Science and Skiing IV E-Book

Erich Müller

• Herausgeber: Meyer & Meyer Sport (UK) Ltd.
• Kategorie: Lebensstil
• Serie: Science and Skiing
• Sprache: Englisch
• Veröffentlichungsjahr: 2010

Seitenzahl: 914

Beschreibung

The book contains the proceedings of the Fourth International Congress on Science and Skiing, which was held at St. Christoph am Arlberg, Tyrol, Austria. The conference was organized and hosted by the Department of Sport Science at the University of Salzburg, Austria, and by the Christian Doppler Laboratory "Biomechanics in Skiing", Salzburg, Austria. It was also part of the programs of the steering group "Science in Skiing" of the World Commission of Sports Science and contains a broad spectrum of current research work in alpine and nordic skiing and in snowboarding. In the proceedings of this congress, the keynotes and invited lectures as well as the oral presentations are published. The manuscripts were subject to peer review and editorial judgement prior to acceptance.

Leseprobe

SCIENCE AND SKIING IV

SCIENCE AND SKIING IV

Edited by

Erich MüllerStefan LindingerThomas Stöggl

Meyer & Meyer Sport

British Library Cataloguing in Publication DataA catalogue record for this book is available from the British Library

Science and Skiing IVErich Müller, Stefan Lindinger, Thomas Stöggl (Eds.)Maidenhead: Meyer & Meyer Sport (UK) Ltd., 2009ISBN: 978-1-84126-255-0

All rights reserved, especially the right to copy and distribute,including the translation rights. No part of this work may be reproduced—including by photocopy, microfilm or any other means—processed, stored electronically, copied or distributed in any form whatsoeverwithout the written permission of the publisher.

© 2009 by Meyer & Meyer Sport (UK) Ltd.Aachen, Adelaide, Auckland, Budapest, Cape Town, Graz, Indianapolis,Maidenhead, New York, Ölten (CH), Singapore, TorontoMember of the World Sport Publishers’ Association (WSPA)www.w-s-p-a.orgPrinted by: CPI Wöhrmann Print ServiceISBN: 9781841262550eISBN 9781841264295E-Mail: [email protected]

Contents

Introduction

PART ONE: KEYNOTE PAPERS

Vibration exposure in alpine skiing and consequences for muscle activation levels

P. Federolf, V. von Tscharner, D. Haeufle, B. Nigg, M. Gimpl and E. Müller

Importance of sensorimotor training for injury prevention and athletic performance

A. Gollhofer and M. Gruber

Eccentric exercise in alpine skiing

H. Hoppeler and M. Vogt

Alpine skiing technique - practical knowledge and scientific analysis

S. Loland

Stimuli and stimulation: hypoxia and mechanics

J. Mester, S. Achtzehn, M. de Marées, E. Engelmeyer, A. M. Liphardt and F. Suhr

PART TWO: INVITED PAPERS

Diet and muscle fatigue during two weeks of alpine ski training

D. W. Bacharach and K. J. Bacharach

Prediction of ankle ligament elongations in snowboarding using a kinematic model

S. Delorme, M. Lamontagne and S. Tavoularis

The competitive Cross - Country Skier - an impressive human engine

H.-C. Holmberg

Equipment development and research for more performance and safety 1

V. Senner, S. Lehner and H. Böhm

PART THREE: ALPINE SKIING

Alpine skiing and snowboarding training system using induced virtual environment

V. Aleshin, S. Klimenko, M. Manuilov and L. Melnikov

Heart rate recovery in young alpine skiers with congenital heart disease

M. Bernhörster, A. Rosenhagen, M. Castano, L. Vogt, R. Hofstetter and W. Banzer

Emotional experiences and FLOW in easy bump pistes

T. Brandauer, T. Felder and V. Senner

How to ski faster: art or science?

M. Brodie, A. Walmsley and W. Page

Modeling edge-snow interactions using machining theory

C. A. Brown

Predictors of falls in downhill skiing and snowboarding

M. Burtscher, R. Pühringer, I. Werner, R. Sommersacher and W. Nachbauer

Preliminary results on the role of the coach-athlete relationship in a developing ski nation

S. Chroni, I. Lefoussi and M. Kalomirou

Measurement of dynamical ski behavior during alpine skiing

M. Fauve, M. Auer, A. Lüthi, H. Rhyner and J. Meier

Analysis of skiers’ performance using GPS

P. J. Gómez-López, O. Hernán and J. V. Ramírez

System-Theory-Based-Model-Building for a practice and theory of alpine skiing

H. Haag

Calculation of the pressure distribution between ski and snow

D. Heinrich, P. Kaps, M. Mössner, H. Schretter and W. Nachbauer

Eccentric and concentric torque of knee extension and flexion in alpine ski racers

H. Hoshino, K. Tsunoda and T. Sasaki

Influence of the skier’s body geometry on the duration of the giant slalom turn

Z. Hraski and M Hraski

Description of race cources and estimation of ground reaction forces by GPS-Data and video

A. Huber, K.-H. Waibel and P. Spitzenpfeil

Identification of the physical characteristics that discriminate between competitive levels and specialties of alpine skiers

F.M. Impellizzeri, E. Rampinini, M. Freschi, N. A. Maffiuletti, M. Bizzini and P. Mognoni ΐ

Development of a measuring system on ski deflection and contacting snow pressure in turns

H. Kagawa, T. Yoneyama, D. Tatsuno, N. Scott and K. Osada

Not the skier - but the slope turns the skis

G. Kassat

Athlete responses to using a real time Optical Navigation Feedback System during ski training

R. Kirby

Influence of physical fitness on individual strain during recreational skiing in the elderly

S. Krautgasser, P. Scheiber, J. Kröll, S. Ring-Dimitriou and E. Müller

EMG signal processing by wavelet transformation - applicability to alpine skiing

J. Kröll, J. M. Wakeling, J. Seifert and E. Müller

Effects of a mock-up force plate on riding technique and perception - a prerequisite for comprehensive biomechanical analyses in mogul skiing

N. Kurpiers, U. G. Kersting and P. R. McAlpine

Robot imitating human skiing used for teaching and equipment testing

L. Lahajnar and B. Nemec

Applications of physics education research to skiing pedagogy for coaches and instructors

R. LeMaster

H:Q ratios in open versus closed kinetic chain: what is the relevance for alpine ski racers?

