A LONGITUDINAL STUDY OF THE TAKE-OFF AND TRANSITION PHASE IN SKI-JUMPING AT INTERSPORTTOURNEE INNSBRUCK 1992-1994

The ski-jump is realized in a very variable external conditions influenced by differences in the jumping hill constructions, approach velocities, surfaces (snow, mat, ceramic) and climatic conditions. The take-off phase is also determined by many other factors relating to the structure of movement abilities of individuals and their specific personal patterns of the take-off. The body dimensions can also influence the pattern of the take-off in the last period (it is characterized e.g. by a very low values of Rohrer’s Index, RI = 1.07 - 1.15 by the best jumpers). The change of flight position to the "V" style in the last 2-3 years can also be the factor which could influence the realization of the take-of f . The previous suggestions bring about following questions: - What does the present pattern of the take-off and transition phase look like ? - Are there any differences in the pattern of the take-off and transition phase in the last three-year period ? The event of the World Cup Intersporttournee Innsbruck is a very suitable opportunity to solve this problem. Here the set of all the best world athletes regularly take part on the same date (January 4) each year. During the last three years 1992, 1993, and 1994 the take-off and transition phase being taped at the same position of the cameras in the terraine. By using of the programme package The System of Kinematic Analyses of Ski-jumping, which was developed in our Laboratory, the 2-D analyses were realized for both observed phases. The set of angle and speed parameters describe the anal zed phases. From the sets of all athletes in 't1he rounds (n = 50 - 60) the sets of the best present jumpers (n = 15) were selected according to the length of jump. The statistical analyses were realized for the whole set of the lSt round athletes (correlation and factor analyses) and for the selected sets of the best jumpers. The comparison of the results from different periods of the complete and selected sets of athletes was the starting point for the solution of our problem

A COMPARISON BETWEEN THE KINEMATIC CHARACTERISTICS OF THE TRANSITION PHASE OF SKI-JUMPING ON JUMPING HILLS WITH DIFFERENT CRITICAL POINTS

The jumping hill construction is one of the major external factors which influence the ski-jump. The increase in the jumper's velocity reduces the time for the mainparts of the ski-jump. It is necessary to determine the influence of these changes on the transition phase in the ski-jump. The transition phase is the section from the edge of the hill to the beginning of the flight phase. This part is determined by many factors which occur during the takeoff. The magnitude of the aerodynamic forces increases with the high velocity. Therefore, for the quick implementation of the transition phase, the rotation of the ski-jumper has to increase. We suppose, that the inter individual differences between various performance levels of jumpers will increase. The purpose of this study was to find relationships between the kinematic characteristics of the transition phase on jumping hills with different constructional characteristics and to determine the degree to which jumpers at various skill levels are able to manipulate the technique. The study was carried out at the events held on the jumping hills with different critical points: - GP Frenstat pod Radhostem (K=90) – Intersport tournee Innsbruck 1995 (K=109) - World Championship in the ski flight Planica 1994 (K=185).The 2-D analyses were implemented using the System of Kinematic Analysis of Ski-jumping, which was presented on the XI1 International Symposium of Sport Biomechanics in Budapest. This system allows us to find the basic angle, length and velocity parameters for the transition phase of the ski jump. The sets of competitors in the 1st round (n=50-80) were divided -into three groups (n=12-15,B-best, M-middle, Glow) according to the length of jump. The statistical analyses were using the statistic package Statgraphics

COMPARISON OF THE FORCE-TIME STRUCTURE OF THE VERTICAL JUMP BETWEEN MEN AND WOMEN

INTRODUCTION The vertical jump is a relatively simple movement situation which is very ofkn used for the study of the performance in take-off activities, quality of the muscles, coordination of the movement etc. (e.g. Komi & Bosco, 1978; Bobbert, F. M.,1988; Sanders, R. H., 1992,1993 and others). The vertical jump can be used as a very suitable model for the solution of many problems in sport pedagogy, effectiveness of the training process and studying of the movement quality of man. The object of our research is not only the final performance, (i.e. final characteristic of the jump - height of jump), but we are interested in the course of the movement, timing, stability - reproducibility of the movement and other aspects. This study was a part of a larger research project. The main goal of this study is to focus on the following questions: What was the inter-individual variability of the structure of the vertical jump? How was the stability (reproducibility) of the movement during the vertical jump? What were the differences in the structure of the vertical jump between the men and women? The classical counter-movement vertical jump was at the center of our interest. Students of physical education - men (n = 54, body height = 178.40 ± 6.12 cm, body weight = 70.29± 6.36 kg, age = 18 - 20 years) and women (n = 47, body height = 8.48± 6.20 cm, body weight 9.72 ± 6.44 kg, age = 18-20 years) were the subjects of the research. They performed two counter-movement vertical jumps. The vertical component Fz was registered by using the KISTLER platform. The reaction force Fz(t) was analyzed on an on-line system by using our own software which derived the velocity-time and distance-time functions from the Fz(t) curve and computed 23 biornechanical variables describing the structure of the vertical jump from the point of view of time, force, impulse, velocity, and the track of the center of gravity. Data were elaborated by statistical procedures based on STATGRAPHICS package (basic statistical characteristics, t-test, correlation analysis). Statistical characteristics of measured variables have provided the information about the inter-individual variability of the time, force, track, and velocity structure of the movement in the vertical jump for both men and women. This information was the basis for the next step of our research. Reproducibility of the structure of the vertical jump varies for different groups of variables (rtt = 0.50 - 0.98). The highest stability was found in the strength parameters (take-off force, braking and accelerating impulse, rtt = 0.91-0.98) and the lowest level of stability for the time structure of the movement (at = 0.45-0.66). Statistical analysis has confmed a significant difference in the structure of the vertical jump between the group of men and women

