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  • 1.
    Andersson, Erik
    et al.
    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.
    Ørtenblad, Niels
    Mid Sweden University, Faculty of Human Sciences, Department of Health Sciences.
    Energy System Contributions And Determinants Of Performance In Classical Sprint Cross-Country Skiing2014In: Proceedings for the 19th ECCS in Amsterdam, The Netherlands, 2014Conference paper (Refereed)
  • 2.
    Beaven, Martyn
    et al.
    Mid Sweden University, Faculty of Human Sciences, Department of Health Sciences.
    Willis, Sarah
    Mid Sweden University, Faculty of Human Sciences, Department of Health Sciences.
    Cook, Christian
    School of Sport, Health and Exercise Sciences, Bangor University, Bangor, United Kingdom.
    Holmberg, Hans-Christer
    Mid Sweden University, Faculty of Human Sciences, Department of Health Sciences.
    Physiological comparison of concentric and eccentric arm cycling in males and females2014In: PLoS ONE, ISSN 1932-6203, E-ISSN 1932-6203, Vol. 5, no 9, p. Art. no. e112079-Article in journal (Refereed)
    Abstract [en]

    Lower body eccentric exercise is well known to elicit high levels of muscular force with relatively low cardiovascular and metabolic strain. As a result, eccentric exercise has been successfully utilised as an adaptive stressor to improve lower body muscle function in populations ranging from the frail and debilitated, to highly-trained individuals. Here we investigate the metabolic, cardiorespiratory, and energy costs of upper body eccentric exercise in a healthy population. Seven men and seven women performed 4-min efforts of eccentric (ECC) or concentric (CON) arm cycling on a novel arm ergometer at workloads corresponding to 40, 60, and 80% of their peak workload as assessed in an incremental concentric trial. The heart rate, ventilation, cardiac output, respiratory exchange ratio, and blood lactate concentrations were all clearly greater in CON condition at all of the relative workloads (all p<0.003). Effect size calculations demonstrated that the magnitude of the differences in VO2 and work economy between the ECC and CON exercise ranged from very large to extremely large; however, in no case did mechanical efficiency (ηMECH) differ between the conditions (all p>0.05). In contrast, delta efficiency (ηΔ), as previously defined by Coyle and colleagues in 1992, demonstrated a sex difference (men>women; p<0.05). Sex differences were also apparent in arteriovenous oxygen difference and heart rate during CON. Here, we reinforce the high-force, low cost attributes of eccentric exercise which can be generalised to the muscles of the upper body. Upper body eccentric exercise is likely to form a useful adjunct in debilitative, rehabilitative, and adaptive clinical exercise programs; however, reports of a shift towards an oxidative phenotype should be taken into consideration by power athletes. We suggest delta efficiency as a sensitive measure of efficiency that allowed the identification of sex differences.

  • 3.
    Born, D. -P
    et al.
    Integrative and Experimental Exercise Science, Institute for Sport Sciences, University of Wuerzburg, Wuerzburg, Germany .
    Faiss, R.
    Swiss Federal Institute of Sport, Section for Elite Sport, Magglingen, Switzerland .
    Willis, Sara J.
    Mid Sweden University, Faculty of Human Sciences, Department of Health Sciences.
    Strahler, J.
    Clinical Biopsychology, University of Marburg, Marburg, Germany.
    Millet, G. P.
    ISSUL Institute of Sport Sciences, University of Lausanne, Lausanne, Switzerland.
    Holmberg, Hans-Christer
    Mid Sweden University, Faculty of Human Sciences, Department of Health Sciences.
    Sperlich, B.
    Integrative and Experimental Exercise Science, Institute for Sport Sciences, University of Wuerzburg, Wuerzburg, Germany .
    Circadian variation of salivary immunoglobin A, alpha-amylase activity and mood in response to repeated double-poling sprints in hypoxia2016In: European Journal of Applied Physiology, ISSN 1439-6319, E-ISSN 1439-6327, Vol. 116, no 1, p. 1-10Article in journal (Refereed)
    Abstract [en]

    Purpose: To assess the circadian variations in salivary immunoglobin A (sIgA) and alpha-amylase activity (sAA), biomarkers of mucosal immune function, together with mood during 2 weeks of repeated sprint training in hypoxia (RSH) and normoxia (RSN). Methods: Over a 2-week period, 17 competitive cross-country skiers performed six training sessions, each consisting of four sets of five 10-s bouts of all-out double-poling under either normobaric hypoxia (FiO2: 13.8 %, 3000 m) or normoxia. The levels of sIgA and sAA activity and mood were determined five times during each of the first (T1) and sixth (T6) days of training, as well as during days preceding (baseline) and after the training intervention (follow-up). Results: With RSH, sIgA was higher on T6 than T1 (P = 0.049), and sAA was increased on days T1, T6, and during the follow-up (P &lt; 0.01). With RSN, sIgA remained unchanged and sAA was elevated on day T1 only (P = 0.04). Similarly, the RSH group demonstrated reduced mood on days T1, T6, and during the follow-up, while mood was lowered only on T1 with RSN (P &lt; 0.01). Conclusions: The circadian variation of sIgA and sAA activity, biomarkers of mucosal immune function, as well as mood were similar on the first day of training when repeated double-poling sprints were performed with or without hypoxia. Only with RSH did the levels of sIgA and sAA activity rise with time, becoming maximal after six training sessions, when mood was still lowered. Therefore, six sessions of RSH reduced mood, but did not impair mucosal immune function. © 2015, Springer-Verlag Berlin Heidelberg.

  • 4.
    Born, DP
    et al.
    Department of Sport Science, University of Würzburg.
    Faiss, R
    ISSUL-Department of Physiology, Faculty of Biology and Medicine, University of Lausanne, Switzerland.
    Willis, Sarah
    Mid Sweden University, Faculty of Human Sciences, Department of Health Sciences.
    Strahler, J
    University of Marburg, Clinical Biopsychology, Marburg, Germany.
    Holmberg, Hans-Christer
    Mid Sweden University, Faculty of Human Sciences, Department of Health Sciences.
    Millet, GP
    ISSUL-Department of Physiology, Faculty of Biology and Medicine, University of Lausanne, Switzerland.
    Sperlich, Billy
    Mid Sweden University, Faculty of Human Sciences, Department of Health Sciences.
    Repeated Sprint Training By Elite Cross-Country Skiers Under Hypoxic Conditions Does Not Influence Their Mucosal Immune Function To A Greater Extent Than Identical Normoxic Training2014In: Proceedings of the 19th Annual Congress of the ECSS, 2014, p. 3-Conference paper (Refereed)
  • 5.
    Cheng, Arthur J.
    et al.
    Karolinska Institutet.
    Willis, Sarah J.
    Mid Sweden University, Faculty of Human Sciences, Department of Health Sciences.
    Zinner, Christoph
    Mid Sweden University, Faculty of Human Sciences, Department of Health Sciences.
    Chaillou, Thomas
    Karolinska Institutet; Örebro universitet.
    Ivarsson, Niklas
    Karolinska Institutet.
    Ørtenblad, Niels
    University of Southern Denmark, Odense, Denmark.
    Lanner, Johanna T.
    Karolinska Institutet.
    Holmberg, Hans-Christer
    Mid Sweden University, Faculty of Human Sciences, Department of Health Sciences. Karolinska Institutet.
    Westerblad, Håkan
    Karolinska Institutet.
    Post-exercise recovery of contractile function and endurance in humans and mice is accelerated by heating and slowed by cooling skeletal muscle2017In: Journal of Physiology, ISSN 0022-3751, E-ISSN 1469-7793, Vol. 595, no 24, p. 7413-7426Article in journal (Refereed)
    Abstract [en]

