Browsing by Author "Moreira, Marc"
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- Análise de variáveis preditivas do deslize aquatic através de um modelo de path-analysisPublication . Morais, J.E.; Costa, M.J.; Jesus, Sérgio; Moreira, Marc; Feitosa, Wellington G.; Silva, A.J.; Marinho, D.A.; Barbosa, Tiago M.A velocidade de nado depende da propulsão e arrasto hidrodinâmico. Para um nadador se deslocar no meio aquático tem de produzir a mesma quantidade de propulsão e arrasto hidrodinâmico (Barbosa et al., 2010)
- Characterization of speed fluctuation and drag force in young swimmers: a gender comparisonPublication . Barbosa, Tiago M.; Costa, M.J.; Morais, J.E.; Morouço, Pedro; Moreira, Marc; Garrido, Nuno D.; Marinho, D.A.; Silva, A.J.The aim of this study was to compare the speed fluctuation and the drag force in young swimmers between genders. Twenty-three young pubertal swimmers (12 boys and 11 girls) volunteered as subjects. Speed fluctuation was measured using a kinematical mechanical method (i.e., speedo-meter) during a maximal 25-m front crawl bout. Active drag, active drag coefficient and power needed to overcome drag were measured with the velocity perturbation method for another two maximal 25 m front crawl bouts with and without the perturbation device. Passive drag and the passive drag coefficient were estimated using the gliding decay velocity method after a maximal push-off from the wall while being fully immersed. The technique drag index was also assessed as a ratio between active and passive drag. Boys presented meaningfully higher speed fluctuation, active drag, power needed to overcome drag and technique drag index than the girls. There were no significant gender differences for active drag coefficient, passive drag and passive drag coefficient. There were positive and moderate- strong associations between active drag and speed fluctuation when controlling the effects of swim velocity. So, increasing speed fluctuation leads to higher drag force values and those are even higher for boys than for girls.
- Comparação do coeficiente de arrasto calculado com recurso a três formas distintas de medição da área de secção transversa do tronco de nadadoresPublication . Morais, J.E.; Costa, M.J.; Moreira, Marc; Morouço, Pedro; Garrido, Nuno D.; Silva, A.J.; Marinho, D.A.; Barbosa, Tiago M.O acto de nadar é caracterizado pela aplicação intermitente de uma força propulsiva para ultrapassar o arrasto hidrodinâmico. Entre outros, o arrasto é condicionado pela área de superfície frontal, pela forma e pela velocidade a que um objecto se desloca no meio aquático (Marinho et al., 2010).
- Comparison of young swimmer’s active drag coefficient using three methods to compute trunk transverse surface areaPublication . Morais, J.E.; Costa, M.J.; Moreira, Marc; Barbosa, Tiago M.Foi objectivo deste estudo comparar o coeficiente de arrasto activo, calculado com recurso a três formas distintas de medição da\área de secção transversa do tronco (ASTI). A amostra foi composta por 23 sujeitos. entre os quais 12 ~o sexo masculino e 11 do sexo feminino. Foi utilizado o método de perturbação de velocidade de Kolmogorov para calcular o arrasto activo e respectivo coeficiente de arrasto. O cálculo do coeficiente de arrasto foi efectuado de três formas distintas: i) com recurso à ASTI medida através de fotogrametria; ii) com recurso ASTI estimada a partir das equações de Morais et alo (2011); e iii) com recurso à ASTI estimada através da equação de Clarys. Foram utilizados três procedimentos no processo de comparação: i) comparação de valores médios; ii) análise de regressão linear simples; e iH) plot de Bland Altman. Todos os pares estudados apresentaram diferenças significativas (p < .001) na comparação de valores médios. No entanto, as análises de regressão lineares simples entre os pares estudados, registaram correlações significativas (p < .001), e o plot de Bland Altman, para todas as condições estudadas, registou mais de 80% dos plots dentro do intervalo de confiança de 95 %. Constatou-se que as equações de Morais et alo foram aquelas que apresentaram menor diferença (13.81 ± 9.24%), comparativamente com a de Clarys (26.87 ± 5.61 %) em relação aos valores de ASIT medidos. Sugere-se assim a aplicação destas equações para a estimação da ASTI.
