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PHYSIOLOGICAL AND BIOMECHANICAL FACTORS DETERMINING CROSS-COUNTRY SKIING PERFORMANCE
Mid Sweden University, Faculty of Human Sciences, Department of Health Sciences. (Nationellt vintersportcentrum)
2016 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

Cross-country (c.c.) skiing is a complex sport discipline from both physiological and biomechanical perspectives, with varying course topographies that require different proportions of the involved sub-techniques to be utilised. A relatively new event in c.c. skiing is the sprint race, involving four separate heats, each lasting 2-4 min, with diverse demands from distance races associated with longer durations. Therefore, the overall aim of the current thesis has been to examine the biomechanical and physiological factors associated with sprint c.c. skiing performance through novel measurements conducted both in the field (Studies I-III) and the laboratory (Studies IV and V).

In Study I sprint skiing velocities and sub-techniques were analysed with a differential global navigation satellite system in combination with video recording. In Studies II and III the effects of an increasing velocity (moderate, high and maximal) on the biomechanics of uphill classical skiing with the diagonal stride (DS) (Study II) and herringbone (HB) (Study III) sub-techniques were examined.

In Study I the skiers completed the 1,425 m (2 x 712 m) sprint time trial (STT) in 207 s, at an average velocity of 24.8 km/h, with multiple technique transitions (range: 21-34) between skiing techniques (i.e., the different gears [G2-7]). A pacing strategy involving a fast start followed by a gradual slowing down (i.e., positive pacing) was employed as indicated by the 2.9% faster first than second lap. The slower second lap was primarily related to a slower (12.9%) uphill velocity with a shift from G3 towards a greater use of G2. The maximal oxygen uptake ( O2max) was related to the ability to maintain uphill skiing velocity and the fastest skiers used G3 to a greater extent than G2. In addition, maximal speed over short distances (50 and 20 m) with the G3 and double poling (DP) sub-techniques exerted an important impact on STT performance.

Study II demonstrated that during uphill skiing (7.5°) with DS, skiers increased cycle rate and cycle length from moderate to high velocity, while cycle rate increased and cycle length decreased at maximal velocity. Absolute poling, gliding and kick times became gradually shorter with an elevated velocity. The rate of pole and leg force development increased with elevated velocity and the development of leg force in the normal direction was substantially faster during skiing on snow than previous findings for roller skiing, although the peak force was similar in both cases. The fastest skiers applied greater peak leg forces over shorter durations.

Study III revealed that when employing the HB technique on a steep uphill slope (15°), the skiers positioned their skis laterally (“V” between 25 to 30°) and planted their poles at a slight lateral angle (8 to 12°), with most of the propulsive force being exerted on the inside forefoot. Of the total propulsive force, 77% was generated by the legs. The cycle rate increased across all three velocities (from 1.20 to 1.60 Hz), while cycle length only increased from moderate to high velocity (from 2.0 to 2.3 m). Finally, the magnitude and rate of leg force generation are important determinants of both DS and HB skiing performance, although the rate is more important in connection with DS, since this sub-technique involves gliding.

In Studies IV and V skiers performed pre-tests for determination of gross efficiency (GE), O2max, and Vmax on a treadmill. The main performance test involved four self-paced STTs on a treadmill over a 1,300-m simulated course including three flat (1°) DP sections interspersed with two uphill (7°) DS sections.

The modified GE method for estimating anaerobic energy production during skiing on varying terrain employed in Study IV revealed that the relative aerobic and anaerobic energy contributions were 82% and 18%, respectively, during the 232 s of skiing, with an accumulated oxygen (O2) deficit of 45 mL/kg. The STT performance time was largely explained by the GE (53%), followed by O2 (30%) and O2 deficit (15%). Therefore, training strategies designed to reduce energetic cost and improve GE should be examined in greater detail.

