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

THE STRUCTURE OF GROUND REACTION FORCE IN VERTICAL COUNTER MOVEMENT JUMP AT DIFFERENT INTENSITIES

The aim of the study was to ascertain the structure of ground reaction force CMJ (counter movement jump) at varying intensity of take-off, and further, to evaluate the mechanisms of performing final force impulse. CMJ, in three intensive varieties comprising maximal intensity, 75% intensity and 50% intensity, was conducted in a group of 44 university students. The vertical component of reaction force F(t) was analyzed in terms of force, time and track take-off parameters. Statistical analysis confirmed differences between take-offs at different intensities in the magnitude of force impulse, track and time variables of the F(t) curve. The crucial factor influencing the creation of force impulse is the range of the CG track in the preparation and acceleration phases

A COMPARISON OF VARIOUS METHODS FOR THE ASSESSMENT OF VERTICAL JUMP HEIGHT

INTRODUCTION: The final result of the vertical jump (height of jump) is used both in research studies as well as in practice. The most frequent methods of assessing the height of a vertical jump are based on computations derived from the force-time curve (KISTLER, etc.). The comparison of the height of jump measured by KISTLER with the height of jumps measured and computed using other methods (e.g., Sargent jump, computation from time of non-contact phase, etc.) have resulted in differences among the values of the height of jump. The main goal of this paper is the comparison of various methods of computation of vertical jump height using kinetic and kinematic analysis. METHODS: A group of 51 male physical education students (age: 18-24 years, height: 1.78 ± 0.07 m, body mass: 75.11 ± 6.54 kg) was the subject of the research. A countermovement jump (CMJ) with an arm swing was performed on a KISTLER platform and registered with two videocameras. One camera registered the subject in the frontal plane and the second registered the detail view of the ankle and foot from the lateral plane. By using a 2D kinematic analysis the track of the center of mass and the ankle were computed, and the heights of these points at different phases of the jump were evaluated. The heights of three selected anatomical points were also computed at different phases of the CMJ. The forcetime function registered by the KISTLER platform was analyzed using software developed in our lab. The height of the jump, the height of the lift of the ankle and the time of the flight phase were evaluated. Ten different ways of computing the height of jump were used in this study. Statistical analysis was performed using the Statgraphics package (analysis of variance and correlation analysis). RESULTS: Statistical analysis confirmed significant differences among the various methods of height of jump measurement. The KISTLER measured height of jumps was approximately 0.13 m lower than those measured by kinematic analysis. The height of the ankle is the main factor influencing this difference. The vertical lift of the anatomical point fossa jugularis resulted in almost the same values as the height of jump of the center of gravity measured by the kinematic analysis (height: center of mass = 0.59 m, ankle = 0.58 m). A very high level of correlation dependence among the measured values (r = 0.88-0.97) indicated the height accuracy of the methods used for the measurement of the height of the jump. CONCLUSIONS: The results have shown that the measurement of the height of jump depends on the method used. The height of jump measured by the KISTLER platform is actually lower than in reality. The reason for these differences is the plantar flexion of the foot

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

VERIFICATION OF TEST OF ANTAGONISTIC MUSCLE GROUPS COOPERATION

Manipulation activities pertain to movement manifestations of the upper limbs into target position within a given range. The preciseness of quality of the performed movement depends on the level of cooperation extended by antagonistic muscle groups under control of the central nervous system. A number of studies have been published on the field of motor control dealing with analysis of movement in one joint with one degree of freedom (Zelaznik, 1996; Jaric et al., 2000). The aim of this study is to verify reliability of the test of cooperation of antagonistic muscle groups in a simple forearm movement

THE WEIGHT OF PROJECTILE AND THROW DISTANCE

The throw distance depends on initial speed, elevation angle, weight of projectile and its aerodynamic properties. In terms of biomechanics, the initial speed is dependant on the weight of projectile, force capacity of the subject and the throwing technique. When addressing motion equation of oblique throw inclusive of air resistance and projectile weight we get an equation expressing maximal throwing distance Xm (Packel & Yuen, 2004; De Mestre, 1990): Xm = (v0)^2*sin(2*alpha)/g * (1 - 2 * sqrt(2) * k*v0^3/3*m*g^2) The aim of the study is to analyze the influence of projectile weight on throw distance under stabilized aerodynamic parameters

