EFFECTS OF PROPRIOCEPTIVE TRAINING ON EXPLOSIVE STRENGHT, AGLILITY AND COORDINATION OF YOUNG RHYTHMIC GYMNASTS

e aim of this study was to examine the in uence of proprioceptive training on explosive strength, agility and coordination in young rhythmic gymnasts. e study was conducted on a sample of 74 healthy girls, aged 7 to 9 years of age who train rhythmic gymnastics. e whole sample was divided into two groups: experimental (43 girls) and control (31 girls). e experimental group had the proprioception training before their regular trainings for 12 weeks (24 trainings), while the control group had only rhythmic gymnastics trainings. E ects of proprioceptive trainings on the examined motor abilities were estimated by two explosive strength tests, three coordination tests and two agility tests. All respondents were tested before the application of the experimental treatment (pre-test) and a er its completion (post-test). To examine di erences in the achieved results between the initial and nal measurement for each group, t-test for dependent samples was used. To determine di erences between groups at the initial and nal measurement, t-test for independent samples was used. By comparing results from the initial and nal measurement, improvement in all tests for the observed abilities was perceived in the experimental group, while improvement in coordination tests and one agility test was noticed in the control group. Testing di erences in results between groups in the nal measurement showed that there are di ered only in agility tests, and in favour of the experimental group. Based on the obtained results, the conclusion was that the application of proprioceptive training in rhythmic gymnasts can contribute to improvement of agility, while in other observed abilities we cannot conclusively claim that improvement was the direct product of proprioceptive training.


INTRODUCTION
Motor abilities are in the basis of every physical activity, from usual, everyday movements to performance of various sport techniques.ey signi cantly contribute to biological but also to psychological and social aspects of life, and care of their development multiplies the invested e ort through health improvement and building of emotionally stable personality with an adequate social status.
Given the importance of motor abilities, they are o en subject for research.Professionals constantly search for di erent training methods and types of training that can contribute to their improvement, especially in the period of growth and development.
Proprioceptive training is the type of training whose in uence on di erent motor abilities has not been fully investigated.It is directed towards the stimulation of proprioceptors with the aim to provoke adequate motor response, which primarily contributes to stability of joints and balance of the whole body, and then also more precise and more e cient performance of all kinds of movements.is improves proprioception itself as well as a series of other motor abilities, which, thanks to the timely reception of stimuli from proprioceptors, can be expressed more e ciently.e most important for the e ciency of expressing motor abilities are stimuli emerging from intrafusal muscle bres, the so called "muscle spindles", Golgi tendon organs and Pacinian corpuscles.ese receptors react to the changes in tension and length of muscles and tendons, at speed of these changes, as well as changes in posture of the body and parts of the body (Harris & Dudley 2000;Lephart & Fu 2000).Excitation of these receptors are transferred along a erent pathways to lower or higher level of the central nervous system, so that the timely activation of the adequate motor units enables sustaining stability of the body during static and dynamic activities (Laskowski, Newcomer-Aney, & Smith, 1997).
Proprioceptive training was rst used in rehabilitation, most o en in ankle and knee injuries.It was found that its application improved the functional stability of joints, that it contributed to improvement of the clinical picture in disturbed postural status and signi cantly reduces the frequency of repeated injuries (Irrgang et al., 1994;Weste et al., 1996;Bernier & Perrin, 1998;Elis & Rosenbaum, 2001;Vad et al., 2002;Liu Ambrose et al., 2003).It was very quickly accepted in elite sports primarily as a prevention of injuries.A large number of authors emphasizes that the improvement of neuro-muscle response to excitation of kinaesthetic receptors can be a key factor in the e ective reduction of the risk from injuries (Gau n, Tropp & Odenrick, 1988; Sheth et al., 1997;Robbins & Waked, 1998;Eils, Schröter et al., 2010).Conscious movements initiated in the cerebral cortex are too slow to prevent an injury in urgent situations, and it is estimated that the spinal re exes are those that contribute to quicker and timely activation of the stabiliser muscles (Laskowski et al., 1997).
In healthy persons positive e ects of this training are primarily re ected in the improvement of the ability to keep the balance i.e., in reduction of postural oscillations (Ho man & Payne, 1995), while its in uence on di erent motor abilities is not completely researched.Most authors examined the in uence of proprioceptive training on the ability to balance and they all emphasize its positive in uence on this ability, both in adults (Gio sidou et al., 2006; Yaggie & Campbell, 2006;Granacher, Gollhofer & Kriemler, 2010;Romero-Franco et al., 2012), and in children (Dobrijević, Moskovljević and Dabović, 2016).When it comes to strength, various authors agree that the application of proprioceptive training has no in uence on this motor ability, but that it positively a ect the rate of force development (Gruber & Gollhofer, 2004; Granacher et al., 2010).
Findings of di erent authors considering inuence of proprioceptive training on the explosive strength and agility are di erent, o en even opposed (Yaggie & Campbell, 2006;Cressey et al., 2007;Šimek, Milanović & Jukić. 2008; Granacher et al., 2010).ere are insu cient data on in uence of proprioceptive training on coordination (Lukić, 2010), and the existing ones do not o er clear answer to this question.
ere are few data on the in uence of proprioceptive training on the development of motor abilities in athletes, i.e. its place in the tness preparation of athletes.Given that the in uence of proprioceptive training on the explosive strength, agility and coordination is not completely examined, that the previous studies dealt with the sample of adults, and that there are data on the in uence of this training on the speci c technique, but not on the motor abilities in rhythmic gymnastics, there came the idea on realisation of this study.e aim of this study was to examine the in uence of proprioceptive training on agility, coordination and explosive strength of leg muscles in young rhythmic gymnasts.