A GENERAL VERSUS AN INDIVIDUAL MODEL OF THE SKI JUMPING TECHNIQUE

INTRODUCTION The stochastic models which are based on the results of biomechanical analyses of the ski jump (kinematic analysis, eg ARNOT, 1995; dynamic analysis of the take-off, e.g. VAVERKA, 1987) help us to solve the basic question of the relationship between the biomechanical variables and the criterion (validity). Statistical models form the output used to select the set of observed variables which represent the parameters for the effective ski jumping technique The results of many studies have shown that the validity of the biomechanical variables are very different in different phases of the ski jump. Contrary to what has been seen in practice it has been repeatedly found that the statistical dependence between take-off variables and the criterion are relatively low (R2 = 0.2-0.3) In comparison with the flight phases (R2= 0.6-0.9). The hypothesis of an individual model for the take-off is supported by the multifactor theory of the take-off (VAVERKA, 1987) in which the principle optimisation of the take-off factors and individualisation of the take-off have been defined. This paper represents an attempt to determine a practical model for ski-jumping technique. METHODOLOGY The system for the 20 kinematic analyses of the ski-jump (VAVERKA, 1994; take-off phase) and the Peak Performance Analyses System (flight phase) have been used in this study. The set of 11 variables for both the take-off and flight phase served as the input matrix for the statistical analyses (Intersporttournee event in Innsbruck 1993-1995, n=155). The set of 18 world class level athletes were selected for the study of intra-individual variability for the take-off phase. The average number of analysed take-offs by individuals was 7.6 jumps (range=5-13 takeoffs). Analyses of variance, multiple range of analyses of variance, regression, correlation and factor analyses computed by the STATGRAPHICS package were used. RESULTS The results of the statistical analyses on the inter-individual variability (5 matrices for the take-off phase and 6 matrices for the flight phase) demonstrated a low level of validity for the take-off parameters (R2 =0.15-0.20) and increased validity for the flight parameters (R2=0. 7-0.8) The statistical analyses of differences between individuals has shown that there are the significant differences in the aerodynamics and forward-backward position for the centre of gravity (relates to the factor of rotation). CONCLUSIONS The results of the statistical analyses have shown the predominant tendencies of individualisation of the take-off model. A very successful take-off for an individual could be realised by the use of many different patterns of movement. From the results of the flight phase we can accept a general pattern for the performance this ski-jumping phase REFERENCES Arndt, A. et al. (1995). Journal of Applied Biomechanics, 11, 224-237. Vaverka, F. (1987). Biomechanics of Ski-jumping (Czech language), Monograph, Univerzita Palackeho Olomouc, 235 pp. Vaverka, F. et al. (1994). In. Biomechanics in Sports XII, Proceedings, 285-287

THE RELATIONSHIPS BETWEEN ANTHROPOMOTORIC BODY DIMENSIONS AND THE FORCE - TIME STRUCTURE OF THE VERTICAL JUMP

INTRODUCTION: The take - off activities are quite various and many of their modifications are used in sport. The final result of the jump is influenced by a great variety of factors such as the quality of produced muscle strength timing of the jump, range of movement, arm activities etc. The basic determinants of many movement activities are the body dimensions (length and mass variables). This paper is focused on the questions concerning the relationship between the forcetime structure of the vertical jump (time, distance, velocity, force, final results) and the body dimensions. METHODS: The counter-movement vertical jump (CMJ) with an arm swing was registered on a KISTLER platform. The reaction force Fz (t) was analysed on an ON-LINE system using software developed in our lab. 23 variables describing the structure of CMJ from the point of view of time, distance, velocity of the centre of mass (CM), and produced force were computed in real time. Eleven values of body dimensions were measured for each subject (length variables of the lower limbs, body height, mass, width of knee, and ankle). The subjects of this research were two groups of students of physical education (men, n=54, age: 18 - 20 years, height: 178.40 ± 6.12cm, body mass: 79.00 ± 6.36 kg; women, n=47, height: 168.48 ± 6.20 cm, body mass: 59.77 ± 6.44 kg). Correlation and factor analysis (STATGRAPHICS package) were used for the statistical analysis. RESULTS: The factor analysis of eleven anthropometric values showed two groups of dependent variables (length parameters and body height - 1st factor, and body mass and width variables - 2nd factor). The three factor model of the CMJ structure selected three groups of dependent variables for both the men and women (1st - time and distance variables, 2nd - impulse momentum and variables of the final results of CMJ, 3rd - variables of the preparatory phase of the CMJ). The factor analysis of body dimension and CMJ variables has shown that the body dimensions are an independent group of variables and that they do not have a relationship to the CMJ structure. CONCLUSION: Factor analysis confirms the relative independence of the three groups of CMJ variables (time and distance, impulse momentum and final variables of the CMJ, the preparatory phase variables). The set of body dimension parameters does not have a relationship to the structure of CMJ. This finding was the same for both groups of men and women