    Key points: We investigated whether intramuscular temperature affects the acute recovery of exercise performance following fatigue-induced by endurance exercise. Mean power output was better preserved during an all-out arm-cycling exercise following a 2 h recovery period in which the upper arms were warmed to an intramuscular temperature of ˜ 38°C than when they were cooled to as low as 15°C, which suggested that recovery of exercise performance in humans is dependent on muscle temperature. Mechanisms underlying the temperature-dependent effect on recovery were studied in intact single mouse muscle fibres where we found that recovery of submaximal force and restoration of fatigue resistance was worsened by cooling (16-26°C) and improved by heating (36°C). Isolated whole mouse muscle experiments confirmed that cooling impaired muscle glycogen resynthesis. We conclude that skeletal muscle recovery from fatigue-induced by endurance exercise is impaired by cooling and improved by heating, due to changes in glycogen resynthesis rate.

    Manipulation of muscle temperature is believed to improve post-exercise recovery, with cooling being especially popular among athletes. However, it is unclear whether such temperature manipulations actually have positive effects. Accordingly, we studied the effect of muscle temperature on the acute recovery of force and fatigue resistance after endurance exercise. One hour of moderate-intensity arm cycling exercise in humans was followed by 2 h recovery in which the upper arms were either heated to 38°C, not treated (33°C), or cooled to ∼15°C. Fatigue resistance after the recovery period was assessed by performing 3 × 5 min sessions of all-out arm cycling at physiological temperature for all conditions (i.e. not heated or cooled). Power output during the all-out exercise was better maintained when muscles were heated during recovery, whereas cooling had the opposite effect. Mechanisms underlying the temperature-dependent effect on recovery were tested in mouse intact single muscle fibres, which were exposed to ∼12 min of glycogen-depleting fatiguing stimulation (350 ms tetani given at 10 s interval until force decreased to 30% of the starting force). Fibres were subsequently exposed to the same fatiguing stimulation protocol after 1-2 h of recovery at 16-36°C. Recovery of submaximal force (30 Hz), the tetanic myoplasmic free [Ca2+] (measured with the fluorescent indicator indo-1), and fatigue resistance were all impaired by cooling (16-26°C) and improved by heating (36°C). In addition, glycogen resynthesis was faster at 36°C than 26°C in whole flexor digitorum brevis muscles. We conclude that recovery from exhaustive endurance exercise is accelerated by raising and slowed by lowering muscle temperature.

  • 6.
    Fabré, Nicolas
    et al.
    Mid Sweden University, Faculty of Human Sciences, Department of Health Sciences.
    Mourot, Laurent
    Univ Franche Comte, Culture Sport Hlth Soc, Res Unit EA4660, F-25030 Besancon, France.
    Zoppirolli, Chiara
    Univ Verona, Dept Neurol Neuropsychol Morphol & Movement Sci, Ctr Res Mt Sport & Hlth, CeRiSM, Rovereto, Italy.
    Andersson, Erik
    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.
    Alterations in aerobic energy expenditure and neuromuscular function during a simulated cross-country skiathlon with the skating technique2015In: Human Movement Science, ISSN 0167-9457, E-ISSN 1872-7646, Vol. 40, p. 326-340Article in journal (Refereed)
    Abstract [en]

    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.

  • 7. Faiss, R
    et al.
    Cheng, AJ
    Karolinska Institute.
    Willis, Sara
    Mid Sweden University, Faculty of Human Sciences, Department of Health Sciences.
    Zinner, Christoph
    Mid Sweden University, Faculty of Human Sciences, Department of Health Sciences.
    Ivarsson, N
    Karolinska Institutet.
    Chaillou, T
    Karolinska Institutet.
    Holmberg, Hans-Christer
    Mid Sweden University, Faculty of Human Sciences, Department of Health Sciences.
    Westerblad, H
    Karolinska Institutet.
    Elevated Temperature Accelerates Recovery of Mouse and Human Skeletal Muscle Following Fatigue2015In: Abstract Book for the 20th Annual ECSS Congress, 2015Conference paper (Refereed)
    Abstract [en]

    Introduction

    This study was designed to determine whether elevated muscle temperature allows muscles to recover their force or power more rapidly following fatigue

    Methods

    Intact single fibers from mouse flexor digitorum brevis muscle were fatigued at 31˚C (70-Hz 350-ms tetani once every 10s until initial force decreased to 30%).  During a subsequent 2-hr recovery period, the fibers were perfused in Tyrode solution at either 31°C (physiological temperature) or 36°C and isometric force and cytoplasmic free [Ca2+] ([Ca2+]i) were measured during 30-Hz tetani evoked periodically.  In addition, seven human subjects performed fatiguing arm exercise consisting of 3 x 5min maximal effort arm cycling at 100 rpm followed by 4 x 15 min at an intensity of 50% of VO2peak. Then followed 2hr of recovery during which both arms were either heated or not heated at 5˚C above physiological temperatures using arm cuffs continuously perfused with temperature-regulated water; the order of heating vs. not heating was randomized between two visits. Intramuscular temperature was recorded with probes inserted 1.5 cm into the lateral head of the triceps brachii muscle. During the recovery period, subjects consumed 1.0 g/hr/kg body weight carbohydrates to support glycogen repletion. After recovery, the subjects repeated the 3 x 5 min time trials to evaluate the effect of the recovery intervention.

    Results

    Recovery from fatigue in mouse single fibers was dependent on muscle glycogen restoration since fibers perfused with glucose-free Tyrode did not recover contractile force (P<0.05). After 30 min of recovery, the tetanic [Ca2+]i was 107±10% and 92 ± 8% and the corresponding forces were 69±15% vs.49±14% of the initial values for the heated and non-heated muscles, respectively.  In seven human subjects, 2h of muscle heating also appeared to improve muscle recovery, leading to higher mean power output in the post-recovery arm cycling time trial than without muscle heating.