In Study V metabolic responses and pacing strategies during the four successive STTs were investigated. The first and the last trials were the fastest (both 228 s) and were associated with both a substantially larger and a more rapid anaerobic energy supply, while the average O2 during all four STTs was similar. The individual variation in STT performance was explained primarily (69%) by the variation in O2 deficit. Furthermore, positive pacing was employed throughout all the STTs, but the pacing strategy became more even after the first trial. In addition, considerably higher (~ 30%) metabolic rates were generated on the uphill than on the flat sections of the course, reflecting an irregular production of anaerobic energy. Altogether, a fast start appears important for STT performance and high work rates during uphill skiing may exert a more pronounced impact on skiing performance outdoors, due to the reduction in velocity fluctuations and thereby overall air-drag.

Place, publisher, year, edition, pages
Östersund: Mittuniversitets tryckeri Sundsvall , 2016. , 74 p.
Series
Mid Sweden University doctoral thesis, ISSN 1652-893X ; 248
Keyword [en]
cycle characteristics, energy cost, energy yield, incline, joint angles, kinematics, kinetics, mechanics, Nordic skiing, oxygen deficit, oxygen demand, technique transitions, total metabolic rate.
National Category
Medical and Health Sciences
Identifiers
URN: urn:nbn:se:miun:diva-27898ISBN: 978-91-88025-69-2 (print)OAI: oai:DiVA.org:miun-27898DiVA: diva2:935790
Public defence
2016-06-10, Q221, Mittuniversitetet, Östersund, 13:00 (English)
Opponent
Supervisors
Note

Vid tidpunkten för disputationen var följande delarbeten opublicerade: delarbete 5 inskickat

At the time of the doctoral defence the following papers were unpublished: paper 5 submitted

Available from: 2016-06-13 Created: 2016-06-12 Last updated: 2016-06-13Bibliographically approved
List of papers
1. Analysis of sprint cross-country skiing using a differential global navigation satellite system
Open this publication in new window or tab >>Analysis of sprint cross-country skiing using a differential global navigation satellite system
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2010 (English)In: European Journal of Applied Physiology, ISSN 1439-6319, E-ISSN 1439-6327, Vol. 110, no 3, 585-595 p.Article in journal (Refereed) Published
Abstract [en]

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.

Keyword
Aerobic power; Body composition; DXA; Kinematics; Maximal velocity; Performance; Skating; Technique analysis; Time-trial; Transition References
National Category
Sport and Fitness Sciences
Identifiers
urn:nbn:se:miun:diva-10879 (URN)10.1007/s00421-010-1535-2 (DOI)000282214600014 ()20571822 (PubMedID)2-s2.0-78049327299 (Scopus ID)
Projects
Innovative Biomechanical Olympic Performance TechnologyIntegrative Physiology & Biomechanics
Available from: 2010-01-06 Created: 2010-01-06 Last updated: 2017-12-12Bibliographically approved
2. The effects of skiing velocity on mechanical aspects of diagonal cross-country skiing
Open this publication in new window or tab >>The effects of skiing velocity on mechanical aspects of diagonal cross-country skiing
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2014 (English)In: Sports Biomechanics, ISSN 1476-3141, E-ISSN 1752-6116, Vol. 13, no 3, 267-284 p.Article in journal (Refereed) Published
Abstract [en]

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.

Keyword
Cycle characteristics, kinetics, Nordic skiing
National Category
Sport and Fitness Sciences
Identifiers
urn:nbn:se:miun:diva-23433 (URN)10.1080/14763141.2014.921236 (DOI)000343289000007 ()2-s2.0-84908071182 (Scopus ID)
Available from: 2014-11-21 Created: 2014-11-17 Last updated: 2017-12-05Bibliographically approved
3. Biomechanical analysis of the herringbone technique as employed by elite cross-country skiers
Open this publication in new window or tab >>Biomechanical analysis of the herringbone technique as employed by elite cross-country skiers
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2014 (English)In: Scandinavian Journal of Medicine and Science in Sports, ISSN 0905-7188, E-ISSN 1600-0838, Vol. 24, no 3, 542-552 p.Article in journal (Refereed) Published
Abstract [en]

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.

