THE DEVELOPMENT LEVEL OF THE SPECIAL ENDURANCE OF ELITE SERBIAN FEMALE BASKETBALL PLAYERS BASED ON THE RESULTS OF A MODIFIED “30-15IFT” INTERMITTENT TEST

The article basically aims to present the applicability of the modifi ed “30-15IFT” test on a sample of the senior women’s national basketball team of Serbia. The technology we employed enabled us to acquire a number of parameters about the test as such and the study subjects’ endurance. In addition to the level of development of specifi c indicators of the special endurance of female basketball players, we were interested in the differences between individual player types. The results show that after about 13 minutes of running the subjects on average achieved a maximum speed of 15.5 km/h, with a maximum heart rate of 187.4 beats·min-1, a maximum lactate concentration of 7.8 mmol-1, maximum relative oxygen uptake of 52.2 ml·min-1/kg-1, a maximum minute volume of exhaled carbon dioxide of 3473.5 ml·min-1 and a maximum lung ventilation of 117.6 l·min-1. In the last two variables statistically signifi cant differences were found between individual types of players (guards, forwards and centers). The fi eld “30-15IFT” intermittent fi tness test proved to be suitable for assessing the current functional abilities of male and female basketball players and for identifying variations in their fi tness in different periods of training. However, some issues concerning the applicability of the test for scientifi c and research purposes still have to be clarifi ed.

these movements is long enough to enable the repletion of creatine phosphate, then the energy needed for movement is generated through anaerobic alactate processes.In the opposite case, when a player moves for a longer time at an only slightly lower intensity, they start generating energy through the process of anaerobic glycolysis.During a moderately paced game over a longer period of time a player mainly consumes the aerobic energy.A player who is capable of generating energy at an aerobic level for a

INTRODUCTION
The movements basketball players make during a game are manifold and differ in terms of intensity, the length of the distance run and duration of the breaks between them.To cope with the strain during a game basketball players use aerobic and anaerobic energy (Brittenham, 1996;Marlow, 2003).Movements such as consecutive jumps, changes in movement direction, various types of acceleration, rapid counter-attacks (short sprints) and short defensive slides are usually very intense.If the break between longer time has some advantages over other players as the energy-yielding anaerobic processes are activated later and thus the problems in the body caused by acidosis occur later.
In the 40 minutes of a game a basketball player runs a distance of 6,000 to 7,500 m in total (Erčulj et al., 2007;Erčulj et al. 2008;Abdelkrim et al., 2010).According to Abdelkrim et al. (2007Abdelkrim et al. ( , 2010)), all highly intensive activities account for 16.1±1.4% of the game, whereas an individual highly intensive movement lasts for only 1.8±0.1 s on average.The movements typical of moderate intensive activity account for 28.1±2.3% of the playing time and last for 2.1±0.2s on average.The share of low-intensity activities is 25.8±1.5%,whereas individual activities last on average for 1.9±0.1 s.A player walks, stands or performs activities classifi ed as 'rest', during which the player's capabilities and energy sources recover, for about 30% of the playing time.The same authors establish that in 19.3±3.5% of the playing time a player's heart rate exceeds 95% of their maximum value, whereas in 56.0±6.3% of the playing time the heart rate falls within the interval of 85-95% of maximum heart rate.According to some researchers, the average concentration of lactates during a game equals 4.0 to 6.1 mmol/l of blood (Stone, 2007;Abdelkrim et al., 2007;Abdelkrim et al., 2010), whereas the highest concentration of lactate usually exceeds 8.5 mmol/l of blood (Stone, 2007;McInnes et al., 1995).
Similarly to most other team sports and ball games, basketball also features alternating active and passive phases as a consequence of stopping the clock.The ratio between the active and passive phases is about 1:1 (Dežman & Erčulj, 2005).During the breaks for time-outs (minutes of rest, small and big errors, fouls, substitution and other circumstances) and at the time of substitution when a player leaves the game, their cardiovascular and respiratory systems are still functioning intensively to compensate for a potential oxygen defi cit and acidosis which may have occurred during a longer highly intensive effort.During a minute's rest the heart rate of highly trained basketball players can nearly reach the baseline and the recovery process persists at a high level throughout the game.Basketball players with a lower level of training have a poorer energy-recovery and regeneration capacity and their fatigue increases cor-respondingly (Dežman & Erčulj, 2005).
In view of the above, we can establish that endurance and functional abilities play an important role among a number of factors of playing performance in basketball.In the basketball training process a lot of attention is paid to identifying the development level of the abovementioned functional abilities and evaluating them.For this purpose, different measurement instruments and diagnostic procedures are used.In practice, the special endurance of basketball players is mainly investigated using so-called fi eld tests.These are conducted in conditions very similar to those in a training session or competition and they attempt to record the ways of moving and the loadings in basketball to the maximum extent possible.There is a large number of endurance tests in practice that can be divided into continuous and intermittent (Šibila et al., 2009).The latter are particularly suitable for testing basketball players' special endurance because interval loading is characteristic of basketball play.Such tests include the 30-15IFT Intermittent Fitness Test (Buchheit, 2005a;Buchheit, 2005b).It was originally developed to establish the special endurance of handball players (Šibila et al., 2009), but was modifi ed for this study to measure the special endurance of basketball players and its applicability was tested in practice.
The article basically aims to present the applicability of the modifi ed 30-15IFT test in establishing special fi tness in basketball to the professional basketball community.The test was used to establish the special endurance of elite female basketball players, namely the senior women's national team of Serbia.For the purpose of scientifi c research, we used additional technology in implementing the test that enabled us to acquire additional data about the test and the players' endurance.The study sought to identify and analyse the level of their functional abilities at the group (national team) and player type levels.We wish and hope that the fi ndings of this study will help the coaches of basketball clubs and national teams to assess the special endurance of their female players and compare them against those of the best Serbian female basketball players.

