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The bilateral strength and power asymmetries in untrained boys

100%
Maly T., Zahalka F., Mala L., Cech P.
Open Medicine
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2014
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vol. 10
|
issue 1
EN
The aim of the study was to identify the level of isokinetic strength and power of lower limbs in 13-year- old untrained boys (n=22, height: 158.5±8.0 cm, mass: 49.1±12.6 kg), to determine bilateral deficit between the limbs in the tests and examine their mutual relationship. Maximum peak muscle torque of knee extensors (PTQ) and flexors (PTH) on dominant (DL) and non-dominant leg (NL) were measured by isokinetic dynamometer. Three types of a vertical jump: countermovement jump with (CMJFA) and without arms (CMJ) and squat jump (SJ) were performed on two force platforms. We found the significant effect (p<.01) of independent vari- ables (knee extensors, flexors, AV) and their interaction on PT. AV did not indicate any significant effect on bilat- eral ratio of knee extensors (F4,84=.74, p>.05, ηp2=0.03), however a significant effect of AV was found in knee flexors (F4,84=2.70,p<.05, ηp2=.114). The type of jump had no effect on the difference between force exerted by DL and NL (F1,21=.102, p>.05, ηp2=.01). Bilateral deficit (Q:Q, H:H) did not significantly correlate with bilateral deficit in jumps (p>.05). Despite the possibility of identifying muscle asymmetries in the sense of strength imbalances, their mutual relation- ship with results in isokinetic dynamometry and power jump tests is still unclear.
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Kinematic Analysis of the Take-Off and Start of the Early Flight Phase on a Large Hill (HS-134 m) during the 2009 Nordic World Ski Championships

88%
Janura M., Cabell L., Svoboda Z., Elfmark M., Zahalka F.
Journal of Human Kinetics
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2011
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vol. 27
5-16
EN
The take-off is often considered the most significant and difficult phase of a ski jump. Thus, the purpose of this study was to compare three groups of ski jumpers representing different skill levels during the execution of the take-off and start of the early flight phase in ski jumping. A total of 30 athletes, recruited from competitors performing ski jumps on an HS-134 m jumping hill, were categorized into three groups based on jump-length execution. Two-dimensional (2-D) kinematic data were collected from the lower extremities, trunk, and skis of the ski jumpers. Findings indicated that the ski jumpers with shorter jump length demonstrated significantly smaller in-run velocity (p < .05), while the elite and mediocre level ski jumpers exhibited a significantly faster shift of the thigh at the transition from take-off into the early flight of the jump (p < .05) than did the low-level ski jumpers. In addition, the centre of body mass (CoM) of the elite group shifted significantly more forward over the skis (p < .01) than did that of the other two groups. Finally, interindividual differences existed among ski jumpers at similar performance levels. The largest coefficients of variation (CVs) were found for the position changes of the trunk and shank behind the jumping hill edge.
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