miun.sePublications
Change search
Refine search result
1 - 36 of 36
CiteExportLink to result list
Permanent link
Cite
Citation style
  • apa
  • ieee
  • modern-language-association-8th-edition
  • vancouver
  • Other style
More styles
Language
  • de-DE
  • en-GB
  • en-US
  • fi-FI
  • nn-NO
  • nn-NB
  • sv-SE
  • Other locale
More languages
Output format
  • html
  • text
  • asciidoc
  • rtf
Rows per page
  • 5
  • 10
  • 20
  • 50
  • 100
  • 250
Sort
  • Standard (Relevance)
  • Author A-Ö
  • Author Ö-A
  • Title A-Ö
  • Title Ö-A
  • Publication type A-Ö
  • Publication type Ö-A
  • Issued (Oldest first)
  • Issued (Newest first)
  • Created (Oldest first)
  • Created (Newest first)
  • Last updated (Oldest first)
  • Last updated (Newest first)
  • Disputation date (earliest first)
  • Disputation date (latest first)
  • Standard (Relevance)
  • Author A-Ö
  • Author Ö-A
  • Title A-Ö
  • Title Ö-A
  • Publication type A-Ö
  • Publication type Ö-A
  • Issued (Oldest first)
  • Issued (Newest first)
  • Created (Oldest first)
  • Created (Newest first)
  • Last updated (Oldest first)
  • Last updated (Newest first)
  • Disputation date (earliest first)
  • Disputation date (latest first)
Select
The maximal number of hits you can export is 250. When you want to export more records please use the Create feeds function.
  • 1.
    Hebert-Losier, Kim
    et al.
    Mid Sweden University, Faculty of Human Sciences, Department of Health Sciences.
    Beaven, C. Martyn
    Mid Sweden University, Faculty of Human Sciences, Department of Health Sciences.
    THE MARS FOR SQUAT, COUNTERMOVEMENT, AND STANDING LONG JUMP PERFORMANCE ANALYSES: ARE MEASURES REPRODUCIBLE?2014In: JOURNAL OF STRENGTH AND CONDITIONING RESEARCH, ISSN 1533-4287, Vol. 28, no 7, p. 1849-1857Article in journal (Refereed)
    Abstract [en]

    The MARS for squat, countermovement, and standing long jump performance analyses: are measures reproducible? J Strength Cond Res 28(7): 18491857, 2014-Jump tests are often used to assess the effect of interventions because their outcomes are reported valid indicators of functional performance. In this study, we examined the reproducibility of performance parameters from 3 common jump tests obtained using the commercially available Kistler Measurement, Analysis and Reporting Software (MARS). On 2 separate days, 32 men performed 3 squat jumps (SJs), 3 countermovement jumps (CMJs), and 3 standing long jumps (LJs) on a Kistler force-plate. On both days, the performance measures from the best jump of each series were extracted using the MARS. Changes in the mean scores, intraclass correlation coefficients (ICCs), and coefficients of variations (CVs) were computed to quantify the between-day reproducibility of each parameter. Moreover, the reproducibility quantifiers specific to the 3 separate jumps were compared using nonparametric tests. Overall, an acceptable between-day reproducibility (mean +/- SD, ICC, and CV) of SJ (0.88 +/- 0.06 and 7.1 +/- 3.8%), CMJ (0.84 +/- 0.17 and 5.9 +/- 4.1%), and LJ (0.80 +/- 0.13 and 8.1 +/- 4.1%) measures was found using the MARS, except for parameters directly relating to the rate of force development (i.e., time to maximal force) and change in momentum during countermovement (i.e., negative force impulse) where reproducibility was lower. A greater proportion of the performance measures from the standing LJs had low ICCs and/or high CVs values most likely owing to the complex nature of the LJ test. Practitioners and researchers can use most of the jump test parameters from the MARS with confidence to quantify changes in the functional ability of individuals over time, except for those relating to the rate of force development or change in momentum during countermovement phases of jumps.

  • 2.
    Hebert-Losier, Kim
    et al.
    Mid Sweden University, Faculty of Human Sciences, Department of Health Sciences. Department of Sports Science, National Sports Institute of Malaysia, National Sports Complex, Bukit Jalil, Kuala Lumpur, Malaysia.
    Zinner, Christoph
    Mid Sweden University, Faculty of Human Sciences, Department of Health Sciences. Department of Sport Science, Julius-Maximilians-University Würzburg, Würzburg, Germany.
    Platt, Simon
    Mid Sweden University, Faculty of Human Sciences, Department of Health Sciences.
    Stöggl, Thomas
    Mid Sweden University, Faculty of Human Sciences, Department of Health Sciences. University of Salzburg, Salzburg, Austria.
    Holmberg, Hans-Christer
    Mid Sweden University, Faculty of Human Sciences, Department of Health Sciences.
    Factors that Influence the Performance of Elite Sprint Cross-Country Skiers2017In: Sports Medicine, ISSN 0112-1642, E-ISSN 1179-2035, Vol. 47, no 2, p. 319-342Article in journal (Refereed)
    Abstract [en]

    Background: Sprint events in cross-country skiing are unique not only with respect to their length (0.8–1.8 km), but also in involving four high-intensity heats of ~3 min in duration, separated by a relatively short recovery period (15–60 min). Objective: Our aim was to systematically review the scientific literature to identify factors related to the performance of elite sprint cross-country skiers. Methods: Four electronic databases were searched using relevant medical subject headings and keywords, as were reference lists, relevant journals, and key authors in the field. Only original research articles addressing physiology, biomechanics, anthropometry, or neuromuscular characteristics and elite sprint cross-country skiers and performance outcomes were included. All articles meeting inclusion criteria were quality assessed. Data were extracted from each article using a standardized form and subsequently summarized. Results: Thirty-one articles met the criteria for inclusion, were reviewed, and scored an average of 66 ± 7 % (range 56–78 %) upon quality assessment. All articles except for two were quasi-experimental, and only one had a fully-experimental research design. In total, articles comprised 567 subjects (74 % male), with only nine articles explicitly reporting their skiers’ sprint International Skiing Federation points (weighted mean 116 ± 78). A similar number of articles addressed skating and classical techniques, with more than half of the investigations involving roller-skiing assessments under laboratory conditions. A range of physiological, biomechanical, anthropometric, and neuromuscular characteristics was reported to relate to sprint skiing performance. Both aerobic and anaerobic capacities are important qualities, with the anaerobic system suggested to contribute more to the performance during the first of repeated heats; and the aerobic system during subsequent heats. A capacity for high speed in all the following instances is important for the performance of sprint cross-country skiers: at the start of the race, at any given point when required (e.g., when being challenged by a competitor), and in the final section of each heat. Although high skiing speed is suggested to rely primarily on high cycle rates, longer cycle lengths are commonly observed in faster skiers. In addition, faster skiers rely on different technical strategies when approaching peak speeds, employ more effective techniques, and use better coordinated movements to optimize generation of propulsive force from the resultant ski and pole forces. Strong uphill technique is critical to race performance since uphill segments are the most influential on race outcomes. A certain strength level is required, although more does not necessarily translate to superior sprint skiing performance, and sufficient strength-endurance capacities are also of importance to minimize the impact and accumulation of fatigue during repeated heats. Lastly, higher lean mass does appear to benefit sprint skiers’ performance, with no clear advantage conferred via body height and mass. Limitations: Generalization of findings from one study to the next is challenging considering the array of experimental tasks, variables defining performance, fundamental differences between skiing techniques, and evolution of sprint skiing competitions. Although laboratory-based measures can effectively assess on-snow skiing performance, conclusions drawn from roller-skiing investigations might not fully apply to on-snow skiing performance. A low number of subjects were females (only 17 %), warranting further studies to better understand this population. Lastly, more training studies involving high-level elite sprint skiers and investigations pertaining to the ability of skiers to maintain high-sprint speeds at the end of races are recommended to assist in understanding and improving high-level sprint skiing performance, and resilience to fatigue. Conclusions: Successful sprint cross-country skiing involves well-developed aerobic and anaerobic capacities, high speed abilities, effective biomechanical techniques, and the ability to develop high forces rapidly. A certain level of strength is required, particularly ski-specific strength, as well as the ability to withstand fatigue across the repeated heats of sprint races. Cross-country sprint skiing is demonstrably a demanding and complex sport, where high-performance skiers need to simultaneously address physiological, biomechanical, anthropometric, and neuromuscular aspects to ensure success.

