INTRODUCTION: Wearing jumping boots during take-off Simulation reduces speed and increases duration of the take-off phase (Schwameder et al., 1997). A diverse footwear is reflected in take-off kinematics and in the engagement of muscles (Virmavirta & Komi, 2000; Virmavirta & Komi, 2001). "Natural" variability and asymmetry (in the "physiological" extent) is a component of healthy biological Systems, however the sequence of movements beyond the ski jumping hill edge requires reduction in such an asymmetry. This study aims to compare ' the magnitudes of take-off forces on the right and left lower limbs during the take-off. METHOD: A group of young Nordic combined competitors (n = 28, age = 16.21 ± 1.47 yrs, mass = 63.0 ± 8.29 kg) performed take-off from an in-run position. Two trials in training footwear (IRJt) were followed by two trials in jumping footwear and outfit (IRJs). Distribution of load in the lower limbs (LE) was assessed in quiet standing (30 s). Take-off was performed on two force plates Kistler 9286AA. This was followed by training at a ski jumping hill where all Jumpers performed 10 jumps. By means of dynamometric plates Kistler Z18402-100, the take-off force was measured for the left and right lower limbs 6 m before the jumping hill edge. Data were analyzed with programme STATISTICA, verslon 6.0. RESULTS: The difference in load of LE in quiet standing position ranged between 0-5.55 kg (0-7.37%). The difference in load of LE is 0.19-12.16% at the beginning of IRJt and 0.31- 10.66% in IRJs. Stability of take-off performance at ski jumping hill is rather high. The coefficient of reliability for overall take-off speed (vigour) amounts to 0.95, whereas the value for take-off speed on individual limbs is 0.84 or 0.89, respectively. The most significant difference in size of take-off force LE was detected for IRJt. DISCUSSION: The difference between take-off force on the right and left lower limbs is reduced by increase in restraining factors (jumping boots) and by increase in performance difficulty (jumping hill). Changes in in-run position (e.g. between two training sessions) cause significant changes in distribution of force between LE. CONCLUSION: There exist significant differences between take-off forces on the right and left lower limbs. When performing take-off, the difference in load of LE in comparison with quiet standing position increases. Reliability of load size on the right and left lower limbs in repeated take-offs at ski jumping hill is rather high.
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