S. Lembert, C. Raschner, H.-P. Platzer, C. Patterson and E. Mildner

Physiological profile of Swiss elite alpine skiers - a 10-year longitudinal comparison

N. A. Maffiuletti, K. Jordan, H. Spring, F. M. Impellizzeri and M. Bizzini

Effects of ski stiffness in a sequence of ski turns

M. Mössner, D. Heinrich, P. Kaps, H. Schretter and W. Nachbauer

Power endurance testing in alpine ski racing

C. Patterson, C. Raschner, H.-P. Platzer and S. Lembert

Acquisition of EMG signals during slalom with different ski boots 399 N. Petrone, G. Marcolin, M. De Gobbi, M. Nicoli and C. Zampieri

Loading conditions and neuromuscular activity during vertical knee flexion-extension and turn-like movements in a new skiing simulator under vibration conditions

R. Pozzo, F. Zancolò, A. Canclini and G. Baroni

Turn characteristics and energy dissipation in slalom

R. Reid, M. Gilgien, T. Moger, H. Tj0rhom, P. Haugen, R. Kipp and G. Smith

Transfer from inline-skating to alpine skiing learning in physical education

B. Román, Ma. T. Miranda, M. Martínez and J. Viciana

Quantitative assessment of physical activity during leisure alpine skiing

A. Rosenhagen, C. Thiel, L. Vogt and W. Banzer

Guided Alpine Skiing - Physiological demands on elderly recreational skiers

P. Scheiber, S. Krautgasser, J. Kröll, E. Ledl-Kurkowski and E. Müller

Biomechanical basis for differential learning in alpine skiing

W. I. Schöllhorn, P. Hurth, T. Kortmann and E. Müller

Cumulative muscle fatigue during recreational alpine skiing

J. Seifert, J. Kröll and E. Müller

Mechanical load and muscular expenditure in alpine ski racing and implications for safety and material considerations

P. Spitzenpfeil, A. Huber and K. Waibel

Relationship between vertical jumps and different slalom courses

V. Strojnik and A. Dolenec

A step forward in 3D measurements in alpine skiing: a combination of an inertial suit and DGPS technology

M. Supej

Measurement of ski deflection and ski-snow contacting pressure in an actual ski turn on the snow surface

D. Tatsuno, T. Yoneyama, H. Kagawa, N. Scott and K. Osada

Physiologic characteristics of leisure alpine skiing and snowboarding

C. Thiel, A. Rosenhagen, L. Roos, M. Huebscher, L. Vogt and W. Banzer

The influence of the laterality of the lower limbs on the symmetry of connected carving turns

F. Vaverka and S. Vodickova

The method of time analysis of a carving turn and its phases

S. Vodickova and F. Vaverka

Respiratory and metabolic demands of field versus laboratory tests in young competitive alpine ski racers

S. P. von Duvillard, D. Bacharach and F. Stanek

Assessment of timing and performance based on trajectories from low-cost GPS/INS positioning

A. Waegli, F. Meyer, S. Ducret, J. Skaloud and R. Pesty

Performance analyses in alpine ski racing regarding the characters of slopes and course settings

K. Waibel, A. Huber and P. Spitzenpfeil

PART FOUR: CROSS COUNTRY SKIING

3D analysis of the technique in elite ski-touring and cross-country skiers engaged in world cup races and on a treadmill

A. Canclini, G. Baroni, R. Pozzo, M. Pensini and G. Rossi

Individual modeling of the competition activities for elite female ski races during the 2006-2007 season

A. Cepulénas

Intra- and inter-individual variations in the daily haemoglobin and hematocrit concentration in elite cross country skiers caused by different body positions, state of hydration, exercise and altitude

E. Engelmeyer, M. de Marées, S. Achtzehn, C. Lundby, B. Saltin and J. Mester

Visibility and availability of GPS in cross-country skiing

A. Krüger, K. Sikorski, J. Edelmann-Nusser and K. Witte

Simulation of classical skiing using a new ski tester

V. Linnamo, V. Kolehmainen, P. Vähäsöyrinki and P. Komi

Balance performance of elderly cross-country skiers - standing still or swaying smart?

V. Lippens and V.Nagel

Biomechanics in classical cross-country skiing - past, present and future

W. Rapp, S. Lindinger, E. Müller and H.-C. Holmberg

Biomechanical factors of biathlon shooting in elite and youth athletes

G. Sattlecker E. Müller and S. Lindinger

Effectiveness of ski and pole forces in ski skating

G. Smith, B. Kvamme and V. Jakobsen

Competition analysis of the last decade (1996 – 2008) in crosscountry skiing

T. Stöggl, J. Stöggl and E. Müller

PART FIVE: SNOWBOARDING

Jump landings in snowboarding: an observational study

P. McAlpine, N. Kurpiers and U. Kersting

Influence of physical fitness parameters on performance in elite snowboarding

H.-P. Platzer, C. Raschner, C. Patterson and S. Lembert

Optimizing snowboard cross and ski cross starts: a new laboratory testing and training tool

C. Raschner, H.-P. Platzer, C. Patterson, M. Webhofer, A. Niederkofler, S. Lembert and E. Mildner

Lift generation in soft porous media with application to skiing or snowboarding

Q. Wu and Q. Sun

PART SIX: SKI JUMPING

Kinematic analysis of the landing phase in ski jumping

F. Greimel, M. Virmavirta and H. Schwameder

Stability during ski jumping flight phase

F. Hildebrand, V. Drenk and S. Müller

The relationship between the timing of take-off action and flight length by using the doll-model

T. Sasaki, K. Tsunoda, H. Hoshino, S. Miyake and M.Ono

PART SEVEN: HIGH ALTITUDE TRAINING IN SKIING

Effect of hypoxic training on angiogenetic regulators and mesenchymal stem cells

M. de Marées, P. Wahl, F. Suhr, S. Achtzehn, A. Schmidt, W. Bloch and J. Mester

The anatomical hazards of the grip wrist tunnel syndromes

S. Provyn, P. Van Roy and J. P. Clarys

Oxygen uptake during local vibration and cycling

B. Sperlich, H. Kleinöder, M. de Marées, D. Quarz and J. Mester

Effects of short term high-intensity exercise under noroxic and hypoxic conditions and warming up on erythrocyte and plasma lactate concentrations after a giant slalom simulation

P. Wahl, C. Zinner, E. Lenzen, M. Hägele, S. Achtzehn, W. Bloch and J. Mester

Introduction

The Fourth International Congress on Science and Skiing was held at St. Christoph a. A., Tyrol, Austria. It was the follow up conference of the first two International Congresses on Skiing and Science, which were also held in St. Christoph a. A., Austria, in January 1996 and in January 2000 and of the Third International Congress on Science and Skiing, which was held in Aspen, Colorado, USA, in April 2004.

The conference was organized and hosted by the Department of Sport Science at the University os Salzburg, Austria, and by the Christian Doppler Laboratory “Biomechanics in Skiing”, Salzburg, Austria. It was also again part of the programmes of the steering group “Science in Skiing” of the World Commission of Sports Science.

The scientific programme offered again a broad spectrum of current research work in Alpine and Nordic skiing and in snowboarding. The highlights of the congress were eight keynote and four invited lectures. The scientific programme of the congress was completed by 2 work shops, 82 oral presentations and 76 poster presentations.

In the proceedings of this congress, the keynotes and invited lectures as well as the oral presentations are published. The manuscripts were subject to peer review and editorial judgement prior to acceptance.

We hope that these congress proceedings will again stimulate many of our colleagues throughout the world to enhance research in the field of skiing so that at the Fifth International Congress on Science and Skiing, which will be organized in the winter 2010/11, many new research projects will be presented.

Erich MüllerStefan LindingerThomas Stöggl

We would like to express our cordial thanks to Elke Lindenhofer for the time and the energy which she invested in the editting of this book.

