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KINEMATIC ANALYSIS OF THE “SWASTIKA” MODERN DANCE ELEMENT 1 Joanna Gorwa, 2 Jacek Jurkojć and 2 Robert Michnik 1 Department of Biomechanics, University School of Physical Education in Poznan, 2 Department of Applied Mechanics. Silesian University of Technology, Gliwice SUMMARY Within the confines of the work analysis of kinematic and ground reactions of dance acrobatic called ‘swastika’ were carried out. Measurements were conducted for woman and man who go in for modern dance. Movement of dancers doing ‘swastika’ was recorded by a set of four Basler camcorders whereas ground reactions by Kistler dynamometric platforms. Kinematic analyses were carried out by means of APAS system and mathematical models. INTRODUCTION Acrobatics of modern dance are full of extremes. Each element of classical dance in modern dance is performed further, lower, is more exaggerated. That leads to recurrent excessive muscles tension. Modern dance, just like classical dance, requires outstanding fitness very often. Modern dance choreographers invent dance elements which can be very dangerous, from biomechanics point of view, for dancers. These dangerous situations, are provoked by these ‘movement creators’, who sometimes don’t have even basic knowledge about human motion system abilities and limitations. Jumps are the most common expressive tasks performed by dancers .It is known, according to previous research, that some of them can cause, during the landing phase (phase of eccentric muscle work caused by necessity of shock absorption), big ground reactions. These reactions can reach even 7.4 BW [1]. Since correct technique is a factor that significantly lowers the risk of injuries, and the degree of control of movement habits, that is the appropriate execution of a particular sports technique, determines the force values observed during the landing phase [7], the authors of this study assessed the kinematic values as well as recorded the technique of performing the „swastika” modern dance element. The similar analyses have not been found in the available literature. This can be caused by a lack of homogeneous terminology of dance elements. METHODS The tests used in this study were performed in the Biomechanical Laboratory of the Department of Biomechanics at the University School of Physical Education in Poznan. The tests were carried out on two participants working as professional modern dancers (a female and a male). Each participant performed the „swastika” element. Figure 1: Location of the markers: R MT - head of the metatarsal bone of the second toe of the right limb, R HEEL - the calcanean tuber of the right limb, R LMAL - center of the lateral malleolus of the right limb, R TIB - right tibia, R LCON - lateral epicondyle of the left femur, R THI - right thigh, R GTRO - greater trochanter of the right femur, L ASIS - left anterior superior iliac spine, R ASIS - anterior superior iliac spine, SACR – L 5 S 1. The dancers performed the movements barefoot. During the experimental measurements kinematic values as well as line graphs of ground reaction forces were determined. The kinematic values were determined with the use of the APAS motion analysis system, ground reaction forces were measured with the use of the Kistler dynamometric platforms. The motion of the participants was recorded with four Basler digital cameras with the sampling rate of 200 Hz. The images recorded by the cameras were transmitted to a computer where the films were processed with the APAS software and the locations of the markers attached to the tested dancers were determined. At the same time ground reaction forces during the landing phase were recorded. Due to the spaciousness of the performed dancing maneuvers the cameras were positioned in a way that permitted a detailed observation of pelvis kinematics as well as the right lower limb during the landing phase. The number of markers as well as their location (Fig. 1), allowed the authors to determine the centers of the lower limb joints, and then the relative angular motion of individual segments of the lower limb and the pelvis. The calculations were performed with the use of a proprietary software developed in the Matlab environment. RESULTS AND DISCUSSION On the basis of the measurement results it was possible to assess the movements performed by the dancers by observing the graphs of ground reaction forces as well as the graphs of angles in the lower limb joints.

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Page 1: KINEMATIC ANALYSIS OF THE “SWASTIKA” MODERN … · KINEMATIC ANALYSIS OF THE “SWASTIKA” MODERN DANCE E LEMENT 1 Joanna Gorwa, ... zagadnienia biomechaniki ruchu człowieka

KINEMATIC ANALYSIS OF THE “SWASTIKA” MODERN DANCE E LEMENT

1 Joanna Gorwa, 2Jacek Jurkojć and 2Robert Michnik 1 Department of Biomechanics, University School of Physical Education in Poznan,

2 Department of Applied Mechanics. Silesian University of Technology, Gliwice

SUMMARY Within the confines of the work analysis of kinematic and ground reactions of dance acrobatic called ‘swastika’ were carried out. Measurements were conducted for woman and man who go in for modern dance. Movement of dancers doing ‘swastika’ was recorded by a set of four Basler camcorders whereas ground reactions by Kistler dynamometric platforms. Kinematic analyses were carried out by means of APAS system and mathematical models. INTRODUCTION Acrobatics of modern dance are full of extremes. Each element of classical dance in modern dance is performed further, lower, is more exaggerated. That leads to recurrent excessive muscles tension. Modern dance, just like classical dance, requires outstanding fitness very often. Modern dance choreographers invent dance elements which can be very dangerous, from biomechanics point of view, for dancers. These dangerous situations, are provoked by these ‘movement creators’, who sometimes don’t have even basic knowledge about human motion system abilities and limitations. Jumps are the most common expressive tasks performed by dancers .It is known, according to previous research, that some of them can cause, during the landing phase (phase of eccentric muscle work caused by necessity of shock absorption), big ground reactions. These reactions can reach even 7.4 BW [1]. Since correct technique is a factor that significantly lowers the risk of injuries, and the degree of control of movement habits, that is the appropriate execution of a particular sports technique, determines the force values observed during the landing phase [7], the authors of this study assessed the kinematic values as well as recorded the technique of performing the „swastika” modern dance element. The similar analyses have not been found in the available literature. This can be caused by a lack of homogeneous terminology of dance elements. METHODS The tests used in this study were performed in the Biomechanical Laboratory of the Department of Biomechanics at the University School of Physical Education in Poznan. The tests were carried out on two participants working as professional modern dancers (a female and a male). Each participant performed the „swastika” element.

