A STUDY OF VERTICAL JUMP PERFORMANCE AMONG U-19 VOLLEYBALL PLAYERS BY PLAYING POSITIONS

: The purpose of this study was to compare the vertical jump performance among under-19 age group male volleyball players by playing positions. A sample of Forty eight (N = 48) male volleyball players (mean ± SD: age 18.35 ± 0.56 years, height 182.23 ± 5.12 cm, weight 75.56 ± 5.77 kg, BMI 22.67 ± 1.26), which includes twelve each blockers, setters, liberos and spikers, who participated in inter-district school competitions, was selected from various schools affiliated to Punjab School Education Board. All the participants were informed about aim and methodology of the study and they volunteered to participate in this study. Vertical jump test was conducted to see the vertical jump performance of the subjects.One way Analysis of Variance (ANOVA) was applied to find out the significance of differences with regard to vertical jump performance among blockers, setters, liberos and spikers. Scheffe’s post-hoc test (SPHT) was applied to see the direction and significance of differences where ‘F’ value found statistically significant. The level of significance was set at 0.05.While comparing the means; it revealed that blockers had better explosive leg power than their counterparts, while liberos had shown less explosive leg power than their counterparts. Further, significant differences were found between blockers and liberos with regard to power (p˂ 0.05).


Introduction
Volleyball is an intermittent sport that requires players to compete in frequent short boutsof highintensity exercise, followed by periods of low-intensity activity (Kunstlinger et al., 1987;Viitasalo et al., 1987;Gabbett and Georgieff, 2007).One of the main physical characteristic required in volleyball is lower limb muscle power, expressed by the numerous jumps performed during the games, which are important both for the attacking and blocking actions (Sheppard et al., 2007;2008;). Volleyball requires a lot of jumping. The players jump to spike and block in the game, so jumping is a very important physical performance (Zhong & Huang, 1989). Vertical jump is a necessary component in performing spike and block as well as jumping service skills in volleyball game. Volleyball players' excellent performances are widely associated with efficiency of jumping or lower extremity explosive power which finally introduce vertical jump as one of the most important characteristics of physical fitness in volleyball players (Zhang, 2010). A volleyball team comprises 12 players with team positions broadly defined as setters, spikers, blockers and liberos. Each of these positions plays a specific role in a volleyball match (Gabbett and Georgieff, 2006). An understanding of the vertical jump performance among U-19 volleyball players may be important for talent identification for specific positions in the team. Therefore, the aim of this study was to examine the positional differences in vertical jump performance of U-19 volleyball players by specific playing positions.

Subjects:
A sample of Forty eight (N = 48) male volleyball players (mean ± SD: age 18.35 ± 0.56 years, height 182.23 ± 5.12 cm, weight 75.56 ± 5.77 kg, BMI 22.67 ± 1.26), which includes twelve each blockers, setters, liberos and spikers, who participated in inter-district school competitions, was selected from various schools affiliated to Punjab School Education Board. All the participants were informed about aim and methodology of the study and they volunteered to participate in this study. The purposive sampling technique was used to select the subjects.

Methodology:
Height measurements were taken by using the standard anthropometric rod to the nearest 0.5 cm. Full attentions given make sure that players" body was fully upright and their mandible was parallel to the ground. Taken values recorded as cm. The subject's weights were measured with portable weighing machine to the nearest 0.5 kg. During measurements players were on bare feet and with underwear and measurements recorded as kg. BMI was calculated by the formula of; Body Mass Index =Weight/Height 2 . Vertical jump test was conducted to see the vertical jump performance of the subjects.

Statistical Analysis:
Values are presented as mean values and SD. One-way analysis of variance (ANOVA) was employed. Following the detection of a significant mean effect, Scheffe's post-hocanalysis was performed to locate where specific mean differences were laid. Data was analyzed using SPSS Version 16.0 (Statistical Package for the Social Sciences,version 16.0, SPSS Inc, Chicago, IL, USA).  Table 2 showed that while comparing the means, it revealed that blockers had better explosive leg power than their counterparts, while liberos had shown less explosive leg power than their counterparts. It is evident from table-3 of Analysis of Variance (ANOVA) results that significant differences were found among male volleyball players of different playing positions i.e. blockers, setters, liberos and spikers with regard to the variable power(p˂ 0.05).

RESULTS
Since the obtained F-values were found significant, therefore, the Post-hoc test (Scheffe's) was applied to see the direction and significance of difference between paired means of male volleyball players of different playing positions i.e. blockers, setters, liberos and spikers with regards to the variable power. The results of Post-hoc test (Scheffe's) have been presented in table-4 below.

level of Confidence
A glance at table-4 showed that blockers have exhibited statistically significant(p˂ 0.05) differences with liberos but insignificant (p˃ 0.05) differences with setters and spikerswith regard to the variable power. However, setters have shown statistically insignificant (p˃ 0.05) differences with liberos and spikers on the variable power. It is concluded that blockers had better explosive leg power than their counterparts, while liberos had shown less explosive leg power than their counterparts.

DISCUSSION
The demographic characteristics show that the mean height of volleyball players (182.23 ± 5.12cm) in the present study is greater than the volleyball players of West Bengal, India (173.10 ± 4.19 cm) reported by Bandyopadhya (2007), but lesser than the English volleyball players (191.00 ±5.0 cm) studied by Duncan et al. (2003) and Brazilian national volleyball team (197.0 ± 8.0 cm) studied by Petroski et al. (2013). The taller player in volleyball has an advantage because they can easier control both, defensive and offensive actions over the top of the net. Stamm et al.(2003) concluded that height is a significant factor in the performance of game elements, particularly for attack and block (71-83%).Thus, selection criteria can explain the observed results, as there has been a tendency to recruit the tallest players in this sport (Jankovic & Marelic,1995). Volleyball requires a broad The comparison were made among different playing positions in relation to power it was found that there were significant difference among the Explosive power of the legs is of the utmost importance in volleyball sports. It is mainly used during serving, setting, attacks and blocks, which are essential for scoring a point. Vertical jump performance is one of the best indications of lower limbs muscle power (Bosco,2007). Duncan et al. (2006). According to resultsof the present study blockers had better explosive leg power than their counterparts, while liberos had shown less explosive leg power than their counterparts. There is great similarity between vertical jumping of blockers and spikers which are not noticeable in liberos. The differences in parameters could be explained through game's position of players. The main purpose of volleyball players is achieving greater height on the net (Stec & Smulsky, 2007). Liberos as the backline players participate in receive and digging during the match but blockers and spikers play in front of the net, performing spike and block (Duncan et al., 2006). It is clear that higher jumping is not advantage for liberos whereas it is necessary for spikers and blockers.

CONCLUSIONS
Maximum vertical jump is one of the necessary components in performing spike and block skills in volleyball. It is concluded that blockers had better explosive leg power than their counterparts, while liberos had shown less explosive leg power than their counterparts. It is clear that higher jumping is not advantage for liberos whereas it is necessary for blockers, spikers and setters.