Part One

Keynote Papers

Vibration exposure in alpine skiing and consequences for muscle activation levels

P. Federolf1, V. von Tscharner1, D. Haeufle1, B. Nigg1, M. Gimpl2 and E. Müller2

1 Human Performance Laboratory, University of Calgary, Alberta, Canada

2 Christian Doppler Laboratory Biomechanics in Skiing, University of Salzburg, Austria

1     Introduction

Vibration exposure is known to affect muscle physiology and neuromuscular activity. The effect of whole body vibrations on muscle activation has been studied in the context of balance and postural control, passenger safety in vehicles, and vibration training in sports. Mester et al. (1999) have shown that strong ski vibrations are generated at the ski-snow interface that propagate through the whole body of the skier. The vibrations create resonance phenomena in soft tissue compartments. Vibrations are especially harmful for the brain, the eyes or ears and organs sensitive to vibrations (Griffin, 1975; Zou et al., 2001). They further hamper motion control (steering quality) and increase the risk of falls and injuries.

To prevent the damaging effects of vibrations different damping mechanisms are used by the human body. The main damping is believed to occur in the leg joints: passively by the cartilage and soft tissue attached to the bones or actively by stiffening the joints by muscle contraction (co-contraction). Vibration dependent muscle tuning has been proposed as damping mechanism (Nigg, 1997; Nigg and Liu, 1999). Muscle tuning has been studied for walking and running using accelerometers for measuring the vibrations (Wakeling et al., 2003; Boyer & Nigg, 2007). However, vibrations and possible muscle tuning has not been studied in skiing, an activity with high soft tissue vibrations. Thus, the purpose of this study was

1. to characterize intensity and frequency content of equipment vibrations for different skiing techniques and for different snow conditions using the wavelet analysis method,

2. to quantify simultaneously vibration intensities and muscle activation signals on four muscles of the lower extremities during alpine skiing,

3. to characterize vibration damping within the body,

4. to determine resonance frequencies of the soft tissue compartments of calf, thigh, and hamstrings and

5. to determine whether muscle activation levels change for conditions with different vibration exposure.

2     Methods

Ten experienced skiers completed 24 runs performing 5–7 short turns, 6 carving turns, and gliding in tuck position. The 24 trials of each subject were conducted between 9am, and 12.30pm. For eight of the ten subjects, snow conditions changed from hard frozen to soft snow during this time.

The skiers were equipped with 1-D acceleration sensors (Analog Devices™ (ADXL series), range: 35 to 120g) placed in axial direction on the shaft of the ski boot (parallel to the tibia), on the muscle compartments of triceps surae, quadriceps and hamstrings, and on the skin covering bones close to the ankle, knee hip and neck joints. Muscle activation was measured using bipolar surface EMG sensors on the gastrocnemius, vastus medialis, vastus lateralis, and semitendinosus. All sensor signals were recorded with a mobile EMG measurement device (Biovision™) carried in a backpack. EMG and acceleration signals were collected at a frequency of 2000 Hz.

For each run three specific movements were selected for further analysis: four consecutive short turns (2.8 ± 0.3 sec.), four consecutive carving turns (6.4 ± 0.6 sec.) and two seconds of gliding in tuck position. Short turns are highly dynamic movements in which the muscles act mainly concentric. Carving turns are executed at high speeds with little body motion. Due to centripetal forces the skiers’ muscles are loaded mainly eccentrically. Gliding was executed in the tuck position, characterized by relatively small hip and knee angles. In this position the muscles are mainly isometrically contracted.

The recorded acceleration signal was resolved with a wavelet transformation into intensities calculated for a set of 22 center frequencies between 0.6 and 80 Hz. EMG data was resolved using 13 wavelets with center frequencies between 6.9 and 542 Hz. In both cases, wavelet transformations (von Tscharner, 2000) were used, because the intensity calculated for each wavelet (each frequency range) is normalized with respect to the energy content of the analyzed signal. At a given time, the total intensity was calculated by adding the intensities of all wavelets. The square root of the total intensity is proportional to the signal amplitude and was called magnitude of the signal. The mean total intensity of a signal (EMG or acceleration) during a specific movement was calculated by averaging the total intensity over time. The mean total intensity characterized the vibration intensity or muscle activation level of the selected movement and can be compared between trials. The spectrum of a signal (EMG or acceleration) was calculated by integrating the intensity of each wavelet over time. Hence, the frequency range and frequency resolution of the spectrum derived from the wavelet analysis depended on the number wavelets and on their center frequencies.

Vibration damping within the skier’s body was characterized by dividing the vibration magnitudes determined at hip and neck by the vibration magnitudes measured at the ankle. Ankle vibrations were considered input vibrations for the body. This procedure provided only approximate values for the damping because all vibration signals were recorded with 1-D acceleration sensors.

Resonances of soft tissue compartments were determined by dividing the intensity spectrum measured at a soft tissue compartment by the intensity spectrum measured at the ankle (vibration input). The resonance frequency was determined as the frequency at which this quotient was maximal. Frequencies below 10 Hz were not considered, because the skiing movements are in this range.

To determine if muscle activation levels change if the intensity of the vibration exposure changes, Pearson’s correlation coefficient r between mean total intensity of the EMG signal and the mean total intensity of the acceleration signal was calculated for the 24 trials of each subject.

3     Results

Equipment vibrations measured at the ski boot showed peak accelerations between 20 to 30 g in the steering phase in short turns. Vibrations were small during turn initiation (~2 g) and during gliding (~5 g). In carving vibration amplitudes were in the range of 5 to 20 g. It seemed that vibrations were high when the ski skidded, and when the ground reaction forces were high. Frequency spectra were highly subject specific, but in all subjects the peak intensities were found in the range of 5 to 30 Hz. As the snow turned softer in the course of the day, frequencies above 15 to 20 Hz were increasingly damped.

All subjects showed strong vibration damping within the body. At 10 Hz, mean vibration magnitudes measured at the hip and neck decreased to 30% and 20%, respectively, compared to vibration amplitudes measured at the subject’s ankle. With increasing frequency these vibration amplitudes decreased further. Above 60 Hz the vibration amplitudes were less than 12% for the hip and less than 5% for the ankle.

Resonances frequencies of the muscle compartments were subject, muscle and movement specific. During short and during carving turns resonance frequencies occurred typically in the range of 10 to 30 Hz, in gliding the resonance frequencies were for most subjects and must muscles higher, typically in the 20 to 40 Hz range.

For eight subjects the snow turned significantly softer during the course of the day. In these cases the intensity of the vibrations the skiers were exposed to decreased significantly. The mean total intensity measured at the ankle decreased for short turns and carving by a factor between 2 and 3.5. In straight gliding the vibration intensities decreased by a factor of about 1.5. For short turns and carving, a concurrent decrease of muscle activation levels was observed. In short turns, the correlation coefficient r between the mean total intensity of the vibration exposure and the mean total intensity of the EMG signal was between 0.4 and 0.9. For the muscles the biceps femoris, gastrocnemius, vastus lateralis, and vastus medials the correlation was statistically significant for 6, 7, 6, and 5 of the subjects, respectively. In carving, statistically significant correlations were found for 7, 8, 6, and 5 subjects. Although the variability of

the vibration intensity in straight gliding was much smaller, significant correlations were found for 1, 2, 2, and 3 subjects.

