Maria João Valamatos*
Maria José Valamatos
Pedro Mil-Homens
António Veloso
Universidade Técnica de Lisboa, Faculdade de Motricidade Humana, Portugal.
RESUMO
]]> O objectivo do presente estudo foi avaliar a natureza das alterações na capacidade de produção mecânica do complexo músculo-tendinoso, na fase de impulsão da transposição da barreira, induzidas pela aplicação de um protocolo de fadiga específico à prova de 400 metros barreiras. Sete barreiristas de elite nacional (idade: 24.43 ± 5.68 anos; altura: 1.82 ± 0.06 m; massa: 71.79 ± 5.84 Kg; melhor marca 400mB: 51.55 ± 1.72 s) participaram neste estudo. A acção de transposição da barreira foi filmada com uma câmara de alta velocidade (Redlake PCI1000), que permitiu o cálculo das coordenadas bidimensionais das articulações do membro inferior. Para estimar as alterações de comprimento dos complexos músculo-tendinosos durante a fase de impulsão da transposição da barreira foram utilizadas as equações de regressão adaptadas de Jacobs et al. (14). Uma plataforma de forças tridimensional foi instalada na pista, e as forças de reacção ao apoio (Fz, Fy e Fx) foram registadas a uma frequência de 1000 Hz e sincronizadas com o registo de vídeo. Estes procedimentos foram repetidos antes e após a aplicação do protocolo de fadiga. As diferenças entre condições foram testadas por T-Test para amostras emparelhadas. Os principais resultados mostraram que em condições de fadiga existe um aumento significativo da perda de velocidade horizontal do Centro de Gravidade (CG) (p<.05). Este facto está associado ao aumento significativo do tempo de apoio (p<.001), quer do tempo da fase de amortização (p<.01), quer do tempo da fase de propulsão (p<.05). Contudo, as forças de reacção ao apoio não registaram alterações significativas, embora tenham demonstrado uma tendência para diminuir em situação de fadiga. O aumento da duração da fase de apoio associado a alterações no comportamento angular e, consequentemente, na dinâmica muscular sugerem uma diminuição do stiffness e potência musculares em situação de fadiga.Palavras-chave: atletismo, 400 metros barreiras, cinemática, cinética, fadiga, ciclo muscular de alongamento-encurtamento (CMAE).
ABSTRACT
Dynamic take-off hurdles clearance. Changes on the mechanical power output variables produced by the muscle-skeletal system on the take-off phase of hurdles clearance, induced by a specially designed fatigue protocol.
The purpose of this study was to investigate changes on the mechanical power output variables produced by the muscle-skeletal system on the take-off phase of hurdles clearance, induced by a specially designed fatigue protocol, which was intended to simulate the fatigue condition of the 400 meters hurdles. Seven national elite male athletes (age: 24.43 ± 5.68 years old; height: 1.82 ± 0.06 m; body mass: 71.79 ± 5.84 Kg; 400mH best: 51.55 ± 1.72 s) participated in this study. The performance of the clearance action was high speed video recorded at 250Hz (Redlake PCI1000), and 2D coordinates of the athlete body joints were obtained. The regression equations adapted by Jacobs et al. (14) were used to estimate the length changes of the muscle tendon complex during the contact phase of the take-off of the clearance action. A three axial force platform was installed on the track, and the ground reaction forces (Fz, Fy and Fx) were recorded synchronized with video data. These procedures were repeated before and after a fatigue protocol. The differences between both conditions were tested using T-Tests for paired samples. In the take-off phase of the hurdles clearance there was an increase on the loose of the horizontal velocity in the fatigue conditions (p<.05). This fact was associated with the increase of the total contact time (p<.001), due to a significant increase of both the breaking (p<.001) and the propulsive (p<.05) contact times. However, ground reactions forces did not show any significant changes. The increase of the support time and the changes in angular displacement of the joint of the trail leg, suggested a decrease in the stiffness and power output produced by the muscle-skeletal system, in the fatigue condition.
Key Words: athletics, 400 meters hurdles, kinematics, kinetics, fatigue, stretch-shortening cycle (SSC).
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CORRESPONDÊNCIA
Maria João Valamatos*
Rua D. Mafalda, 19, 7º Dto, Massamá,
]]> 2605-201 Belas, PORTUGAL ]]>