COMPARISON OF THE LOWER EXTREMITIES ’ EXPLOSIVE MUSCULAR STRENGTH VIA JUMPING TESTS IN DIFFERENT PERFORMANCE LEVEL AND AGE GROUPS OF WOMEN VOLLEYBALL PLAYERS

BACKGROUND: Sport performance in volleyball is signifi cantly infl uenced by the quality of the playerʼs jumping abilities, above all on the height of the jump. Results in jumping tests indirectly indicate information about explosive muscle strength. Information about the quality of the results of jumping tests is the starting point for the monitoring of the athlete’s conditioning. OBJECTIVE: This workʼs purpose consists in fi nding out whether there exist some diff erences between women volleyball players according to their age and their sport performance level and whether women volleyball players differ from women university students. A secondary aim of the study is to assess the suitability of using three jumping tests in volleyball. METHODS: For the set of women volleyball players (n = 273) divided into fi ve diff erent age and sport performance categories and for the set of university female students (n = 33), three jump tests were applied – the spike jump test SPJ, the counter movement jump test CMJ and the standing broad jump test SBJ. Statistical analysis was done using the Czech STATISTICA system, version 6 (Kolmogorov-Smirnov test, Spearman coeffi cient correlation, paired t-test and ANOVA for independent samples). RESULTS: Relatively small and mostly statistically insignifi cant diff erences have been found between women volleyball players of various age and sport performance groups. All groups of volleyball players signifi cantly exceeded the university students set in the level of their explosive muscle strength. Our research showed a lower level of jump performance, especially in what concerns the highest sport performance of women players. The initial hypotheses about the usefulness of applying three jumping tests in volleyball were confi rmed. CONCLUSIONS: The diff erences in the results of jumping tests for diff erent age and sport performance groups of women volleyball players are small. The relatively lower level of the jumping abilities of the highest sport performance players was discovered. Experience with applying three jumping tests have shown their convenience to be utilizable in volleyball. Each test has its own specifi city to provide information about the quality of jumping abilities with regards to the sport performance level and to the age of the tested female players.


INTRODUCTION
Concerning current volleyball playing performance, increasing dynamicity, speed and agility within the female players' movement actions is characteristic (Baacke, 1994;Papageorgiou, 1999;Buchtel et al., 2005).Sporting performance is signifi cantly infl uenced by the off ensive phase quality, depending above all on the jump height.Lehnert, Novosad, and Orlová (1993) characterize volleyball performance as a multi-factorial eff ect with a signifi cant representation of the take-off ability factor, which infl uences, within a great range, the off ensive phase quality as well as the blocker's defense activities.
In practice, there are diff erent variants of tests utilized in volleyball, whose selection is given by the char-acteristic of the movement activities which are typical for volleyball (Kaplan, 1997;Papageorgiou & Spitzley, 2002;Přidal & Zapletalová, 2003).Current volleyball is characterized by a great quantity of jumps, skips, hops and other kinds of take off (Abendroth- Smith & Kras, 1999).In volleyball practice, we can divide take off s into two basic skills -the spike jump (from one leg, from both legs) and block jump (from one place, after movement).To ensure the lower extremities explosive muscle strength and also to evaluate the techniques of execution of the spike jump in volleyball, it is convenient to use a counter movement jump after a three to fi ve step run up which has been called the spike jump test (SPJ).The SPJ test evaluates the volleyball playerʼs special jumping knowledge, which is practically identical to the take off execution during a match.The spike jump test is a mat-ter of interest for many authors who approach its examination in order to improve volleyball playersʼ jumping performance and, simultaneously, they consider it to be an effi cient checking means to fi nd out explosive muscle strength level (Bobbert, Huijing, & Van Ingen Schenau, 1987;Coleman, Benham, & Northcott, 1993;Forthomme, Crossier, Ciccarone, Crielaard, & Cloes, 2005;Tillman, Haas, Brunt, & Benett, 2004;Tokuyama, Ohashi, Iwamoto, Takaoka, & Okubo, 2005).
Aside from the specific volleyball SPJ test, one mostly comes across the general take off abilities tests as, for example, the standing broad jump or the counter movement jump (Měkota & Blahuš, 1983;Měkota & Novosad, 2007).Counter movement jumps are often utilized as an easy test to check anaerobic muscle strength development (Komi & Bosco, 1978;and others).In practice, we meet diff erent variants of counter movement jumps according to the sports specialization of the monitored sports groups.The most used is the counter movement jump (CMJ) which is executed with a movement of the arm or with its exclusion.A specifi c variant consists in the counter movement jump from a static lowered position (squat jump) which is used, for example, in ski jumpers testing.The counter movement jump is evaluated by this test with high reliability and validity (Měkota & Blahuš, 1983;Vaverka, 2000;and others) and it makes possible explosive muscle strength comparison between diff erent groups of persons.
Obtaining fi nal information concerning the results of the counter movement jump test (jump height) is not an easy thing.Aside from the imprecise Sargent jump (Sargent, 1921), the more complex systems of jump height measuring are based on calculations of the fl ight phase or with the help of the kinetic analysis of the reaction force measured (Vaverka, 2000).The counter movement jump kinetics analysis resulting from the dynamometrically measured reaction force enables us, besides determining the fi nal characteristics of the achieved jump height, to obtain a great number of other information about the force, speed and race track course of the centre of gravity of an individual (Vaverka, Salinger, & Novosad, 1979;Vaverka, 2000).Detailed information concerning the jump results obtained by the calculation of the fl ight duration or on the basis of kinetic analysis requires specifi c measuring and calculation systems and the testing is usually dependent upon specifi c laboratory conditions.
The results of the men and women volleyball players' take off abilities testing bring us important information for improving training quality (Beal & Elder, 1988;Boyle, 2004;Ejem, 1993Ejem, , 1998)).The standing broad jump is utilized to evaluate youth and beginnersʼ jumping talents.The counter movement jump as well as the standing broad jump are made an integral part of the group of tests which are utilized within the framework of the diagnostics of the representation of the selection of playersʼ test batteries, at youth tournaments and at sports clubs (Ejem, 1998).Lehnert and Zháněl (2009) proposed a testing set of motoric tests in volleyball which comprises groups of tests for senior and youth representation, youth centers, sports secondary schools and selected pupils at primary schools.In volleyball, special tests are utilized, whose content comprises identical movements to the movements used in the game.It consists in special movement abilities tests (Bartlett, 1985;Bartlett, Smith, Davis, & Peel, 1991;Colins & Hodges, 2001).
The purpose of this work consists in comparing the explosive take off strength level by means of motoric tests among women volleyball players of diff erent age and sport performance categories as compared to a set of university female students.We are interested in fi nding out whether there exist any diff erences in their explosive muscle strength related to the age and the sport performance of these women players and whether the women volleyball players diff er from the population of recreational sportswomen.We suppose that as the age and sport performance of women volleyball playersʼ increases, the explosive muscle power will also significantly rise.Another purpose of this study consists in comparison of the diff erent variants of the tests and to determine their usefulness under diff erent conditions of testing in volleyball.

