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Relationship between lower limbs kinematic variables and effectiveness of sprint during maximum velocity phase

Struzik A., Konieczny G., Grzesik K., Stawarz M., Winiarski S., Rokita A.

Acta of Bioengineering and Biomechanics

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2015

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Vol. 17, no. 4

131--138

EN

Purpose: The aim of the study was to determine the relationships between time of running over a 15–25 m section of a 30-meter run along a straight line and changes in the angle and angular velocity observed in ankle, knee and hip joints. Therefore, the authors attempted to answer the question of whether a technique of lower limbs movement during the phase of sprint maximum velocity significantly correlates with the time of running over this section. Methods: A group of 14 young people from the Lower Silesia Voivodeship Team participated in the experiment. A Fusion Smart Speed System was employed for running time measurements. The kinematic data were recorded using Noraxon MyoMotion system. Results: There were observed statistically significant relationships between sprint time over a section from 15 to 25 m and left hip rotation (positive) and between this time and left and right ankle joint dorsi-plantar flexion (negative). Conclusions: During the maximum velocity phase of a 30 m sprint, the effect of dorsi-plantar flexion performed in the whole range of motion was found to be beneficial. This can be attributed to the use of elastic energy released in the stride cycle. Further, hip rotation should be minimized, which makes the stride aligned more along a line of running (a straight line) instead of from side to side.

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Lower extremity power in female soccer athletes : a pre-season and in-season comparison

Pietraszewski B., Siemieński A., Bober T., Struzik A., Rutkowska-Kucharska A., Nosal J., Rokita A.

Acta of Bioengineering and Biomechanics

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2015

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Vol. 17, no. 3

129--135

EN

Purpose: Lower extremity power is an important physical capacity of a soccer athlete. Power represents, and can be modified by, the training of strength and speed. Pre-season and in-season training differs in the relative emphasis on these two quantities. It is nevertheless desirable that the mechanical power remain the same or become higher during the in-season period. The purpose of this study was to identify changes in quantities related to “explosive strength” and to check whether, in collegiate female soccer players, pre- and inseason lower extremity power will remain unaltered. Methods: Twenty collegiate female soccer players, representing all field positions, participated. Lower extremity power was assessed by a series of drop jumps executed from four different heights (15, 30, 45, and 60 cm). Mechanical power was calculated using subject’s mass, jump height, and acceleration due to gravity. This value was further normalized by body mass of each athlete to obtain the relative (or normalized) mechanical power. Results: The normalized lower extremity mechanical power was highest when landing from the 30 cm height for both pre- and inseason periods. However, contrary to expectations, it turned out lower during the in-season than during the pre-season test, even though no significant differences were found between the corresponding jump heights. Conclusions: It is concluded that altered, perhaps inadequate, training strategies were employed during the in-season period. Besides, advantages of adding the relative mechanical power as a season readiness indicator are underlined compared with relying on the jump height alone.

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Podwajacz częstotliwości z symetryzatorem koplanarnym

Rokita A.

Prace Przemysłowego Instytutu Telekomunikacji

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1998

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Vol. 47, nr 121

27-31

PL

Opisano podwajacz częstotliwości typu rezystywnego w układzie prostownika dwupołówkowego, zawierający dwie diody Schottky’ego i prosty symetryzator planarny. Podwajacz pracuje w paśmie Ku w zakresie częstotliwości obejmującym niemal oktawę, ze stratami przemiany 12 ÷ 16 dB. Przedstawiono w zarysie zasadę działania i procedurę projektowania podwajacza. Wykazano, że model nie wykorzystuje w pełni potencjalnych możliwości układu i możliwa jest istotna poprawa parametrów podwajacza.