4     Discussion

Vibration intensities observed at the equipment level (at the ski boot) differ for different skiing styles. This can be explained by different speeds, different skisnow interaction mechanisms (e.g. lateral skidding vs. cutting of the snow surface vs. gliding), or different equipment resonances (e.g. in case of edged skis torsional modes are excited, in case of flat skis mainly bending modes are excited). The results of this study also clearly indicate that the snow properties have substantial effect on the vibration intensity.

The vibrations present at the equipment level can be considered as the input vibrations the skier’s body is exposed to. Even at slow speeds and simple skiing styles used in this study, which are typical for recreational skiing, substantial and potentially hazardous vibration exposure levels were found. Accelerations measured during straight gliding exceeded the recommended limits of vibration exposure of international standards for work place safety (ISO Standard 2631) by a factor 10. Accelerations measured during carving or short turns exceeded these limits by a factor 20 or 30, respectively.

The high acceleration values found in this study at the ski level (input) may suggest that in addition to the motion control issues created by vibrations, the skier may also be at risk of sustaining injuries directly induced by vibrations. The most sensitive organs for vibrations injuries are the sensory systems of eyes (Griffin 1975) and ears (Zou et al., 2001). However, vibration injuries due to skiing were so far not reported and professions involving skiing, such as ski instructor or mountain guide, have not been associated with chronic injuries of the sensory organs. A possible explanation for this discrepancy is that the body posture assumed in skiing, with angled ankle, knee and hip joints, is well suited for damping the vibrations the body is exposed to. As a result, the sensitive organs in the head are well protected from the vibrations originating at the feet. This explanation is supported by the data found in this study: The vibration intensities measured at ankles, hip, and neck of the subjects indicate that vibrations are effectively damped within the body.

There are different damping mechanisms which might be used by the body including joint damping and damping through muscle tuning. In both cases, muscle action is needed to either maintain a desired joint angle, or to tune muscle stiffness. Consequently, it was expected that muscle activation levels increase if the intensity of the vibration exposure increases. During short turns and during carving the majority of the correlation coefficients calculated between EMG and acceleration data in fact showed a clear and statistically significant positive correlation. However, while all skiers showed this correlation in two or more of their muscles, most skiers also had muscles whose activity did not correlate with the vibration exposure levels. Two points should be considered when interpreting this result: (a) the primary function of muscle activity is the execution of the movement task. Although the movement task was similar during the 24 trials of each subject, fluctuations from changing choice in the route, from different snow surface conditions, and other influencing factors will create fluctuations in the muscle activation and might obscure the impact of vibration exposure levels. (b) when considering muscle tuning: only one muscle is required to change the resonance properties of the whole muscle compartment. It might be a more effective damping strategy, if the body avoids resonance by activating only specific muscles instead of all muscles in the muscle compartment. In gliding, only a small fraction of the subjects showed the expected correlation between muscle activation levels and vibration exposure levels. This can be explained by two additional points: (a) in gliding, compared to the other analyzed movements, the differences in vibration levels was much smaller, hence, fluctuations have a more severe effect on the calculated correlation. (b) In executing gliding the skiers have more “degrees of freedom” in their choice of body position and movements compared to short turns or carving turns which are well trained, automated movements, executed very similarly each time. In gliding, skiers may for example shift their weight between left leg and right leg to prevent fatigue. Such voluntary movements will cause strong fluctuations in the muscle activation levels, which render a correlation to vibration levels impossible.

References

Boyer K., Nigg B., 2007, Quantification of the input signal for soft tissue vibration during running, Journal of Biomechanics, 40 (8): 1877–1880.

Griffin, M. J., 1975, Levels of whole body vibration affecting human vision. Aviation Space and Environmental Medicine, 46 (8): 1033–1040.

Mester, J., Spitzenpfeil, P., Schwarzer, J., Seifritz, F., 1999, Biological reaction to vibration - implications for sport. Journal of Science and Medicine in Sport 2 (3): 211–226.

Nigg B., Liu W., 1999, The effect of muscle stiffness and damping on simulated impact force peaks during running. Journal of Biomechanics, 32 (8): 849–856.

Von Tscharner (2000). Intensity analysis in time-frequency space of surface myoelectric signals by wavelets of specified resolution, Journal of Electromyography and Kinesiology 10: 433–445.

Wakeling J., Liphardt A.-M., Nigg B., 2003, Muscle activity reduces soft-tissue resonance at heel-strike during walking, Journal of Biomechanics, 36 (12): 1761–1769.

Zou J, Bretlau P, Pyykkö I, Starck J, Toppila E., 2001, Sensorineural hearing loss after vibration: an animal model for evaluating prevention and treatment of inner ear hearing loss, Acta Oto-Laryngologica, 121 (2): 143–148.

Importance of sensorimotor training for injury prevention and athletic performance

A. Gollhofer and M. Gruber

Department of Sport Science, University of Freiburg, Germany

1 Introduction

A vast number of public campaigns propagate that active life style and participation in sports has many benefits for health. Alpine skiing is popular and attractive and definitely the most important winter sport activity at all. From elite Alpine Skiing we receive fascinating impressions about the flexibility, the powerful actions as well as the highly skilled compensative reactions necessary to preserve movement control in difficult situations. Bodily fitness and highly developed motor coordination is a prerequisite to exert and/or counteract rapid forces changes and to activate and control the limbs and the body during a downhill race or slalom competition.

Participation in sports, however, can also be harmful (Bahr et al 2003). In Alpine Skiing the technical development of the skiers and the bindings reduced a larger number of injuries by approximately one half (Duncan et al 1995). However, the rate of the knee injuries, more specifically, the rate for anterior cruciate ligament (ACL) injuries is increasingly high. Pujol et al (2007) provided evidence that 10% of all injuries in snow sports are injuries to the ACL. In their comparison of the top 30 athletes in the world, they reported an injury rate for males and females of 50% for ACL injuries during 25 years of competitive skiing.

Due to the long lever arms of the thigh and the shank and due to the fixation of the skiboot on the skies, the knee joint complex has especially in Alpine Skiing to tolerate and compesate huge rotational moments. For the ACL injuries in skiing two mechanisms are discussed: (A) A combination of hyperextension and anterior pivot shift when landing on the ski tails with extended knees and (B) a coincident valgus-flexions-external rotation moment applied typically occurring when the skier straddles the gate.

In the past, knee injuries have been related to deficits in muscular strength and strength training was consequently applied to meet the requirements of the sport discipline. In recent years an increasing number of papers showed that intra- and inter-muscular coordination of the muscles encompassing the knee joint complex is of high importance. Thus, in order to minimize the injury risks, preventive training setups are designed to address coordinative adaptation. For Alpine Skiing, however, an assessment of their potential role is still not investigated under controlled conditions.

2     Mechanical and/or sensory function of the ACL?

In the present chapter the functional neuromuscular properties of the hamstring muscles and the ACL are discussed in order to “motivate” specific training programs for an improved active knee joint control.