THE INFLUENCE OF HEAD POSITION ON POSTURAL STABILITY

The influence of head position on the stance stability was studied in a set of 51 healthy university students (men, n = 21; women, n = 30) in a bipedal stance and the stance on left and right leg respectively. The head position was standardised by observation of a fixed point through dominant and nondominant eye. Two AMTI force plates and 3D kinematic analysis (APAS system) were used for the evaluation of posture stability. No significant differences were found in the bipedal stance in all test procedures. The differences in the head positions have statistically and significantly influenced only the posture stability by stance on the left leg in both groups (dominant eye right and left) in contrast to the stance on the right leg where the differences were not statistically significant

THE INFLUENCE OF BODY HEIGHT ON THE SERVE IN TENNIS

A theoretical model expressing the relationship between the dimensions of the tennis court and the height at which the ball is stroked when served is the starting point for a study of the influence of the body height of a player on the serve in tennis. A model of the flight of the ball expressed as a straight line has provided us with the theoretical information we need at the beginning regarding the angle of the serve and the active distance of the impact of the ball as dependent on the height at which the ball is stroked. The characteristics of the model were confronted with the real values acquired in a kinematic analysis of the first and second serves of two top world-class players. An increase in the height of a player appears to be a dominant factor which positively influences the direction of the flight of the ball and the speed of the serve

A LONGITUDINAL STUDY OF INTRA-INDIVIDUAL VARIABILITY IN THE EXECUTION OF THE IN-RUN POSITION IN SKI JUMPING

INTRODUCTION: The change of flight in ski jumping (V-style) has influenced a change in the take-off process. When considering this fact, it is necessary to determine whether the same applies to the in-run position – one of the basic phases of ski jumping. The ski jumper must master three basic tasks of the in-run position: maintenance of equilibrium, acquisition of maximum approach velocity and preparation for take-off. The main goal of this paper was to determine whether a set of various models of the in-run position exists for selected competitors. METHODS: Data for this study were collected from the Intersport tournee Innsbruck between 1992 and 1998 at a distance of 18 m prior to the edge of the jumping hill. A 2D kinematic analysis was used to evaluate the in-run position of the ski jumpers (500 analyses). The in-run position was evaluated using eight angle parameters. Jumpers were chosen from among the competitors who jumped at least four times in this event. Assessments of inter-individual and intraindividual variability were made. For analysis of the results, a computer statistical package ‘Statgraphics’ (one-way analysis of variance, Kruskal-Wallis one-way analysis by ranks, cluster analysis) was used. RESULTS: A large range for the analyzed angles existed for the group of selected competitors. The changes occurring among the selected segments of the body varied with each individual sportsman. The athletes under study could be divided into several qualitative groups: high stability of the lower extremities position (subjects 1 and 2), high stability of the upper extremities position (subject 3), high stability of the lower extremities with regard to the trunk position (subjects 4 and 5), in-run position with low stability (subject 6), etc. The position of the center of gravity for subjects 1, 4, 7, 8 and 9 was often stable even with high variability of the other parameters. The data supported the concept that the influence of anthropometric and physiological characteristics is very important. CONCLUSIONS: Changes in the in-run position were found in all ski jumpers in the period between 1992 and 1998. Statistically significant differences (interindividual variability) existed among years of measurement. Within the group of selected ski jumpers the execution of the in-run position varied for both body position and the position of the segments of the body. There existed an individual solution of this movement situation for most ski jumpers – it can be called an individualized model of the in-run position

COMPARISON OF THE KEY KINEMATIC PARAMETERS OF DIFFICULT HANDPSRING AND TSUKAHARA VAULTS PERFORMED BY ELITE MALE GYMNASTS

The current study compared the key kinematic parameters of two difficult groups of vaults performed by elite male gymnasts. Five top-level male gymnasts (n=5) who participated in the 2010 World Cup competition performed Handspring and Tsukahara vault groups graded 6.2 points. For the 3D spatial movement analysis, we used two digital camcorders with a frame rate of 50 Hz. The data was digitized by the SIMI MOTION software. Temporal, spatial, velocity and angular variables were measured in critical phases of a vault. To establish the differences between the means, the effect size (ES) was calculated. Although both vaults have the same initial evaluation, the Handspring group requires highest peak, longer horizontal displacement of CoG and longer duration of the second flight phase and can be, in terms of performance, considered difficult