Effect of weighted sled towing on sprinting effectiveness, power and force-velocity relationship.

This study aimed to compare the components of force-velocity (F-V) and power-velocity (P-V) profiles and the mechanical effectiveness of force application (or force ratio-RF) among various sled-towing loads during the entire acceleration phase of a weighted sled sprint. Eighteen sprinters performed four 50-m sprints in various conditions: unloaded; with a load corresponding to 20% of the athlete's body mass (BM); with a load of 30% BM; and with a load of 40% BM. Data were collected with five video cameras, and the images were digitised to obtain velocity from the derivation of the centre-of-mass position. F-V and P-V components and RF were estimated from sprinting velocity-time data for each load using a validated method that is based on an inverse dynamic approach applied to the sprinter's centre-of-mass (it models the horizontal antero-posterior and vertical ground reaction force components) and requires only measurement of anthropometric and spatiotemporal variables (body mass, stature and instantaneous position or velocity during the acceleration phase). The theoretical maximal velocity decreased with load compared with the unloaded condition (for 20% BM: -6%, effect size (ES) = 0,38; for 30% BM: -15%, ES = 1.02; for 40% BM: -18%, ES = 1.10). The theoretical maximal horizontal force (F0) and maximal power were not different among conditions. However, power at the end of the acceleration phase increased with load (40% BM vs 0%: 72%; ES = 2.73) as well as the maximal mechanical effectiveness (12%; ES = 0.85). The linear decrease in RF was different between 30 or 40% BM and the unloaded condition (-23%; ES = 0.74 and 0.66). Better effectiveness may be developed with 40% BM load at the beginning of the acceleration and with the various load-induced changes in the components of the F-V and P-V relationships, allowing a more accurate determination of optimal loading conditions for maximizing power.

Influência das variáveis antropométricas na economia de corrida e no comprimento de passada em corredoras de rendimento / Influence of the anthropometric variables in the running economy and the stride length in performance of the female

O objetivo do estudo foi investigar a relação entre economia de corrida (ECO), comprimento de passada (CP) e dimensões corporais. Cinco mulheres correram em duas intensidades submáximas: uma velocidade correspondente a velocidade utilizada em treino (12 km.h-1) e, uma velocidade próxima da velocidade no limiar anaeróbio (14 km.h-1). A massa corporal, o percentual de gordura, a estatura, o comprimento de passada e o comprimento de passada relativo ao comprimento de perna foram determinadas em ambas as velocidades. Foi feito o teste de correlação de Pearson (p menor que 0,05). Os resultados demonstram a influência da velocidade submáxima de corrida na relação entre dimensões corporais (estatura e massa corporal) com a ECO e com o CP. Verificaram-se correlações negativas entre estatura e massa corporal com o consumo submáximo de oxigênio e, um a correlação positiva entre massa corporal com o CP a12 km.h-1. Dessa forma, estes resultados permitem concluir que os mecanismos de adaptação podem ser diferentes de acordo com a velocidade de corrida. A relação entre dimensões corporais com ECO e CP são muito importantes para predizer o desempenho em provas de meio-fundo.

This study was designed to investigate the relationship between running economy (ECO), step length (CP) and body dimensions. Five female were tested for one submaximal velocity, very close to usual training intensities (12km.h-1), and one high submaximal velocity, near the anaerobic threshold (14 km.h-1). Body weight, body fat, height, leg length and relative low extremity length were determined. The test of Pearson´s correlation (p smaller that 0.05) were performed. The results indicate an effect of the submaximal velocity on the relationship between body dimensions (height and body weight) with ECO and CP. The results show an inverse correlation between height and body weight with the submaximal oxigen uptake and, direct correlation between body weight with CP in 12 km.h-1. Thus, this result allows us to make the assumption that mechanisms of adaptation can be different according to the running speed. The relationships between body dimensions with ECO and CP are very important for performance of running.

Comparação do ângulo da articulação subtalar durante velocidades submáximas de corrida / Comparison of the subtalar joint angle during submaximal running speeds

O objetivo foi descrever o comportamento da pronação máxima (PM), da velocidade máxima de pronação (VP) e do cruzamento linear (CL) dos pés direito e esquerdo, de 23 corredores de rendimento, durante corrida em esteira rolante, em velocidades de 11 e 13 km.h-1 para mulheres e, 14 e 16 km.h-1 para homens, relacionadas a uma média de 70 por cento e 75 por cento do consumo máximo de Oxigênio (VO2máx). A análise estatística (Teste T de Students para amostras dependentes e independentes, com p<0,05), demonstrou que, com o aumento da intensidade submáxima de corrida, houve um aumento significativo na PM e, com aumento da velocidade linear de corrida, houve um aumento significativo na VP. Em relação ao CL, acreditamos que este esteja influenciado pela técnica de corrida imposta pelo corredor.