The mechanical function of the ACL in conjunction with PCL to ensure passively knee joint stability has been intensively investigated (Woo et al 1991). Quite a few histological research papers revealed that the ACL contains also mechanoreceptors (Freeman/Wyke 1967; Haus/Halata 1990) and it has been discussed whether these receptors may have functional importance as a feedback loop to secure and control the integrity of the knee joint. It has been argued that the hamstring muscles need to provide effective tension in order to avoid excessive anterior tibia displacements (Johansson et al 1990, 1991; Solomonow et al 1987). More recent studies confirmed the existence of a reflex arc between the ACL and the hamstrings in humans (Friemert et al 2005a; Friemert et al 2005b). Functionally, an intact reflex connexion between ACL and hamstring muscle could lead to a quick muscular reaction if the ligament is stretched. This would ensure a muscular security against excessive anterior tibia displacements. The segmented hamstring reflex activity found in the experiments was attributed to a short latency response (SLR) and a medium latency response (MLR) (Friemert et al 2005b).

Based on biomechanical and neurophysiological research Melnyk et al (2007) could show, that the MLR reflex response is functionally specific: In patients with a history of ACL rupture, the excitability of the stretch evoked reflex was considerably changed. Compared to the healthy leg, the latency of the MLR was prolonged and the amplitude of the anterior tibia translation which was measured with a standardized test stimulus significantly increased. From subjects reporting “giving way” symptoms after ACL injury they presented data that this “feeling” is not simply related to the decrease in mechanical joint stability. For the MLR component of the stretch response a significant prolonged latency could be observed. Thus, “giving way” is also associated with altered stretch reflex excitability that takes place on the spinal level. In their paper they concluded, that sensorimotor function may be influenced by appropriate training stimuli. It was suggested that sensorimotor training early after ACL rupture might be promising for a rapid restoration of joint function.

3     Benefits from sensorimotor training

Knee joint stiffness of the right leg was measured with an apparatus (Fig.1) allowing application of fast impulses to induce an anterior tibia translation in the knee joint. By two linear potentiometers tibia displacement calculated as the difference between the thigh and shank against a mounting frame.

Fig. 1: Device to induce anterior tibia displacements at the knee joint. With two linear potentiometers the relative displacement of patella and tibia plateau with respect to the mounting frame allow quantification of the anterior displacement of the shank relative to the thigh.

In order to study the reflex regulation, mechanical stimuli were adjusted which displaced the shank in anterior direction. Within 50 ms following the initial onset in displacement the maximum force of 358.2 ± 52.1 N was reached.

Following SMT the group training with ski boots showed increased knee joint stiffness for a given tibia displacement concomitant with enhanced emg responses of the hamstring muscles (Fig. 2). These findings underline the importance of fast hamstring actions to stabilize the knee joint which was reported for ACL-injured subjects during isometric leg extensions (McNair et al 1992). In the same line, the simulations based on a 3D model of the lower limb showed that increased hamstring force was superior to reduced quadriceps force in order to stabilize the ACL-deficient knee during gait (Shelbourne et al 2005).

Fig. 2: Individual and mean alterations of knee joint stiffness and hamstring reflex size (mean amplitude voltage of M. biceps femoris and M. semitendinosus from 30–90 ms after mechanical stimulus) before and after a 4 week sensori-motor training.

Considering knee joint injuries, it is of major importance that the enhanced activities of the hamstring muscles get directly feedback about the actual ACL load. Therefore, the adaptations following SMT have been taken to explain the reduced risk of suffering an ACL injury. However, an overall preventive effect of SMT on knee joint injuries is not yet proved according to prospective studies. There were no preventive effects reported after balance board training, considering acute knee joint injuries, in handball (Wedderkopp et al 1999) and volleyball players, respectively (Verhagen et al 2004).

Whether a SMT with a fixed ankle joint will increase the preventive effect in Alpine Skiing has urgently to be answered in future prospective training studies.

References

Bahr R, Kannus P and Van Mechelen W. (2003) Epidemiology and Prevention of Sports Injuries. In: Textbook of Sports Medicine, edited by Kjaer M, Krogsgaard M, Magnusson P, Engebretsen L,Roos H, Takala T and Woo SLY. Malden: Blackwell Science: 299–314

Duncan JB, Hunter R, Purnell M, Freeman J. Meniscal (1995) Injuries associated with anterior cruciate ligament tears in alpine skiers. Am J Sports Med 23:170–172

Freeman MA, Wyke B (1967) The innervation of the knee joint. An anatomical study and histological study in the cat. J Anat 101:505–532

Friemert B, Bumann-Melnyk M, Faist M, Schwarz W, Gerngross H, Claes L (2005b) Differentiation of hamstring short latency and medium latency response of the hamstring after tibia translation. Exp Brain Res 160:1–9

Friemert B, Faist M, Spengler C, Gerngross H, Claes L, Melnyk M (2005a) Intraoperative direct mechanical stimulation of the anterior cruciate ligament elicits short and medium latency hamstring reflexes. J Neurophysiol 94:3996–4001

Gruber M, Bruhn S, Gollhofer A (2006) Specific adaptations of neuromuscular control and knee joint stiffness following sensorimotor training. Int J Sports Med 27: 636641

Gruber M, Gollhofer A (2004) Impact of sensorimotor training on the rate of force development and neural activation. Eur J Appl Physiol 92:98–105

Haus J, Halata Z (1990) Innervation of the anterior cruciate ligament. Int Orthop 14:293–296

Johansson H, Sjolander P, Sojka P (1990) Activity in receptors afferents from the anterior cruciate ligament evokes reflex effects on fusimotor neurones. Neurosci Res 8:54–59

Johansson H, Sjolander P, Sojka P (1991) A sensory role for the cruciate ligaments. Clin Orthop 268:161–178

McNair PJ, Wood GA, Marshall RN (1992) Stiffness of the hamstring muscle and its relationship to function in anterior cruciate ligament deficient individuals. Clin Biomech 7: 131–137

Melnyk M, Faist M, Gothner M, Claes L, Friemert B (2007) Changes in stretch reflex excitability are related to “Giving Way” symptoms in patients with anterior cruciate ligament rupture. J Neurophysiol 97: 474–480

Pujol N, Roussaux Blanchi MP, Chambat P (2007) The incidence of anterior cruciate ligament injuries among competitive alpine skiers. A 25-year investigation. The American Journal of Sports Medicine 35:1070–1074

Shelbourne KB, Torry MR, Pandy MG (2005) Effect of muscle compensation on knee instability during ACL-deficient gait. Med Sci Sports Exerc 37: 642–648

Solomonow M, Baretta R, Zhou BH, Shoji H, Bose B, Beck C, D’Ambrosia R (1987) The synergistic action of the anterior cruciate ligament and thigh muscle in maintaining joint stability. Am J Sports Med 15:207–231

Taube, W., Gruber, M., Beck, S., Faist, M., Gollhofer, A., & Schubert, M (2007) Cortical and spinal adaptations induced by balance training: correlation between stance stability and corticospinal activation. Acta Physiol. 189, 347–358

