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- Andersson, Erik, 1984-, et al.
(författare)
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Biomechanical analysis of the herringbone technique as employed by elite cross-country skiers
- 2014
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Ingår i: Scandinavian Journal of Medicine and Science in Sports. - : Wiley-Blackwell. - 0905-7188 .- 1600-0838. ; 24:3, s. 542-552
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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.
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| 4. |
- Andersson, Erik, et al.
(författare)
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The effects of skiing velocity on mechanical aspects of diagonal cross-country skiing
- 2014
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Ingår i: Sports Biomechanics. - : Informa UK Limited. - 1476-3141 .- 1752-6116. ; 13:3, s. 267-284
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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.
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| 5. |
- Pellegrini, Barbara, et al.
(författare)
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Biomechanical and energetic determinants of technique selection in classical cross-country skiing
- 2013
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Ingår i: Human Movement Science. - : Elsevier. - 0167-9457 .- 1872-7646. ; 32:6, s. 1415-1429
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Tidskriftsartikel (refereegranskat)abstract
- Classical cross-country skiing can be performed using three main techniques: diagonal stride (DS), double poling (DP), and double poling with kick (DK). Similar to other forms of human and animal gait, it is currently unclear whether technique selection occurs to minimize metabolic cost or to keep some mechanical factors below a given threshold. The aim of this study was to find the determinants of technique selection. Ten male athletes roller skied on a treadmill at different slopes (from 0° to 7° at 10km/h) and speeds (from 6 to 18km/h at 2°). The technique preferred by skiers was gathered for every proposed condition. Biomechanical parameters and metabolic cost were then measured for each condition and technique. Skiers preferred DP for skiing on the flat and they transitioned to DK and then to DS with increasing slope steepness, when increasing speed all skiers preferred DP. Data suggested that selections mainly occur to remain below a threshold of poling force. Second, critically low values of leg thrust time may limit the use of leg-based techniques at high speeds. A small role has been identified for the metabolic cost of locomotion, which determined the selection of DP for flat skiing.
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| 6. |
- Zoppirolli, Chiara, et al.
(författare)
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The effectiveness of stretch-shortening cycling in upper-limb extensor muscles during elite cross-country skiing with the double-poling technique
- 2013
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Ingår i: Journal of Electromyography & Kinesiology. - : Elsevier BV. - 1050-6411 .- 1873-5711. ; 23:6, s. 1512-1519
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Tidskriftsartikel (refereegranskat)abstract
- This investigation was designed to evaluate the effectiveness of stretch-shortening cycling (SSCEFF) in upper-limb extensor muscles while cross-country skiing using the double-poling technique (DP). To this end, SSCEFF was analyzed in relation to DP velocity and performance. Eleven elite cross-country skiers performed an incremental test to determine maximal DP velocity (V-max). Thereafter, cycle characteristics, elbow joint kinematics and poling forces were monitored on a treadmill while skiing at two sub-maximal and racing velocity (85% of Vmax). The average EMG activities of the triceps brachii and latissimus dorsi muscles were determined during the flexion and extension sub-phases of the poling cycle (EMG(FLEX), EMG(EXT)), as well as prior to pole plant (EMG(PRE)). SSCEFF was defined as the ratio of aEMG(FLEX) to aEMG(EXT). EMG(PRE) and EMG(FLEX) increased with velocity for both muscles (P < 0.01), as did SSCEFF (from 0.9 +/- 0.3 to 1.3 +/- 0.5 for the triceps brachii and from 0.9 +/- 0.4 to 1.5 +/- 0.5 for the latissimus dorsi) and poling force (from 253 +/- 33 to 290 +/- 36 N; P < 0.05). Furthermore, SSCEFF was positively correlated to Vmax, to EMG(PRE) and EMG(FLEX) (P < 0.05). The neuromuscular adaptations made at higher velocities, when more poling force must be applied to the ground, exert a major influence on the DP performance of elite cross-country skiers. (C) 2013 Elsevier Ltd. All rights reserved.
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