  • 3.
    Hurst, Howard T
    et al.
    University of Central Lancashire, United Kingdom.
    Swarén, Mikael
    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.
    Ericsson, Fredrik
    Swedish Cycling Federation, Stockholm, Sweden.
    Sinclair, Jonathan
    University of Central Lancashire, United Kingdom.
    Atkins, Stephen
    University of Central Lancashire, United Kingdom.
    Holmberg, Hans-Christer
    Mid Sweden University, Faculty of Human Sciences, Department of Health Sciences.
    GPS-Based Evaluation of Activity Profiles in Elite Downhill Mountain Biking and the Influence of Course Type2013In: Journal of Science and Cycling, ISSN 2254-7053, Vol. 2, no 1, p. 25-32Article in journal (Refereed)
    Abstract [en]

    This study aimed to profile the activity patterns of elite downhill (DH) mountain bikers during off-road descending, and to determine the influence of course types on activity patterns. Six male elite DH mountain bikers (age 20 ± 2 yrs; stature 178.8 ± 3.1 cm; body mass 75.0 ± 3.0 kg) performed single runs on one man-made (MM) and one natural terrain (NT) DH courses under race conditions. A 5 Hz global positioning systems (GPS) unit, including a 100 Hz triaxial accelerometer, was positioned in a neoprene harness between the C7 and T2 vertebrae on each rider. GPS was used to determine the temporal characteristics of each run for velocity, run time, distance, effort, heart rate (HR), rider load (RLd) which reflects instantaneous rate of change in acceleration, and accumulated rider load (RLdAcc), which reflects change in acceleration over the event duration. Significant differences were found between NT and MM courses for mean velocity (p<.001), peak velocity (p=.014), mean RLd (p=.001) and peak RLd (p=.002). Significant differences were also found both within and between courses for all velocity parameters, when analysed by intensity zone (p<.05). No significant differences were found between courses for HR parameters by zone, though significant differences were revealed between HR zones within courses (p<.05). This study indicates that course terrain has a significant impact on the activity profiles of DH and that GPS can provide a practical means of monitoring these differences in activity.

  • 4.
    Hurst, Howard T
    et al.
    U niversity of Central Lancashire, Preston , United Kingdom.
    Swarén, Mikael
    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.
    Ericsson, Fredrik
    Swedish Cycling Federation, Stockholm, Sweden.
    Sinclair, Jonathan
    Atkins, Stephen
    Holmberg, Hans-Christer
    Mid Sweden University, Faculty of Human Sciences, Department of Health Sciences.
    Influence of course type on upper body muscle activity in elite cross-country and downhill mountain bikers during off road downhill cycling2012In: Journal of Science and Cycling, ISSN 2254-7053, Vol. 1, no 1, p. 2-9Article in journal (Refereed)
  • 5.
    Hurst, HT
    et al.
    University of Central Lancashire, Preston, UK.
    Swarén, Mikael
    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.
    Ericsson, F
    Swedish Cycling Federation, Stockholm, Sweden.
    Holmberg, Hans-Christer
    Mid Sweden University, Faculty of Human Sciences, Department of Health Sciences.
    ANAEROBIC POWER AND CADENCE CHARACTERISTICS OF ELITE CROSS-COUNTRY AND DOWNHILL MOUNTAIN BIKERS2012In: 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. 602-603Conference paper (Refereed)
    Abstract [en]

    Introduction

     

    Mountain biking (MTB) is composed of several sub-disciplines, with Olympic Cross-Country (XCO) and Downhill (DH) being the most popular. Much of the current research on MTB pertains to the aerobic demands of XCO racing, with comparisons often made to road cycling. No studies have compared elite level XCO and DH bikers. Therefore, the aim of this study was to investigate the anaerobic power and cadence characteristics of elite XCO to DH riders.

    Methods

     

    Twelve male elite mountain bikers (n=6 XCO, n=6 DH; age 21.83 ± 3.71 yrs; stature 179.67 ± 4.40 cm; mass 72.50 ± 5.45 kg) took part in this study. An inertial load cycling test was performed as described in previous studies(3),on an SRM cycle ergometer instrumented with a scientific version SRM Powermeter. Inertial load was adjusted to ensure riders achieved 130-150 revs.min-1 within 4-7 s. Peak power (Wpeak), cadence at Wpeak (CADopt) and power to weight ratio (W.kg-1) were calculated for each rider as the mean from 3 trials. Statistical differences between XCO and DH were determined using independent t-tests with significance set at p≤0.05.

    Results

    A significant difference between DH and XCO was found for CADopt (114.93 ± 5.41 and 107.96 ± 4.63 revs.min-1, p<0.05), respectively. No other differences were revealed between groups. The mean recorded values for DH and XCO were 1137.76 ± 135.84 and 1113.86 ± 75.22 W for Wpeak and 15.21 ± 2.05 and 15.95 ± 0.75 W.kg-1 for power to weight ratio, respectively.

    Discussion

     

    The findings of comparable Wpeak between groups may indicate that high anaerobic power is not a prerequisite for success in elite DH. However, significant differences were found in CADopt, where DH riders had a higher cadence when producing Wpeak compared to XCO riders. This may reflect training specificity and the greater emphasis on repeated accelerations in DH(2) and the lower cadences elicited by XCO riders(1). Further research is therefore warranted to compare laboratory and field-based performance in these two population groups.

  • 6.
    Hébert-Losier, Kim
    Univeristy of Otago.
    An Investigation of the Influence of Knee Flexion Angle on the Activity of the Triceps Surae Muscles during the Heel-Raise Test2011Doctoral thesis, monograph (Other academic)
    Abstract [en]

    Background: The heel-raise test (HRT) is used in clinical practice and research to assess the triceps suare (TS) muscles. The test involves repetitive unilateral heel-raises in upright stance. The test is administered with the knee straight for gastrocnemius medialis (GM) and lateralis (GL), and with the knee bent for soleus (SOL). The maximum number of heel-raises which can be performed is utilised as a clinical outcome measure and informs clinical decisions. The use of knee flexion (KF) to direct HRT assessment towards SOL or GAST currently relies on fundamental principles and has a limited evidence-base.

    Aims: The primary aim of this research was to investigate the influence of KF angle on SOL, GM, and GL activity and fatigue during the HRT. Secondary aims were to explore the total number of heel-raises completed, and the influence of age group on TS muscle activity and fatigue.

    Methods: Specific literature reviews were undertaken to contextualise the HRT within a comprehensive anatomical and biomechanical framework, and the experimental research involved a sequence of biomechanical studies. Seventeen subjects participated in a preliminary study that involved heel-raise testing to fatigue in two KF positions and generalised estimation equations were used to determine whether select KF angles were maintained. Forty-eight subjects, stratified by age and gender, participated in the main experimental study. Surface electromyography (EMG) activity of SOL, GM, and GL during maximum voluntary isometric contractions (MVIC) was collected in 0°KF, 45°KF, and 90°KF to inform EMG normalisation. Subjects then completed 10 unilateral heel-raises in 0°KF and 45°KF to investigate EMG amplitudes (% of MVIC) and heel-raises to fatigue for power spectrum analysis (median frequency and normalised slope). Mixed-effects models and stepwise regressions were used for the main analysis.