Place, publisher, year, edition, pages
Wiley-Blackwell, 2014
Keyword
Cycle characteristics, Cycle length, Cycle rate, Joint angles, Kinetics, Leg force, Pole force, Snow
National Category
Medical and Health Sciences
Identifiers
urn:nbn:se:miun:diva-18147 (URN)10.1111/sms.12026 (DOI)000335984500020 ()2-s2.0-84900796950 (Scopus ID)
Available from: 2013-01-08 Created: 2013-01-08 Last updated: 2017-12-06Bibliographically approved
4. Energy system contributions and determinants of performance in sprint cross-country skiing
Open this publication in new window or tab >>Energy system contributions and determinants of performance in sprint cross-country skiing
2017 (English)In: Scandinavian Journal of Medicine and Science in Sports, ISSN 0905-7188, E-ISSN 1600-0838, Vol. 27, no 4, 385-398 p.Article in journal (Refereed) Published
Abstract [en]

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.

Keyword
Energetic cost, incline, oxygen demand, oxygen uptake, oxygen deficit, technique transitions.
National Category
Medical and Health Sciences
Identifiers
urn:nbn:se:miun:diva-27227 (URN)10.1111/sms.12666 (DOI)000395709400002 ()26923666 (PubMedID)2-s2.0-84959270767 (Scopus ID)
Funder
Swedish National Centre for Research in Sports
Note

Article first published online: 29 FEB 2016

Available from: 2016-03-14 Created: 2016-03-14 Last updated: 2017-07-07Bibliographically approved
5. Metabolic responses and pacing strategies during successive sprint skiing time trials
Open this publication in new window or tab >>Metabolic responses and pacing strategies during successive sprint skiing time trials
2016 (English)In: Medicine & Science in Sports & Exercise, ISSN 0195-9131, E-ISSN 1530-0315, Vol. 48, no 12, 2544-2554 p.Article in journal (Refereed) Published
Abstract [en]

PURPOSE: To examine the metabolic responses and pacing strategies during the performance of successive sprint time trials (STTs) in cross-country skiing. METHODS: Ten well-trained male cross-country skiers performed four self-paced 1300-m STTs on a treadmill, each separated by 45 min of recovery. The simulated STT course was divided into three flat (1°) sections (S1, S3 and S5) involving the double poling sub-technique interspersed with two uphill (7°) sections (S2 and S4) involving the diagonal stride sub-technique. Treadmill velocity and V˙O2 were monitored continuously and gross efficiency was used to estimate the anaerobic energy supply. RESULTS: The individual trial-to-trial variability in STT performance time was 1.3%, where variations in O2 deficit and V˙O2 explained 69% (P < 0.05) and 11% (P > 0.05) of the variation in performance. The first and last STTs were equally fast (228 ± 10 s), and ~ 1.3% faster than the second and the third STTs (P < 0.05). These two fastest STTs were associated with a 14% greater O2 deficit (P < 0.05), while the average V˙O2 was similar during all four STTs (86 ± 3% of V˙O2max). Positive pacing was used throughout all STTs, with significantly less time spent on the first than second course half. In addition, metabolic rates were substantially higher (~_30%) for uphill than for flat skiing, indicating that pacing was regulated to the terrain. CONCLUSIONS: The fastest STTs were characterized primarily by a greater anaerobic energy production, which also explained 69% of the individual variation in performance. Moreover, the skiers employed positive pacing and a variable exercise intensity according to the course profile, yielding an irregular distribution of anaerobic energy production.

National Category
Medical and Health Sciences
Identifiers
urn:nbn:se:miun:diva-27899 (URN)10.1249/MSS.0000000000001037 (DOI)000389605600024 ()27414686 (PubMedID)2-s2.0-84978485238 (Scopus ID)
Note

Available online from 12th July 2016.

Available from: 2016-06-13 Created: 2016-06-13 Last updated: 2017-11-28Bibliographically approved

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