    Discussion

    Elevating muscle temperature by 5°C above physiological temperature accelerates recovery in mouse muscle in-vitro and in human skeletal muscle in-vivo and this appears to depend on faster muscle glycogen resynthesis following fatigue.

  • 8.
    Faiss, R.
    et al.
    Institute of Sport Sciences, University of Lausanne, Lausanne, Switzerland.
    Willis, Sarah
    Mid Sweden University, Faculty of Human Sciences, Department of Health Sciences.
    Born, D. -P
    Department of Sport Science, University of Wuppertal, Wuppertal, Germany.
    Sperlich, B.
    Department of Sport Science, University of Wuppertal, Wuppertal, Germany.
    Vesin, J. -M
    Applied Signal Processing Group, Swiss Federal Institute of Technology, Ecole Polytechnique Fédérale de Lausanne, Lausanne, Switzerland .
    Holmberg, Hans-Christer
    Mid Sweden University, Faculty of Human Sciences, Department of Health Sciences.
    Millet, G. P.
    Institute of Sport Sciences, University of Lausanne, Lausanne, Switzerland .
    Repeated double-poling sprint training in hypoxia by competitive cross-country skiers2015In: Medicine & Science in Sports & Exercise, ISSN 0195-9131, E-ISSN 1530-0315, Vol. 47, no 4, p. 809-817Article in journal (Refereed)
    Abstract [en]

    Purpose: Repeated-sprint training in hypoxia (RSH) was recently shown to improve repeated-sprint ability (RSA) in cycling. This phenomenon is likely to reflect fiber type-dependent, compensatory vasodilation, and therefore, our hypothesis was that RSH is even more beneficial for activities involving upper body muscles, such as double poling during cross-country skiing. Methods: In a double-blinded fashion, 17 competitive cross-country skiers performed six sessions of repeated sprints (each consisting of four sets of five 10-s sprints, with 20-s intervals of recovery) either in normoxia (RSN, 300 m; FiO2, 20.9%; n = 8) or normobaric hypoxia (RSH, 3000 m; FiO2, 13.8 %; n = 9). Before (pre) and after (post) training, performance was evaluated with an RSA test (10-s all-out sprints-20-s recovery, until peak power output declined by 30%) and a simulated team sprint (team sprint, 3×3-min all-out with 3-min rest) on a double-poling ergometer. Triceps brachii oxygenation was measured by near-infrared spectroscopy. Results: From pretraining to posttraining, peak power output in the RSA was increased (P < 0.01) to the same extent (29% ± 13% vs 26% ± 18%, nonsignificant) in RSH and in RSN whereas the number of sprints performed was enhanced in RSH (10.9 ± 5.2 vs 17.1 ± 6.8, P < 0.01) but not in RSN (11.6 T 5.3 vs 11.7 ± 4.3, nonsignificant). In addition, the amplitude in total hemoglobin variations during sprints throughout RSA rose more in RSH (P < 0.01). Similarly, the average power output during all team sprints improved by 11% T 9% in RSH and 15% T 7% in RSN. Conclusions: Our findings reveal greater improvement in the performance of repeated double-poling sprints, together with larger variations in the perfusion of upper body muscles in RSH compared with those in RSN. © 2014 by the American College of Sports Medicine.

  • 9.
    Gejl, K. D.
    et al.
    Univ Southern Denmark, SDU Muscle Res Cluster, Dept Sports Sci & Clin Biomech, Campusvej 55, DK-5230 Odense M, Denmark.
    Hvid, L. G.
    Univ Southern Denmark, SDU Muscle Res Cluster, Dept Sports Sci & Clin Biomech, Campusvej 55, DK-5230 Odense M, Denmark.
    Willis, Sarah J.
    Mid Sweden University, Faculty of Human Sciences, Department of Health Sciences.
    Andersson, Erik
    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. Swedish Olympic Comm, Stockholm, Sweden.
    Jensen, R.
    Univ Southern Denmark, SDU Muscle Res Cluster, Dept Sports Sci & Clin Biomech, Campusvej 55, DK-5230 Odense M, Denmark.
    Frandsen, U.
    Univ Southern Denmark, SDU Muscle Res Cluster, Dept Sports Sci & Clin Biomech, Campusvej 55, DK-5230 Odense M, Denmark.
    Hansen, J.
    Rigshosp, Ctr Inflammat & Metab, Dept Infect Dis, DK-2100 Copenhagen, Denmark.
    Plomgaard, P.
    Rigshosp, Ctr Inflammat & Metab, Dept Infect Dis, DK-2100 Copenhagen, Denmark.
    Ortenblad, N.
    Univ Southern Denmark, SDU Muscle Res Cluster, Dept Sports Sci & Clin Biomech, Campusvej 55, DK-5230 Odense M, Denmark.
    Repeated high-intensity exercise modulates Ca2+ sensitivity of human skeletal muscle fibers2016In: Scandinavian Journal of Medicine and Science in Sports, ISSN 0905-7188, E-ISSN 1600-0838, Vol. 26, no 5, p. 488-497Article in journal (Refereed)
    Abstract [en]

    The effects of short-term high-intensity exercise on single fiber contractile function in humans are unknown. Therefore, the purposes of this study were: (a) to access the acute effects of repeated high-intensity exercise on human single muscle fiber contractile function; and (b) to examine whether contractile function was affected by alterations in the redox balance. Eleven elite cross-country skiers performed four maximal bouts of 1300m treadmill skiing with 45min recovery. Contractile function of chemically skinned single fibers from triceps brachii was examined before the first and following the fourth sprint with respect to Ca2+ sensitivity and maximal Ca2+-activated force. To investigate the oxidative effects of exercise on single fiber contractile function, a subset of fibers was incubated with dithiothreitol (DTT) before analysis. Ca2+ sensitivity was enhanced by exercise in both MHC I (17%, P<0.05) and MHC II (15%, P<0.05) fibers. This potentiation was not present after incubation of fibers with DTT. Specific force of both MHC I and MHC II fibers was unaffected by exercise. In conclusion, repeated high-intensity exercise increased Ca2+ sensitivity in both MHC I and MHC II fibers. This effect was not observed in a reducing environment indicative of an exercise-induced oxidation of the human contractile apparatus.

