ThesisPDF Available

Force production in alpine skiers: On- & off-snow assessment & relationship with performance

Authors:

Abstract

The literature characterizing force production during skiing, and the associated capacities of skiers, is complicated to synthesize due to aging results or relatively unspecific assessments. The overarching aim of this doctoral thesis was to clarify the importance of force output for skiing and of specific force-production capacities for different ski disciplines. The thesis comprised two themes: 1) characterizing the force output of skiers (N=15) on a giant-slalom course using kinematic and kinetic data from a global positioning system and boot-mounted force-platforms, respectively; and 2) measurement of dynamic and isometric force, the effect of countermovement on force production at different velocities, and specific strength-endurance across disciplines, and performance levels, in national skiers (N=31). The conclusions from Theme 1 were that radial force output applied to turn the skis was linked with performance (r=0.55– 0.72, p<.032) and depended on both total magnitude and the ability to apply the force effectively (β=0.64–1.00, p<.001). Higher total force was associated with a greater output of the outside limb and a smaller difference between the limbs (β=0.92–1.00 and -0.65– - 0.92, respectively, p<.001). For Theme 2, athletes from speed and technical disciplines displayed different dynamic and isometric force qualities, with the former showing superior dynamic force at low velocities (ω2=0.17, p<.001) and in isometric conditions (ω2=0.16–0.22, p<.003). Overall, performance was linked with a more force-dominant profile (ω2=0.34; r=0.60–0.67, p<.001) and increased rate of force development characteristics (r=-0.50– -0.82, p<.048). Robust associations existed between maximum isometric force and speed discipline performance (r=-0.88, p<.001), and a trend for higher values in better technical athletes (r=-0.49, p=.052). Force production at moderate velocities did not separate disciplines, nor was it associated with performance. Variability in the shift of mechanical characteristics and inverse correlations between force augmentation at different velocities (rs=-0.74, p<.001) indicated countermovement effect depended on extension velocity. Skiers exhibited a smaller countermovement effect at low velocities (rrb=-0.68, p<.001), with the opposite observation for sprinters (rrb=0.43, p=.008). ‘Moderate’ velocities failed to differentiate groups. Better skiers produced greater force at low speeds with a smaller countermovement effect, which supports velocity-specific strength qualities. The ski-specific strength-endurance assessment yielded some discriminative results, but, due to difficulties selecting and assessing the relevant capacities, the principal value of this section lies in direct future protocol design. This thesis generally supports the assertion that force-production capacities partly limit force output during skiing. On snow, both high force-output capacity and effectiveness of application were associated with performance. Off snow, better-ranked athletes possessed the highest capacity for specific force-production capabilities. High-level skiers appear to display a dominance of force production at low speeds and in isometric conditions compared to other sports, which should be considered in their testing and training.
THÈSE
Pour obtenir le grade de
DOCTEUR DE L’UNIVERSISAVOIE MONT BLANC
Spécialité : Biologie de la motricité
Arrêté ministériel : 25 Mai 2016
Présentée par
Matthew Rex CROSS
Thèse dirigée par Pierre SAMOZINO,
Jean-Benoît MORIN et Nicolas COULMY
préparée au sein du Laboratoire Interuniversitaire de Biologie de
Motricité (LIBM)
dans l'École Doctorale Sciences et Ingénierie des
Systèmes de l’Environnement et des Organisations (SISEO)
Production de force des skieurs
alpins : évaluation sur et hors neige
et relation avec la performance
Thèse soutenue publiquement le
9 Décembre 2020,
devant le jury composé de :
Pr. Stefan LINDINGER
PU, University of Gothenburg, Gothenburg (Rapporteur externe)
Dr. Josef, KRÖLL
MCF, University of Salzburg, Salzburg (Rapporteur externe)
Dr. Nicola MAFFIULETTI
Human Performance Lab, Schulthess Clinic, Zurich (Examinateur)
Pr. Michael McGUIGAN
PU, Auckland University of Technology, Auckland (Examinateur, Président du Jury)
Dr. Frédérique HINTZY
MCF, Université Savoie Mont Blanc, Le Bourget-du-Lac (Examinatrice)
Dr. Pierre SAMOZINO
MCF, Université Savoie Mont Blanc, Le Bourget-du-Lac (Directeur)
Pr. Jean-Benoît MORIN
PU, Université Jean Monnet, Saint-Etienne (Co-directeur)
Dr. Nicolas COULMY
Fédération française de ski, Annecy (Co-directeur)
FORCE PRODUCTION IN
ALPINE SKIERS:
ON- & OFF-SNOW ASSESSMENT &
RELATIONSHIP WITH PERFORMANCE
Matthew Rex Cross
Université Savoie Mont Blanc
Laboratoire Interuniversitaire de Biologie de la Motricité
PhD 2020
THIS PAGE IS INTENTIONALLY LEFT BLANK
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ABSTRACT
FORCE PRODUCTION IN ALPINE SKIERS: ON- AND OFF-SNOW
ASSESSMENT AND RELATIONSHIP WITH PERFORMANCE
The literature characterizing force production during skiing, and the associated
capacities of skiers, is complicated to synthesize due to aging results or relatively
unspecific assessments. The overarching aim of this doctoral thesis was to clarify the