THE ACCURACY OF THE SKI-JUMPER'S TAKE-OFF

Introduction The Ski-jumper's take-off is the key phase in Ski-jumping. The difficulty lies in the take-off is done a t great speed (20-30 m.6- ) and in a very short amount of time (0.2-0,4sec.). Based on multifactor theory .We have defined 5 factors which are necessary to solve in one movement act: vigour, accuracy, aerodynamics, rotation, arm activity (VAVERKA, 1987).The take-off is accurate in the moment when the acceleration of the center of gravity is finished and passes through the edge of the take-off area. Problem The main goals of t h i s paper are: - quantification of the take-off accuracy (kinematic and dynamic Aspect), - the relation of the accuracy t o the other factors of the take-off and to final performance in ski-jumping, - to create a model of take-off accuracy (kinematic and dynamic point of view) which would be useful in ski-jumper's training method We have been interested in solving these problems Prom the years 1984-1992. We used the following methods: - dynamometry of the ski-jumper's take-off in natural conditions of the jumping hill in Frenstat p.R. (the length of measured platform 6 m, artificially covered jumping-hill), about 800 take-offs were analysed, - kinematic analyses of the take-off (in years 1990-1991, about450 take-offs) analysed from different jumping hills - measurement of the speed during the run-on phase, - statistical and graphical methods. Results The long term observation of these problems revealed: - a large variability of this factor in relation to different levels of performers, different forms of hill surfaces, and patterns of take-off force-time curves, - close relation of accuracy to the length of jump and other factors of the take-off, especially vigour, - t h e possibility to create a statistical model enabling the quantification of the take-off accuracy by using results from dynamometric measurements and kinematic analyses

COMPARISON OF ISOMETRIC AND DYNAMIC METHODS OF STRENGTH TRAINING PROGRAM

The purpose of this study was to determine the difference in the quality of muscle strength employing two methods of strength training (isometric, dynamic). Nineteen male university students volunteered to participate in the experiment, encompassing a five week strength training sessions. The dynamic method was applied to the elbow flexion and extension of the right side (load totalling 60 % of maximal performance) and the isometric method applied on the same muscle groups of the left side (maximal voluntary isometric contraction). Pre- and post-test measurements included maximal isometric strength, the angle a expressed the speed of increasing muscle strength and the number of repetitions performed for each exercise (at a of load 60 % max), as a measure of muscle endurance. No differences were found between the results of strength training when using both methods (isometric, dynamic). A five week training program improved the isometric force by about 8-14 % of pre-test values, and by about 34-54 % in repetition exercises with the load. No differences were exhibited in the rate of the speed of increasing muscle strength

THE ANALYSIS OF GAIT IN INDIVIDUALS WITH TRANSFEMORAL AMPUTATION USING A BIONIC KNEE DESIGN: A CASE STUDY

Walking is the body´s natural means of moving from one location to another. It is also the most convenient means of traveling short distances (Perry, 1992). Approximately 4500 new amputations of lower extremities are performed annually in the Czech Republic. Worldwide, 200 – 500 million major amputations are performed each year. Major limb amputations of lower extremities account for approximately 85% of all cases of amputations (Ellis, 2005). The loss of a lower extremity causes the inability to walk without a prosthetic aid. Biomechanics has an important place in the multidisciplinary team, which is essential for the complex care of amputees (Janura, Svoboda, Kozakova, & Birgusova, 2006). New prosthetic designs may enable people with transfemoral amputation perform sports (running) activities in the future. However, it is necessary to master walking with a prosthesis first. The aim of our study is to describe the selected biomechanical parameters of gait in patients with a two-year experience with a bionic knee

THE ANALYSIS OF GAIT IN INDIVIDUALS WITH TRANSFEMORAL AMPUTATION USING A BIONIC KNEE DESIGN: A CASE STUDY

Walking is the body´s natural means of moving from one location to another. It is also the most convenient means of traveling short distances (Perry, 1992). Approximately 4500 new amputations of lower extremities are performed annually in the Czech Republic. Worldwide, 200 – 500 million major amputations are performed each year. Major limb amputations of lower extremities account for approximately 85% of all cases of amputations (Ellis, 2005). The loss of a lower extremity causes the inability to walk without a prosthetic aid. Biomechanics has an important place in the multidisciplinary team, which is essential for the complex care of amputees (Janura, Svoboda, Kozakova, & Birgusova, 2006). New prosthetic designs may enable people with transfemoral amputation perform sports (running) activities in the future. However, it is necessary to master walking with a prosthesis first. The aim of our study is to describe the selected biomechanical parameters of gait in patients with a two-year experience with a bionic knee