METHOD
Five sets of women volleyball players (n = 273) and one set of recreational sport practicing university female students (n = 33) participated in this research.
In TABLE 1 are presented the basic characteristics of the tested persons according to their number, age and body sizes.The monitored groups were teams of women players of diff erent age categories and the control group consisted in recreational women volleyball players, female students of the fi rst year at the Technical University of Ostrava.The measuring was done within the period 2003-2005 at the Human Movement Diagnostics Center of the University of Ostrava and in the sports hall of the University Sports Club of the Technical University of Ostrava and this, always within the period from October-November to the end of the training cycle preparation phase.
Three tests were selected to evaluate explosive muscle strength level: the SPJ -spike jump test, the CMJcounter movement jump, SBJ -standing broad jump.The spike jump test is a typical volleyball element where, after a three step run up, the player takes off vertically with the accompanying arm movement.The counter movement jump is a standardized take off with counter movement and accompanying arm movement (Vaverka, 2000).The standing broad jump is a classical motoric test (Měkota & Blahuš, 1983).The testing was done according to the principles mentioned in the literature (Měkota & Blahuš, 1983).
To evaluate the results of the SPJ and CMJ tests, the professional system called FITRO Jumper II (manufactured by FITRONIC, s. r. o., Bratislava) was utilized.The jump evaluation results from the measuring by the described system is based on the measurement of the support and non-support phases of the jump.The system provides a great number of variables characterizing the counter movement jump, among which the following ones have been selected for the purpose of this study -HJ -jump height (cm), P -power within the take off active phase (W) and Pʼ -average power computed in the whole jumping cycle (W/kg).
The measuring of all of these three tests was always done in one single day.Prior to each test, the measuring women participants warmed up and performed eff ectuated training in the course of which the jump execution technique was explained to them and corrected.Prior to the beginning of each test, the female participants also had to successfully perform three training jumps.Between each individual test, the time interval was two minutes for each participant.In each test, three succeeding attempts were recorded and the fi nal result was the best jump from the height point of view.
For the statistical analysis, the following tests were selected -a test of experimental data distribution (Kolmogorov-Smirnov), the paired t-test, the Spearman rank correlation coeffi cient ation and the ANOVA (Scheff é post-hoc test).All of the calculations were done in the program called STATISTICA Cz, version 6 by StatSoft, Inc. (2001).

