Staigiosios jėgos poveikis šoklumui: eksperimentų analizė ir skaitinis modeliavimas

The aim of this work is to understand which factor — explosive force R or average take-off force Fvid — infl uences vertical jump height, take-off time and relative jump power. We also want to contradict the opinion that ability to jump may be evaluated using only height of a jump and that height of a jump is specifi ed by explosive force. 14 members of Lithuanian junior handball team were examined. Each of them performed three jumps on the force platform without damping squat, knees bent at 90° angle. We measured take-off time tat , velocity at the take-off moment vat, maximum height reached by the center of body mass (COM) hmax, average relative take-off force Fvid , relative explosive force R and relative jump power sant P . Vertical jump was modelled as vertical movement of point of mass affected by internal body force. Two types of internal body force were constructed for use in numerical experiments: 1) during the take-off vertical internal body force grows constantly (i. e. R = const); 2) internal body force grows for some short time period then stays fi xed till the take-off moment. The latter case models the dynamics of internal body force which is observed during physical experiments. Model parameters (take-off time, averaged internal body force, etc.) were used from the data of physical experiments. Modelling results show that in order to jump higher the vertical internal body force or take-off time (or both parameters) must be increased. In order to reach the same height quicker the internal vertical body force must be increased and the take-off time must be decreased, i. e. the explosive force must be increased. Analytical study of the model revealed that height of a jump is strongly affected by the explosive force only in the case when internal vertical body force grows constantly. However, during physical experiments when subject jumps the generated internal vertical force grows only for a very short time period, therefore the impact of explosive force to the height of a vertical jump is minimal (r = 0.17). Meanwhile, the take-off time and jump power depends on a magnitude of explosive force (r = –0.58 and r = –0.78 respectively). Numerical experiments conducted in this work confi rmed the data from our and other authors’ physical experiments and allow us to conclude that: a) Jump height is barely affected by explosive force and mainly depends on impulse of an internal vertical body force; b) explosive force affects the take-off time and magnitude of relative power; c) hopping, as a physical ability of a human body, must be evaluated using both height and speed of a jump. The best parameter to describe jumping ability is relative jump power.