importance of force output for skiing and of specific force-production capacities for
different ski disciplines. The thesis comprised two themes: 1) characterizing the force
output of skiers (N=15) on a giant-slalom course using kinematic and kinetic data from
a global positioning system and boot-mounted force-platforms, respectively; and 2)
measurement of dynamic and isometric force, the effect of countermovement on force
production at different velocities, and specific strength-endurance across disciplines,
and performance levels, in national skiers (N=31). The conclusions from Theme 1 were
that radial force output applied to turn the skis was linked with performance (r=0.55
0.72, p<.032) and depended on both total magnitude and the ability to apply the force
effectively (β=0.641.00, p<.001). Higher total force was associated with a greater output
of the outside limb and a smaller difference between the limbs (β=0.921.00 and -0.65 -
0.92, respectively, p<.001). For Theme 2, athletes from speed and technical disciplines
displayed different dynamic and isometric force qualities, with the former showing
superior dynamic force at low velocities (ω2=0.17, p<.001) and in isometric conditions
(ω2=0.160.22, p<.003). Overall, performance was linked with a more force-dominant
profile (ω2=0.34; r=0.600.67, p<.001) and increased rate of force development
characteristics (r=-0.50 -0.82, p<.048). Robust associations existed between maximum
isometric force and speed discipline performance (r=-0.88, p<.001), and a trend for higher
values in better technical athletes (r=-0.49, p=.052). Force production at moderate
velocities did not separate disciplines, nor was it associated with performance.
Variability in the shift of mechanical characteristics and inverse correlations between
force augmentation at different velocities (rs=-0.74, p<.001) indicated countermovement
effect depended on extension velocity. Skiers exhibited a smaller countermovement
effect at low velocities (rrb=-0.68, p<.001), with the opposite observation for sprinters
(rrb=0.43, p=.008). ‘Moderate’ velocities failed to differentiate groups. Better skiers
iv
produced greater force at low speeds with a smaller countermovement effect, which
supports velocity-specific strength qualities. The ski-specific strength-endurance
assessment yielded some discriminative results, but, due to difficulties selecting and
assessing the relevant capacities, the principal value of this section lies in direct future
protocol design. This thesis generally supports the assertion that force-production
capacities partly limit force output during skiing. On snow, both high force-output
capacity and effectiveness of application were associated with performance. Off snow,
better-ranked athletes possessed the highest capacity for specific force-production
capabilities. High-level skiers appear to display a dominance of force production at low
speeds and in isometric conditions compared to other sports, which should be
considered in their testing and training.
PRODUCTION DE FORCE DES SKIEURS ALPINS : EVALUATION SUR
ET HORS NEIGE ET RELATION AVEC LA PERFORMANCE
La littérature caractérisant la production de force en ski alpin, et les capacités associées
des skieurs, est compliquée à synthétiser en raison de résultats anciens ou d'évaluations
relativement peu spécifiques. L'objectif global de cette thèse de doctorat était de clarifier
l'importance de la production de force en ski et des capacités de production de force
spécifiques pour différentes disciplines. La thèse comprenait deux thèmes
expérimentaux: 1) la caractérisation de la production de force des skieurs (N=15) sur un
parcours de slalom géant à l'aide de données cinématiques et cinétiques issues d'un
système de positionnement global et de plates-formes de force montées sur les
chaussures; et 2) la mesure des capacités de force dynamique et isométrique, l'effet du
contre-mouvement sur la production de force à différentes vitesses et l'évaluation
spécifique de l’endurance de force dans les deux disciplines de ski alpin à différents
niveaux de performance, chez les skieurs nationaux (N=31). Les conclusions du Thème
1 étaient que la force radiale appliquée sur les skis lors des virages était liée à la
performance (r=0,550,72, p<,032), et dépendait à la fois de l’intensité de la force
résultante et de la capacité à appliquer cette force efficacement (β=0,641,00, p<,001). Un
niveau élevé de force résultante produite était associé à des niveaux élevés de force sur
la jambe extérieure et intérieure au virage (β=0,921,00 et -0,65 -0.92, respectivement,
v
p<.001). Pour le Thème 2, les athlètes des disciplines de vitesse et technique ont présenté
différentes qualités de force dynamique et isométrique, les premiers montrant une force
dynamique supérieure à basse vitesse (ω2=0,17, p<,001) et dans des conditions
isométriques (ω2=0,160,22, p<,003). Dans l'ensemble, la performance était liée à la fois à
un profil à dominance force (ω2=0,34; r=0,600,67, p<,001) et à un taux de développement
de la force élevé (r=-0,50 -0,82, p<,048). Des associations très fortes existaient entre la
force isométrique maximale et la performance pour les disciplines de vitesse (r=-0,88,
p<,001) et pour les athlètes de technique (r=-0,49, p=,052). La production de force à des
vitesses modérées ne distinguait pas les disciplines, ni n'était associée à la performance.