Diff erences between the selected groups
From the jump height and from the point of view of the statistical structure of the important diff erences between the groups, we can see a similar picture for each variant of the tests (TABLE 2).In all of the three tests, the checked set of female students reaches lower values of jump height and length in what concerns the standing broad jump than the other women volleyball players group.The diff erences between the female students and the women volleyball players are statistically signifi cant (except for the counter movement jump at U15).In the test results, the diff erences between the sets of women volleyball players are relatively small and in many cases, they remain statistically insignifi cant.
With a general view to the structure of the statistically signifi cant diff erences between the groups, the spike jump test diff ers from two classical tests concerning counter movement jumps and the standing broad jump.Concerning the spike jump test, we can fi nd differences between U15 and all of the other groups and in what concerns the classical tests, the number of signifi cant diff erences between the women players' groups decreases.It is interesting to notice that the diff erences between women -national top level or other groups of women volleyball players, are not statistically signifi cant in the SPJ test.On the other hand, within the framework The complex comparison of the diff erences between the sets in each individual test is shown in graphical illustration (Fig. 1a).The curves expressing the greatness of the jump height and length in all of the three tests are practically the same from the point of view of their course.Having identical models in the tests results in graphical illustration for the diff erent groups of tested women players, evidencing the fact that all of the three tests provide almost the same information concerning the explosive muscular strength level.

Test comparison from the power point of view
The term "power" (P) is defi ned using the physical value called a "watt" (W) and it diff ers from the traditional terms used to describe performance in the sense of the result of a sports activity.The results illustrate that the diff erences in the P performance greatness between the diff erent tested groups have a similar trend in both cases of vertical jumps (Fig. 1b).The relative performance Pʼ analysis (W/kg) brought us practically identical information about the diff erences between the selected groups compared to those we can fi nd in the P value.When we compare the trends of the curves expressing the tests results of each individual group and the P performance curves (Fig. 1), we can see a high range of similarity.The statistical signifi cance of the diff erences between the performance values is similar to the diff erences in testing between the results of the three tests.The mentioned facts illustrate that, in order to quantify the level of explosive muscle strength, only test results expressed in jump height or length provide a suffi cient and quality indicator.

Diff erence between the spike jump test and the counter movement jump
The diff erence between both variants of SPJ and CMJ jumps is statistically signifi cant for all of the sets (women volleyball players p < 0.01, female students p < 0.05) and in all cases, the SPJ height is higher than the CMJ height (TABLE 3).The gain amplitude in the jump height for the SPJ, expressed in percentage of CMJ, is within the range of 15-19% for volleyball players and amounts to 10% only for the female students.The results proved that the connection of the run up with the take off increases the jump height from 15% to 20% of their basic performance in CMJ.

