THE INFLUENCE OF BODY HEIGHT ON THE SERVE IN TENNIS

A theoretical model expressing the relationship between the dimensions of the tennis court and the height at which the ball is stroked when served is the starting point for a study of the influence of the body height of a player on the serve in tennis. A model of the flight of the ball expressed as a straight line has provided us with the theoretical information we need at the beginning regarding the angle of the serve and the active distance of the impact of the ball as dependent on the height at which the ball is stroked. The characteristics of the model were confronted with the real values acquired in a kinematic analysis of the first and second serves of two top world-class players. An increase in the height of a player appears to be a dominant factor which positively influences the direction of the flight of the ball and the speed of the serve

A LONGITUDINAL STUDY OF INTRA-INDIVIDUAL VARIABILITY IN THE EXECUTION OF THE IN-RUN POSITION IN SKI JUMPING

INTRODUCTION: The change of flight in ski jumping (V-style) has influenced a change in the take-off process. When considering this fact, it is necessary to determine whether the same applies to the in-run position – one of the basic phases of ski jumping. The ski jumper must master three basic tasks of the in-run position: maintenance of equilibrium, acquisition of maximum approach velocity and preparation for take-off. The main goal of this paper was to determine whether a set of various models of the in-run position exists for selected competitors. METHODS: Data for this study were collected from the Intersport tournee Innsbruck between 1992 and 1998 at a distance of 18 m prior to the edge of the jumping hill. A 2D kinematic analysis was used to evaluate the in-run position of the ski jumpers (500 analyses). The in-run position was evaluated using eight angle parameters. Jumpers were chosen from among the competitors who jumped at least four times in this event. Assessments of inter-individual and intraindividual variability were made. For analysis of the results, a computer statistical package ‘Statgraphics’ (one-way analysis of variance, Kruskal-Wallis one-way analysis by ranks, cluster analysis) was used. RESULTS: A large range for the analyzed angles existed for the group of selected competitors. The changes occurring among the selected segments of the body varied with each individual sportsman. The athletes under study could be divided into several qualitative groups: high stability of the lower extremities position (subjects 1 and 2), high stability of the upper extremities position (subject 3), high stability of the lower extremities with regard to the trunk position (subjects 4 and 5), in-run position with low stability (subject 6), etc. The position of the center of gravity for subjects 1, 4, 7, 8 and 9 was often stable even with high variability of the other parameters. The data supported the concept that the influence of anthropometric and physiological characteristics is very important. CONCLUSIONS: Changes in the in-run position were found in all ski jumpers in the period between 1992 and 1998. Statistically significant differences (interindividual variability) existed among years of measurement. Within the group of selected ski jumpers the execution of the in-run position varied for both body position and the position of the segments of the body. There existed an individual solution of this movement situation for most ski jumpers – it can be called an individualized model of the in-run position

Verification of reliability of measurement systems for swimming analysis

Sophisticated technologies and measuring devices are increasingly being used for the analysis of performance and swimming techniques. At BUT, the Tachograph II and Swimming Inertial Measure Unit (SwIMU) measuring systems were developed for swimming analysis. To evaluate the measured data, the SwimDataViewer software was developed for both measuring systems. To verify the reliability of the Tachograph, 34 race swimmers were measured (15 F, 19 M), and 28 race swimmers (16 M, 12 F) were measured with SwIMU. All swimmers swam a 6x25m front crawl. Pullout and the first three and last two strokes of the arms were not included in the data evaluation. The intraclass correlation coefficient (ICC) was used to verify the reliability of the monitored parameters. The values of measured parameters in the front crawl for Tachograph (SwIMU) were ICC = 0.992 (0.991) for the average value of speed, ICC = 0.958 (0.960) for efficiency, ICC = 0.971 (0.988) for the frequency of the arms, and finally, ICC = 0.978 (0.992) for the frequency of the legs. The ICC coefficient for all monitored parameters in both devices showed a high degree of reliability. From this perspective, both devices are suitable for use in coaching and research practice

THE INFLUENCE OF HEAD POSITION ON POSTURAL STABILITY

The influence of head position on the stance stability was studied in a set of 51 healthy university students (men, n = 21; women, n = 30) in a bipedal stance and the stance on left and right leg respectively. The head position was standardised by observation of a fixed point through dominant and nondominant eye. Two AMTI force plates and 3D kinematic analysis (APAS system) were used for the evaluation of posture stability. No significant differences were found in the bipedal stance in all test procedures. The differences in the head positions have statistically and significantly influenced only the posture stability by stance on the left leg in both groups (dominant eye right and left) in contrast to the stance on the right leg where the differences were not statistically significant