METHOD
is research represents a longitudinal study conducted on a sample of girls who train rhythmic gymnastics to examine the e ects of proprioceptive training on agility, coordination and explosive strength of legs.

Samples
e sample of respondents was comprised of 74 healthy girls (aged 8±0.8) who have been training rhythmic amateur gymnastics in the "In" Gymnastic Club in Belgrade.All girls have been involved in this type of training for 1-2 years, and their training sessions are 60 minutes twice a week.Using the random sample method, they were divided into two groups, experimental (Е) -43 girls and control (К) -31 girls.Girls and their parents were informed about all details of the study, and the parents provided the written consent for participation of girls in the study.

Experimental protocol
All respondents were tested before the commencement of the experiment (initial measurement-Т1) and a er 12 weeks of the application of the experimental treatment ( nal measurement -Т2).
e sample of variables encompassed two variables for agility assessment, three for coordination and two for explosive leg strength assessment.All variables were measured with standardized tests whose validity and reliability had already been con rmed: • Agility -20 yards test (20Y) (Milanović, 2003) and Lateral agility test -change of direction lateral test (LAT) (Metikoš et al., 1989)

Testing
e respondents were familiar with the test protocol before the beginning of measurement.Each respondent had one trial, followed by two measurements, and a better result was used for the analysis.Breaks between trials were 3-5 minutes, which was enough for the respondent recovery and to avoid a potential in uence of fatigue in the subsequent performance (Spencer et al., 2008).Before each test, the respondents were instructed to nish the given task as quickly as possible in agility and coordination tests, while in explosive strength tests they were giv-en instructions to jump as high as possible (CMJ), or as long as possible (LJ).All tests were completed in the morning hours in the sport centre hall "Novi Beograd".During testing the respondents wore sports out t.
20 yards test (20Y) is done by 20-yard-run at maximum speed with one 90 0 turn and two 180 0 turns.In the initial position, the respondent is turned laterally in the direction of movement.e respondent starts from the middle; she runs to the right marker cone (5y=4.55m),then to the le marker cone (10y=9.1m),and at the end to the one in the middle (5y=4.55m).Lateral agility test (LAT) is done by moving sideways (sideway steps) with maximum speed along the 4-meter drawn path.e respondent stands behind the start line, turned laterally in the direction of movement.She starts at the sign made by the person who measures time and moves along the path for 6 times (6x4m), without changing the orientation in space (only the direction of movement is changed).
Jumping over and pulling under (PiP) is done in the space 7.5m long, where at each 1.5m there is one segment of vertical vaulting box placed, the total of four, and 1.5m behind the last segment there is the line for turning back.e respondent stands behind the start line and at the sign made by the person who measures time, she starts moving.She jumps over the rst and crawls under the second to get through in both directions.
Twisting/agility in the air (OuV) is done when the respondent starts moving from the position sitting on 4 medicine balls, facing the opposite direction to the direction of movement.At the sign of the person who is measuring, the respondent has to do backward roll as quickly as possible, stands up, and performs a forward roll over the medicine balls without touching them.A er the forward roll, the respondent turns round for 180 0 and touches all 4 medicine balls with her palms.
Figure eight with bending and jumping (OsS) is performed by moving between three posts placed in a line at the distance of 2.5m.e elastic tape is stretched between them, at hip height of the respondent between the rst and the second, and at the knee height between the second and the third.
e respondent should go round the post for as short time as possible bending down under the elastic tape placed at hip height and jumping over the elastic tape placed at knee height.
Long jump (LJ) is done on a at, non-slippery surface marked with a place for jumping and for take-o .e task for the respondent is to jump as long as possible, and the distance is measured from the jump line from the place where the respondent touches the ground with her heels.Countermovement jump, CMJ is done on a contact surface (Newtest Powertimer, 300-series).e respondent stands upright on the surface with her feet as wide apart as hips.en she performs countermovement jump with arm swing.