DISCUSSION
Between the groups of women volleyball players (except for the U15), there are very small and statistically insignifi cant diff erences in the jump height.National top level players reach the best performances in all of the tests and they diff er from other groups in CMJ and SBJ classical motoric tests only.Tillman, Hass, Brunt, and Bennett (2004) mention that, in what concerns top women volleyball players, the technique of jump execution has an infl uence on the jump height.With regards to the Hsieh and Heise (2008) studies results, they affi rm that top level women volleyball players should reach better results in jump height.It seems that concerning the group of the tested national top level players, the take off quality is not so high.The participation of the players in the Czech national top level competition is certainly infl uenced by other qualities (physical proportion, technique, playing experience, etc.) and suitable attention is not given to the take off level.The similar results of the tests for national top level women players and U18 players are certainly the consequence of the state of aff airs in which a lot of young and promising U18 players Diff erences between women volleyball players and women players at the recreational level in what concerns explosive muscle strength level are naturally signifi cant and expected.The question we can ask ourselves is whether a diff erence within a range of 7 to 12 cm for the SPJ test and of 2 to 9 cm for the CMJ between the systematically trained volleyball players and the players at recreational level is suffi cient.If we compare the results of our studies with the data published in the literature (Lehnert, Novosad, & Orlová, 1993;Voight & Vetter, 2003) we can see that the tested players of the Czech top level competition reach a lower level in what concerns explosive muscle strength than the world top level players.During World championship junior teams testing, Lehnert, Novosad, and Orlová (1993) mention a counter movement jump average height of 41 cm and of 47 cm for the spike jump test.If we express the top national level women playersʼ measured values in percentages of the best worldwide junior playersʼ jump height (jump height = 100%), then the tested top national level women players reach the value of 92% for the spike jump test and of 90% for the counter movement jump.The mentioned confrontation with the data obtained at the world level junior teams shows some lack in explosive muscle strength at the level of the tested highest Czech national competition players.
Diff erent complications of counter movement jump analyses enable us to obtain a great quantity of numbers and other information and this not only concerning the jump height but also regarding the time, force and track structure of the given movement (Vaverka, 2000).The method utilized in this study has provided information about the performances P and Pʼ in the case of a given jump.The confrontation of the P and Pʼ performance size in the cases of SPJ and CMJ tested jumps made us realize that the diff erences between the tested sets in these values have the same character as the diff erences in the jump height (Fig. 1).This fact is understandable, because the volleyball women playersʼ physical structure is very similar and their performance greatness while jumping depends especially, when body proportions are at a standard level, on the height reached during the jump.From the practical point of view, if the experimenter does not solve any specifi c problems, fi nding out the jump height appears to be suffi cient to determine the level of the lower extremitiesʼ explosive muscle strength.
The diff erences in the jump height which we found while comparing two variants of SPJ and CMJ jumps were signifi cant for all of the tested sets.The SPJ jump height is 5.2-5.9cm (115-119%) higher for women volleyball players and 2.2 cm (110%) for the female students than the CMJ height (100%) is.These diff erences show that the connection of run up and take off increases the jump height.The above mentioned fact is confi rmed by numerous literature sources (Shahbazi, Mirabedi, & Gaeini, 2007).Lehnert, Novosad, and Orlová (1993) describe the spike jump as a test evaluating the volleyball playersʼ special jumping abilities.The studiesʼ results showed that there were smaller diff erences in the SPJ test values between the performing groups of players than between the results of the CMJ and SBJ classical test.It seems that the SPJ test execution technique probably reduces the diff erences between various women volleyball playing groups.
The basic problem of the diagnostics of those two variants of counter movement jumps consists in technical limits requiring complicated technology.Their application is mostly possible under laboratory conditions.The studiesʼ results proved the utility of the information obtained from the standing broad jump classical test.Because of its simplicity and great measuring precision, the SBJ test appears to be a suitable diagnostics instrument which can be especially utilized in beginners and youth in order to fi nd out their level of talent for jumping and also to check the eff ectiveness of training for the whole performing spectrum of women volleyball players.

CONCLUSION
Women volleyball players signifi cantly diff er from the recreationally sporting women population in their explosive muscle strength level.Concerning height in the spike jump test, the diff erences are relatively small and mostly statistically insignifi cant between the diff erent sport performance levels of women volleyball players.Regarding the counter movement jump, national top level players reach a higher jump height than the youth categories and concerning the standing broad jump they also diff er from all the rest of the monitored groups.The studiesʼ results show that the national top level players and national level players have not reached the expected diff erences in their lower extremitiesʼ explosive muscle strength.The height of the jump and the variable power (P) derived from the measured result of the jump provide similar information about the quality of the jump.
Experience with the testing of the standing broad jump shows that it is a quality and easily done test for basic orientation in the jumping abilities level of players.Its utilization is especially suitable at the training practice level for youth and talented players' selection.To diagnose the women volleyball playersʼ jumping level, it is suitable to use the counter movement jump and the spike jump test.These studies proved that the connection of the run up in the spike jump test increases the jump height by 15-20% of the counter movement jump height.With regards to the relatively small diff erences in the jump height between the individuals in the CMJ, we recommend the utilization of exact measuring procedures requiring collaboration with specialized biomechanical laboratories (using Kistler or similar systems).METODA: U souboru volejbalistek (n = 273) rozděleného do pěti rozdílných věkových a výkonnostních skupin a souboru vysokoškolských studentek (n = 33) byly aplikovány tři testy explozivní síly dolních končetin: smečařský vertikální skok (SPJ), vertikální skok s protipohybem (CMJ) a skok daleký z místa (SBJ).Statistické metody byly aplikovány v systému Statistica CZ (Kolmogorov-Smirnov, Spearmanův koefi cient korelace, párový t-test a ANOVA pro nezávislé výběry -Scheff é post-hoc test).

TABLE 1
Selected sets of volleyball players -women, basic information the CMJ and SBJ general motoric tests, the national top level women players diff er more in comparison to the other groups in jump height and length.

TABLE 3
Diff erences between spike jump test (SPJ) and counter movement jump (CMJ) participate in the championship matches of national top level competition.At the present time, the Czech highest level volleyball competition is composed, for a high percentage of it, of junior aged players (U18).However, we could expect that highly intensive training preparation in the womenʼs top national level competition would bring greater diff erences between top level players and lower level performing players in volleyball.