Specifics of Physical Activity Children Early and Middle School Age

Při hodnocení pohybové aktivity dětí je obvykle zachována standardní klasifikace věkových kategorií. Mladším školním věkem označujeme poměrně širokou etapu od 6 do 11, resp. 12 let věku člověka. Při deskripci a interpretaci dat o pohybové aktivitě (PA) dětí je ale nutné zohlednit specifika průběhu ontogeneze v tomto věkovém období a zaměřit se na jejich podrobnější zkoumání. Cílem práce je komparace úrovně pohybové aktivitydětí z 1. stupně základních škol v jednotlivých segmentech dne a týdne z pohledu 2 fází ontogeneze: raného školního věku a středního školního věku. Hodnota aktivního energetického výdeje (AEE : kcal × kg-1 × den-1) byla získána prostřednictvím akcelerometru Caltrac a průměrný denní počet kroků (KROKY : kroky × den-1) pedometrem Yamax Digi Walker. Týdenním měřením byly zjištěny v ukazatelích PA mezi oběmasledovanými soubory signifikantní rozdíly (p<0,001) téměř ve všech sledovaných segmentech dne a týdne. Nejmenší rozdíl v hodnotách byl ale zjištěn v době pobytu dětí ve škole. U dětí středního školního věku zůstává hodnota AEE v době volného času, po ukončení školní výuky, stejná jako u dětí v raném školním věku. Ve dnech víkendu je AEE oproti hodnotám raného školního věku nižší.When evaluating the physical activity of children, it is usual to maintain a standard classification of age. Early school age is a relatively wide stage from 6 to 11 (resp.12) old years. In the description and interpretation of data about the PA of children it is also important to take account the specifics of ontogeny in this age group and focus on a more detailed study. The aim is to compare the physical activity levels of children of primary schools in the various segments of the day and over a two-week period in terms of ontogenesis stages of development. Active energy expenditure (kcal × kg-1 × den-1) was obtained by the Caltrac and daily number of steps (kroky × den-1) by pedometers Yamax Digi Walker. Weekly measurements revealed significant differences in the PA (p <0,001) and between indicators PA monitored files observed in all segments of the day and week. The smallest difference in values was detected after school. For children of middle school, age remains AEE value during free time after school, which is the same as in the early school age. Values were lower at the weekends compared to other times

Kinematic chains in ski jumping in-run posture

The concept of kinematic chains has been systematically applied to biological systems since the 1950s. The course of a ski jump can be characterized as a change between closed and open kinematic chains. The purpose of this study was to determine a relationship between adjacent segments within the ski jumper’s body’s kinematic chain during the in-run phase of the ski jump. The in-run positions of 267 elite male ski jumpers who participated in the FIS World Cup events in Innsbruck, Austria, between 1992 and 2001 were analyzed (656 jumps). Two-dimensional (2-D) kinematic data were collected from the bodies of the subjects. Relationships between adjacent segments of the kinematic chain in the ski jumper’s body at the in-run position are greater nearer the chain’s ground contact. The coefficient of determination between the ankle and knee joint angles is 0.67. Changes in the segments’ positions in the kinematic chain of the ski jumper’s body are stable during longitudinal assessment. Changes in shank and thigh positions, in the sense of increase or decrease, are the same.Web of Science391736