Figure 1: Location of the markers: R MT - head of the metatarsal bone of the second toe of the right limb, R HEEL - the calcanean tuber of the right limb, R LMAL - center of the lateral malleolus of the right limb, R TIB - right tibia, R LCON - lateral epicondyle of the left femur, R THI - right thigh, R GTRO - greater trochanter of the right femur, L ASIS - left anterior superior iliac spine, R ASIS - anterior superior iliac spine, SACR – L5S1.

The dancers performed the movements barefoot. During the experimental measurements kinematic values as well as line graphs of ground reaction forces were determined. The kinematic values were determined with the use of the APAS motion analysis system, ground reaction forces were measured with the use of the Kistler dynamometric platforms. The motion of the participants was recorded with four Basler digital cameras with the sampling rate of 200 Hz. The images recorded by the cameras were transmitted to a computer where the films were processed with the APAS software and the locations of the markers attached to the tested dancers were determined. At the same time ground reaction forces during the landing phase were recorded. Due to the spaciousness of the performed dancing maneuvers the cameras were positioned in a way that permitted a detailed observation of pelvis kinematics as well as the right lower limb during the landing phase. The number of markers as well as their location (Fig. 1), allowed the authors to determine the centers of the lower limb joints, and then the relative angular motion of individual segments of the lower limb and the pelvis. The calculations were performed with the use of a proprietary software developed in the Matlab environment. RESULTS AND DISCUSSION On the basis of the measurement results it was possible to assess the movements performed by the dancers by observing the graphs of ground reaction forces as well as the graphs of angles in the lower limb joints.

Page 2: KINEMATIC ANALYSIS OF THE “SWASTIKA” MODERN … · KINEMATIC ANALYSIS OF THE “SWASTIKA” MODERN DANCE E LEMENT 1 Joanna Gorwa, ... zagadnienia biomechaniki ruchu człowieka

Analyzing the graphs of ground reaction forces the authors observed high values of ground reaction forces (2,65BW– for the female and 3,75BW - for the male). The duration times of the landing phase in case of classical dancing movements are very short. a)

b)

|Figure 2: Vertical component of ground reaction obtained during landing from ‘swastika’ jump. a) male, b) female The impulse value of maximal vertical ground reaction component, acting on dancer foot while he or she is landing after jump, can be dangerous and can cause damages to their joints and spine [5]. It’s obvious that value of vertical component of ground reaction depends on the way how dancer is able to absorb the shock. a)

b)

Figure 3: Anatomical angle of foot in saggital plane obtained during landing from ‘swastika’ jump. a) male, b) female On the basis of analysis of joint angles and ground reactions one can state that: • the dancers foot, at the moment of contact with ground, is

plantar flexed in such a way that only toes are in contact with ground

• maximal ground reaction occurs when the foot is parallel to the floor. In such position center of pressure is directly under the ankle joint what decrease moment of muscle forces caused by vertical component of ground reaction (what obviously also decrease values of forces generated by muscles). Additionally moment arms of horizontal ground

reactions are smaller because ankle joint is lower. In this way dancer try to reduce joint reactions.

CONCLUSIONS The testing methodology presented in this study allows for simultaneous determination of kinematics of movements performed by dancers as well as ground reaction forces. It enables one to analyze the influence of the technique of the performed movements on the values of external loads (ground reaction forces). ACKNOWLEDGEMENTS Special thanks to all the dancers who have taken part in the research. The study was supported by research grant no NN 404 515938of the Ministry of Science and Higher Education in Poland REFERENCES 1. Dworak L.B., Gorwa J., Kmiecik K., Mączyński J. (2005)

A study characterizing dynamic overloads of professional dancers. Biomechanical approach. Acta of Bioengineering and Biomechanics, 7(1), 77-84.

2. Gorwa J.(2008) Przeciążenia dynamiczne oraz biomechaniczny profil u tancerzy uprawiających taniec klasyczny i współczesny. PhD Thesis

3. Liederbach M. (1984) Movement and function in dance. In Brownstein B., Bronner S. Evaluation, treatment and outcomes in orthopedic and sports physical, 8, 253- 310.

4. Micheli L. (1983) Back injuries in dancers. Clinical Journal of Sports Medicine, 2(3), 473-484.

5. Nosiadek L., Ruchlewicz T., Staszkiewicz R. (2007) Siła reakcji podłoża i parametry kinematyczne ciała w fazie lądowania po zeskoku z różnych wysokości. Wybrane zagadnienia biomechaniki ruchu człowieka pod redakcją Czesława Urbanika, 143-161.

6. Picon A., Lobo da Costa P., De Sousa F., De Sacco I., Amadio A. (2000) Biomechanical approach to ballet movements: a preliminary study. ISBS, Hong Kong, 472-475

7. Rutkowska- Kucharska A., Bober T., Serafin R. (2004) Obciążenie układu ruchu w sporcie. W Biocybernetyka i Inżynieria Biomedyczna. Część III Biomechanika Sportu. Analiza biomechaniczna obciążeń w sporcie, 631- 648.

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