L'objectif général de ce travail doctoral était d'étudier la plasticité de la fonction posturale à travers l’étude des effets d’un programme d'entraînement unilatéral ou d’une expérience sportive et/ou motrice. Pour cela, les effets de différents types d'exercices chroniques (volontaire et électro-induit) et aigus (tâche posturale répétée, échauffement et fatigue) ont été testés sur le contrôle postural monopodal en condition statique et dynamique. Les principaux résultats montrent que le programme d'entraînement unilatéral constitué de contractions volontaires et de contractions électro-induites n'a pas amélioré le contrôle postural du membre ipsilatéral et du membre controlatéral en dépit de l'augmentation de la force musculaire pour les deux membres chez des jeunes adultes sains non actifs. L'absence de résultat relatif au contrôle postural pourrait, principalement, être liée aux modalités et conditions des programmes d'entraînement qui n’étaient pas suffisamment proches des conditions écologiques du contrôle postural. En revanche, l'exercice aigu non-fatiguant comme l'échauffement a amélioré le contrôle postural monopodal chez des jeunes étudiants sportifs quelle que soit la jambe sur laquelle ils étaient évalués. Cependant, cette amélioration n’apparait qu’au bout de 10-15 minutes selon la jambe considérée après l'arrêt de l'exercice. Par ailleurs, chez des athlètes pratiquant des sports symétriques et asymétriques, les exercices aigus non-fatiguant comme la répétition d’une tâche posturale et l'échauffement, ont engendré des effets bénéfiques sur le contrôle postural monopodal statique et ont permis de distinguer la jambe dominante de la jambe non-dominante. En revanche, l'exercice aigu fatiguant a perturbé le contrôle postural indépendamment de la nature du sport pratiqué et de la jambe évaluée. / The overall objective of this thesis was to study the plasticity of postural function by investigating the effects of a unilateral training program or a sport and/or motor experience. Hence, the effects of various types of chronic (voluntary and electro-induced) and acute exercises (repeated postural task, warm-up and fatigue) were tested on monopodal postural control in static and dynamic conditions. The main findings show that the unilateral training program of voluntary contractions and electro-induced contractions did not improve postural control of the ipsilateral and contralateral limbs despite the increase in muscle strength for both in healthy non-active young adults. The lack of postural control outcome may be primarily related to the conditions of training programs that were not sufficiently close to the ecological conditions of postural control. In contrast, non-fatiguing high-intensity exercise such as warm-up improved monopodal postural control in young sports students regardless of which leg they were assessed. However, this improvement does not appear until 10-15 minutes according to the considered leg after stopping the exercise. Moreover, in athletes practicing symmetrical and asymmetrical sports, the non-fatiguing, acute exercises such as the repetition of a postural task and the warm-up, generated beneficial effects on the static monopodal postural control and enabled to distinguish the dominant leg of the non-dominant leg. In contrast, the fatiguing acute exercise disrupted postural control regardless of the nature of sport practiced and the leg assessed.

Sammanfattning Syfte och frågeställningar: Syftet med undersökningen var att ta ett första steg mot att skapa ett testbatteri, som objektivt kan mäta fotbollspelares tekniska prestationsförmåga med boll, samt konstruera en rad övningar som innefattar viktiga fotbolls-specifika tekniker och testa dessa övningars reliabilitet genom ”test-retest”. Syftet med studien var också att göra en jämförelse i prestation mellan varje spelares dominanta och icke-dominanta fot, från tillslagsövningar där båda fötterna används.   Metod: Tolv herrjuniorer (16-19 år) och sju damjuniorer (15-17 år) på elitnivå genomförde ett testbatteri bestående av totalt 21 övningar för mätning av de fotbollsspecifika teknikerna nick, mottagning, driva med boll samt tillslag. Åtta av männen (16-19 år) återgenomförde testbatteriet för utvärdering av testbatteriets reliabilitet. Korrelationen mellan vardera övningens testresultat från den första testomgången (test) och den andra testomgången (retest) bestämdes genom användandet av Pearsons korrelationskoefficienter (r). Skillnader i kvantifierad prestation mellan dominant och icke-dominant fot beräknades med hjälp av ett beroende t-test. Resultat: Fem av övningarna genererade signifikanta korrelationer mellan resultaten från de båda testomgångarna. Dessa övningar var: precisionsskott på stillaliggande boll med dominant fot (r=0,949), skotthastighet med dominant fot (r=0,734), mottagning med bröstkorgen av boll levererad i luften (r=0,743), samt övningarna rak sprint utan boll och rak sprint med boll där kvoten mellan de två sistnämnda övningarna visade på signifikant korrelation (r=0,805). I båda grupperna förelåg en signifikant skillnad i prestation mellan dominant och icke-dominant fot i övningarna; skotthastighet, långpass på marken samt upprepade tillslag. Herrjuniorerna uppvisade dessutom en signifikant skillnad i prestation i övningen skottprecision på studsande boll. Slutsats: Det ringa deltagareantalet gör att resultaten i studien bör tolkas med försiktighet. Studien visa dock att en objektiv utvärdering av flera fotbollsspecifika tekniker är möjlig och några av övningarna visade hög korrelation mellan test och retest. Då resultaten i vissa avseenden pekar på signifikanta skillnader i prestation mellan dominant och icke-dominant fot anser författarna att båda fötterna bör testas i utvärderingar av en spelares tekniska förmåga. / Abstract Aim: The aim of the study was to create and evaluate a test battery, which in an objective way could measure a group of soccer players’ technical performance, and further, to create a series of exercises, which incorporate important soccer-specific techniques, and test the exercises for reliability through “test-retest”. The aim of the study was also to make a comparison between dominant leg and non-dominant leg in exercises where both feet were being used. Method: Twelve male elite junior players (age 16-19) and seven women junior players (age 15-17) underwent a test battery consisting of a total of 21 exercises to measure the soccer-specific techniques of heading, controlling, running with the ball, and touch of the ball. Eight of the men (age 16-19) underwent the test battery again in order to evaluate the reliability of the test battery (”retest”). The correlation between each exercise’s test result from the first test session (”test”) and the second test session (“retest”) was determined by the use of Pearson’s correlation coefficients (r). The differences in quantified performance between dominant leg and second best foot non-dominant leg were calculated by the use of a paired t-test. Results: Five of the exercises showed significant correlation between the results from the two test sessions. These exercises were: dead ball precisionshot using best foot (r=0,949), shotspeed using best foot (r=0,734), controlling airborne ball with chest (r=0,743) and the exercises straight forward sprint without the ball and straight forward sprint with the ball from which the ratio between the two last mentioned exercises showed significant correlation (r=0,805). In both groups there were a significant difference in performance between best and second-best foot in the exercises of; shooting speed, ground long passing, and repeated touches. In addition, the male juniors showed a significant difference in performance in the exercise of shooting precision on bouncing ball. Conclusions: The low number of participants leads to the notion that the results of the study should be interpreted with precaution. The study however shows that an objective evaluation of several soccer-specific techniques is possible and that a couple of the exercises showed high correlation between ”test” and ”retest”. Since the results in some aspects point towards significant differences in performance between second-best foot and best foot, the authors’ opinion is that both feet should be tested in an evaluation of a soccer player’s technical ability.