Varijabilnost gibanja konja u hodu tijekom hipoterapijskog jahanja

The impulses emitted from the back of a horse during hippotherapy stimulate the rider’s postural reflex mechanisms, resulting in balance and coordination training. The objectives of this study were to evaluate the movement variability of the horse’s back and limbs and to determine significant relationships between the movement of the selected body points on the horse. Two English thoroughbreds and twelve female riders participated in six sessions of hippotherapy. Three-dimensional (3-D) videography was used to assess movement of the selected points on the horse’s back and limbs. The spatiotemporal parameters of the horse’s walk showed no significant changes throughout the entire measuring process. Horse movement within a given session was stable, and overall, inter-individual (between-horse) variability was greater than intra-individual variability. The maximum differences in the vertical displacement of the horse’s back across individual sessions were significant. With respect to the range of movement of the caudal part of the horse’s back, it is necessary to consider the instability of movements during longitudinally repeated sessions.Impulsi s leđa konja za vrijeme hipoterapijskog jahanja podražuju jahačeve posturalne refleksne mehanizme, što rezultira treningom ravnoteže i koordinacije. Ciljevi ovog istraživanja bili su vrednovati varijabilnosti gibanja leđa i udova konja i utvrditi značajnost veza između gibanja odabranih točaka na tijelu konja. Dva čistokrvna engleska konja i dvanaest jahačica sudjelovalo je u šest hipoterapijskih sesija. Trodimenzionalna videografija se koristila za utvrđivanje gibanja izabranih točaka na konjskim leđima i udovima. Kinematički parametri konjskog hoda nisu se značajno mijenjali tijekom cijelog procesa mjerenja. Gibanje konja tijekom jedne sesije bilo je stabilno i, generalno, inter-individualna varijabilnost kinematičkih parametara između konja bila je veća nego intra-individualna varijabilnost između mjerenja u svih 6 sesija. Maksimalne razlike u okomitim pomacima leđa konja između pojedinačnih sesija bile su značajne. Promatra li se donji dio leđa konja, potrebno je u obzir uzeti nestabilnost gibanja tijekom ponovljenih jahačkih sesija

Gender and age related differences in leg stiffness and reactive strength in adolescent team sports players

The aim of the present study was to identify potential gender differences in leg stiffness and reactive strength during hopping tasks in 13 to16-year old team sports players. Reactive strength index (RSI) and leg stiffness were obtained in two consecutive seasons from 51 girls (U14: n = 31, U16: n = 20) and 65 boys (U14: n = 32, U16: n = 33). A significant main effect on absolute (U14: p = 0.022, η² = 0.084; U16: p < 0.001, η² = 0.224) and relative leg stiffness (U14 p<0.001; η² = 0.195; U16; p = 0.008, η² = 0.128) for gender was found in both groups with values higher in boys than in girls. For absolute and relative stiffness gender differences in the U14 group were significant in the 1st year only (p=0.027 and p=0.001), and for the U16s in the 2nd year only (p < 0.001 and p = 0.022). For RSI, a significant main effect for gender was observed in the U16 group only (p < 0.001 η² = 0.429) with values significantly higher in boys than in girls in both years of measurement (p = 0.001; p < 0.001). Results of this study support previous limited findings, mostly related to non-athletes, suggesting lower stretch-shortening cycle capability in adolescence female compared to male, however our data only partly supports the theory that quality of neuromuscular functions increases with age until post puberty

Changes in speed and strength in female volleyball players during and after a plyometric training program Změny rychlostně-silových předpokladů volejbalistek v průběhu a po absolvování plyometrického tréninkového programu

The goal of this article was the validation of a plyometric training program and the evaluation of the changes in monitored speed and explosive power predispositions during and after the end of the training program. The program was applied to a group of female youth volleyball players (n = 11) twice a week during an eight week period. Their actual level of explosive power and locomotor speed was evaluated before, during and after the intervention was completed. The levels were determined with the following tests: the standing vertical jump, the vertical jump with an approach and the shuttle run for 6 x 6 m. There were positive changes in the average values of test scores during the period of testing, but the dynamics of the changes in the explosive power and the speed were different. Other increases in all the characteristics were noticeable when the final measurements were made six weeks after the completion of the training program. Examination of the differences in the test scores by the follow up group, before the beginning and six weeks after finishing the intervention, was centred on objectively and statistically important changes in the volleyball players' motor predispositions (p < .05). The results of the program support the opinion that plyometric exercises are effective tools in the development of explosive power and speed in young athletes. Cílem studie bylo ověřit v tréninkové praxi program sestávající z vybraných plyometrických cvičení a zhodnotit změny sledovaných rychlostně-silových předpokladů v průběhu a po jeho absolvování. Program byl aplikován u volejbalistek kadetské kategorie (n = 11) 2x týdně po dobu 8 týdnů. Aktuální úroveň výbušné síly a lokomoční rychlosti byla hodnocena před, v průběhu a po skončení intervence testy dosah jednoruč po výskoku z místa, dosah jednoruč výskokem po smečařském rozběhu a rychlostní člunkový běh na 6 x 6 m. V období realizace programu docházelo k pozitivním změnám průměrných hodnot testových skóre, avšak dynamika změn ukazatelů odrazové síly a rychlosti byla odlišná. Další nárůst výkonnosti u všech sledovaných ukazatelů byl zaznamenán při výstupním měření (šest týdnů po absolvování tréninkového programu). Posouzení rozdílů testových skóre sledovaného souboru před intervencí a šest týdnů po jejím skončení ukázalo na věcně i statisticky významné změny ve výkonnosti hráček (p < .05) Výsledky studie podporují názor, že plyometrická cvičení jsou efektivním prostředkem rozvoje výbušné odrazové síly a rychlosti sportující mládeže

