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  • 1.
    Gejl, K. D.
    et al.
    Institute of Sports Science and Clinical Biomechanics, University of Southern Denmark, Campusvej 55, 5230 Odense M, Denmark .
    Hvid, L. G.
    Institute of Sports Science and Clinical Biomechanics, University of Southern Denmark, Campusvej 55, 5230 Odense M, Denmark .
    Frandsen, U.
    Institute of Sports Science and Clinical Biomechanics, University of Southern Denmark, Campusvej 55, 5230 Odense M, Denmark .
    Jensen, Kurt
    Mid Sweden University, Faculty of Human Sciences, Department of Health Sciences. Institute of Sports Science and Clinical Biomechanics, University of Southern Denmark, Campusvej 55, 5230 Odense M, Denmark .
    Sahlin, K.
    Åstrand Laboratory, Swedish School of Sport and Health Sciences, Stockholm, Sweden .
    Ørtenblad, Niels
    Mid Sweden University, Faculty of Human Sciences, Department of Health Sciences. Institute of Sports Science and Clinical Biomechanics, University of Southern Denmark, Campusvej 55, 5230 Odense M, Denmark .
    Muscle glycogen content modifies SR Ca2+ release rate in elite endurance athletes2014In: Medicine & Science in Sports & Exercise, ISSN 0195-9131, E-ISSN 1530-0315, Vol. 46, no 3, p. 496-505Article in journal (Refereed)
    Abstract [en]

    Purpose: The aim of the present study was to investigate the influence of muscle glycogen content on sarcoplasmic reticulum (SR) function and peak power output (Wpeak) in elite endurance athletes. Methods: Fourteen highly trained male triathletes (V̇O2max = 66.5 ± 1.3 mL O2·kg·min), performed 4 h of glycogen-depleting cycling exercise (HRmean = 73% ± 1% of maximum). During the first 4 h of recovery, athletes received either water (H2O) or carbohydrate (CHO), separating alterations in muscle glycogen content from acute changes affecting SR function and performance. Thereafter, all subjects received CHO-enriched food for the remaining 20-h recovery period. Results: Immediately after exercise, muscle glycogen content and SR Ca release rate was reduced to 32% ± 4% (225 ± 28 mmol·kg dw) and 86% ± 2% of initial levels, respectively (P < 0.01). Glycogen markedly recovered after 4 h of recovery with CHO (61% ± 2% of preexercise) and SR Ca release rate returned to preexercise level. However, in the absence of CHO during the first 4 h of recovery, glycogen and SR Ca release rate remained depressed, with the normalization of both parameters at the end of the 24 h of recovery after receiving a CHO-enriched diet. Linear regression demonstrated a significant correlation between SR Ca release rate and muscle glycogen content (P < 0.01, r = 0.30). The 4 h of cycling exercise reduced Wpeak by 5.5%-8.9% at different cadences (P < 0.05), and Wpeak was normalized after 4 h of recovery with CHO, whereas Wpeak remained depressed (P < 0.05) after water provision. Wpeak was fully recovered after 24 h in both the H2O and the CHO group. Conclusion: In conclusion, the present results suggest that low muscle glycogen depresses muscle SR Ca release rate, which may contribute to fatigue and delayed recovery of Wpeak 4 h postexercise. © 2014 by the American College of Sports Medicine.

  • 2.
    Hébert-Losier, Kim
    et al.
    Mid Sweden University, Faculty of Human Sciences, Department of Health Sciences.
    Jensen, Kurt
    Mid Sweden University, Faculty of Human Sciences, Department of Health Sciences. Univ Southern Denmark, Inst Sports Sci & Clin Biomech, Odense, Denmark.
    Holmberg, Hans-Christer
    Mid Sweden University, Faculty of Human Sciences, Department of Health Sciences.
    Jumping and hopping in elite and amateur orienteering athletes and correlations to sprinting and running2014In: International Journal of Sports Physiology and Performance, ISSN 1555-0265, E-ISSN 1555-0273, Vol. 9, no 6, p. 993-999Article in journal (Refereed)
    Abstract [en]

    PURPOSE:

    Jumping and hopping are used to measure lower-body muscle power, stiffness, and stretch-shortening-cycle utilization in sports, with several studies reporting correlations between such measures and sprinting and/or running abilities in athletes. Neither jumping and hopping nor correlations with sprinting and/or running have been examined in orienteering athletes.

    METHODS:

    The authors investigated squat jump (SJ), countermovement jump (CMJ), standing long jump (SLJ), and hopping performed by 8 elite and 8 amateur male foot-orienteering athletes (29 ± 7 y, 183 ± 5 cm, 73 ± 7 kg) and possible correlations to road, path, and forest running and sprinting performance, as well as running economy, velocity at anaerobic threshold, and peak oxygen uptake (VO(2peak)) from treadmill assessments.