    Results: The preliminary study identified that select KF angles were reasonably well maintained during testing and subjects completed an average of 40 heel-raises in the two KF positions. The investigation of (EMG) muscle activity during MVIC developed a normalisation protocol specific to capturing SOL, GM, and GL peak activity. Data collected from heel-raises demonstrated higher SOL (p=.005) and lower GM (p<.001) and GL (p<.001) amplitudes in 45°KF rather than 0°KF; however, KF did not influence fatigue of the individual TS muscles. GM and GL fatigued at the same rate (p=.088), to the same extent (p=.385), and faster than SOL (p<.001) in both angles. GM (p=.008), but not GL (p=.118), fatigued more than SOL. Similar maximum numbers of heel-raises were performed in 0°KF (n=45) and 45°KF (n=48). Age did not influence any of the variables analysed.

    Conclusion: The research results question the common utilisation of KF to direct the HRT towards SOL or GAST assessment. Although influences of KF on EMG amplitudes were statistically significant, they may not be clinically meaningful. KF did not influence TS fatigue or the total number of heel-raises. While these findings do not imply the absence of clinical or rehabilitative benefits from HRT procedures in select KF positions, the evidence challenges the common perceptions and definitions that the test assesses SOL with the knee bent and GAST with the knee straight.

  • 7.
    Hébert-Losier, Kim
    et al.
    Mid Sweden University, Faculty of Human Sciences, Department of Health Sciences.
    Almström, Patrik
    Qualisys AB.
    Holmberg, Hans-Christer
    Mid Sweden University, Faculty of Human Sciences, Department of Health Sciences.
    The use of a minimal market set for pelvic motion analysis during running2012Conference paper (Refereed)
  • 8.
    Hébert-Losier, Kim
    et al.
    Mid Sweden University, Faculty of Human Sciences, Department of Health Sciences.
    Andersson, Erik
    Mid Sweden University, Faculty of Human Sciences, Department of Health Sciences.
    Stöggl, Thomas
    Mid Sweden University, Faculty of Human Sciences, Department of Health Sciences.
    BIOMECHANICAL DIFFERENCES IN TOP LEVEL CROSS-COUNTRY SKIERS AT MAXIMAL VELOCITY2012In: / [ed] Anni Hakkarainen, Stefan Lindinger and Vesa Linnamo, 2012, p. 63-63Conference paper (Refereed)
  • 9.
    Hébert-Losier, Kim
    et al.
    Mid Sweden University, Faculty of Human Sciences, Department of Health Sciences.
    Erikson, Anders
    KTH Mechanics, Royal Institute of Technology, Osquars backe 18, 10044 Stockholm, Sweden.
    Leg stiffness measures depend on computational method2014In: Journal of Biomechanics, ISSN 0021-9290, E-ISSN 1873-2380, Vol. 47, no 1, p. 115-121Article in journal (Refereed)
    Abstract [en]

    Leg stiffness is often computed from ground reaction force (GRF) registrations of vertical hops to estimate the force-resisting capacity of the lower-extremity during ground contact, with leg stiffness values incorporated in a spring-mass model to describe human motion. Individual biomechanical characteristics, including leg stiffness, were investigated in 40 healthy males. Our aim is to report and discuss the use of 13 different computational methods for evaluating leg stiffness from a double-legged repetitive hopping task, using only GRF registrations. Four approximations for the velocity integration constant were combined with three mathematical expressions, giving 12 methods for computing stiffness using double integrations. One frequency-based method that considered ground contact times was also trialled. The 13 methods thus defined were used to compute stiffness in four extreme cases, which were the stiffest, and most compliant, consistent and variable subjects. All methods provided different stiffness measures for a given individual, but the between-method variations in stiffness were consistent across the four atypical subjects. The frequency-based method apparently overestimated the actual stiffness values, whereas double integrations' measures were more consistent. In double integrations, the choice of the integration constant and mathematical expression considerably affected stiffness values, as variations during hopping were more or less emphasized. Stating a zero centre of mass position at take-off gave more consistent results, and taking a weighted-average of the force or displacement curve was more forgiving to variations in performance. In any case, stiffness values should always be accompanied by a detailed description of their evaluation methods, as our results demonstrated that computational methods affect calculated stiffness.

  • 10.
    Hébert-Losier, Kim
    et al.
    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.
    A survey of the exercises prescribed to prevent injuries during recreational alpine skiing and snowboarding2013In: Proceedings for the 18th Annual Congress of the ECSS / [ed] Erich Mueller, Josef Kröll, Stefan Josef Lindinger, Jurgen Pfusterschmied, Thomas Stöggl, 2013, p. 64-Conference paper (Refereed)
  • 11.
    Hébert-Losier, Kim
    et al.
    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.
    Biomechanics of the heel-raise test performed on an incline in two knee flexion positions2013In: Clinical Biomechanics, ISSN 0268-0033, E-ISSN 1879-1271, Vol. 28, no 6, p. 664-671Article in journal (Refereed)
    Abstract [en]

    BACKGROUND:

    Although single-legged heel-raise cycles are often performed on an incline in different knee flexion positions to discriminate the relative contribution of the triceps surae muscles, detailed kinematic and kinetic analyses of this procedure are not available. Our study characterizes and compares the biomechanics and clinical outcomes of single-legged heel-raise cycles performed to volitional exhaustion on an incline with the knee straight (0°) and bent (45°), considering the effect of sex and age.

    METHODS:

    Fifty-six male and female volunteers, with equal numbers of younger (20 to 40 years of age) and older (40 to 60 years of age) individuals, completed a maximal number of heel-raise cycles on an incline at both nominal knee angles. Kinematic and kinetic data were acquired during testing using a 3D motion capturing system and multi-axial force plate. The impact of fatigue on performance was quantified using changes in maximal voluntary isometric contraction force and biomechanical performance of cycles.

    FINDINGS:

    Overall, participants completed three more cycles and maintained better biomechanical performance with 45° than 0° of knee flexion. More precisely, the decreases in maximal heel-raise heights, plantar-flexion angles at maximal height and ranges of ankle motion per cycle were all smaller with the knee bent. However, several outcomes indicated similar plantar-flexion fatigue at both knee angles. Males demonstrated a more rapid decline in peak ground reaction forces during testing; but otherwise, neither sex nor age significantly impacted outcomes.

    INTERPRETATION:

    It is concluded that the differences discerned here in the biomechanics of single-legged heel-raise cycles performed at 0° and 45° of knee flexion to volitional exhaustion on an incline may be too small to identify in clinical settings or reflect substantial alterations in the relative contribution of the triceps surae muscles.

  • 12.
    Hébert-Losier, Kim
    et al.
    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.
    Dynamometric indicators of fatigue from repeated maximal concentric isokinetic plantar-flexion contractions are independent of knee flexion angles and age, but differ for males and females.2014In: Journal of Strength and Conditioning Research, ISSN 1064-8011, E-ISSN 1533-4287, Vol. 28, no 3, p. 843-855Article in journal (Refereed)
    Abstract [en]

    Sex and age are reported to influence the maximal dynamometric performance of major muscle groups, inclusive of ankle plantar-flexors. Knee flexion (KF) also impacts plantar-flexion function from where stems utilization of 0[degrees] and 45[degrees] of KF for clinical assessment of gastrocnemius and soleus, respectively. The influence of KF, sex and age on dynamometric indicators of plantar-flexion fatigue was examined in 28 males and 28 females recruited in two different age groups (above and below 40 years). Each subject performed 50 maximal concentric isokinetic plantar-flexions at 60 deg[middle dot]s-1 with 0[degrees] and 45[degrees] of KF. Maximal voluntary isometric contractions were determined before and after isokinetic trials; and maximal, minimal and normalized linear slopes of peak power during testing. Main effects of and two-way interactions between KF, sex, age and order of testing were explored using mixed-effect models and stepwise regressions. At 0[degrees] and 45[degrees], the fatigue indicators in younger and older individuals were similar and not influenced by testing order. However, peak isokinetic power and isometric torque declined to greater extents in males than females and, moreover, KF exerted greater impacts on the absolute plantar-flexion performance and maximal-to-minimal reduction in isokinetic power in males. Because KF wielded no pronounced effect on fatigue indicators, this test may perhaps be used over time with no major concern regarding the exact knee angle. Our findings indicate that sex, rather than age, should be considered when interpreting dynamometric indicators of fatigue from repeated maximal concentric isokinetic plantar-flexions, e.g., when establishing normative values or comparing outcomes.