METHOD
The sample of study subjects included thirteen (13) female basketball players, members of the Serbian national team, of whom four were guards, four forwards and fi ve centers.Their average age was 24.30 (±3.77) years, body height 182.15 (± 8.60) cm and body weight 71.84 (±7.51) kg.The measurements took place in July 2010 at Zlatibor (Serbia) after the end of the senior women's 2009/2010 competition season, when the national team had only just started the preparations for the 2011 European Championship qualifi cations.Before the testing, the study subjects provided signed informed consent forms.All were healthy and had no injuries.
The study investigated the special endurance of female basketball players using the 30-15IFT Intermittent Fitness Test (Buchheit, 2005a;Buchheit, 2005b).The result of the basic version of the test is the maximum (fi nal) velocity of running (V max ) during the test (km•h -1 ).For the purpose of scientifi c research, we conducted the test using technology that enabled us to acquire additional data about the test and the players' endurance.Besides measuring the heart rate, we carried out ergospirometry and, after the test, measured the blood lactate concentration.The sample of variables thus encompassed the following physiological parameters which were measured in the course of and after the test, i.e. exercise: • HR max -maximum heart rate during the test.
The measured interval was an average of 5 s (beats•min -1 ).• LA3 min -lactate concentration in the 3 rd minute after the exercise (mmol•l -1 ) • VO 2max -maximum oxygen uptake during the test (ml•min -1 ) • VO 2 /kg max -relative maximum oxygen uptake per body mass kilogramme (ml•min -1 •kg -1 ) • VCO 2max -maximum minute volume of exhaled carbon dioxide during the test (ml•min -1 ) • VE max -maximum lung ventilation during the test (l•min -1 ) • RQ -respiratory quotient (1) • DV -respiratory volume (l) The maximum (fi nal) velocity of running was defi ned based on the result of the modifi ed intermittent fi tness test (30-15IFT) as the last successfully performed interval of 30 s (V max ).The running velocity in the initial interval was 8 km/h and it increased by 0.5 km/h in every subsequent interval in line with Table 1, until the last successfully performed interval.
The heart rate during the test and the maximum heart rate during the test were established using a Polar heart rate monitor (model S410).The RR recording interval was applied which saves every recorded heart beat.
The concentration of lactates was established in the third minute after the exercise (test) had been completed.We sampled blood from a hyperemic earlobe of the subject.The Ebio Plus lactate analyser manufactured by Eppendorf (Germany) was used.The 10 μl sample of capillary blood was immediately diluted and stored in cuvettes until measurement.The measurement accuracy was 0.1 mmol•L -1 .
The measurement of gases in exhaled air was conducted with a K4B2 device (COSMED, Italy) before and during the 30-15IFT intermittent fi tness test.
The 30-15IFT intermittent fi tness test (Buchheit, 2005a; Buchheit, 2005b) was originally developed to measure the special endurance of handball players (Šibila et al., 2009).For this study, to measure the special endurance of basketball players, we modifi ed the test by reducing the 40 m distance to 20 m, and the loading parameters during running were adjusted accordingly (see Table 1).A detailed description of the test and the measurement procedure has already been published by the authors (Erčulj et al., 2012) and is therefore not included in this article.