Experimental program of proprioceptive training model
In the period of 12 weeks (24 trainings), the experimental group had proprioceptive training before their regular rhythmic gymnastics trainings, while the control group had only regular trainings for that time.e proprioceptive training started 15 minutes before regular rhythmic gymnastics trainings, and partially continued during the regular training.
is type of organization was applied because of the scope of work in the experimental and the control group, which was achieved because the time of active exercises and rest alternated in equal time intervals in proprioceptive training.e program of proprioceptive training was realized using various boards for this kind of training, such as T-board, wobble board, balance board, then with Pilates balls, low balance beam, so mat.e participants were asked to maintain the balanced position for as long as possible on proprioceptive boards in unstable conditions, participants used the beam to perform exercise on the small surface of support, and the mat was used to stimulate the proprioceptrs by changing the quality of surface (performing exercise on hard and subsequently on so surface).Di erent tasks were done with eyes open and closed, on one or both legs, and in later phases speci c technique of rhythmic gymnastics was introduced (for example, balancing with a ball, rotating hoop or rope, throwing and catching...) all with the aim of making tasks more complex and increasing stimulation of proprioceptors.Proprioceptive training included warming up for 5 to 7 minutes and the main phase of the training organized by the method of stations.During each training session the respondents had 3 tasks done in 3 series with equal time of exercising and recovery between series (Jukić et al., 2003).e girls were most o en organized in pairs, so that one was doing the exercise while the other had a rest.e contents of this program were realized at the beginning of the training, and the total duration of the active phase of proprioceptive training per respondent was not longer than 10 minutes, so that there would be no nervousness and muscular fatigue.A special attention was directed towards concentration of respondents at doing tasks, because it increased e ciency of ow of stimuli in central nervous system (Voight and Cook, 1996), which contributes to a greater eciency of exercising.

Statistical data processing
Data collected in this study were arranged and processed in statistical procedures of Microso excel program, version 15 and SPSS 22.0.From the eld of descriptive statistics, the arithmetic mean (Mean), standard deviation (SD) and standard error of the measurement (SEM) were calculated for each variable.Shapiro-Wilks test was used for testing normal distribution.From the eld of comparative statistics, t-test for independent samples was used to determine di erences in results between the control and experimental group separately for initial andnal measurement, as well as the t-test for dependent samples to determine di erences in results between the initial and nal measurement.

RESULTS
Testing di erences between groups at the initial measurement (Table 1) showed that they do not differ in any of the applied tests.Table 2 shows di erences in the achieved results between the initial and nal measurement in both groups.
ese results show that the experimental group showed improvement in all tests, while the control group showed improvement in all coordination tests and in one agility test (LAT).By comparing the results between the experimental and the control group in the nal measurement (Table 1), it was determined that there are di erences between results only in agility tests.