  • 13.
    Hébert-Losier, Kim
    et al.
    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.
    Exercise prescription to prevent injuries during recreational skiing and snowboarding2015In: Physiotherapy, ISSN 0031-9406, E-ISSN 1873-1465, Vol. 101, no Suppl. 1, p. e552-Article in journal (Refereed)
  • 14.
    Hébert-Losier, Kim
    et al.
    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.
    Knee angle-specific MVIC for triceps surae EMG signal normalization in weight and non weight-bearing conditions2013In: Journal of Electromyography & Kinesiology, ISSN 1050-6411, E-ISSN 1873-5711, Vol. 23, no 4, p. 916-923Article in journal (Refereed)
    Abstract [en]

    Varying the degree of weight-bearing (WB) and/or knee flexion (KF) angle during a plantar-flexion maximal voluntary isometric contraction (MVIC) has been proposed to alter soleus and/or gastrocnemius medialis and lateralis activation. This study compared the surface EMG signals from the triceps surae of 27 men and 27 women during WB and non weight bearing (NWB) plantar-flexion MVICs performed at 0° and 45° of KF. The aim was to determine which condition was most effective at eliciting the greatest EMG signals from soleus, gastrocnemius medialis, and gastrocnemius lateralis, respectively, for subsequent use for the normalization of EMG signals. WB was more effective than NWB at eliciting the greatest signals from soleus (p=0.0021), but there was no difference with respect to gastrocnemius medialis and lateralis (p⩾0.2482). Although the greatest EMG signals during MVICs were more frequently elicited at 0° of KF from gastrocnemius medialis and lateralis, and at 45° from soleus (p<0.001); neither angle consistently captured peak gastrocnemius medialis, gastrocnemius lateralis or soleus activity. The present findings encourage more consistent use of WB plantar flexion MVICs for soleus normalization; confirm that both WB and NWB procedures can elicit peak gastrocnemius activity; and emphasize the fact that no single KF angle consistently evokes selective maximal activity of any individual triceps surae muscle.

  • 15.
    Hébert-Losier, Kim
    et al.
    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.
    What are the Exercise-Based Injury Prevention Recommendations for Recreational Alpine Skiing and Snowboarding?: A Systematic Review2013In: Sports Medicine, ISSN 0112-1642, E-ISSN 1179-2035, Vol. 43, no 5, p. 355-366Article in journal (Refereed)
    Abstract [en]

    Background Skiing and snowboarding are two activities that significantly contribute to the total number of sports-related injuries reported per year. Strength, endurance and cardiovascular fitness are central components in sports injury prevention. Providing exercises and training recommendations specific to recreational skiers and snowboarders is important in both injury prevention and reducing the prevalence and cost associated with alpine winter sports injuries. Objective The aim of this paper was to systematically review the literature for injury prevention recommendations specific to recreational alpine skiers and snowboarders. The focus was to discern recommendations that targeted physical fitness, exercise and/or training in the prevention of musculoskeletal injuries in these two sports. Data Sources Fourteen electronic databases were searched in October 2011 using relevant MeSH terms and key words. Study Selection Articles were included if they addressed injury prevention, recreational alpine skiing or snowboarding and musculoskeletal injuries. Only original research articles published in peer-reviewed journals, and in the English-language, were reviewed. Articles on elite athletes were excluded. Study Appraisal and Synthesis Methods Two independent reviewers quality assessed articles meeting inclusion criteria using a modified version of the Downs and Black Quality Assessment Checklist. Data on study population, study design, study location and injury prevention recommendation( s) were extracted from articles using a standard form and subsequently categorized to facilitate data synthesis. Results A total of 30 articles met the inclusion criteria and were reviewed, having an average +/- standard deviation quality score of 72 % +/- 17 % (range: 23-100 %). Overall, 80 recommendations for the prevention of musculoskeletal injuries in recreational alpine skiers and snowboarders were identified and classified into five main groups: equipment (n = 24), education and knowledge (n = 11), awareness and behaviour (n = 15), experience (n = 10) and third-party involvement (n = 20). No recommendations pertained to physical fitness, exercise and/or training per se, or its role in preventing injury. Limitations A comprehensive meta-analysis was not possible because several articles did not report data in sufficient detail. Conclusions The importance of targeting physical fitness in injury prevention is accepted in sports medicine and rehabilitation; yet, there was a paucity of articles included in this review that explicitly investigated this aspect with regards to recreational alpine skiing and snowboarding. The most frequent recommendations for preventing skiing and snowboarding injuries concerned equipment or the involvement of third parties. The dominance of equipment-related measures in the injury prevention literature may be rationalized from a sports biomechanics viewpoint, as these activities involve high velocities and impact forces. Nonetheless, this also indicates a need for appropriate levels of strength, endurance and conditioning to meet the technical demands of these sports. Bearing this in mind, future research is encouraged to investigate the role of physical fitness, exercise and training in decreasing the incidence and severity of skiing and snowboarding injuries in recreational athletes.

  • 16.
    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.

  • 17.
    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.

  • 18.
    Hébert-Losier, Kim
    et al.
    Mid Sweden University, Faculty of Human Sciences, Department of Health Sciences.
    Mourot, L.
    Univ Franche Comte, Res Unit Dept EA4660 Dept, Culture Sport Hlth Soc, F-25030 Besancon, France.
    Holmberg, Hans-Christer
    Mid Sweden University, Faculty of Human Sciences, Department of Health Sciences.
    Elite and amateur orienteers' running biomechanics on three surfaces at three speeds2015In: Medicine & Science in Sports & Exercise, ISSN 0195-9131, E-ISSN 1530-0315, Vol. 47, no 2, p. 381-389Article in journal (Refereed)
    Abstract [en]

    PURPOSE: Orienteering athletes must adapt to running on various surfaces, with biomechanics likely contributing to performance. Here, our aims were to identify the effect of athletic status and of surface on the running biomechanics of orienteers. METHODS: Seven elite and seven amateur male orienteers ran 20 m on road, path, and forest surfaces at maximal, 3.8 m·s, and 85% of maximal speeds. A three-dimensional motion capturing system monitored temporal gait and lower extremity kinematic parameters. Data were analyzed using mixed effects models that considered surface (road-path-forest), group (elite-amateur), and surface-group interaction effects. RESULTS: Forest running at maximal speed was slower and involved longer step and cycle times, greater knee extension at foot strike, smaller peak hip flexion and dorsiflexion during stance, and increased ranges of vertical pelvis motion compared with those observed on the road. Elites specifically exhibited greater hip extension at foot strike, larger dorsiflexion at toe-off, and lower pelvis at foot strike and toe-off, whereas amateurs displayed longer stance, greater plantarflexion at foot strike, and greater knee with lesser ankle motion. At the slowest speed, subjects exhibited greater knee flexion at foot strike, greater dorsiflexion at toe-off, shorter strides, smaller peak dorsiflexion during stance, and greater hip, knee, and vertical pelvis motions on forest than on road surfaces. Elites specifically demonstrated shorter stance, step, and cycle times whereas amateurs did not. CONCLUSIONS: Orienteering athletes adjusted their running biomechanics when off-road, with distinct adaptations observed in elite versus amateur competitors. The vertical pelvis motion was consistently greater when running off-road, coherent with reported increases in energy expenditure. However, our athletes did not exhibit more crouched lower limb postures when sprinting in the forest, indicating alternative responses to off-road running to that previously proposed by "Groucho" running.