Verhagen E, van der BA, Twisk J, Bouter L, Bahr R, Van Mechelen W (2004) The effect of a proprioceptive balance board training program for the prevention of ankle sprains: a prospective controlled trial. Am J Sports Med 32: 1385–1393

Wedderkopp N, Kaltoft M, Lundgaard B, Rosendahl M, Froberg K (1999) Prevention of injuries in young female players in European team handball. A prospective intervention study. Scand J Med Sci Sports 9: 41–47

Woo SL, Hollis JM, Adams DJ, Lyon RM, Takai S (1991) Tensile properties of the human femur-anterior cruciate ligament-tibia complex. The effects of specimen age and orientation. Am J Sports Med 19:217–225

Eccentric exercise in alpine skiing

H. Hoppeler and M. Vogt

Department of Anatomy, University of Bern, Baltzerstrasse 2, CH-3000 Bern 9

1 Background

In normal human movement muscles are used both to provide positive and negative external work. Positive work is a consequence of concentric muscle contractions, i.e. contractions in which activated muscles shorten (“shortening contraction”) and thus provide the external work. Typical dominant concentric muscle activities are observed during cycling, swimming or uphill walking. In cycling and swimming, the positive work of concentric exercise is dissipated mainly to overcome the frictional resistance of air or water. In the case of uphill walking, concentric muscle shortening leads to upward movement of the body’s center of mass, thus increasing the body’s potential energy against gravity. Eccentric contractions are defined as muscle activities that occur when the force applied to the muscle exceeds the force produced by the muscle. Under these conditions the activated muscle is lengthened (“lengthening contraction”). Eccentric contractions are generally used to decelerate or brake. This is classically illustrated by downhill walking during which eccentric contractions dissipate the potential energy gained by uphill walking. Eccentric muscle contractions are also used to tension tendons upon impact in order to allow tendons to be lengthened and thus to store energy. This energy can subsequently been released by elastic recoil (thus providing positive external work) to reduce the energetic cost of locomotion. The roles of concentric and eccentric muscle contractions in locomotion have succinctly been reviewed by (Dickinson et al. 2000). It is of interest to note that the topics of eccentric muscle contractions or eccentric exercise is massively under researched. A cursory glance at PubMed indicates that there are at least one order of magnitude more research papers published using concentric than eccentric exercise modalities.

The interest of eccentric exercise in alpine skiing stems from the fact that alpine skiing is dominantly eccentric in nature (Berg and Eiken. 1999). These authors (Berg et al. 1995) had shown for giant slalom turns that the eccentric lengthening phase of the knee extensors lasted twice as long as the concentric push-off phase (1.0 vs. 0.5 sec). Moreover, EMG activity on the outside leg during eccentric muscle actions significantly exceed that of concentric actions and was similar to the maximum isometric knee extension as estimated in laboratory tests. The maximum eccentric torque developed on the outside leg at the peak of a turn acts against the combined gravitational and centrifugal forces experienced by the skiers (Hintermann et al. 1995). Maximal eccentric torque and dosage of eccentric contraction by knee extensors may be the key limiting factors determining the maximum speeds at which gates can be passed in competitive alpine skiing. In view of the fact that it is common knowledge that training procedures should closely match competitive activity - there is surprisingly little emphasis put on specifics of eccentric training modalities for alpine skiers.

The current review reports some of the main physiological conditions of eccentric muscle exercise and eccentric muscle training. It further describes the properties of an eccentric training device (eccentric ergometer) primarily designed for rehabilitation as well as the use of this eccentric ergometer as a training adjunct in competitive alpine skiers.

2     Physiology of eccentric exercise

Comparing eccentric to concentric muscle contractions, four main distinctions can be made:

1. At the same shortening velocities (i.e. same angular velocities of limb movement) eccentric contractions are observed to produce far greater forces than concentric contractions (Asmussen 1953). ). For the case of the human knee extensors the difference in peak torque between concentric and eccentric contractions at 2.6 rad/s angular velocity can be as much as twofold (Colliander and Tesch 1989) It is further of note that the decrease of force production with increasing speed of isotonic contraction described by Hill (1938) is absent for eccentric contractions. This circumstance is putting muscle tissue at risk in particular at high negative angular velocities.

2. At similar force developments, eccentric contractions require substantially lower electromyographic activities (Asmussen 1953; Bigland-Ritchie and Woods 1976). This indicates that fewer motor units are recruited to produce the same tension as in concentric contractions. With fewer motor units active, eccentric motor tasks are inherently more difficult to control and coordinate.

3. The energetic cost of producing negative work during eccentric exercise is considerably lower than the cost of producing positive work during concentric exercise (Asmussen 1953; Bigland-Ritchie and Woods 1976; Knuttgen 1986). It is reported that there is an up to six-fold difference of the metabolic cost of producing concentric vs. eccentric work. As a consequence, the physiological responses such as pulmonary ventilation, heart rate, cardiac output and muscle blood flow are reduced accordingly with eccentric vs. concentric work.

4. Eccentric exercise can produce substantial damage to muscle cell structure (Friden et al. 1981; Friden et al. 1991), resulting in delayed onset of muscle soreness (DOMS) temporary decrease in muscle performance and an increase of muscle creatine kinase in the peripheral blood (see Clarkson et al. 1987). The structural and muscle functional deteriorations observed after eccentric exercise are fully reversible over a period of weeks and repeated bouts of eccentric exercise induce a protection of muscle tissue from the damaging consequences of unaccustomed eccentric exercise (Clarkson et al. 1992, McHugh 2003). (all refs in NFP)

In view of the very specific conditions of eccentric exercise outlined above (high mechanical load at low metabolic requirements and challenging coordination task) we felt that eccentric exercise should be evaluated as a training adjunct for alpine skiers.

3     Design and applications of an eccentric ergometer

We custom built an eccentric recumbent ergometer designed to deliver in excess of 3000 Watts of mechanical power (Fig. 1).

Fig. 1: An alpine junior skier training on our custom build eccentric ergometer

The ergometer is computer controlled and can be programmed to drive pedals forwards or backwards. Desired power output and cadence can freely be selected from a menu. The necessary torque to be supplied by the subject in order to achieve a selected power output at a selected cadence is displayed on the computer screen overlaid with the trace indicating the actual instantaneous torque delivered by the subjects. The subject is required to match the two curves as closely as possible. This is a visual - motor coordination task of considerable difficulty requiring constant attention. The software offers the option to estimate the difference of the executed vs. the target torque by the root mean square (RMS) of the difference of the two signals (indicated by the hatched area in Fig. 2). The ergometer can thus provide a numerical assessment of the quality of the coordination of the eccentric performance of a subject.

The same ergometer was previously used in a rehabilitation setting involving heart infarct patients (Steiner et al. 2004). In this setting, the ergometer was used to maximize mechanical load on lower extremity muscles within the low metabolic capacity of these patients. Maximal average mechanical loads attained during rehabilitation of heart infarct patients were up to 380 Watts.