  • 10. Heil, D
    et al.
    Willis, Sarah
    Mid Sweden University, Faculty of Human Sciences, Department of Health Sciences.
    Determinants of both classic and skate cross country ski performance in competitive junior and collegiate skiers2012In: Science and Skiing V / [ed] Erich Muller, Stefan Lindinger, Thomas Stöggl, Meyer & Meyer Sport, 2012, p. 513-522Chapter in book (Refereed)
  • 11.
    Heil, D.P.
    et al.
    Montana State University.
    Willis, Sarah
    Montana State University.
    Determinants of both classic and skate cross country ski performance in competitive junior and collegiate skiers2010In: Science and Skiing VArticle, book review (Refereed)
  • 12.
    Hoppe, Matthias W.
    et al.
    Berg Univ Wuppertal, Res Ctr Performance Diagnost & Training Advice, D-42097 Wuppertal, Germany .
    Baumgart, Christian
    Berg Univ Wuppertal, Res Ctr Performance Diagnost & Training Advice, D-42097 Wuppertal, Germany .
    Sperlich, Billy
    Berg Univ Wuppertal, Res Ctr Performance Diagnost & Training Advice, D-42097 Wuppertal, Germany .
    Ibrahim, Hassan
    Berg Univ Wuppertal, Res Ctr Performance Diagnost & Training Advice, D-42097 Wuppertal, Germany .
    Jansen, Christian
    Berg Univ Wuppertal, Res Ctr Performance Diagnost & Training Advice, D-42097 Wuppertal, Germany .
    Willis, Sarah J.
    Mid Sweden University, Faculty of Human Sciences, Department of Health Sciences.
    Freiwald, Juergen
    Berg Univ Wuppertal, Res Ctr Performance Diagnost & Training Advice, D-42097 Wuppertal, Germany .
    COMPARISON BETWEEN THREE DIFFERENT ENDURANCE TESTS IN PROFESSIONAL SOCCER PLAYERS2013In: Journal of Strength and Conditioning Research, ISSN 1064-8011, E-ISSN 1533-4287, Vol. 27, no 1, p. 31-37Article in journal (Refereed)
    Abstract [en]

    Hoppe, MW, Baumgart, C, Sperlich, B, Ibrahim, H, Jansen, C, Willis, SJ, and Freiwald, J. Comparison between three different endurance tests in professional soccer players. J Strength Cond Res 27(1): 31-37, 2013-The aims of this study were (a) to assess and correlate interval shuttle run test (ISRT) performance, maximum oxygen uptake ((V) over dotO(2)max), running economy (RE), running velocity at the first rise in blood lactate concentrations above baseline (vLT) and running velocity at 4 mmol.L-1 blood lactate concentration (v4) in professional soccer players and (b) to investigate whether a correlation exists between the respective results of time to exhaustion (T-lim) from continuous and intermittent endurance tests, respectively. Eleven male professional field soccer players (mean +/- SD: age 23.8 +/- 3.0 years, (V) over dotO(2)max 58.2 +/- 4.9 ml.kg(-1).min(-1)) completed a continuous Incremental Test with lactate measurements to determine vLT and v4, a continuous Ramp Test with gas exchange analysis to determine (V) over dotO(2)max and RE, and an intermittent ISRT to determine intermittent endurance capacity during the first week of preseason preparation. There were significant correlations between ISRT performance and (V) over dotO(2)max (r = 0.70, p < 0.05), and between T-lim in both continuous endurance tests (r = 0.89, p < 0.01). Between all other variables no significant correlations were found overall (best r = 0.60, p > 0.05). The assessment of all values of (V) over dotO(2)max, RE, vLT, and v4 should be included when investigating aerobic endurance performance among groups or over time in professional soccer players. Although (V) over dotO(2)max, RE, vLT, and v4 have been regarded as important factors of aerobic performance in endurance related sports, the present data revealed that (V) over dotO(2)max was the only factor, which correlated with intermittent endurance capacity in professional soccer players. Hence, (V) over dotO(2)max should be increased through soccer-specific training interventions including universal agility components. The T-lim in continuous and intermittent endurance tests differs and is therefore an independent endurance performance factor in professional soccer players.

  • 13.
    Hébert-Losier, Kim
    et al.
    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.
    The reproducibility of three different indicators of fatigue from plantar- flexion isokinetic testing at two knee flexion angles is not sufficient to be termed 'acceptable'2013In: Isokinetics and exercise science, ISSN 0959-3020, E-ISSN 1878-5913, Vol. 21, no 3, p. 227-236Article in journal (Refereed)
    Abstract [en]

    OBJECTIVE: To characterize the reproducibility of three indicators of fatigue (FIs) specific to concentric plantar-flexion isokinetic testing at knee flexion (KF) angles of 0 degrees (straight) and 45 degrees (bent). METHODS: On two separate days one week apart, thirty-four males performed 50 consecutive maximal concentric isokinetic plantar-flexion contractions at 60 degrees/s with 0 degrees and 45 degrees of KF. Differences in the pre- and post-maximal voluntary isometric contraction torques (FIstatic), powers during the initial five and last five isokinetic contractions (FIdynamic) and powers during the 50 isokinetic contractions (FIslope) were used as FIs. Changes in means, intra-class correlation coefficients (ICCs) and coefficients of variations (CVs) were computed to quantify the reproducibility of the FIs. Comparisons were made between the two KF angles and three FIs using two-way repeated measures ANOVA. RESULTS: For both KF angles and three FIs, ICCs ranged from 0.52 to 0.71 and CVs from 10.0 to 29.3%. The CVs from the two isokinetic-based FIs were lower than those from the isometric FI and a trend towards larger ICCs at 0 degrees was observed. CONCLUSIONS: The reproducibility of the three FIs was not sufficient to be termed 'acceptable'. The FIslope and FIdynamic were more reproducible than FIstatic and are recommended - with the knee straight rather than bent - until more reliable indicators become available.

  • 14.
    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)
  • 15.
    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)
  • 16.
    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.

  • 17.
    Kazior, Zuzanna
    et al.
    Mid Sweden University, Faculty of Human Sciences, Department of Health Sciences.
    Willis, Sarah
    Mid Sweden University, Faculty of Human Sciences, Department of Health Sciences.
    Calbet, JAL
    Holmberg, Hans-Christer
    Mid Sweden University, Faculty of Human Sciences, Department of Health Sciences.
    Blomstrand, E
    Effect of concurrent endurance and strength training on MAFbx and MuRF-1 expression2012Conference paper (Refereed)
  • 18.
    Kazior, Zuzanna
    et al.
    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.
    Moberg, Marcus
    Swedish Sch Sport & Hlth Sci, Stockholm, Sweden.
    Apro, William
    Swedish Sch Sport & Hlth Sci, Stockholm, Sweden.
    Calbet, Jose A. L.
    Univ Las Palmas Gran Canaria, Dept Phys Educ, Las Palmas Gran Canaria, Spain.
    Holmberg, Hans-Christer
    Mid Sweden University, Faculty of Human Sciences, Department of Health Sciences.
    Blomstrand, Eva
    Swedish Sch Sport & Hlth Sci, Stockholm, Sweden.
    Endurance Exercise Enhances the Effect of Strength Training on Muscle Fiber Size and Protein Expression of Akt and mTOR2016In: PLoS ONE, ISSN 1932-6203, E-ISSN 1932-6203, Vol. 11, no 2, article id e0149082Article in journal (Refereed)
    Abstract [en]