  • 19.
    Hébert-Losier, Kim
    et al.
    Univeristy of Otago.
    Newsham-West, Richard J.
    Schneiders, Anthony G.
    Univeristy of Otago.
    Sullivan, S. John
    Univeristy of Otago.
    Raising the standards of the calf-raise test: a systematic review.2009In: Journal of science and medicine in sport / Sports Medicine Australia, ISSN 1878-1861, Vol. 12, no 6, p. 594-602Article in journal (Refereed)
    Abstract [en]

    The calf-raise test is used by clinicians and researchers in sports medicine to assess properties of the calf muscle-tendon unit. The test generally involves repetitive concentric-eccentric muscle action of the plantar-flexors in unipedal stance and is quantified by the number of raises performed. Although the calf-raise test appears to have acceptable reliability and face validity, and is commonly used for medical assessment and rehabilitation of injuries, no universally acceptable test parameters have been published to date. A systematic review of the existing literature was conducted to investigate the consistency as well as universal acceptance of the evaluation purposes, test parameters, outcome measurements and psychometric properties of the calf-raise test. Nine electronic databases were searched during the period May 30th to September 21st 2008. Forty-nine articles met the inclusion criteria and were quality assessed. Information on study characteristics and calf-raise test parameters, as well as quantitative data, were extracted; tabulated; and statistically analysed. The average quality score of the reviewed articles was 70.4+/-12.2% (range 44-90%). Articles provided various test parameters; however, a consensus was not ascertained. Key testing parameters varied, were often unstated, and few studies reported reliability or validity values, including sensitivity and specificity. No definitive normative values could be established and the utility of the test in subjects with pathologies remained unclear. Although adapted for use in several disciplines and traditionally recommended for clinical assessment, there is no uniform description of the calf-raise test in the literature. Further investigation is recommended to ensure consistent use and interpretation of the test by researchers and clinicians.

  • 20.
    Hébert-Losier, Kim
    et al.
    Mid Sweden University, Faculty of Human Sciences, Department of Health Sciences.
    Platt, Simon
    Mid Sweden University, Faculty of Human Sciences, Department of Health Sciences.
    Hopkins, William G.
    Victoria Univ, Coll Sport & Exercise Sci, Melbourne, Vic 8001, Australia.
    Sources of Variability in Performance Times at the World Orienteering Championships2015In: Medicine & Science in Sports & Exercise, ISSN 0195-9131, E-ISSN 1530-0315, Vol. 47, no 7, p. 1523-1530Article in journal (Refereed)
    Abstract [en]

    Purpose An improvement equal to 0.3 of the typical variation in an elite athlete's race-to-race performance estimates the smallest worthwhile enhancement, which has not yet been determined for orienteers. Moreover, much of the research in high-performance orienteering has focused on physical and cognitive aspects, although course characteristics might influence race performance. Analysis of race data provides insights into environmental effects and other aspects of competitive performance. Our aim was to examine such factors in relation to World Orienteering Championships performances. Methods We used mixed linear modelling to analyze finishing times from the three qualification rounds and final round of the sprint, middle-distance, and long-distance disciplines of World Orienteering Championships from 2006 to 2013. Models accounted for race length, distance climbed, number of controls, home advantage, venue identity, round (qualification final), athlete identity, and athlete age. Results Within-athlete variability (coefficient of variation, mean SD) was lower in the final (4.9% +/- 1.4%) than in the qualification (7.3% +/- 2.4%) rounds and provided estimates of smallest worthwhile enhancements of 1.0%-3.5%. The home advantage was clear in most disciplines, with distance climbed particularly impacting sprint performances. Small to very large between-venue differences were apparent. Performance predictability expressed as intraclass correlation coefficients was extremely high within years and was high to very high between years. Age of peak performance ranged from 27 to 31 yr. Conclusions Our results suggest that elite orienteers should focus on training and strategies that enhance performance by at least 1.0%-3.5% for smallest worthwhile enhancement. Moreover, as greater familiarity with the terrain likely mediated the home advantage, foreign athletes would benefit from training in nations hosting the World Orienteering Championships for familiarization.

  • 21.
    Hébert-Losier, Kim
    et al.
    Mid Sweden University, Faculty of Human Sciences, Department of Health Sciences.
    Schneiders, Anthony G.
    Univeristy of Otago.
    García, José A.
    University of Otago.
    Sullivan, S. John
    Univeristy of Otago.
    Simoneau, Guy G.
    Marquette University.
    Influence of knee flexion angle and age group on triceps surae muscle fatigue during heel-raises.2012In: Journal of Strength and Conditioning Research, ISSN 1064-8011, E-ISSN 1533-4287, Vol. 26, no 11, p. 3134-3147Article in journal (Refereed)
    Abstract [en]

    The triceps surae muscle-tendon unit is one of the most commonly injured in elite and recreational athletes, with high prevalence in middle-age adults. Performing maximal numbers of unilateral heel-raises is used to assess, train, and rehabilitate triceps surae endurance; and conventionally prescribed in 0° knee flexion for gastrocnemius and 45° for soleus. However, the extent of muscle-selectivity conferred through change in knee angle is lacking for heel-raises performed to volitional fatigue. This study investigated the influence of knee angle on triceps surae muscle fatigue during heel-raises and determined whether fatigue differed between middle-age and younger-age adults. Forty-eight healthy individuals of 18-25 and 35-45 years performed maximal numbers of unilateral heel-raises in 0° and 45° knee flexion. Median frequencies and linear regression slopes were calculated from soleus, gastrocnemius medialis, and gastrocnemius lateralis surface electromyographic signals. Stepwise mixed-effect regressions were used for analysis. Subjects completed an average of 45 and 48 heel-raises in 0° and 45° knee flexion; respectively. Results indicated that the three muscles fatigued during testing as all median frequencies decreased and regression slopes were negative. Consistent with muscle physiology and fiber typing, fatigue was greater in gastrocnemius medialis and lateralis than soleus (p<.001). However, knee angle did not influence triceps surae muscle fatigue parameters (p=.814), with similar soleus and gastrocnemius fatigue in 0° and 45° knee flexion. These findings contrast with the traditionally described clinical use of heel-raises in select knee angles for gastrocnemius and/or soleus. Furthermore, no difference in triceps surae fatigue between the two age groups was able to be determined, despite the reported higher prevalence of injury in middle-age individuals.

  • 22.
    Hébert-Losier, Kim
    et al.
    Univeristy of Otago.
    Schneiders, Anthony G
    Univeristy of Otago.
    García, José A.
    University of Otago.
    Sullivan, S. John
    Univeristy of Otago.
    Simoneau, Guy G.
    Marquette University.
    Peak triceps surae muscle activity is not specific to knee flexion angles during MVIC.2011In: Journal of Electromyography & Kinesiology, ISSN 1050-6411, E-ISSN 1873-5711, Vol. 21, no 5, p. 819-26Article in journal (Refereed)
    Abstract [en]

    There is limited research on peak activity of the separate triceps surae muscles in select knee flexion (KF) positions during a maximum voluntary isometric contraction (MVIC) used to normalize EMG signals. The aim of this study was to determine how frequent peak activity occurred during an MVIC for soleus (SOL), gastrocnemius medialis (GM), and gastrocnemius lateralis (GL) in select KF positions, and if these peaks were recorded in similar KF positions. Forty-eight healthy individuals performed unilateral plantar-flexion MVIC in standing with 0°KF and 45°KF, and in sitting with 90°KF. Surface EMG of SOL, GM, and GL were collected and processed in 250 ms epochs to determine peak root-mean-square amplitude. Peak activity was most frequently captured in standing and rarely in sitting, with no position selective to SOL, GM or GL activity. Peak GM and GL activity was more frequent in 0°KF than 45°KF, and more often in similar KF positions than not. Peak SOL activity was just as likely in 45°KF as 0°KF, and more in positions similar to GM, but not GL. The EMG amplitudes were at least 20% greater in positions that captured peak activity over those that did not. The overall findings support performing an MVIC in more than one KF position to normalize triceps surae EMG. It is emphasized that no KF position is selective to SOL, GM, or GL alone.

