Development of motor competence in childhood and adolescence

This dissertation aimed to investigate the development of motor competence in childhood and adolescence. As a starting point, a systematic review was conducted to investigate the instruments used for the evaluation of motor competence. This review identified a gap in the literature regarding the existence of an instrument to assess motor competence based on the three theoretical constructs (stability, locomotor, manipulative). In an attempt to fill this gap, a valid quantitative instrument was proposed. To meet this purpose, 584 children, between 6 and 14 years of age, were evaluated in nine motor tasks, three for each construct. The final instrument comprised two motor tasks for each construct (stability, locomotor, manipulative) and presented very good fit indexes. This instrument was used to analyse the motor competence behaviour by gender in different age groups, indicating that generally boys outperformed girls and both genders increased their performance across age groups. However, different motor competence growth rates appear in both genders across age groups. In addition, children with high and low motor competence were compared regarding some of their health related fitness variables. We found that, regardless of age and gender, the group with better motor proficiency always showed better results in health related fitness. We found positive moderate to high correlations between motor competence and the variables of cardiovascular fitness and muscular fitness, and an inverse correlation with body composition across the four age groups. We also found that motor competence explained 75% of the variance of the health related fitness for the total sample, with locomotion as the primary predictor. However, when analysing the four age groups, stability skills seem to play an important role in health related fitness in the transition from childhood to adolescence. In conclusion, educational and health policies should consider the development of motor competence as an essential strategy to promote healthy development throughout life.

Adaptation of motor control to training and disuse : contribution of muscle synergy analysis and movement variability

The well-known degrees of freedom problem originally introduced by Nikolai Bernstein (1967) results from the high abundance of degrees of freedom in the musculoskeletal system. Such abundance in motor control have two sides: i) because it is unlikely that the Central Nervous System controls each degree of freedom independently, the complexity of the control needs to be reduced, and ii) because there are many options to perform a movement, a repetition of a given movement is never the same. It leads to two main topics in motor control and biomechanics: motor coordination and motor variability. The present thesis aimed to understand how motor systems behave and adapt under specific conditions. This thesis comprises three studies that focused on three topics of major interest in the field of sports sciences and medicine: expertise, injury risk and fatigue. The first study (expertise) has focused on the muscle coordination topic to further investigate the effect of expertise on the muscle synergistic organization, which ultimately may represent the underlying neural strategies. Studies 2 (excessive medial knee displacement) and 3 (fatigue) both aimed to better understand its impact on the dynamic local stability. The main findings of the present thesis suggest: 1) there is a great robustness in muscle synergistic organization between swimmers at different levels of expertise (study 1, chapter II), which ultimately indicate that differences in muscle coordination is mainly explained by peripheral adaptations; 2) injury risk factors such as excessive medial knee displacement (study 2, chapter III) and fatigue (study 3, chapter IV) alter the dynamic local stability of the neuromuscular system towards a more unstable state. This change in dynamic local stability represents a loss of adaptability in the neuromuscular system reducing the flexibility to adapt to a perturbation.

O desenvolvimento e as transições da carreira atlética dos jogadores de futebol de elite : estudo de caso num contexto de Seleção Nacional

A compreensão do desenvolvimento da carreira atlética e, em particular, das estratégias de ajustamento dos desportistas aos momentos de mudança no seu percurso de envolvimento no desporto, é fundamental para desenhar as facetas dos contextos promotores do talento, às quais a investigação tem vindo a destacar uma atenção especial nas últimas décadas. Nesse sentido, este estudo teve como objetivo descrever o processo de desenvolvimento e transições da carreira de futebolista de elite, esclarecendo as principais características e vivências ao longo do seu percurso desportivo. Para o efeito, foram realizados três estudos onde se incluem uma revisão sistemática de literatura e dois estudos de caso, com recurso a entrevistas semiestruturadas a 11 atletas de elite retirados que exercem funções nas seleções nacionais de futebol. Os resultados esclarecem o papel da prática precoce e diversificada, do suporte parental e da relação com o treinador como determinantes da carreira atlética. A participação em atividades desportivas informais e diversificadas é percecionada como promotora do desenvolvimento de competências técnicas e de relacionamento com pares, enquanto a especialização é observada como potenciadora, sobretudo, das competências de nível motor. Ao contrário de outros estudos realizados, as transições de júnior para sénior e do término da carreira foram identificadas como processos que não constituíram uma ameaça para os futebolistas. Finalmente, conclui-se que os atletas de elite vivenciam grandes dificuldades em conciliar as atividades académicas com a prática do futebol e o risco de abandono dos estudos surge regularmente associado à aproximação da subida ao escalão sénior pelo aumento da exigência e do investimento numa carreira profissional.