    Reports concerning the effect of endurance exercise on the anabolic response to strength training have been contradictory. This study re-investigated this issue, focusing on training effects on indicators of protein synthesis and degradation. Two groups of male subjects performed 7 weeks of resistance exercise alone (R; n = 7) or in combination with preceding endurance exercise, including both continuous and interval cycling (ER; n = 9). Muscle biopsies were taken before and after the training period. Similar increases in leg-press 1 repetition maximum (30%; P< 0.05) were observed in both groups, whereas maximal oxygen uptake was elevated (8%; P< 0.05) only in the ER group. The ER training enlarged the areas of both type I and type II fibers, whereas the R protocol increased only the type II fibers. The mean fiber area increased by 28% (P< 0.05) in the ER group, whereas no significant increase was observed in the R group. Moreover, expression of Akt and mTOR protein was enhanced in the ER group, whereas only the level of mTOR was elevated following R training. Training-induced alterations in the levels of both Akt and mTOR protein were correlated to changes in type I fiber area (r = 0.55-0.61, P< 0.05), as well as mean fiber area (r = 0.55-0.61, P< 0.05), reflecting the important role played by these proteins in connection with muscle hypertrophy. Both training regimes reduced the level of MAFbx protein (P< 0.05) and tended to elevate that of MuRF-1. The present findings indicate that the larger hypertrophy observed in the ER group is due more to pronounced stimulation of anabolic rather than inhibition of catabolic processes.

  • 19.
    Larsen, Filip J.
    et al.
    Swedish Sch Sport & Hlth Sci, Stockholm, Sweden.
    Schiffer, Tomas A.
    Karolinska Inst, Dept Physiol & Pharmacol, SE-17177 Stockholm, Sweden.
    Örtenblad, Niels
    Univ Southern Denmark, Inst Sports Sci & Clin Biomech, Muscle Res Cluster, Odense, Denmark.
    Zinner, Christoph
    Mid Sweden University, Faculty of Human Sciences, Department of Health Sciences. Univ Wurzburg, Dept Sport Sci, D-97070 Wurzburg, Germany.
    Morales-Alamo, David
    Res Inst Biomed & Hlth Sci IUIBS, Las Palmas Gran Canaria, Canary Islands, Spain.
    Willis, Sarah J.
    Mid Sweden University, Faculty of Human Sciences, Department of Health Sciences.
    Calbet, Jose A.
    Res Inst Biomed & Hlth Sci IUIBS, Las Palmas Gran Canaria, Canary Islands, Spain.
    Holmberg, Hans-Christer
    Mid Sweden University, Faculty of Human Sciences, Department of Health Sciences.
    Boushel, Robert
    Univ British Columbia, Sch Kinesiol, Vancouver, BC V5Z 1M9, Canada.
    High-intensity sprint training inhibits mitochondrial respiration through aconitase inactivation2016In: The FASEB Journal, ISSN 0892-6638, E-ISSN 1530-6860, Vol. 30, no 1, p. 417-427Article in journal (Refereed)
    Abstract [en]

    Intense exercise training is a powerful stimulus that activates mitochondrial biogenesis pathways and thus increases mitochondrial density and oxidative capacity. Moderate levels of reactive oxygen species (ROS) during exercise are considered vital in the adaptive response, but high ROS production is a serious threat to cellular homeostasis. Although biochemical markers of the transition from adaptive to maladaptive ROS stress are lacking, it is likely mediated by redox sensitive enzymes involved in oxidative metabolism. One potential enzyme mediating such redox sensitivity is the citric acid cycle enzyme aconitase. In this study, we examined biopsy specimens of vastus lateralis and triceps brachii in healthy volunteers, together with primary human myotubes. An intense exercise regimen inactivated aconitase by 55-72%, resulting in inhibition of mitochondrial respiration by 50-65%. In the vastus, the mitochondrial dysfunction was compensated for by a 15-72% increase in mitochondrial proteins, whereas H2O2 emission was unchanged. In parallel with the inactivation of aconitase, the intermediary metabolite citrate accumulated and played an integral part in cellular protection against oxidative stress. In contrast, the triceps failed to increase mitochondrial density, and citrate did not accumulate. Instead, mitochondrial H2O2 emission was decreased to 40% of the pretraining levels, together with a 6-fold increase in protein abundance of catalase. In this study, a novel mitochondrial stress response was highlighted where accumulation of citrate acted to preserve the redox status of the cell during periods of intense exercise.

  • 20.
    Mourot, L.
    et al.
    Clinical Investigation Centre in Technologic Innovation, INSERM CIT808, University Hospital of Besançon, France .
    Fabre, Nicolas
    Mid Sweden University, Faculty of Human Sciences, Department of Health Sciences.
    Andersson, Erik
    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.
    Hébert-Losier, Kim
    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. Swedish Olymp Comm, Stockholm, Sweden.
    Impact of the initial classic section during a simulated cross-country skiing skiathlon on the cardiopulmonary responses during the subsequent period of skate skiing2014In: Applied Physiology, Nutrition and Metabolism, ISSN 1715-5320, Vol. 39, no 8, p. 911-919Article in journal (Refereed)
    Abstract [en]

    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.

  • 21.
    Mourot, Laurent
    et al.
    EA4660 and Exercise Performance, Health, Innovation Platform, University of Franche-Comté, Besançon, France.
    Fabre, Nicolas
    Mid Sweden University, Faculty of Human Sciences, Department of Health Sciences.
    Andersson, Erik
    Mid Sweden University, Faculty of Human Sciences, Department of Health Sciences.
    Willis, Sarah
    Mid Sweden University, Faculty of Human Sciences, Department of Health Sciences.
    Buchheit, Martin
    Dept of Sport Science, Myorobie Association, Montvalezan, France .
    Holmberg, Hans-Christer
    Mid Sweden University, Faculty of Human Sciences, Department of Health Sciences.
    Cross-Country Skiing and Postexercise Heart-Rate Recovery2015In: International Journal of Sports Physiology and Performance, ISSN 1555-0265, E-ISSN 1555-0273, Vol. 10, no 1, p. 11-16Article in journal (Refereed)
    Abstract [en]

    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.

