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1

Comparison of two approaches for calculation of the geometric and inertial characteristics of the human body of the Bulgarian population

Nikolova G., Toshev Y.

Acta of Bioengineering and Biomechanics

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2008

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Vol. 10, nr 1

3-8

EN

On the basis of a representative anthropological investigation of 5290 individuals (2435 males and 2855 females) of the Bulgarian population at the age of 30–40 years (YORDANOV et al. [1]) we proposed a 3D biomechanical model of human body of the average Bulgarian male and female and compared two different possible approaches to calculate analytically and to evaluate numerically the corresponding geometric and inertial characteristics of all the segments of the body. In the framework of the first approach, we calculated the positions of the centres of mass of the segments of human body as well as their inertial characteristics merely by using the initial original anthropometrical data, while in the second approach we adjusted the data by using the method based on regression equations. Wherever possible, we presented a comparison of our data with those available in the literature on other Caucasians and determined in which cases the use of which approach is more reliable.

2

Experimental assessment of the drag coefficient during butterfly swimming in hydraulic flume

Taiar R., Bertucci W., Letellier Th., Benkemis I., Toshev Y.

Acta of Bioengineering and Biomechanics

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2005

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Vol. 7, nr 2

98-108

EN

A body when moving in a fluid is to withstand drag that is proportional to the drag coefficient, the frontal surface area, and the square of the body velocity relative to the fluid velocity (VOGEL [14]). The aim of our study was to determine the relationships between the drag coefficient (CD) and the Reynolds number (Re) for a high-level swimmer. In TAIAR et al. [12], three most propulsive butterfly positions have been defined: the end of the external sweep (beginning of the cycle), the end of the internal sweep (middle of the cycle), and the end of the thrust (end of the cycle). These three positions were reproduced using real-size mannequins articulated ui real-velocity conditions. Experiments have been done ui the large-scale hydraulic flume of the University' of Nantes. Two types of the curves CD (Re) were obtained: for the "best swimmer" and for ''other swimmers". Following the swimming of the ex-word champion Pankratov during the World Championship m Rome (1994) the mannequin representing the "best swimmer" has been positioned similarly to the ex-world champion at the beginning, in the middle and at the end of cycle. The body positions of Pankratov have been obtained using the image analysis software Schleihaui 4.0. In order to obtain the curves CD (Re) representing "other swimmers", the body positions of lower-level swimmers have been used at the beginning, in the middle and at the end of swimming cycle. The two types of curves show well the gap between the techniques of the "best swimmer" and "other swimmers". Our study shows the importance of the body position dining the swimming cycle to minimizing the drug and to assuring better propulsion, i.e. better performance. The results show that the most effective swimmers optimise the body positions in order to reduce the frontal surface and therefore to minimize the drag.

3

Estimation of smimmers anthropometric parameters and surface areas in real swimming conditions

Taiar R., Lodini A., Rouard A., Toshev Y.

Acta of Bioengineering and Biomechanics

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2005

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Vol. 7, nr 1

85-95

EN

The main aim of this study was to propose and to test a reliable method allowing us to obtain data both from static numeric images and numeric video images taken in real swimming conditions and using appropriate computer procedure. Based on these images it is possible to estimate the swimmer's anthropometric parameters and the projected frontal surface (PFS) during swimming. Measurements of sportsmen anthropometric parameters, including swimmers, are usually carried out in a static anatomic position using standard anthropometric method. In the present study, this common method is compared with a new approach which enables us to carry out the anthropometric measurements using numeric images collected both in static and in real swimming conditions. This method offers two advantages: the results are obtained in real dynamic conditions and the measurements are characterized by a high precision and repeatability. The proposed measurement approach is suitable also for other applications in the field of biomechanics.

4

Performance modelling of butterfly swimmers: links between morphometric, kinematic and hydrodynamic variables

Taiar R., Toshev Y., Lodini A., Rouard A., Toshev Y.

Acta of Bioengineering and Biomechanics

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2004

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Vol. 6, nr 2

77-88

EN

The aim of the study is to explain the performance of butterfly swimmers over 100 m butterfly using a set of selected morphometric, kinematic and hydrodynamic parameters. Parametric modelling and mul-tivariate analysis are used in order to define synthetic variables (indices) describing kinematic and morphometric parameters. The possibility of predicting the performance V]00 (mean velocity over 100 m butterfly) using morphology variables is tested. The results showed that the parametric model proposed describes well the performance. The selected kinematic parameter X|lip (instantaneous hip displacement) varies little among the swimmers, whereas for the parameter k (describing the variation of the displacement patterns) highly different values have been obtained. Hip displacements vary essentially according to their shapes - high k values corresponding to swimmers acceleration at the end of the cycle, and low k values corresponding to swimmers with more regular displacements. Thus, k was selected as the only parameter to describe the hip displacement patterns. A negative relation between the performance and the hydrodynamic variables has been obtained confirming that every increase of flow resistance get worse performance. A positive relation between the performance and the individual morphological data has been found, i.e. light and sharp swimmers have in general higher performance. No relation between k and the morphology has been observed. On the contrary, a negative relation between the hydrodynamic variables and the morphology has been obtained.