    RESULTS:

    During SJs and CMJs, elites demonstrated superior relative peak forces, times to peak force, and prestretch augmentation, albeit lower SJ heights and peak powers. Between-groups differences were unclear for CMJ heights, hopping stiffness, and most SLJ parameters. Large pairwise correlations were observed between relative peak and time to peak forces and sprinting velocities; time to peak forces and running velocities; and prestretch augmentation and forest-running velocities. Prestretch augmentation and time to peak forces were moderately correlated to VO(2peak). Correlations between running economy and jumping or hopping were small or trivial.

    CONCLUSIONS:

    Overall, the elites exhibited superior stretch-shortening-cycle utilization and rapid generation of high relative maximal forces, especially vertically. These functional measures were more closely related to sprinting and/or running abilities, indicating benefits of lower-body training in orienteering.

  • 3.
    Hébert-Losier, Kim
    et al.
    Mid Sweden University, Faculty of Human Sciences, Department of Health Sciences.
    Jensen, Kurt
    Mid Sweden University, Faculty of Human Sciences, Department of Health Sciences.
    Mourot, Laurent
    Culture Sport Health Society and Exercise Performance Health Innovation Platform, Franche-Comté University, Besançon, France .
    Holmberg, Hans-Christer
    Mid Sweden University, Faculty of Human Sciences, Department of Health Sciences. Department of Food and Nutrition, and Sport Science, University of Gothenburg, Gothenburg, Sweden.
    The influence of surface on the running velocities of elite and amateur orienteer athletes2014In: Scandinavian Journal of Medicine and Science in Sports, ISSN 0905-7188, E-ISSN 1600-0838, Vol. 24, no 6, p. 448--455Article in journal (Refereed)
    Abstract [en]

    We compared the reduction in running velocities from road to off-road terrain in eight elite and eight amateur male orienteer athletes to investigate whether this factor differentiates elite from amateur athletes. On two separate days, each subject ran three 2-km time trials and three 20-m sprints "all-out" on a road, on a path, and in a forest. On a third day, the running economy and maximal aerobic power of individuals were assessed on a treadmill. The elite orienteer ran faster than the amateur on all three surfaces and at both distances, in line with their better running economy and aerobic power. In the forest, the elites ran at a slightly higher percentage of their 2-km (∼3%) and 20-m (∼4%) road velocities. Although these differences did not exhibit traditional statistical significance, magnitude-based inferences suggested likely meaningful differences, particularly during 20-m sprinting. Of course, cognitive, mental, and physical attributes other than the ability to run on different surfaces are required for excellence in orienteering (e.g., a high aerobic power). However, we suggest that athlete-specific assessment of running performance on various surfaces and distances might assist in tailoring training and identifying individual strengths and/or weaknesses in an orienteer.

  • 4.
    Höök, Martina
    et al.
    Mid Sweden University, Faculty of Human Sciences, Department of Health Sciences.
    Jensen, Kurt
    Mid Sweden University, Faculty of Human Sciences, Department of Health Sciences.
    Willis, Sarah J
    Mid Sweden University, Faculty of Human Sciences, Department of Health Sciences.
    Holmberg, Hans-Christer
    Mid Sweden University, Faculty of Human Sciences, Department of Health Sciences.
    Changes in maximal double poling performance during and after mderate altitude training in elite cross-country skiers2013In: Proceedings for the 6th International Congress on Science and Skiing / [ed] Erich Mueller, Josef Kröll, Stefan Josef Lindinger, Jurgen Pfusterschmied, Thomas Stöggl, 2013, p. 95-Conference paper (Refereed)
  • 5.
    Jensen, Kurt
    et al.
    Mid Sweden University, Faculty of Human Sciences, Department of Health Sciences.
    Höök, Martina
    Mid Sweden University, Faculty of Human Sciences, Department of Health Sciences.
    Wedholm, Lars
    Mid Sweden University, Faculty of Human Sciences, Department of Health Sciences.
    Björklund, Glenn
    Mid Sweden University, Faculty of Human Sciences, Department of Health Sciences.
    Holmberg, Hans-Christer
    Mid Sweden University, Faculty of Human Sciences, Department of Health Sciences.
    How work economy changes during a summer season with roller skiing training and its influence on performance2012In: Science and Skiing V / [ed] Erich Mueller, Stefan Lindinger, Thomas Stöggl, Meyer & Meyer Sport, 2012, p. 523-529Chapter in book (Refereed)
  • 6.
    Jensen, Kurt
    et al.
    Mid Sweden University, Faculty of Human Sciences, Department of Health Sciences.
    Höök, Martina
    Mid Sweden University, Faculty of Human Sciences, Department of Health Sciences.
    Wedholm, Lars
    Mid Sweden University, Faculty of Human Sciences, Department of Health Sciences.
    Björklund, Glenn
    Mid Sweden University, Faculty of Human Sciences, Department of Health Sciences.
    Holmberg, Hans-Christer
    Mid Sweden University, Faculty of Human Sciences, Department of Health Sciences.
    How work efficiency changes during a summer season with roller skiing training and its influence on performace2010In: Proceedings for the fifth international conference on Science and Skiing / [ed] Erich Mueller, Salzburg: Meyer & Meyer Sport, 2010, p. 75-Conference paper (Refereed)
  • 7.
    Jensen, Kurt
    et al.
    Mid Sweden University, Faculty of Human Sciences, Department of Health Sciences.
    Höök, Martina
    Mid Sweden University, Faculty of Human Sciences, Department of Health Sciences.
    Willis, Sarah
    Mid Sweden University, Faculty of Human Sciences, Department of Health Sciences.
    Holmberg, Hans-Christer
    Mid Sweden University, Faculty of Human Sciences, Department of Health Sciences.
    Changes in physical performance parameters during and after moderate altitude training in elite cross-country skiers2014In: Science & Skiing VI / [ed] Erich Muller, Josef Kroll, Stefan Lindinger, Meyer & Meyer Sport, 2014, p. 414-420Chapter in book (Refereed)
  • 8.
    Jensen, Kurt
    et al.
    Mid Sweden University, Faculty of Human Sciences, Department of Health Sciences.
    Höök, Martina
    Mid Sweden University, Faculty of Human Sciences, Department of Health Sciences.
    Willis, Sarah J
    Mid Sweden University, Faculty of Human Sciences, Department of Health Sciences.
    Holmberg, Hans-Christer
    Mid Sweden University, Faculty of Human Sciences, Department of Health Sciences.
    Changes in physical performance parameters during and after moderate altitude training in elite cross country skiers2013In: Proceedings for the 6th International Congress on Science and Skiing / [ed] Erich Mueller, Josef Kröll, Stefan Josef Lindinger, Jurgen Pfusterschmied, Thomas Stöggl, 2013, p. 115-Conference paper (Refereed)
    Abstract [en]