  • 22. Seifert, J
    et al.
    Portmann, J
    Heil, D
    Willis, Sarah
    Mid Sweden University, Faculty of Human Sciences, Department of Health Sciences.
    Energy expenditure of professional ski patrollers during patient transport2012In: Science and Skiing V / [ed] Erich Muller, Stefan Lindinger, Thomas Stöggl, Meyer & Meyer Sport, 2012, p. 394-400Chapter in book (Refereed)
  • 23.
    Seifert, J.G.
    et al.
    Montana State University.
    Portmann, J
    Montana State University.
    Heil, D.P.
    Montana State University.
    Willis, Sarah
    Montana State University.
    Energy expenditure of professional ski patrollers during patient transport2010In: Science and Skiing VArticle in journal (Refereed)
  • 24.
    Sjökvist, Jesper
    et al.
    Mid Sweden University, Faculty of Human Sciences, Department of Health Sciences. Swedish Olymp Comm, Stockholm, Sweden.
    Sandbakk, O.
    Norwegian Univ Sci & Technol, Dept Neurosci, Ctr Elite Sports Res, N-7034 Trondheim, Norway.
    Willis, Sara J.
    Mid Sweden University, Faculty of Human Sciences, Department of Health Sciences.
    Andersson, Erik
    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. Swedish Olymp Comm, Stockholm, Sweden.
    The effect of incline on sprint and bounding performance in cross-country skiers2015In: Journal of Sports Medicine and Physical Fitness, ISSN 0022-4707, E-ISSN 1827-1928, Vol. 55, no 5, p. 405-414Article in journal (Refereed)
    Abstract [en]

    Aim. Aim of the present study was to investigate performance and kinematics of cross-country skiers during sprint running and bounding on different inclines, in relationship to maximal strength, power and skiing performance. Methods. On day one, the maximal strength of 14 elite skiers was tested using a mid-thigh isometric pull and maximal relative leg power determined using squat and countermovement jumps. Day two involved 15-m maximal sprints and 5-step bounding at 0 degrees, 7.5 degrees and 15 degrees inclines. From video recordings sprint, step, contact and flight times; step length and frequency; total number of sprint steps and average bounding velocity were determined. Skiing performance was assessed using International Ski Federation (FIS) points from the preceding season and compared to strength, power, bounding and sprint performance, and kinematics. Results. On steeper inclines sprint time was higher and bounding distance shorter (both P<0.001), and step frequency during sprinting and bounding, reduced and increased respectively (P<0.001). Isometric maximal strength correlated strongly with bounding distance on the two steeper inclines (r=0.76 and 0.83). Squat and countermovement jump heights correlated moderately with sprint performance at both 7 degrees and 15 degrees, and bounding performance on all three inclines (r=0.55-0.65). The distance bounded uphill correlated moderately with FIS points (r=-0.55 and -0.67). Conclusion. Incline influenced sprinting and bounding performance and kinematics. Maximal leg power is important for both sprinting and bounding uphill, while maximal strength is important for the latter. The skiers with better FIS rankings bounded farther on steeper inclines, suggesting that this capacity is beneficial for cross-country skiing performance.

  • 25.
    Sjökvist, Jesper
    et al.
    Mid Sweden University, Faculty of Human Sciences, Department of Health Sciences.
    Sandbakk, Ø
    Willis, Sarah
    Mid Sweden University, Faculty of Human Sciences, Department of Health Sciences.
    Andersson, Erik
    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.
    Effect of different inclines on sprinting, bounding, and one-leg hopping performance in endurance-trained athletes2012In: Book of Abstracts of the 17th Annual Congress of the European College of Sport Science in Bruges, Belgium from 4-7 July 2012. / [ed] Meeusen, R., Duchateau, J., Roelands, B., Klass, M., De Geus, B., Baudry, S., Tsolakidis, E., 2012, p. 288-289Conference paper (Refereed)
  • 26.
    Stöggl, Thomas
    et al.
    Mid Sweden University, Faculty of Human Sciences, Department of Health Sciences.
    Bishop, Phil
    University of Alabama, AL, USA.
    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.
    Physiological and biomechanical response to rifle carriage in elite biathletes2013In: Proceedings for the 6th International Congress on Science and Skiing / [ed] Erich Mueller, Josef Kröll, Stefan Josef Lindinger, Jurgen Pfusterschmied, Thomas Stöggl, 2013, p. 81-Conference paper (Refereed)
  • 27.
    Stöggl, Thomas
    et al.
    Mid Sweden University, Faculty of Human Sciences, Department of Health Sciences. Department of Sport Science and Kinesiology, University of Salzburg, Salzburg, Austria .
    Bishop, Phillip
    Department of Exercise Science and Kinesiology, University of Alabama, Tuscaloosa, AL, United States .
    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. Swedish Olympic Committee, Stockholm, Sweden .
    Effect of carrying a rifle on physiology and biomechanical responses in biathletes2015In: Medicine & Science in Sports & Exercise, ISSN 0195-9131, E-ISSN 1530-0315, Vol. 47, no 3, p. 617-624Article in journal (Refereed)
    Abstract [en]

    Purpose: This study aimed to assess the effect of carrying a rifle on the physiological and biomechanical responses of well-trained biathletes. Methods: Ten elite biathletes (five men and five women) performed ski skating with (R) or without a rifle (NR) on a treadmill using the V2 (5- incline) and V1 techniques (8-) at 8 and 6 kmIhj1, respectively, as well as at racing intensity (approximately 95% of peak oxygen uptake (VO2peak), 10.7 T 0.8 and 7.7 T 0.9 kmIhj1, respectively). VO2, ventilation (VE), HR, blood lactate concentration (BLa), and cycle characteristics as well as pole and leg kinetics were evaluated during these trials. Results: Metabolic data were all higher for R than for NR, as follows:VO2, +2.5%;VE, +8.1%; RER, +4.2%; all P G 0.001; HR, +1.7%; and BLa, +15.1%; both P G 0.05. Biomechanically, carrying a rifle reduced cycle time and length, poling and arm swing times, and leg ground contact time and increased cycle rate, the peak and impulse of leg force, average cycle force, and impulse of forefoot force (all P G 0.05). With the exception of elevated pole forces when V2 skating at racing velocity, there were no differences between the peak and impulse of pole force. The difference inVE between R and NR was greater for the women than that for men (P G 0.05), and the difference in BLa also tended to be larger for the women (P G 0.1). Conclusions: Carrying a rifle elevated physiological responses, accelerated cycle rate, and involved greater leg work, with no differences between the V1 and V2 techniques.