4     Eccentric exercise with alpine skiers

Training protocols

In patients, elderly, untrained subjects or in endurance athletes, a negative work exercise program on the eccentric ergometer has to be started very carefully (Gerber et al. 2006, Daepp et al. 2007). When applying a low load of only 130 watts for 15 minutes untrained subjects get strong muscle soreness within 24 hours post exercise (Klossner et al. 2007). As in alpine skiing eccentric muscle action is very dominant during sport specific tasks (Berg et al. 1999), a higher initial training load can applied on elite skiers. Typically training on the eccentric bike can be started at around 400 watts for 20 minutes without getting muscle soreness in skiers (Weisskopf and Vogt 2007). Within 5 training sessions, alpine skiers were able to double the eccentric load up to 800 watts.

Effect of eccentric exercise on jumping performance

In competitive sports, exercise training on an eccentric ergometer was first applied to high school basket ball players (Lindstedt et al. 2002). These athletes trained for 6 weeks (30 min three times per week). During the training period the eccentric load was gradually increased until they were working at nearly 500 watts during the last three weeks. A weight training control group was drawn from the same high school basket ball players. All eccentric-trained subjects increased their jump height, with an overall mean increase by 8% (+5cm). In response to eccentric training, hopping frequency increased by 11%, suggesting an enhanced strain energy storage and recovery possibly related to an increased stiffness of the muscle-tendon unit.

We applied a similar 6-week eccentric training protocol on eight junior alpine skiers. They trained for 20 minutes on the eccentric ergometer in addition to 40 minutes concentric weight training during the same session three times per week. 7 subjects served as a concentric weight trained control group (60 min per session). Counter movement jumping height increased exclusively in the eccentric-trained group by 7.9% (+4.1cm, see also Fig. 3), similar to the results of the basket ball player study (Lindstedt et al. 2002). For the eccentric trained group, no changes were measured in peak and mean power during the concentric phase of counter movement jump as well as in squat jump height and performance. No changes in jumping performance and height were found in the concentric trained control group. Theses results therefore support the concept that eccentric exercise leads to improved storage and recovery of elastic energy. In this study, leg muscle mass (measured by DXA) increased by 1.9% (+242g) in the eccentric trained group only. Muscle fiber type distribution remained unchanged during eccentric training (type I fibers: pre 56%, post 59%, p=0.25) but decreased significantly in the concentric training group (type I fibers: pre 73%, post 67%, p<0.05). A significant between group effect was detected (p=0.01) for changes in fiber type composition.

Fig. 3: Changes in jumping height of junior alpine skiers performing multiple week concentric weight training (n=7) or training on the eccentric ergometer (n=8). Mean change ± S.E.M.

These studies show that double leg jumping performance (e.g. height) during counter movement jumps can be increased in well trained athletes without using jumps in the training sessions. It seems that this effect can primarily be attributed to changes in stiffness of the muscle-tendon complex.

Coordination or dosage eccentric muscle action

For alpine competitive alpine skiers the precise dosage of eccentric muscle action is very important to maximize speed in each turn. With our custom build eccentric ergometer dosage of eccentric muscle action can be visualized in real time feedback mode on a computer screen (Fig 2) and evaluated by software. A precise dosage of eccentric muscle action on the eccentric ergometer poses high coordinative demands to non-familiarized subjects. In an earlier study, eleven men elite skiers performed a 20 minute single bout exercise program on the eccentric ergometer (Vogt et al. 2003). A significant relationship between the dosage of eccentric muscle action and whole season slalom performance (FIS-points) was found. When repeating the exercise session a second time some days later the dosage of eccentric muscle action was improved significantly by more than 10%. This pilot study indicated that the quality of eccentric muscle action is a determinant of slalom performance or at least correlated to it and that dosage of eccentric work can rapidly be trained. Upon repetition of this study some years later on world class slalom skiers of Swiss-Ski National Team a similar result with a significant correlation between dosage of eccentric muscle action and slalom FIS points could be demonstrated (Fig 4, Weisskopf and Vogt, 2007).

Fig. 4: Correlation between FIS points and coordination (dosage) of eccentric muscle action (%SD) in world class slalom alpine skiers. %SD was averaged during the first 20 minute training session of a three week eccentric training cycle.

From these studies we tentatively concluded that good coordination/dosage of eccentric muscle action is very important for elite skiers in particular for slalom competition. We further suggest that our custom build eccentric ergometer allows for evaluating and improving dosage and coordination of muscle action during eccentric exercise.

Mild eccentric exercise for rehabilitation from knee injury

Knee injuries are very common in competitive alpine skiers. Especially anterior cruciate ligament rupture (ACL-R) is a typical injury in alpine skiing. Our experience shows that in the early rehabilitation phase mild eccentric exercise can be applied in a save and efficacious mode in alpine skiers (Gerber et al 2006). In this study it was concluded that eccentric exercise may mitigate the prevalent muscle size and strength deficits commonly observed after ACL-R. In our and others experience these rehabilitation programs have to be started with a very low cadence (20 – 40 rpms) and low loads (50 watts).

Future perspectives

In our opinion strength exercise training on the eccentric ergometer is a potentially promising possibility to optimize athletic performance in alpine skiers. Training programs should be carried out in off-season training phases in addition to conventional strength training. They may also be useful as adjuncts during rehabilitation from knee surgery. Muscles seem to need more than 24 hours to recover from mild eccentric exercise (Klossner et al. 2007). We therefore recommend a maximum of 3 training sessions per week.

References

Berg HE, Eiken O, Tesch PA. Involvement of eccentric muscle actions in giant slalom racing. Med Sci Sports Exerc. 1995 Dec;27(12):1666–70.

Berg HE, Eiken O. Muscle control in elite alpine skiing. Med Sci Sports Exerc. 1999 Jul;31(7):1065–7.

Dickinson MH, Farley CT, Full RJ, Koehl MA, Kram R, Lehman S. How animals move: an integrative view. Science. 2000 Apr 7;288(5463):100–6. Review.

Gerber JP, Marcus RL, Dibble LE, Gries PE, LaStayo PC. Early application of negative workd via eccentric ergometry following Anterior Cruciate Ligament rconstruction, J orthopaed & Sports Phys Ther 2006 36(5), 298–307.

Hintermeister RA, O’Connor DD, Dillman CJ, Suplizio CL, Lange GW, Steadman JR. Muscle activity in slalom and giant slalom skiing. Med Sci Sports Exerc. 1995 Mar;27(3):315–22.

Klossner S, Daepp Ch, Schmutz S, Vogt M, Hoppeler H, Flueck M. Muscle transcriptome activation with mild eccentric ergometer exercise. Pflugers Arch. 2007 455(3):555–62.

Lindstedt SL, Reich TE, Keim P, LaStayo PC. Do muscles function as adaptable locomotor springs? J Exp Biol. 205, 2211–2216, 2002.

Steiner R, Meyer K, Lippuner K, Schmid JP, Saner H, Hoppeler H. Eccentric endurance training in subjects with coronary artery disease: a novel exercise paradigm in cardiac rehabilitation? Eur J Appl Physiol. 2004 May;91(5–6):572–8.

Vogt M, Daepp Ch, Blatter J, Weisskopf R, Sutter G, Hoppeler H. Training zur Optimierung der Dosierung exzentrischer Muskelaktivität. Schweiz. Z. Sportmed. Sporttraumat. 2003 51(4), 188–91.