La variabilité du décalage des relations force-vitesse avec le contre-mouvement et les
corrélations inverses entre l'augmentation de la force à différentes vitesses (rs=-0,74,
p<,001) indiquait que l'effet de contre-mouvement dépendait de la vitesse d'extension.
Les skieurs ont montré un effet de contre-mouvement plus faible à basse vitesse (rrb=-
0,68, p<,001), avec l'observation contraire pour les sprinteurs (rrb=0,43, p=,008). Les
vitesses « modérées » n’ont pas réussi à différencier les groupes. Les meilleurs skieurs
ont produit une plus grande force à basse vitesse avec un effet de contre-mouvement
plus petit, ce qui soutient l'existence de qualités de force spécifiques à la vitesse.
L’évaluation de l’endurance de force spécifique au ski a fourni des informations
discriminantes entre les disciplines mais, en raison des interactions entre les paramètres
de test et les capacités réelles de l'athlète, la valeur principale de ce projet n’a été que
d'orienter la conception future du protocole. Cette thèse soutient généralement
l'affirmation selon laquelle la production de force en ski est en partie limitée par les
capacités de production de force. Lors du ski, la capacité de production de force élevée
et l'efficacité de l'application étaient associées à la performance. Les athlètes les mieux
classés possédaient la plus grande capacité de production de force des membres
inférieurs sur des qualités spécifiques. Les skieurs de haut niveau semblent afficher une
meilleure capacité de production de force à basse vitesse et dans des conditions
isométriques par rapport aux autres sports.
vi
Dedicated to Gary Douglas Oldcorn
25 Sept 1954 17 June 2019
vii
ACKNOWLEDGEMENTS
This work could never have been realized without the support and guidance of many.
While contributions to specific projects are mentioned throughout this thesis, this section
stands as the only informal part of an otherwise formal document where I can sincerely
express my gratitude to those who played an essential role in my journey.
Firstly, thank you, Pierre Samozino, for your clear and unwavering direction of the
thesis. You are someone whom I enjoy working with immensely, as one of the few
individuals who seem to balance incredible attention to detail and scientific scrutiny,
with a perspective firmly rooted in practicality. Thank you for taking a leap of faith in
supervising me, and calmly managing the numerous difficulties we met in this project.
Whenever I was in doubt, or struggling with various scientific concepts, you were
always able to provide a clear and leveled perspective of the way forwardalways one
foot in front of the other and stepping out from among the trees to see the forest. Your
patience and good humor were continually grounding, and precisely what I needed in
a supervisor.
Thank you, Nicolas Coulmy, for making this unique position possible, and supporting
me in balancing the challenging new factors associated with my PhD-working role with
the Federation. My situation was (to say the least) unique, and it was a steep learning
curve to be thrust into a new sport with a limited scientific (and sporting!) background.
Thank you for persisting, and for the enjoyable moments shared on- and off-snow.
Jean-Benoît Morin - thank you for your ongoing support, and the clear and balanced
voice you brought to the thesis. As always, it’s a pleasure to work and tweet with you -
I look forward to future exciting collaborations that progress our field a little further
forward each project.
