-cellular compartments, the depletion of glycogen during STT 1 was associated with the volumes of glycogen before STT 1. In conclusion, the depletion of spatially distinct glycogen compartments differs during supra-maximal exercise. Furthermore, the depletion changes with repeated exercise and is fibre type-dependent.
|
|
| 9. |
- Mourot, Laurent, et al.
(författare)
-
Cross-Country Skiing and Postexercise Heart-Rate Recovery
- 2015
-
Ingår i: International Journal of Sports Physiology and Performance. - : Human Kinetics. - 1555-0265 .- 1555-0273. ; 10:1, s. 11-16
-
Tidskriftsartikel (refereegranskat)abstract
- Postexercise heart-rate (HR) recovery (HRR) indices have been associated with running and cycling endurance-exercise performance. The current study was designed (1) to test whether such a relationship also exists in the case of cross-country skiing (XCS) and (2) to determine whether the magnitude of any such relationship is related to the intensity of exercise before obtaining HRR indices. Ten elite male cross-country skiers (mean +/- SD; 28.2 +/- 5.4 y, 181 +/- 8 cm, 77.9 +/- 9.4 kg, 69.5 +/- 4.3 mL.min(-1) . kg(-1) maximal oxygen uptake [VO2max]) performed 2 sessions of roller-skiing on a treadmill: a 2 x 3-km time trial and the same 6-km at an imposed submaximal speed followed by a final 800-m time trial. VO2 and HR were monitored continuously, while HRR and blood lactate (BLa) were assessed during 2 min immediately after each 6-km and the 800-m time trial. The 6-km time-trial time was largely negatively correlated with VO2max and BLa. On the contrary, there was no clear correlation between the 800-m time-trial time and VO2, HR, or BLa. In addition, in no case was any clear correlation between any of the HRR indices and performance time or VO2max observed. These findings confirm that XCS performance is largely correlated with VO2max and the ability to tolerate high levels of BLa; however, postexercise HRR showed no clear association with performance. The homogeneity of the group of athletes involved and the contribution of the arms and upper body to the exercise preceding determination of HRR may explain this absence of a relationship.
|
|
| 10. |
- Mourot, L., et al.
(författare)
-
Impact of the initial classic section during a simulated cross-country skiing skiathlon on the cardiopulmonary responses during the subsequent period of skate skiing
- 2014
-
Ingår i: Applied Physiology, Nutrition and Metabolism. - : Canadian Science Publishing. - 1715-5320 .- 1715-5312. ; 39:8, s. 911-919
-
Tidskriftsartikel (refereegranskat)abstract
- The aim of this study was to assess potential changes in the performance and cardiorespiratory responses of elite cross-country skiers following transition from the classic (CL) to the skating (SK) technique during a simulated skiathlon. Eight elite male skiers performed two 6 km (2 × 3 km) roller-skiing time trials on a treadmill at racing speed: one starting with the classic and switching to the skating technique (CL1-SK2) and another employing the skating technique throughout (SK1-SK2), with continuous monitoring of gas exchanges, heart rates, and kinematics (video). The overall performance times in the CL1-SK2 (21:12 ± 1:24) and SK1-SK2 (20:48 ± 2:00) trials were similar, and during the second section of each performance times and overall cardiopulmonary responses were also comparable. However, in comparison with SK1-SK2, the CL1-SK2 trial involved significantly higher increases in minute ventilation (VE, 89.8 ± 26.8 vs. 106.8 ± 17.6 L·min-1) and oxygen uptake (VO2; 3.1 ± 0.8 vs 3.5 ±0.5 L·min-1) 2 min after the transition as well as longer time constants for VE, VO2, and heart rate during the first 3 min after the transition. This higher cardiopulmonary exertion was associated with ~3% faster cycle rates. In conclusion, overall performance during the 2 time trials did not differ. The similar performance times during the second sections were achieved with comparable mean cardiopulmonary responses. However, the observation that during the initial 3-min post-transition following classic skiing cardiopulmonary responses and cycle rates were slightly higher supports the conclusion that an initial section of classic skiing exerts an impact on performance during a subsequent section of skate skiing.
|
|
