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

Stability of hot plastic deformation

26.00; Translated from Czech. (Hutn. Listy 1989 v. 44(4) p. 241-247)Available from British Library Document Supply Centre- DSC:9023.19(VR-Trans--4374)T / BLDSC - British Library Document Supply CentreSIGLEGBUnited Kingdo

Effect of carbide phase on the flow stress of austenite in hot working

21.00; Translated from Czech. (Hutn. Listy 1988 v. 43(11) p. 772-777)Available from British Library Document Supply Centre- DSC:9023.19(VR-Trans--4103)T / BLDSC - British Library Document Supply CentreSIGLEGBUnited Kingdo

Determining the limit of diffusion instability of deformation by the tensile test

26.00; Translated from Czech (Hutn. Listy 1990 v. 45(4) p. 274-279)Available from British Library Document Supply Centre- DSC:9023.19(VR-Trans--4689)T / BLDSC - British Library Document Supply CentreSIGLEGBUnited Kingdo

Relationship between recrystallisation and precipitation in controlled forming microalloy carbon steels

26.00; Translated from Czech (Hutn. Listy 1990 v. 45(4) p. 268-274)SIGLEAvailable from British Library Document Supply Centre- DSC:9023.19(VR-Trans--4688)T / BLDSC - British Library Document Supply CentreGBUnited Kingdo

Biomechanics research in Faculty of Physical Culture Palacký University Olomouc and Human Motion Diagnostic Center University of Ostrava

This action is realized by the project NEXLIZ - CZ.1.07/2.3.00/30.0038, which is co-financed by the European social fund and the state budget of the Czech republic