Hodnocení variability dynamických parametrů chůze u osob s jednostrannou trans-tibiální amputací The variability assessment of the dynamic gait parameters of persons with unilateral trans-tibial amputation

Při anal&yacute;ze pohybov&eacute; činnosti člověka mus&iacute;me vždy ře&scaron;it ot&aacute;zky, kter&eacute; se vztahuj&iacute; k validitě naměřen&yacute;ch hodnot. Realizace každ&eacute;ho pohybu, tedy i chůze, se vyznačuje určitou m&iacute;rou variability. Přitom variabilitu v určit&eacute;m rozsahu nelze považovat jako něco negativn&iacute;ho, co může b&yacute;t způsobeno probl&eacute;my v nervov&eacute;m nebo kosterně-svalov&eacute;m syst&eacute;mu. "Přirozen&aacute;" variabilita (varia bilita ve "fyziologick&eacute;m" rozsahu) je souč&aacute;st&iacute; zdrav&yacute;ch biologick&yacute;ch syst&eacute;mů. Reedukace chůze u osob s trans-tibi&aacute;ln&iacute; amputac&iacute; se projevuje ve změně variability kinematick&yacute;ch a dynamick&yacute;ch charakteristik. Pro možnost kvantifikace těchto změn a pro určen&iacute; vlivu různ&yacute;ch typů protetick&yacute;ch chodidel (klasick&eacute; &ndash; SACH, dynamick&eacute; &ndash; SUREFLEX) jsme provedli dynamickou anal&yacute;zu chůze u 11 mužů (věk 46,1 &plusmn; 12,0 roku, hmotnost 82,5 &plusmn; 13,9 kg) s jednostrannou trans-tibi&aacute;ln&iacute; amputac&iacute;. Interindividu&aacute;ln&iacute; variabilita v r&aacute;mci dan&eacute; skupiny je vět&scaron;&iacute; v porovn&aacute;n&iacute; s intraindividu&aacute;ln&iacute; variabilitou. Hodnoty koeficientu reliability jsou pro měřen&eacute; parametry (čas, s&iacute;la, impuls s&iacute;ly) v antero-posteriorn&iacute;m a ve vertik&aacute;ln&iacute;m směru vět&scaron;&iacute; než 0,976. Jejich velikost souvis&iacute; s individu&aacute;ln&iacute;mi vlastnostmi sledovan&yacute;ch osob. Pro oba typy protetick&eacute;ho chodidla, podobně jako pro zdravou končetinu, jsou tendence pro stabilitu dynamick&yacute;ch parametrů podobn&eacute;. Stabilita měřen&yacute;ch parametrů v medio-later&aacute;ln&iacute;m směru se v&yacute;znamně snižuje uvnitř sledovan&eacute; skupiny i pro jednotliv&eacute; osoby. Velikost variability při různ&eacute; rychlosti chůze souvis&iacute; se zdravotn&iacute;m stavem a se stupněm pohybov&eacute; aktivity dan&eacute;ho probanda. Pro osoby, kter&eacute; vykon&aacute;vaj&iacute; běžn&eacute; denn&iacute; aktivity v omezen&eacute;m rozsahu, je variabilita dynamick&yacute;ch parametrů chůze niž&scaron;&iacute; při použit&iacute; klasick&eacute;ho chodidla. Human gait is a genetically fixed motion model. The use of prosthesis changes the structure of the gait, the distribution of energy increases. The aim of this study was to compare the intra and inter individual variability of the basic dynamic gait parameters of physically active persons with unilateral trans-tibial amputation. A group of 11 males (age 46.1 ± 12.0 years, body weight 82.5 ± 13.9 kg) with unilateral trans-tibial amputation was analysed. The basic dynamic parameters (AMTI) of the gait of each subject with conventional and dynamic prosthetic foot were measured. The interindividual variability in the group of the evaluated person is higher in comparison with the intraindividual variability. The sizes of the coefficients of reliability are exceeded for measured parameters (time, force, force impulse) in anteroposterior and in vertical direction the value 0.976. The extent of these values depends on the individual properties of evaluated person (for example the instability of the knee etc.)