  • 28.
    Willis, Sarah
    et al.
    Mid Sweden University, Faculty of Human Sciences, Department of Health Sciences.
    Heil, D
    Can sprint skiing on an indoor track predict on-snow skate sprint performance in competitive skiers?2012In: Science and Skiing V / [ed] Erich Muller, Stefan Lindinger, Thomas Stöggl, Meyer & Meyer Sport, 2012, p. 588-595Chapter in book (Refereed)
  • 29.
    Willis, Sarah
    et al.
    Montana State University.
    Heil, D.P.
    Montana State University.
    Can sprint skiing on an indoor track predict on-snow skate sprint performance in competitive skiers?2010In: Science and Skiing VArticle in journal (Refereed)
  • 30.
    Willis, Sarah J
    et al.
    Mid Sweden University, Faculty of Human Sciences, Department of Health Sciences.
    Hébert-Losier, Kim
    Mid Sweden University, Faculty of Human Sciences, Department of Health Sciences.
    Andersson, Erik
    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.
    Ørtenblad, Niels
    Mid Sweden University, Faculty of Human Sciences, Department of Health Sciences.
    DOUBLE POLING MUSCLE ACTIVATION AND FATIGUE DURING A SIMULATED CLASSIC SPRINT CROSS-COUNTRY SKIING COMPETITION2013In: Proceedings for the 6th International Congress on Science and Skiing / [ed] Erich Mueller, Josef Kröll, Stefan Josef Lindinger, Jurgen Pfusterschmied, Thomas Stöggl, 2013, p. 16-16Conference paper (Refereed)
  • 31.
    Willis, Sarah J.
    et al.
    Mid Sweden University, Faculty of Human Sciences, Department of Health Sciences.
    Sjökvist, Jesper
    Mid Sweden University, Faculty of Human Sciences, Department of Health Sciences.
    Sandbakk, Øyvind
    Andersson, Erik
    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.
    BOUNDING ADAPTATIONS AT DIFFERENT INCLINES IN ELITE CROSS-COUNTRY SKIERS2012In: / [ed] Anni Hakkarainen, Stefan Lindinger and Vesa Linnamo, 2012, p. 58-59Conference paper (Refereed)
  • 32.
    Zinner, Christoph
    et al.
    Mid Sweden University, Faculty of Human Sciences, Department of Health Sciences. Univ Wurzburg, Dept Sport Sci, Wurzburg, Germany.
    Morales-Alamo, David
    Univ Las Palmas Gran Canaria, Las Palmas Gran Canaria, Spain.
    Örtenblad, Niels
    Mid Sweden University, Faculty of Human Sciences, Department of Health Sciences. Univ Southern Denmark, Inst Sports Sci & Clin Biomech, Odense, Denmark.
    Larsen, Filip J.
    Swedish Sch Sport & Hlth Sci, Stockholm.
    Schiffer, Tomas A.
    Linköping Univ, Dept Med & Hlth Sci, Linköping.
    Willis, Sarah J.
    Mid Sweden University, Faculty of Human Sciences, Department of Health Sciences.
    Gelabert-Rebato, Miriam
    Univ British Columbia, Sch Kinesiol, Vancouver, BC, Canada.
    Perez-Valera, Mario
    Univ Las Palmas Gran Canaria, Las Palmas Gran Canaria, Spain.
    Boushel, Robert
    Univ British Columbia, Sch Kinesiol, Vancouver, BC, Canada.
    Calbet, Jose A. L.
    Univ British Columbia, Sch Kinesiol, Vancouver, BC, Canada; Univ Las Palmas Gran Canaria, Las Palmas Gran Canaria, Spain.
    Holmberg, Hans-Christer
    Mid Sweden University, Faculty of Human Sciences, Department of Health Sciences. Univ British Columbia, Sch Kinesiol, Vancouver, BC, Canada; UiT Arctic Univ Norway, Sch Sport Sci, Tromso, Norway.
    The Physiological Mechanisms of Performance Enhancement with Sprint Interval Training Differ between the Upper and Lower Extremities in Humans2016In: Frontiers in Physiology, ISSN 1664-042X, E-ISSN 1664-042X, Vol. 7, no SEP, article id 426Article in journal (Refereed)
    Abstract [en]

    To elucidate the mechanisms underlying the differences in adaptation of arm and leg muscles to sprint training, over a period of 11 days 16 untrained men performed six sessions of 4-6 x 30-s all-out sprints (SIT) with the legs and arms, separately, with a 1-h interval of recovery. Limb-specific VO(2)peak, sprint performance (two 30-s Wingate tests with 4-min recovery), muscle efficiency and time-trial performance (TT, 5-min all-out) were assessed and biopsies from the m. vastus lateralis and m. triceps brachii taken before and after training. VO(2)peak and Wmax increased 3-11% after training, with a more pronounced change in the arms (P < 0.05). Gross efficiency improved for the arms (+8.8%, P < 0.05), but not the legs (-0.6%). Wingate peak and mean power outputs improved similarly for the arms and legs, as did TT performance. After training, VO2 during the two Wingate tests was increased by 52 and 6% for the arms and legs, respectively (P < 0.001). In the case of the arms, VO2 was higher during the first than second Wingate test (64 vs. 44%, P < 0.05). During the TT, relative exercise intensity, HR, VO2, VCO2, V-E, and V-t were all lower during arm-cranking than leg-pedaling, and oxidation of fat was minimal, remaining so after training. Despite the higher relative intensity, fat oxidation was 70% greater during leg-pedaling (P = 0.017). The aerobic energy contribution in the legs was larger than for the arms during the Wingate tests, although VO2 for the arms was enhanced more by training, reducing the O-2 deficit after SIT. The levels of muscle glycogen, as well as the myosin heavy chain composition were unchanged in both cases, while the activities of 3-hydroxyacyl-CoA-dehydrogenase and citrate synthase were elevated only in the legs and capillarization enhanced in both limbs. Multiple regression analysis demonstrated that the variables that predict TT performance differ for the arms and legs. The primary mechanism of adaptation to SIT by both the arms and legs is enhancement of aerobic energy production. However, with their higher proportion of fast muscle fibers, the arms exhibit greater plasticity.

  • 33.
    Zinner, Christoph
    et al.
    Mid Sweden University, Faculty of Human Sciences, Department of Health Sciences.
    Willis, Sara
    Mid Sweden University, Faculty of Human Sciences, Department of Health Sciences.
    Morales-Alamo, D
    U of Las Palmas de Gran Canaria.
    Larsen, F
    Karolinska Institutet.
    Schiffer, T
    Karolinska Institutet.
    Boushel, R
    Gymnastik och Idrottshögskolan i Stockholm.
    Örtenblad, Niels
    Mid Sweden University, Faculty of Human Sciences, Department of Health Sciences. Syddanskt Universitet.
    Calbet, J
    U of Las Palmas de Gran Canaria.
    Holmberg, Hans-Christer
    Mid Sweden University, Faculty of Human Sciences, Department of Health Sciences.
    Sprint interval training or arms and legs elevates peak VO2 and improves arm exercise economy2015Conference paper (Refereed)
    Abstract [en]

    Introduction

    Interval cycle sprint training (SIT) has been shown to improve anaerobic capacity, VO2max and biomarkers of muscle oxidative capacity in as little as 2 weeks in previously untrained adults. The present study was designed to characterize and compare systemic VO2 and exercise performance after SIT engaging the arms and legs.

     

    Methods

    Sixteen healthy, untrained men (23.9 ± 3.7 yrs; 183.8 ± 6.8 cm; 80.3 ± 14.1 kg) performed six sessions of 4-6x30 sec all-out sprints with the legs then arms (or vice versa) separated by a 1-h recovery over an 11-day period. Limb-specific VO2peak, anaerobic capacity (2x30-sec Wingate tests with 4 min of recovery), a 4-min submaximal work economy test, and a 5-min all-out time trial (TT) were conducted before and after the training program. Muscle biopsies (from the m. vastus lateralis and m. triceps brachii) were taken before and after the training period.