To my PhD office mates, Clément Delhaye and Jean Romain Rivière you both have
been an invaluable part of my journey. Clément, thank you for the many hours we spent
together setting gates in frigid temperatures at 6 am, followed by even greater hours
spent working together with the (often painstaking) data analysis. Some of my favorite
memories in France were from our work together, and it is difficult to state how much I
learned from you. Jean, thank you for being willing to discuss and give your valuable
viii
take on numerous topics, both within and outside of your main domain of expertise.
Thank you for teaching me the ways of the ‘force’ (-endurance) and playing ‘translator’
in testing sessions where the validity of the data depended on the accuracy of imparted
information. Your unwavering personal supportparticularly during difficult private
moments in the middle of the PhDwas unquestionably part of getting across the
finishing line. I owe you many beers for simplifying the puzzling process of French
administrative tasks.
Maximilien Bowen thank you for the time spent working together to develop a variety
of interesting, exciting, and completely-outside-of-my-area technologies we used in this
thesis.
Frédérique Hintzy thank you for your contribution to the PhD it was a huge task
being the chief-directrice of such a daunting on-snow collection. I have very fond
memories of our time working together, and notably testing all the burgers Avoriaz has
to offer.
Patricia Coulié, Laurent Messonnier, Baptiste Morel, Thomas Rupp, and the rest of the
LIBM staff thank you for welcoming me into the lab environment. Caroline Prince,
Hervé di Domenico, Thibaut Gregoire, and Arthur Peyrard thank you for creating a
welcoming and friendly lab environment and for being ready and willing always to
share a coffee.
Thanks to the Fédération française de ski, and everyone with whom I had the pleasure
of rubbing shoulders. Notably, to my colleagues at the Département Sportif et
Scientifique, Valentin Bottollier, Christelle Bonnin Arnould, Bruno Fleury, Loïc Le
Quellec, Christine Quilez, Laurent Schmitt, and at the Center National d'Entraînement,
Lucas Bernat-Salles, Bill Brenier, Jérémy Coint, Regis Mecca, Jean Pierre Mollie,
Olivier Pédron, and all others. It has been a pleasure working as part of the same team.
A special thanks to Amy Nguyen, for the times we shared on various DSS expeditions,
for teaching me to ski, and for introducing me to Claude François.
Romain Hurtault, Thibault Trameau, Adrien Reymond, Jeremy Miahle, and Robin
Schmidt thanks for your willingness to work with me on an ambitious project, and for
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welcoming me into the S&C community. Additional thanks to the numerous coaching
staff, physios, and technicians with whom I had the pleasure of rubbing shoulders.
Thank you to the numerous athletes I have worked with these past three years for your
willingness to be involved in this project and your maximal effort presented during the
challenging testing protocols.
Remi Salomé thank you for your friendship in a relatively disconnected part of France,
and the many training and skiing sessions we shared as part of that. Training has always
had a special place in my personal and professional life as a means of managing the
stressors of life, connecting with friends, and applying the concepts from my studies into
my own practice. Your support and encouragement to continue my training were
invaluable to my own physical and mental wellbeing, and to the broader success of the
PhD. Getting to know you over the iron and sharing banter (in ‘Franglaise’) had a greater
impact than you know.
Thank you, Pierre-Florent Busseneau, and Mariana Salazar for your support in
finding our feet in a new country, and your ongoing taxi services to and from Geneva
airport. I am very thankful for your friendship, support, and the little bit of ‘kiwi’ that
you both now exude in France.
Scott R. Brown, Daniel Buckingham, Eric Helms, Luke McQueen, Seth Lenetsky, Riki
Lindsay, and Simon Rogers thank you for being there in both professional and
personal support from afar, through it all.
To my family Rex, Robyn, Aimee, Summer, Maddie, Trish, Anna and Cara thank
you for your support in this significant step in my academic journey and all the steps
that preceded it.
To my wife, Frances thank you for being my rock. You make me a better person, and I
can’t imagine the journey without you.
Burton Drake and Maree Palmer thank you for your contribution to my life. Rest in
peace.
Gary Douglas Oldcorn thank you for your professional and personal mentorship. It is
difficult to describe the span of the positive impact you have had on the direction of my
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life. I can say with certainty that my relationship with you has made me a better person.
The world lost you too early, but we were fortunate to have someone of your caliber for
as long as we did. You were a catalyst for my academic journey, and this thesis was
completed in your honor. Rest in peace.
Stefan Lindinger, Josef Kröll, Michael Mcguigan, and Nicola Maffiuletti thank you
for being an essential part of the final steps of the thesis. Your eagerness to be involved
particularly during such a complicated time for everyone involved is thoroughly
appreciated and won’t be forgotten.