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Metabolic responses and pacing strategies during successive sprint skiing time trials
Mid Sweden University, Faculty of Human Sciences, Department of Health Sciences. (Nationellt vintersportcentrum)
Mid Sweden University, Faculty of Human Sciences, Department of Health Sciences.
Mid Sweden University, Faculty of Human Sciences, Department of Health Sciences.
Mid Sweden University, Faculty of Human Sciences, Department of Health Sciences.
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.

Place, publisher, year, edition, pages
2016. Vol. 48, no 12, 2544-2554 p.
National Category
Medical and Health Sciences
Identifiers
URN: urn:nbn:se:miun:diva-27899DOI: 10.1249/MSS.0000000000001037ISI: 000389605600024PubMedID: 27414686Scopus ID: 2-s2.0-84978485238OAI: oai:DiVA.org:miun-27899DiVA: diva2:935851
Note

Available online from 12th July 2016.

Available from: 2016-06-13 Created: 2016-06-13 Last updated: 2017-01-05Bibliographically approved
In thesis
1. PHYSIOLOGICAL AND BIOMECHANICAL FACTORS DETERMINING CROSS-COUNTRY SKIING PERFORMANCE
Open this publication in new window or tab >>PHYSIOLOGICAL AND BIOMECHANICAL FACTORS DETERMINING CROSS-COUNTRY SKIING PERFORMANCE
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
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:nbn:se:miun:diva-27898 (URN)978-91-88025-69-2 (ISBN)
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

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