Weisskopf R & Vogt M. Exzentrisches Training des Slalom Teams. Swiss-Ski Newsletter: Science Report 1, www.swiss-ski.ch, 2007.

Alpine skiing technique - practical knowledge and scientific analysis

S. Loland

Norwegian School of Sport Sciences, Oslo, Norway

1  Introduction

Imagine a skilled downhill skier carving turns in a steep descent. The skier balances on a thin steel edge at speeds more than 100 kilometres per hour. From the neuromuscular activity at the local level via the interaction through skis and poles with a constantly changing surface to the very experiential Gestalt of a well executed run, this is a highly complex movement pattern. How are we to understand good alpine skiing technique? What are human movement techniques all about?

In the first part of this essay I will depart from the practical insights of technique among expert skiers and coaches and examine if, and possibly in what way, their understandings can be exposed to the systematic and critical tests of movement analysis. The second part explores an alternative route of investigation to better grasp ideas that are difficult to analyze, such as the rhythmic character of good skiing. In the concluding comments, it is speculated as to whether we can expect a merging of apparently contradictory and alternative perspectives on movement technique in the future.

2  Technical elements of alpine skiing

Among experienced practitioners, skiing technique is referred to in a variety of ways. To a certain extent, different skiing communities use different terms and concepts. In more systematic accounts, ranging from Joubert’s classic Skiing - an Art ... A Technique (1978), or LeMaster’s A Skier’s Edge (1999) to introductory material such as that of Loland and Haugen (2000), hypotheses are proposed in terms of the basic principles or technical elements of alpine skiing. In Joubert’s (1978) terminology, technical elements are the building blocks of technique. A technical element is operationalized in terms of a series of sub-elements or movement patterns that, if put together in the right way, make up good skiing.

A first and primary element in Joubert’s scheme is that of balance. The starting point of good balance is the so-called neutral position: hip wide distance between the skis to secure a stable supporting base, a slight bending of the knees to be able to absorb disturbances from an uneven surface, a slightly forward bent upper body and arms stretched outwards and forwards for fine tuning. In the neutral position, the skier is considered to be at the centre of agency in skiing with short distances to all extreme positions whether this implies forward, backwards, sidewise, upwards or downwards movement.

And indeed, moving on skis on an uneven surface poses constant challenges to balancing. To the unskilled skier, moments of instability are experienced as threats of falling. To the expert, moving in and out of balance is done in controlled, playful manners. A typical turning sequence starts in the neutral position and moves into controlling and completion phases in that include complex movements to put the ski on edge and stay in the turn. The skier then returns to the neutral position from which a new turn can be initiated (seefigure 1).

Fig. 1: Good balancing with solid supporting base. Ted Ligethy, SL, Beaver Creek 2005. Photo: Ron LeMaster

a Ron LeMaster

The technical element of balancing and its sub-elements can be systemized as in figure 2.

Fig. 2: Overview of the element of balancing (modified from Loland and Haugen 2000)

Good balancing is a conditio sine qua non in successful skiing. However, this is by no means a sufficient condition. Alpine skiing is about the efficient control of speed and direction. Such control is achieved in several ways. In the practice communities, references are made to ‘skidding’ (which in most contexts is considered an expression of problematic or bad technique), to ‘cutting’ or ‘carving’ turns, ‘getting a grip’ on the snow (LeMaster 1999), or, as Joubert (1978) expresses it, to finding support on the surface.

In learning situations with novice skiers, finding support can be explored with a series of practical exercises. A skier skids down an icy slope, hits a mogul and stops. The support from the surface is direct and concrete, the control over speed is immediate. Alternatively, skiers skid down a slope with the skis turned across the fall line and are challenged to find support from the surface by using ski edges. Usually, the result is skidding.

The next step is to develop control over speed and direction in more efficient ways. The carving turn, in which the front and the back of the ski follow the same line on the surface with a minimum of skidding, is the technical ideal. The ski moves only forward, and not sideways and with a minimum of energy dissipation. Being narrow on the middle and with wide fronts and tails, modern alpine skis are cut for this. Simplistically speaking, when the ski is kept stable on the edge (and not exposed to deformation) on an even surface, it carves a turn with a radius that equals a circle of which the cut of the skis constitutes a part.

A completely clean carving turn is an ideal. As said above, skiing implies gliding on a constantly changing surface. Stable carving requires a constant adaptation and variation of movement. Athletes and coaches talk of sub-elements in quasi-mechanical terms. Edging is achieved by the leaning of the body into the turn, by hip angling, by knee angling, and by angling of the ankles. This is intimately linked to the distribution of forces. As the skier turns towards the fall line, there is an increased challenge from gravitational forces, which again requires increased edging and use of force to uphold support from the surface and stay in the curve. The force requirement is at its maximum before the skier ‘releases’ into a new un-weighted phase in the neutral position and the turning of the skis in a new direction.

In figure 3 this movement pattern is illustrated, and in figure 4 an overview is given of the element of finding support.

Fig. 3: Carving turns. Aksel Lund Svindal, GS, Beaver Creek 2006. Photo: Ron Le- Master

Fig. 4: Overview of the element of finding support (modified from Loland and Haugen 2000)

A skier with good balance and with the skills of finding support on the surface is a proficient skier. Still, even if the technical execution is satisfactory, proficient skiers do not necessarily ski fast. Some skiers are ‘too hard on the surface’, as it is said. They carve too deep, create too much friction and loose speed. Other skiers might be too weak and skid too much, or unstable in their balancing and with a constant change between carving and skidding. Again, the result is speed loss. The expert skier has the particular skill of minimizing speed loss and maximizing speed gain at any given situation in a course. Expert skiers and coaches talk of the key skill of gliding.

As a technical element, gliding has several sub-elements. An expert downhill racer in a straight forward stretch have the skis float on the surface with no edging. The slogan is ‘to reduce pressure on the surface’. Gliding is just as important in curves. An expert slalom or giant slalom skier has the skill of adjusting the frictional forces in optimal ways. The skis carve clean and the skier stays in the curve by using optimal amounts of force; not too little, not too much.

Gliding is intimately tied to the choice of line and to tactical skiing skills. The expert skier is able to adjust the use of technique and choice of line according to local conditions (hard versus soft surface, plain versus uneven, steep versus flat, et cetera) and to the characteristics of the course (traversed or non-traversed, tight or open, et cetera). Moreover, good gliders know that even if the carving turn is the ideal in most circumstances, there are occasions in which skidding in fact can be the fastest solution. The choice between carving and skidding is a delicate one. In a long stretch curve in downhill, the faster line might be a wider one and experts keep their skis in a slight skidding position. This merging of neuromuscular and technical sensitivity with tactical understanding is a characteristic of the good glider.

Fig. 5: Optimal line choice. Aksel Lund Svindal, D, Aare 2006. Photo: Ron LeMaster In figure 6, an overview is given of the element of gliding and its sub-elements.

Fig. 6: Overview of the elements of gliding (modified from Loland and Haugen 2000)

3     Interplay: In search of scientific equivalents

Together, the elements of balancing, finding support, and gliding make up a tentative practice model of good technique (figure 7).