RESULTS
The basic parameters of descriptive statistics were fi rst calculated for all variables, namely for the entire sample of study subjects and for individual player types.The differences between them were established using a one-way analysis of variance (Table 2).
who on average have the maximum oxygen uptake at a velocity of 9 km/h onwards.
A tendency can be observed in Figure 2 that the guards have a lower oxygen uptake on average at all velocities compared to the forwards and centers The result of the basic version of the test is the maximum (fi nal) running velocity (V max ).The results vary between 14.5 and 16.5 km/h and, after about 12 minutes of running, the subjects achieved an average velocity of 15.5 km/h.In terms of playing position, the highest fi nal average velocity was achieved by the wings and the lowest by the centers.In terms of playing position, the maximum measured heart rate was similar for all measured subjects, although large differences were observed with the centers where the heart rate ranged between 169 and 202 beats/min.
Similarly as for V max , it can also be established for LA3 min that the highest values are those of the forwards, namely 8.7 mmol/l of blood on average, the values of the centers were slightly lower (8.4 mmol/l of blood) whereas in the guards a slightly lower average maximum LA3 min was measured.
On average, the oxygen uptake was absolutely the lowest with the guards and the highest with the centers, although a look at the relative values in view of the body mass reveals considerably higher values among the guards compared to the forwards and the centers.
Statistically signifi cant differences were only established in two variables, namely maximum volume of exhaled CO 2 and VE.In both variables the highest values were achieved by the centers on average, and only slightly lower values were observed among the forwards, whereas the measured values for the guards were statistically signifi cantly the lowest.
The values of the respiratory quotient (RQ) and respiratory volume (RV) were higher in tall players (centers and forwards) than in the perimeter players (guards) who achieved the lowest values on average in both abovementioned variables.in the guards compared to forwards and centers who had the highest measured values of lung ventilation at all velocities.
Up to a velocity of 8 km/h, the lung ventilation of all players was very similar on average, whereas at higher velocities a tendency of lower values was seen Velocity (km.hThe volume of exhaled carbon dioxide was very similar on average up to a velocity of 8 km/h for all players, whereas at higher velocities a tendency of lower values was seen in the guards compared to the forwards and the centers who had the highest measured values of lung ventilation at all velocities.The average heart rate during the test gradually and relatively equally increased in all players, regardless of their playing position.

Velocity (km.h
selected elite players, it is diffi cult to evaluate the infl uence of height on the oxygen uptake achieved by the players.This is certainly a question to be dealt with by researchers in the future. The results for the maximum velocity the forwards achieved during running are somewhat surprising because they are contrary to the results of female basketball players of the Slovenian national team, where the highest velocity in the test was achieved by the guards (Erčulj et al., 2012).Some other authors have arrived at similar conclusions as Erčulj et al., 2012, when investigating differences between individual types of female basketball players based on the results of motor tests.This applies to both endurance (Colli et al., 1987;Erčulj, 1996) and some other motor abilities (Bosco, 1999;Erčulj et al., 2003;Erčulj et al., 2009).It remains unclear why in our test the forwards achieved the highest velocity, yet it is true that individual results do not reveal any major differences between the guards and the forwards.Contrary to a similar study involving female members of the Slovenian national team (Erčulj et al., 2012), we can concur with the opinion -based on the measured respiratory indicators -that shorter male and female basketball players (guards) achieve a higher level of endurance than taller players (centers).We therefore recommend that in endurance tests (also including the modifi ed 30-15IFT intermittent fi tness test) heart rate monitors are used and that the values of the subjects' maximum heart rate are established and, if possible, that additional technology is employed to enable a realistic and objective evaluation of the test results as well as a comparison of the individual study subjects.