  • 23.
    Hébert-Losier, Kim
    et al.
    Univeristy of Otago.
    Schneiders, Anthony G.
    Univeristy of Otago.
    Newsham-West, Richard J
    Sullivan, S. John
    Univeristy of Otago.
    Scientific bases and clinical utilisation of the calf-raise test.2009In: Physical Therapy in Sport, ISSN 1466-853X, E-ISSN 1873-1600, Vol. 10, no 4, p. 142-9Article in journal (Refereed)
    Abstract [en]

    BACKGROUND: Athletes commonly sustain injuries to the triceps surae muscle-tendon unit. The calf-raise test (CRT) is frequently employed in sports medicine for the detection and monitoring of such injuries. However, despite being widely-used, a recent systematic review found no universal consensus relating to the test's purpose, parameters, and standard protocols.

    OBJECTIVES: The purpose of this paper is to provide a clinical perspective on the anatomo-physiological bases underpinning the CRT and to discuss the utilisation of the test in relation to the structure and function of the triceps surae muscle-tendon unit.

    DESIGN: Structured narrative review.

    METHODS: Nine electronic databases were searched using keywords and MESH headings related to the CRT and the triceps surae muscle-tendon unit anatomy and physiology. A hand-search of reference lists and relevant journals and textbooks complemented the electronic search.

    SUMMARY: There is evidence supporting the clinical use of the CRT to assess soleus and gastrocnemius, their shared aponeurosis, the Achilles tendon, and the combined triceps surae muscle-tendon unit. However, employing the same clinical test to assess all these structures and their associated functions remains challenging.

    CONCLUSIONS: Further refinement of the CRT for the triceps surae muscle-tendon unit is needed. This is vital to support best practice utilisation, standardisation, and interpretation of the CRT in sports medicine.

  • 24.
    Hébert-Losier, Kim
    et al.
    Univeristy of Otago.
    Schneiders, Anthony G
    Univeristy of Otago.
    Sullivan, S. John
    Univeristy of Otago.
    December 2011 Letters to the Editor-in-Chief: Differentiating the Soleus From the Gastrocnemius With the Heel Raise Test2011In: Journal of Orthopaedic and Sports Physical Therapy, ISSN 0190-6011, E-ISSN 1938-1344, Vol. 41, no 12, p. 983-7Article in journal (Refereed)
    Abstract [en]

    Letters to the Editor-in-Chief of JOSPT as follows:"Early Prognostic Factors in Patients With Whiplash" and Author's Response "Staying Current in the Use of Ultrasound Imaging" and Author's Response"Differentiating the Soleus From the Gastrocnemius With the Heel Raise Test" and Author's ResponseJ Orthop Sports Phys Ther 2011;41(12):983-987. doi:10.2519/jospt.2011.0202.

  • 25.
    Hébert-Losier, Kim
    et al.
    Univeristy of Otago.
    Schneiders, Anthony G.
    Univeristy of Otago.
    Sullivan, S. John
    Univeristy of Otago.
    Newsham-West, Richard J
    García, José A.
    Univeristy of Otago.
    Simoneau, Guy G.
    Marquette University.
    Analysis of knee flexion angles during 2 clinical versions of the heel raise test to assess soleus and gastrocnemius function.2011In: Journal of Orthopaedic and Sports Physical Therapy, ISSN 0190-6011, E-ISSN 1938-1344, Vol. 41, no 7, p. 505-13Article in journal (Refereed)
    Abstract [en]

    STUDY DESIGN: Controlled laboratory study, using a repeated-measures, counterbalanced design.

    OBJECTIVES: To provide estimates on the average knee angle maintained, absolute knee angle error, and total repetitions performed during 2 versions of the heel raise test.

    BACKGROUND: The heel raise test is performed in knee extension (EHRT) to assess gastrocnemius and knee flexion (FHRT) for soleus. However, it has not yet been determined whether select knee angles are maintained or whether total repetitions differ between the clinical versions of the heel raise test.

    METHODS: Seventeen healthy males and females performed maximal heel raise repetitions in 0° (EHRT) and 30° (FHRT) of desired knee flexion. The average angle maintained and absolute error at the knee during the 2 versions, and total heel raise repetitions, were measured using motion analysis. Participants' kinematic measures were fitted into a generalized estimation equation model to provide estimates on EHRT and FHRT performance applicable to the general population.

    RESULTS: The model estimates that average angles of 2.2° and 30.7° will be maintained at the knee by the general population during the EHRT and the FHRT, with an absolute angle error of 3.4° and 2.5°, respectively. In both versions, 40 repetitions should be completed. However, the average angles maintained by participants ranged from -6.3° to 21.6° during the EHRT and from 22.0° to 43.0° during the FHRT, with the highest absolute errors in knee position being 25.9° and 33.5°, respectively.

    CONCLUSION: On average, select knee angles will be maintained by the general population during the select heel raise test versions, but individualized performance is variable and total repetitions do not distinguish between versions. Clinicians should, therefore, interpret select heel raise test outcomes with caution when used to respectively assess and rehabilitate soleus and gastrocnemius function.

  • 26.
    Hébert-Losier, Kim
    et al.
    Mid Sweden University, Faculty of Human Sciences, Department of Health Sciences.
    Stöggl, Thomas
    University of Salzburg.
    Holmberg, Hans-Christer
    Mid Sweden University, Faculty of Human Sciences, Department of Health Sciences.
    Handedness, footedness, and ski-side dominance in elite cross-country skiers2012Conference paper (Refereed)
  • 27.
    Hébert-Losier, Kim
    et al.
    Mid Sweden University, Faculty of Human Sciences, Department of Health Sciences.
    Supej, Matej
    Faculty of Sport, Department of Biomechanics, University of Ljubljana, Ljubljana, Slovenia.
    Holmberg, Hans-Christer
    Mid Sweden University, Faculty of Human Sciences, Department of Health Sciences.
    Biomechanical Factors Influencing the Performance of Elite Alpine Ski Racers2014In: Sports Medicine, ISSN 0112-1642, E-ISSN 1179-2035, Vol. 44, no 4, p. 519-533Article, review/survey (Refereed)
    Abstract [en]

    BackgroundAlpine ski racing is a popular international winter sport that is complex and challenging from physical, technical, and tactical perspectives. Despite the vast amount of scientific literature focusing on this sport, including topical reviews on physiology, ski-snow friction, and injuries, no review has yet addressed the biomechanics of elite alpine ski racers and which factors influence performance. In World Cup events, winning margins are often mere fractions of a second and biomechanics may well be a determining factor in podium place finishes.

    Objective The aim of this paper was to systematically review the scientific literature to identify the biomechanical factors that influence the performance of elite alpine ski racers, with an emphasis on slalom, giant slalom, super-G, and downhill events.

    Methods Four electronic databases were searched using relevant medical subject headings and key words, with an additional manual search of reference lists, relevant journals, and key authors in the field. Articles were included if they addressed human biomechanics, elite alpine skiing, and performance. Only original research articles published in peer-reviewed journals and in the English language were reviewed. Articles that focused on skiing disciplines other than the four of primary interest were excluded (e.g., mogul, ski-cross and freestyle skiing). The articles subsequently included for review were quality assessed using a modified version of a validated quality assessment checklist. Data on the study population, design, location, and findings relating biomechanics to performance in alpine ski racers were extracted from each article using a standard data extraction form.