     

    Results

    VO2peak increased by 10.6% and 5.9% with arm and leg training, respectively (p<0.05), with the increase in the arms significantly greater than in the legs (p=0.02). Work economy was improved for the arms (-9.8%, p<0.05), but not for the legs (-0.9%). Mean power during the TT rose by 13.5% for the arms and 11.8% for the legs (p<0.05). Peak power output and mean power during the two Wingate tests were elevated in both the arms (PPO: 6.7% (p<0.01) and 13.3% (p<0.01); MPO: 6.1% (p<0.01) and 8.4% (p<0.01)) and legs (PPO: 3.1% (p=0.07) and 7.1% (p=0.02); MPO: 3.3% (p<0.01) and 5.6% (p<0.01)). The activity of 3-hydroxyacyl-CoA dehydrogenase (HAD) and levels of muscle glycogen were unchanged in both limbs.

     

    Discussion

    Sprint interval training with arm or leg cycling exercise increased peak pulmonary VO2 during their respective modes over an 11-day training period with a greater increase in the arms. Sprint performance rose to a similar extent in both extremities, yet work economy was improved only in the arms. These findings suggest some limb-specific responsiveness to SIT training.

  • 34.
    Zinner, Christoph
    et al.
    Mid Sweden University, Faculty of Human Sciences, Department of Health Sciences.
    Willis, Sarah
    Mid Sweden University, Faculty of Human Sciences, Department of Health Sciences.
    Jonsson, Malin
    Mid Sweden University, Faculty of Human Sciences, Department of Health Sciences.
    Sperlich, Billy
    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.
    Heart rate responses during biathlon races of different lengths in elite athletes2014In: Science & Skiing VI / [ed] Erich Muller, Josef Kroll, Stefan Lindinger, Meyer & Meyer Sport, 2014, p. 483-494Chapter in book (Refereed)
  • 35.
    Örtenblad, Niels
    et al.
    Mid Sweden University, Faculty of Human Sciences, Department of Health Sciences.
    Hvid, Lars G
    University of Southern Denmark, Odense, Denmark.
    Jensen, Rasmus
    University of Southern Denmark, Odense, Denmark.
    Andersson, Erik
    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.
    Gejl, Kasper D
    University of Southern Denmark, Odense, Denmark.
    Repeated sprint exercise impairs contractile force of isolated single human muscle fibers2013In: Proceedings for the 6th International Congress on Science and Skiing / [ed] Erich Mueller, Josef Kröll, Stefan Josef Lindinger, Jurgen Pfusterschmied, Thomas Stöggl, 2013, p. 93-Conference paper (Refereed)
    Abstract [en]

    INTRODUCTION: The purpose of the present study was, to examine the effects of repeated sprint skiing on the contractile apparatus of single muscle fibres obtained from a group of elite skiers. We have recently demonstrated that prolonged cycling exercise impairs the contractile apparatus of single muscle fibres, and that this can be restored following recovery. However, little is known about the effect of repeated high intensity exercise on single fibre properties, as i.e. during cross-country (cc) sprint competitions. We hypothesize that repeated high intensity exercise in highly trained subjects will impair the contractile apparatus maximum force output.

    METHOD: Eleven elite male sprint talented cc skiers (age 24 ± 4 years; VO2max 5.1 ± 0.5 (diagonal skiing, DIA), 4.9 ± 0.5 (double pooling, DP) L·min-1)) volunteered for the study. The skiers performed a simulated intermittent classic sprint roller skiing competition on a treadmill. The sprint exercise included 4 times1300m, with 45 min recovery between sprints. Each sprint consisted of 3 DP sections (1° uphill) and 2 DIA sections (7° uphill). Muscle biopsies were obtained in arm muscle (m. biceps brachii) before and after the sprint exercises. Muscle fibre bundles were cooled and skinned in a glycerinating solution and stored until analyzed. Single muscle fibre segments (n=232) were isolated and attached to a sensitive force recording transducer, and activated by Ca2+ buffered solutions at pH 7.1 to measure mechanically properties (maximum force Po and Po/cross sectional area (CSA)) and fibre typed by the Sr2+ sensitivity (Hvid et al. 2013).

    RESULTS: Average sprint time was 3min 49s ± 9s, with no difference between sprints. A total of 232 fibres were analysed (150 type I and 82 type II fibres). Type II fibres had a sign. (P<0.05) higher CSA (8103 ± 2334 µm2 (type I) and 8852 ± 2288 µm2 (type II) and Po (0.82 ± 0.43 and 1.24 ± 0.50 mN) than type I fibres. Also type II fibres had a 31% higher Po/CSA (108 ± 55 vs 142 ± 45 kN/m2). Following the intermittent sprint exercise, type II fibres exhibited a sign. (P = 0.01) 20% decrease in Po, with no difference in type I fibres. To test if the decrease in the single fibre Po were associated with oxidative stress we tested if this could be reversed with a strong reducing agent (dithiothreitol, DTT). DTT did not alter Po at pre nor the decrease in type II fibres following sprint exercise.

    DISCUSSION: By using a translational approach from whole body exercise to single fibre measurements, we here we demonstrate that type II fibres from highly trained cross country skiers, has a 20% decrease in Po following repeated sprint. Thus, part of the experienced fatigue following sprint competitions is due to impairments at the level of the contractile apparatus. Further, we did not find any evidence for oxidative stress as a causative component in the observed decrease in Po.

    CONCLUSION: Here we demonstrate for the first time, in highly trained sprint skiers, that repeated sprint impairs single fibre maximum force at the level of the contractile apparatus, which may have a significant impact on muscle function and fatigue.

    REFERENCES: Gejl K, Hvid LG, Ulrik Frandsen U, Jensen K, Sahlin K and Ørtenblad N. Muscle glycogen content modifies SR Ca2+ release rate in elite endurance athletes. Med. Sci. Sports Ex. (2013).

  • 36.
    Ørtenblad, Niels
    et al.
    Mid Sweden University, Faculty of Human Sciences, Department of Health Sciences.
    Hvid, L
    University of Southern Denmark, Odense, Denmark.
    Jensen, R
    University of Southern Denmark, Odense, Denmark.
    Andersson, Erik
    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.
    Gejl, K
    University of Southern Denmark, Odense, Denmark.
    Repeated sprint exercise affects contractile apparatus and force production of isolated human muscle fibers2014In: Science & Skiing VI / [ed] Erich Muller, Josef Kröll, Stefan Lindinger m.fl., Meyer & Meyer Sport, 2014, p. 446-452Chapter in book (Refereed)
1 - 36 of 36
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