CONCLUSION
The modifi ed 30-15IFT intermittent fi tness test is assessed as a good measurement instrument for establishing the special endurance of basketball players.In contrast to some other similar fi eld tests involving incremental exercise, in this specifi c test the interval loading aspect needs to be pointed out because it is similar to the loading during a basketball game or match.The distance at which the study subject performs 30 s of interval running was shortened Throughout the test, regardless of the velocity, the lowest oxygen pulse was observed among the guards, whereas slightly higher values were recorded by the forwards and the highest average oxygen pulse by the centers.

DISCUSSION
If the results by player type are analysed more thoroughly and the differences between them identifi ed, it can be established that they are not statistically signifi cant in any variable except for maximum measured lung ventilation and maximum volume of exhaled carbon dioxide.In the latter two variables, the centers had statistically signifi cantly higher values than the guards.The higher VE and VCO 2 of the centers is probably due to increased acidosis in the centers and consequently higher production of CO 2 resulting from a bicarbonate buffering system which prevented acidosis from rising.In some variables we can talk about tendencies which are probably due to a small number of study subjects in terms of playing position.The relative maximum oxygen uptake (VO 2 /kg max ) is the highest in these players, whereas the absolute maximum oxygen uptake (VO 2max ) is expectedly the highest in the centers who are somewhat taller and heavier on average than the guards and forwards.
Given some of the study results a question arises of whether the guards were more motivated to undergo the test than the forwards and centers.This is diffi cult to verify if we analyse the measured lactate after exercise as the values were the highest with the forwards and the centers.This does not confi rm in any way the thesis about the higher motivation of the guards.
Another very interesting question emerges here, namely the opposite tendencies in VO 2 compared to VO 2 /kg, since during the test at a lower velocity the guards recorded the highest fi gures when the absolute values of VO 2 were observed and the lowest fi gures when the relative values of VO 2 were observed.As there are signifi cantly large differences between female basketball players in terms of body height and since our sample only includes narrowly to 20 m for the purpose of establishing the special endurance of basketball players, whereby the specifics of basketball play were considered and a distance chosen that is roughly the same as the distance a basketball player covers when moving from defence to offence and vice versa.The special nature of loading also stems from the type of movement involving changes in direction (forwards-backwards) which is also typical of basketball.Given the variability and distribution of the results of maximum (fi nal) running velocity which is considered as the result of the basic test, we can conclude that the modifi ed 30-15IFT intermittent fi tness test is a relatively good measurement instrument also in terms of sensitivity.The ratio between the arithmetic mean and standard deviation also speaks in its favour.
As regards the applicability of the test results for scientifi c and research purposes, a question arises of whether the duration of the exercise at an individual level is long enough to enable the strain indicators to develop to a level corresponding to the running velocity.This is one of the fundamental dilemmas to be answered by future researchers.

Figure 1 .
Figure 1.Measuring gases in exhaled air using the K4B2 device during the 30-15IFT test (testing the women's national basketball team of Serbia, Zlatibor, 2010).

Figure 2 .Figure 3 .Figure 3 Figure 4 .
Figure 2. The average measured oxygen uptake (VO 2max ) during the test, up to the velocity at which all three groups of female basketball players still carried out the test

Figure 5 .Figure 6 .
Figure 5.The average respiratory quotient (RQ) during the test, up to the velocity at which all three groups of female basketball players still carried out the test

Figure 7 .Figure 8 .
Figure 7.The average heart rate (HR max ) during the test, up to the velocity at which all three groups of female basketball players still carried out the test

Table 1 .
Parameters of loading in the basketball 30-15IFT BIP test -20 m