- Comparison of young swimmer’s active drag coefficient using three methods to compute trunk transverse surface areaPublication . Morais, J.E.; Costa, M.J.; Moreira, Marc; Silva, A.J.; Marinho, D.A.; Barbosa, Tiago M.O arrasto hidrodinâmico é tido como a força que um nadador tem de vencer de forma a manter o seu deslocamento no meio aquatic, e depende da velocidade, forma, tamanho e area de superYcie frontal (kjendlie e Stallman, 2008). Numericamente o arrasto expressa-se pela equação newtoniana
- Growth influences biomechanical profile of talented swimmers during the summer breakPublication . Moreira, Marc; Morais, J.E.; Marinho, D.A.; Silva, A.J.; Barbosa, Tiago M.; Costa, M.J.This study aimed to analyse the effect of growth during a summer break on biomechanical profile of talented swimmers. Twenty-five young swimmers (12 boys and 13 girls) undertook several anthropometric and biomechanical tests at the end of the 2011–2012 season (pre-test) and 10 weeks later at the beginning of the 2012–2013 season (post-test). Height, arm span, hand surface area, and foot surface area were collected as anthropometric parameters, while stroke frequency, stroke length, stroke index, propelling efficiency, active drag, and active drag coefficient were considered as biomechanical variables. The mean swimming velocity during an all-out 25m front crawl effort was used as the performance outcome. After the 10-week break, the swimmers were taller with an increased arm span, hand, and foot areas. Increases in stroke length, stroke index, propelling efficiency, and performance were also observed. Conversely, the stroke frequency, active drag, and drag coefficient remained unchanged. When controlling the effect of growth, no significant variation was determined on the biomechanical variables. The performance presented high associations with biomechanical and anthropometric parameters at pre-test and post-test, respectively. The results show that young talented swimmers still present biomechanical improvements after a 10-week break, which are mainly explained by their normal growth.
- How informative are the vertical buoyancy and the prone gliding tests to assess young swimmers hydrostatic and hydrodynamic profiles?Publication . Barbosa, Tiago M.; Costa, M.J.; Morais, J.E.; Moreira, Marc; Silva, A.J.; Marinho, D.A.The aim of this research was to develop a path-flow analysis model to highlight the relationships between buoyancy and prone gliding tests and some selected anthropometrical and biomechanical variables. Thirty-eight young male swimmers (12.97 ± 1.05 years old) with several competitive levels were evaluated. It were assessed the body mass, height, fat mass, body surface area, vertical buoyancy, prone gliding after wall push-off, stroke length, stroke frequency and velocity after a maximal 25 [m] swim. The confirmatory model included the body mass, height, fat mass, prone gliding test, stroke length, stroke frequency and velocity. All theoretical paths were verified except for the vertical buoyancy test that did not present any relationship with anthropometrical and biomechanical variables nor with the prone gliding test. The good-of-fit from the confirmatory path-flow model, assessed with the standardized root mean square residuals (SRMR), is considered as being close to the cut-off value, but even so not suitable of the theory (SRMR = 0.11). As a conclusion, vertical buoyancy and prone gliding tests are not the best techniques to assess the swimmer’s hydrostatic and hydrodynamic profile, respectively.