    INTRODUCTION: The Olympic cross country skiing competitions in 2014 will be held in Sochi, Russia at an altitude of approximately 1500m. Although moderate, this altitude is known to reduce performance in highly trained endurance athletes. It is also known that individuals react differently during altitude exposure. The purpose of this study was to evaluate performance changes during and after three weeks of training in moderate altitude in elite skiers.

    METHOD: Four male and three female skiers were tested on a roller skiing treadmill using the classic technique  at sea level (NORM1), after 3 and 20 days at 1500m altitude (ALT1 and ALT2), and 10 days after altitude at sea level (NORM2). The test protocol was a standardized progressive submaximal session of 4 min exercise with 1 min rest between each stage, followed by a 6-10 min progressive “all out” exercise with an increase in first speed and then grade every minute. Oxygen uptake (VO2) was measured continuously during submaximal and maximal exercise. Blood lactate concentrations were measured during the 1 min rest between submax stages and 2 min after the max test. Power at each submax and max stage were calculated from roller ski friction and body weight against gravity [1]. Each stage power was further used for calculations of power at VO2max, (WVO2max), work efficiency at submaximal loads (GE) and for the estimation of O2 cost at maximal work load (used to calculate accumulated O2 deficit (MOD)) [2].

    RESULTS: At NORM1, the skiers’ body mass was 71.9±10.7kg and VO2max 214±12ml/min/kg0.73. The GE varied between 17.9-19.5% during the 3-5 submaximal loads, with no difference between conditions (P>0.05). Also, blood lactate accumulation after submaximal exercise loads showed no difference between conditions (P<0.05). At ALT1, the VO2max and the WVO2max decreased 8.9% and 9.1%, respectively (P<0.05), however there were no differences between ALT1 and ALT2 or from NORM1 and NORM2 (P>0.05). In contrast, the average power output (322±87W) during the “all out” test increased 3.4±2.7% 10 days after the altitude training (P<0.05). Average MOD varied between 57-79 mlO2·kg-1 over the training period, but with no change between conditions (P>0.05). The coefficient of variation (CV%) for the changes in MOD between NORM1 and 2 was 40%.

    DISCUSSION: This study demonstrated that performance (VO2max, WVO2max) deteriorates by 8-9% in a group of elite skiers training at a moderate altitude corresponding to 1500m. No increase in any of the physiological parameters related to performance included in the study was seen after moderate altitude training, except for the maximal power which increased 3.4%. The response after moderate altitude training seems to be related more to anaerobic than aerobic factors. However, this was not confirmed by the MOD in this group of highly trained skiers. The large CV for change in MOD reflects the individual responses to this training.

    CONCLUSION: Small changes of 2-3% in performance in highly trained in elite skiers after moderate altitude training seems not to be related to any single parameter. One should not ignore individual differences in adaptation.

     

    REFERENCES

    1.         Ainegren, M. et al Engineering of Sport 7, Vol 2, 2008: p. 393-400.

    2.         Medbo, J.I.et al J.Appl.Physiol., 1988. 64: p. 50-60.

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