    Results A total of 12 articles met the inclusion criteria, were reviewed, and scored an average of 69 ± 13 % (range 40–89 %) upon quality assessment. Five of the studies focused on giant slalom, four on slalom, and three on downhill disciplines, although these latter three articles were also relevant to super-G events. Investigations on speed skiing (i.e., downhill and super-G) primarily examined the effect of aerodynamic drag on performance, whereas the others examined turn characteristics, energetic principles, technical and tactical skills, and individual traits of high-performing skiers. The range of biomechanical factors reported to influence performance included energy dissipation and conservation, aerodynamic drag and frictional forces, ground reaction force, turn radius, and trajectory of the skis and/or centre of mass. The biomechanical differences between turn techniques, inter-dependency of turns, and abilities of individuals were also identified as influential factors in skiing performance. In the case of slalom and giant slalom events, performance could be enhanced by steering the skis in such a manner to reduce the ski-snow friction and thereby energy dissipated. This was accomplished by earlier initiation of turns, longer path length and trajectory, earlier and smoother application of ground reaction forces, and carving (rather than skidding). During speed skiing, minimizing the exposed frontal area and positioning the arms close to the body were shown to reduce the energy loss due to aerodynamic drag and thereby decrease run times. In actual races, a consistently good performance (i.e., fast time) on different sections of the course, terrains, and snow conditions was a characteristic feature of winners during technical events because these skiers could maximize gains from their individual strengths and minimize losses from their respective weaknesses.

    Limitations Most of the articles reviewed were limited to investigating a relatively small sample size, which is a usual limitation in research on elite athletes. Of further concern was the low number of females studied, representing less than 4 % of all the subjects examined in the articles reviewed. In addition, although overall run time is the ultimate measure of performance in alpine ski racing, several other measures of instantaneous performance were also employed to compare skiers, including the aerodynamic drag coefficient, velocity, section time, time lost per change in elevation, and mechanical energy behaviours, which makes cross-study inferences problematic. Moreover, most studies examined performance through a limited number of gates (i.e., 2–4 gates), presumably because the most commonly used measurement systems can only capture small volumes on a ski field with a reasonable accuracy for positional data. Whether the biomechanical measures defining high instantaneous performance can be maintained throughout an entire race course remains to be determined for both male and female skiers.

    Conclusions Effective alpine skiing performance involves the efficient use of potential energy, the ability to minimize ski-snow friction and aerodynamic drag, maintain high velocities, and choose the optimal trajectory. Individual tactics and techniques should also be considered in both training and competition. To achieve better run times, consistency in performance across numerous sections and varied terrains should be emphasized over excellence in individual sections and specific conditions.

  • 28.
    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.

  • 29.
    Jensby Nedergaard, Niels
    et al.
    Department of Health Science and Technology, Center for Sensory-Motor Interaction, Aalborg University, Aalborg, Denmark.
    Heinen, Frederik
    Department of Health Science and Technology, Center for Sensory-Motor Interaction, Aalborg University, Aalborg, Denmark.
    Sloth, Simon
    Department of Health Science and Technology, Center for Sensory-Motor Interaction, Aalborg University, Aalborg, Denmark.
    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.
    Kersting, Uwe
    Mid Sweden University, Faculty of Human Sciences, Department of Health Sciences.
    The effect of light reflections from the snow on kinematic data collected using stereo-photogrammetry with passive markers2014In: Sports Engineering, ISSN 1369-7072, E-ISSN 1460-2687, Vol. 17, no 2, p. 97-102Article in journal (Refereed)
    Abstract [en]

    This study aimed to compare kinematic data collected during ski-cross starts outdoors on snow in daylight (high albedo) to similar data collected indoors with infiltrating sunlight but without light reflections from the snow (low albedo) using a video-based motion capture system with the active filtering function enabled. A 12-camera 3D motion capture system (Qualisys AB, Sweden) was used to measure test objects and eight skiers performing a ski-cross start on a slope outdoors and on a wooden start ramp indoors. The average residuals and standard deviations of the length of the calibration wand calculated indoors and outdoors by the calibration software were compared using descriptive statistics. Static and moving fixed length measures and thigh length measures were compared using Bland-Altman plots. Calibration residuals were slightly increased outdoors (1.77 mm) compared to indoors (1.54 mm), while wand length varied by 3.63 and 1.51 mm, respectively. Fixed static lengths differed by -8.65 ± 4.94 mm (shorter indoors), whereas fixed moving lengths differed by 0.85 ± 1.05 mm (longer indoors). A randomly chosen marker pair on one segment (Thigh) showed a mean difference of 1.19 ± 22.05 mm (longer indoors). It is concluded that 3D motion capture outdoors on snow in daylight is feasible, provides kinematic data comparable to indoors, and could be used to research biomechanics in snow sports.

  • 30.
    Lussiana, T.
    et al.
    Research Unit EA4660, Culture Sport Health Society and Exercise Performance Health Innovation Platform, Franche-Comté University, Besançon, France .
    Fabre, Nicolas
    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.
    Mourot, L.
    Research Unit EA4660, Culture Sport Health Society and Exercise Performance Health Innovation Platform, Franche-Comté University, Besançon, France .
    Effect of slope and footwear on running economy and kinematics2013In: Scandinavian Journal of Medicine and Science in Sports, ISSN 0905-7188, E-ISSN 1600-0838, Vol. 23, no 4, p. e246-e253Article in journal (Refereed)
    Abstract [en]

    Lower energy cost of running (Cr) has been reported when wearing minimal (MS) vs traditional shoes (TS) on level terrain, but the effect of slope on this difference is unknown. The aim of this study was to compare Cr, physiological, and kinematic variables from running in MS and TS on different slope conditions. Fourteen men (23.4 +/- 4.4 years; 177.5 +/- 5.2cm; 69.5 +/- 5.3kg) ran 14 5-min trials in a randomized sequence at 10km/h on a treadmill. Subjects ran once wearing MS and once wearing TS on seven slopes, from -8% to +8%. We found that Cr increased with slope gradient (P<0.01) and was on average 1.3% lower in MS than TS (P<0.01). However, slope did not influence the Cr difference between MS and TS. In MS, contact times were lower (P<0.01), flight times (P=0.01) and step frequencies (P=0.02) were greater at most slope gradients, and plantar-foot angles - and often ankle plantar-flexion (P=0.01) - were greater (P<0.01). The 1.3% difference between footwear identified here most likely stemmed from the difference in shoe mass considering that the Cr difference was independent of slope gradient and that the between-footwear kinematic alterations with slope provided limited explanations.

  • 31.
    Lussiana, Thibault
    et al.
    Univ Franche Comte, Culture Sport Hlth Soc & Exercise Performance Hlt, Res Unit EA4660, F-25030 Besancon, France..
    Hebert-Losier, Kim
    Mid Sweden University, Faculty of Human Sciences, Department of Health Sciences. Natl Sports Inst Malaysia, Natl Sports Complex, Kuala Lumpur, Malaysia.;Mid Sweden Univ, Dept Hl Natl Sports Inst Malaysia, Natl Sports Complex, Kuala Lumpur, Malaysia.
    Millet, Gregoire P.
    Univ Lausanne, Fac Biol & Med, Dept Physiol, ISSUL Inst Sport Sci, Lausanne, Switzerland..
    Mourot, Laurent
    Univ Franche Comte, Culture Sport Hlth Soc & Exercise Performance Hlt, Res Unit EA4660, F-25030 Besancon, France.;CHRU Besancon, INSERM CIT 808, Clin Invest Ctr, Besancon, France..
    Biomechanical Changes During a 50-minute Run in Different Footwear and on Various Slopes2016In: Journal of Applied Biomechanics, ISSN 1065-8483, E-ISSN 1543-2688, Vol. 32, no 1, p. 40-49Article in journal (Refereed)
    Abstract [en]

    The effects of footwear and inclination on running biomechanics over short intervals are well documented. Although recognized that exercise duration can impact running biomechanics, it remains unclear how biomechanics change over time when running in minimalist shoes and on slopes. Our aims were to describe these biomechanical changes during a 50-minute run and compare them to those observed in standard shoes. Thirteen trained recreational male runners ran 50 minutes at 65% of their maximal aerobic velocity on a treadmill, once in minimalist shoes and once in standard shoes, 1 week apart in a random order. The 50-minute trial was divided into 5-minute segments of running at 0%, + 5%, and -5% of treadmill incline sequentially. Data were collected using photocells, high-speed video cameras, and plantar-pressure insoles. At 0% incline, runners exhibited reduced leg stiffness and plantar flexion angles at foot strike and lower plantar pressure at the forefoot and toes in minimalist shoes from minute 34 of the protocol onward. However, only reduced plantar pressure at the toes was observed in standard shoes. Overall, similar biomechanical changes with increased exercise time were observed on the uphill and downhill inclines. The results might be due to the unfamiliarity of subjects to running in minimalist shoes.