- Is the underwater gliding test a valid procedure to estimate the swimmers’ drag?Publication . Morais, J.E.; Costa, M.J.; Jesus, Sérgio; Mejias, J. Erik; Moreira, Marc; Garrido, Nuno D.; Silva, A.J.; Marinho, D.A.; Barbosa, Tiago M.The aim of this study was to develop a structural equation model for underwater gliding distance based on its determinant variables, in order to confirm whether it is an informative test of young swimmers’ hydrodynamic profile. Methods: Twenty-three subjects (twelve boys and eleven girls with a mean age of 13.61 ± 0.83 years old) were evaluated. The following were determined: (i) the underwater gliding distance; (ii) the squat jump performance; (iii) the passive drag; (iv) the passive drag coefficient; (v) the trunk transverse surface area and; (vi) the gliding velocity. Results: The underwater gliding distance was significantly correlated with the squat jump (rs = 0.47; p = 0.038) and with the coefficient of passive drag (rs = -0.55; p < 0.01) but not with passive drag (rs = 0.41; p = 0.09). The overall model explained 45% of the underwater gliding distance (x2/df = 3.138). Conclusion: The underwater gliding distance seems to be more dependent from the squat jump than from the passive drag. Therefore it seems as if the underwater gliding test is not representative of the swimmers’ passive drag or his /her passive drag coefficient.
- Modeling the links between young swimmers’ performance: energetic and biomechanic profilesPublication . Barbosa, Tiago M.; Costa, M.J.; Marinho, D.A.; Coelho, Joel; Moreira, Marc; Silva, A.J.The aim was to develop a path-flow analysis model for young swimmers’ performance based on biomechanical and energetic parameters, using structural equation modeling. Thirty-eight male young swimmers served as subjects. Performance was assessed by the 200-m freestyle event. For biomechanical assessment the stroke length, the stroke frequency and the swimming velocity were analyzed. Energetics assessment included the critical velocity, the stroke index and the propulsive efficiency. The confirmatory model explained 79% of swimming performance after deleting the stroke index-performance path, which was nonsignificant (SRMR = 0.06). As a conclusion, the model is appropriate to explain performance in young swimmers.
- A path-flow analysis model for active drag force determinant variables in age-group swimmersPublication . Barbosa, Tiago M.; Costa, M.J.; Marques, Mário C.; Moreira, Marc; Silva, A.J.; Marinho, D.A.The role of drag force in competitive swimming is one of the main topics for researchers and field practitioners as it allows enhancing performance. The development of “flow chart” models confirming the relationships between drag force and other determinant variables was never attempted in competitive swimming. Moreover, main research groups dedicate little attention to age-group swimming. PURPOSE: The aim was to develop a structural equation modeling (i.e., path-flow analysis model) for active drag force (Da) based on anthropometric, hydrodynamic and biomechanical determinants in young swimmers. The theoretical model was developed according to main review papers about these determinants. METHODS: Sixteen male swimmers (12.50±0.51 years-old; Tanner stages’ 1 -2) were evaluated. It was assessed: (i) anthropometrical variables such as body mass, height, frontal surface area (FSA); (ii) hydrodynamic variables including drag coefficient and Da with the velocity perturbation method; (iii) the biomechanical variables stroke length (SL), stroke frequency (SF) and swimming velocity after a maximal 25-m bout. It was computed the Spearmen´s Rank Correlation Coefficient between exogenous and endogenous variables. Path-flow analysis was performed with the estimation of linear regression standardized coefficients between exogenous and endogenous variables. When appropriate, according to the theoretical model, simple or multiple linear regression models were computed. The standardized regression coefficients (β) were considered and the significance of each β was assessed with the student’s t-test (p<0.05). The effect size of the disturbance term for a given endogenous variable, which reflects unmeasured variables was 1 -R2. To verify the model fit, root mean square residual was computed (RMSR < 0.1). RESULTS: The Da presented significant association with all exogenous variables, except for SL and SF. Confirmatory model excluded the FSA (RMSR > 0.1). Even so, 95% of Da was explained by remaining variables in the model. CONCLUSION: Confirmatory path-flow model can be considered as not suitable of the theory. For a near future it is advice to develop new FSA estimation equations specific for young swimmers rather than using models developed with adult/elite swimmers.