DISCUSSION
Test results from the initial measurement show that the control and the experimental group do not di er in any of the observed abilities, and that the di erences obtained at the nal measurement can be attributed to the in uence of the experimental factor.
By observing results between the initial and the nal measurement, it can be noted that the experimental group achieved improvement in all tests, while the control group made improvement in coordination tests and one agility test.Based on such results, it can be concluded that the rhythmic gymnastics training itself was su cient as a stimulus for coordination improvement, as expected, given that rhythmic gymnastics belongs to sports in which results depend largely on the development of this ability.By comparing the results between experimental and control group at the nal measurement, there are no di erences between them at the nal meas-urement, so that the improvement in coordination cannot be attributed to in uence of proprioceptive training.According to results of an earlier study, in some coordination tests the authors found the improvement under the in uence of proprioceptive training, but not in all tests; and the study was done on the sample of respondents of both genders, from 15 to 19 years of age (Lukić, 2010).In explosive strength tests, the experimental group showed improvement, while progress was not recorded in the control group.e comparison of the results from the nal measurement points to the fact that the proprioceptive training had no positive in uence on development of this ability.On the other hand, it should be understood that the experimental group had slightly weaker results on the initial measurement, but also slightly better results at the nal measurement.is leads to the conclusion that the rhythmic gymnastics training in combination with proprioceptive explosive strength training may signi cantly improve the explosive strength of legs in girls aged 7-9.Previous studies, conducted on adults and with the use of the same tests, are in favour of positive in uence of proprioceptive training on the explosive leg strength (Cressey et al., 2007;Granacher et al., 2010).Besides, a sensitive period for the explosive strength development is the period between the age of 10 and 12 (Гужаловский, 1984(Гужаловский, , Drabik, 1996)), when a greater reaction of the child's organism to these stimuli can be expected.All the above should be taken into account and investigate the in uence of this training on the explosive strength of legs in children of di erent age, including the sample of children of both genders, in some future studies.

CONCLUSION
Based on the presented results and the discussion it can be clearly concluded that the proprioceptive training has a positive impact on the development of agility in girls aged 7-9, while this type of training proved to be an insu cient stimulus for development of coordination.
Agility, i.e., a segment of this ability which relates to the speed of movement direction change (Sheppard & Young, 2006), showed the tendency of improvement under the in uence of proprioceptive training.Such ndings are in accordance with the results of Yaggie and Campbell (2006), and partially with the results of Šalaj et al. (2007), who found signi cant improvement in this ability under the in uence of proprioceptive training in 20-yard test.Cressey et al. (2007) did not nd a signi cant agility improvement under the in uence of this training, and the reason for it may be the speci c sample of soccer players, who are well known for a highly developed agility.A possible future study should assess the in uence of proprioceptive training on this ability in children of both genders and in di erent periods of development.
Palabras claves: PROPIOCEPCION/ CAPACIDADES MOTRICES / GIMNASIA RÍTMICA / NIÑAS Примљен: 16. 10. 2017 Прихваћен: 20. 03.2018 Dobrijević et al. (2016) point out that the application of proprioceptive training in young rhythmic gymnasts can signi cantly contribute to the development of balance as one of crucial motor abilities for success in this sports branch.Some authors who investigated the in uence of proprioceptive training on the speci c sports technique (Wolf-Cvitak et al., 2002; Šebić-Zuhrić, Rađo and Bonacin, 2007), noted that, relying on the kinaesthetic feeling, learning certain movements in sports, such as rhythmic gymnastics, can signi cantly be sped up and that proprioceptive training represents a signi cant means for improvement of speci c technique in rhythmic gymnastics.

Table 1 .
Testing di erences between groups at the initial and nal measurement (t-test for independent samples) Legend: Е -experimental group; К-control group; SD-standard deviation; t -result of t-test; p-signi cance of di erence

Table 2 .
Testing di erences between the initial and nal measurement (t-test for dependent samples) Legend: MeanD -arithmetic mean of the di erence between the initial and nal measurement; SD-standard deviation; SEM-standard error; t -result of t-test; p-signi cance of di erence; ES-e ect size In combination with the rhythmic gymnastics training, proprioceptive trainings have positive e ects on the explosive strength of legs in girls of this age.e development of the observed motor abilities under the in uence of proprioceptive training in children should be additionally examined, by including into the study children of both genders and di erent age.