  • 32.
    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.

  • 33.
    Sperlich, Billy
    et al.
    Bergische Universität Wuppertal.
    Zinner, Christoph
    German Sport University Cologne.
    Hébert-Losier, Kim
    Mid Sweden University, Faculty of Human Sciences, Department of Health Sciences.
    Born, Dennis-Peter
    Bergische Universität Wuppertal.
    Holmberg, Hans-Christer
    Mid Sweden University, Faculty of Human Sciences, Department of Health Sciences.
    Biomechanical, cardiorespiratory, metabolic and perceived responses to electrically assisted cycling.2012In: European Journal of Applied Physiology, ISSN 1439-6319, E-ISSN 1439-6327, Vol. 112, no 12, p. 4015-4025Article in journal (Refereed)
    Abstract [en]

    The aims of the present study were to characterize the effects of cycling in varying terrain with the assistance of an electric motor with respect to (1) power output, velocity, and electromyography (EMG) signals; (2) cardiorespiratory parameters; (3) energy expenditure (EE); (4) rate of perceived exertion (RPE) and enjoyment and to compare these effects with those of non-assisted cycling. Eight sedentary women (age: 38 ± 15 years, BMI: 25.3 ± 2.1 kg m(-2)) cycled 9.5 km on varying terrain (change in elevation: 102 m, maximum incline: 5.8 %) at their own pace, once with and once without motorized assistance, in randomized order. With electrical assistance, the mean power output (-29 %); EMG patterns of the m. biceps femoris (-49 %), m. vastus lateralis (-33 %), m. vastus medialis (-37 %), and m. gastrocnemius medialis (-29 %); heart rate (-29.1 %); oxygen uptake (-33.0 %); respiratory exchange ratio (-9.0 %); and EE (-36.5 %) were all lower, whereas the mean cycling speed was higher (P < 0.05) than that without such assistance. In addition, following assisted exercise the mean blood lactate concentration and RPE were lower (P < 0.05) and ratings of enjoyment higher (P < 0.05). Moreover, motorized cycling was associated with (1) lower EMG with higher power output and speed; (2) less cardiorespiratory and metabolic effort; (3) lower respiratory exchange ratio; (4) lower RPE with more enjoyment; and (5) sufficient EE, according to present standards, to provide health benefits. Thus, electrically assisted cycling may represent an innovative approach to persuading reluctant sedentary women to exercise.

  • 34.
    Stöggl, Thomas
    et al.
    Mid Sweden University, Faculty of Human Sciences, Department of Health Sciences. Department of Sport Science and Kinesiology, University of Salzburg, Schlossallee 49, 5400 Hallein/Rif, Salzburg, Austria.
    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 Olympic Committee, Stockholm, Sweden .
    Do Anthropometrics, Biomechanics, and Laterality Explain V1 Side Preference in Skiers?2013In: Medicine & Science in Sports & Exercise, ISSN 0195-9131, E-ISSN 1530-0315, Vol. 45, no 8, p. 1569-1576Article in journal (Refereed)
    Abstract [en]

    PURPOSE: In cross-country (XC) skiing, the V1 and V2 alternate skate techniques are asymmetric, and skiers can choose either the right or left side for pole support. The overall purpose of this study was to investigate V1 side preference in elite XC skiers, notably by documenting V1 skate side preference, dominant and nondominant V1peak speeds, left- to right-side differences (ΔL-R) in laboratory-based measurements, and relationships between side preference data. METHODS: Sixteen male elite XC skiers completed one incremental speed test using V1 on their dominant side and another incremental speed test using V1 on their nondominant side while roller-skiing on a treadmill. During these tests, V1peak speed, pole forces, and plantar forces were measured. A whole-body dual-energy x-ray absortiometry (DXA) scan measured anthropometric parameters and questionnaires established side preference for V2 alternate, overall laterality in XC skiing, handedness, footedness, and injury prevalence. RESULTS: Left-to-right V1 side preference was equally distributed among skiers. V1peak speed was approximately 4.5% greater on the dominant versus nondominant sides. V1peak Δ L-R were positively related to Δ L-R in V1-dominant peak pole forces only. Questionnaire data indicated that more skiers preferred V2 alternate right, with moderate correlations between preferred V1 and V2 alternate sides. The expression of a dominant side in V1 and V2 alternate increased as skiing speed increased from moderate to 15-km endurance-race to sprint-race speeds. However, no relationships were established between V1 or V2 side preference and handedness, footedness, or number of one-sided injuries. CONCLUSIONS: ΔL-R in measurements provide limited explanations for V1 side preferences in elite XC skiers. In fact, no systematic relations exist between V1 side preferences and anthropometric, biomechanical, or questionnaire data. Copyright © 2013 by the American College of Sports Medicine.

  • 35.
    Supej, Matej
    et al.
    Univ Ljubljana, Dept Biomech, Ljubljana, Slovenia.
    Hebert-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.
    Impact of the Steepness of the Slope on the Biomechanics of World Cup Slalom Skiers2015In: International Journal of Sports Physiology and Performance, ISSN 1555-0265, E-ISSN 1555-0273, Vol. 10, no 3, p. 361-368Article in journal (Refereed)
    Abstract [en]

    Purpose: Numerous environmental factors can affect alpine-ski-racing performance, including the steepness of the slope. However, little research has focused on this factor. Accordingly, the authors' aim was to determine the impact of the steepness of the slope on the biomechanics of World Cup slalom ski racers. Methods: The authors collected 3-dimensional kinematic data during a World Cup race from 10 male slalom skiers throughout turns performed on a relatively flat (19.8 degrees) and steep (25.2 degrees) slope under otherwise similar course conditions. Results: Kinematic data revealed differences between the 2 slopes regarding the turn radii of the skis and center of gravity, velocity, acceleration, and differential specific mechanical energy (all P < .001). Ground-reaction forces (GRFs) also tended toward differences (P = .06). Examining the time-course behaviors of variables during turn cycles indicated that steeper slopes were associated with slower velocities but greater accelerations during turn initiation, narrower turns with peak GRFs concentrated at the midpoint of steering, more pronounced lateral angulations of the knees and hips at the start of steering that later became less pronounced, and overall slower turns that involved deceleration at completion. Consequently, distinct energy-dissipation-patterns were apparent on the 2 slope inclines, with greater pregate and lesser postgate dissipation on the steeper slope. The steepness of the slope also affected the relationships between mechanical skiing variables. Conclusions: The findings suggest that specific considerations during training and preparation would benefit the race performance of slalom skiers on courses involving sections of varying steepness.

  • 36.
    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)
1 - 36 of 36
CiteExportLink to result list
Permanent link
Cite
Citation style
  • apa
  • ieee
  • modern-language-association-8th-edition
  • vancouver
  • Other style
More styles
Language
  • de-DE
  • en-GB
  • en-US
  • fi-FI
  • nn-NO
  • nn-NB
  • sv-SE
  • Other locale
More languages
Output format
  • html
  • text
  • asciidoc
  • rtf