Comparasion between European elite senior and junior female table tennis players: Rally length and serve-receive game

The aim of the study was to compare elite junior and senior women table tennis players, using three parameters of the table tennis: rally length, serve and receive analysis. Twenty-five junior and twenty-five elite senior matches were analysed (total: 263 sets and 4958 points) between players ranked in Top 25 in ETTU rankings in the last two years. All the athletes used an offensive style of play. The results of non-parametric Mann-Whitney U Test, showed a significantly higher rally length in senior compared to junior category (4.46 vs. 3.93). Moreover, the results of Pearson's Chi-square tests show an association between the age categories and selected parameters (laterality, technique and placement) for both serve and receive. Different behavior between the two categories was noted. The senior players used more the flip technique (22.2 % vs 14.7 %) and short push to return the services of the opponents (32.5 % vs 26.0 %). These results provide useful information to analyze junior players' behavior compared to the senior players in order to plan specific training sessions. It can be also useful to identify some parameters as predictors of the future success for junior players.


Introduction
The career of an athlete is influenced by several factors and is characterized by different periods of transition.
A key moment is identified by Stambulova (2009)  Those expectations are based on talent, ability and/or results in the youth categories. In many cases, those expectations are not based on objective parameters and did not consider that the transition from junior to senior category seems to be one of the biggest obstacles in an athlete's career. As Stambulova (2009)  During this process, many players seem to be unable to make this step. A reason for that could be that senior matches are characterized by a different game plan and junior players need to adapt their game.
Table tennis is a highly complex sport which requires observation and analysis to improve knowledge of the performance, the involvement of new knowledge and skills to enhance performance, and an informed coaching process (Hughes et al., 2004). Performance analysis is concerned with tactical and technical evaluation and movement analysis (Carling et al., 2008). In these analyses, researchers are focused on technique analysis, technical effectiveness, as well as tactical and movement analyses. In these analyses, notational/match analysis dominates, which uses means to record aspects of an individual performance (Djokic et al., 2020b).
Notational analysis studies in table tennis are limited.
During the last few years, more attention is given to this field, but at the moment, there are still low numbers of publications in particular about tactical indicators. Different authors (Leite et al., 2017;Zagatto et al., 2010;Djokic et al., 2017) (2015) analyzed the rally length in women matches using different classes.
To the best of our knowledge, there is a very limited number of publications about serve and receive analysis in table tennis. Djokic et al. (2020a;2020b) analyzed the serve and receive placement of the best European players ranked in top 30 of ETTU ranking list. Malagoli Lanzoni et al. (2014) analyzed the placement of the serve comparing the Asian and European male players and worked on a case study where a player and his opponents are profiled (Malagoli Lanzoni & Di Michele, 2017) also analyzing the area of serve and receive.

Data Sample
The sample consisted of 25 women's junior and 25 women's senior single matches, which were played in 2019 and 2020. For the match selection, the following criteria were applied:

Performance indicators
The data about three different fields were collected: rally length, serve analysis and receive analysis.
• Rally length parameter was chosen to analyze the physical effort difference between senior and junior players. The result could influence the training needs of junior players in order to prepare them for the senior category.
-Rally length: is the sum of the strokes hit by the two athletes during a point. In this study, every time one of the athletes touches the ball with the racket one stroke is counted. The point can finish either with an error (that counts for the rally length) or with a winner. • Serve and receive analyses were selected to report tactical differences that can be eventually noted in the most important strokes of the game, where players try to take advantage and make a tactical decision that gives her edge on her opponent.

Data Collection Process
The footage of the 50 matches selected are available on the official television of European were seen in slow motion (0.5x) to collect all the information needed about the matches in a pre-organized excel form. In case of certain inconsistencies, they were rewinded and seen in slow motion (0.2 X). The software used was Kinovea, a free 2D motion analysis software.

Reliability
For one of the matches, data relative to serves (n = 116), receives (n = 116) and rally (n = 116) were recorded by two different

Statistical Analysis
The descriptive statistical data were inserted in a database.
Before conducting tests regarding rally length, the sample was tested for normality as a normal distribution is a prerequisite for many, especially parametric statistical tests (Cohen, 1988 All of the statistical analyses were done with a level of significance of p≤0.05. For service and receive, Pearson's chi-square tests of independence were performed to examine if there was an association between age category and the behavior of players in selected parameters. All the data were analysed using SPSS 20.0 (IBM Corporation, USA).

Rally Length
The rally length of 2286 points of junior matches and 2668 of senior matches have been analyzed. The mean rally length is 4.50 (SD = 2.54) in the junior category and 5.37 (SD = 3.47) in the senior category respectively. As shown in the methodology paragraph, means are not representative as the sample is not normally distributed.
For this reason, grouped median were used to compare rally length between the categories, resulting in 3.93 for junior category and 4.46 for senior category.

Serve Analysis
The next analysis evaluated the serves for each group.
Total of 2282 serves by junior players and 2667 serves by senior players were analyzed. The last parameter of serve analysis was the service placement for each group of players. The results ( Figure   2) show that short serve in the middle of the table (area 2) is the most utilized by both parties (area 2 Junior = 32.3 % -area 2 Senior = 38.0 %). Second most used placement for Junior players was the area 5 (17.6 %) followed by area 1 (14.5 %). Similar distribution was registered in senior matches (Figure 3), where area 5 (18.8 %) is the second option followed by area 3 and 1 respectively with 11.7 % and 8.9 %. Chi-square results showed a significant association between age groups and the placement of service (χ2 (8, N=4884) = 135.898, p>.001). In total, 4872 receive techniques have been analyzed.
The results ( seniors). The short receive distribution is concentrated in area 2 in both categories (11.5 % Junior -13.6 % Senior).
Differences were registered in the long receives. Juniors prefer to play in the middle and backhand zones (area 8 = 19.0 % and area 9 = 20.7 %), differently for senior that have a greater frequency in the middle of the table (area 8 = 19.7%) and balanced distribution between outer zones (area 7 = 14.0 % and area 9 = 13.7 %).
The chi-square test result has shown a significant association between age groups and the placement of the receive (χ2 (8, N=4312) = 63.714, p <.001).

Discussion
The purpose of this paper was to compare rally length and serve/receive behavior between senior and junior women's matches. The result of the average rally length of senior matches (4.46) was lower than both results of the 6.3 ± 2.8 of Djokic et al. (2017) and 5.11 (SD = 4.46) of Fuchs and Lames (2015). The reason for the differences between the results of (this) these studies could be that each study has used different methods to calculate the average rally length.
Senior players have a higher number of strokes per rally: the reasons for that might be that senior players have more consistency of strokes and higher physical capacity to perform them. The consequence could be that junior    (Djokic et al., 2020a), the short serve prevailed in their serve tactic. In order to minimize the use of the first topspin of the opponent, senior players used short receives more often, while junior players used more long push exploiting the less efficient topspin of the opponent. In men elite seniors (Djokic et al., 2020b), the most frequently used stroke of serving returns was short placed forehand backspin stroke, which is characterized as neutral stroke enabling the continuation of the rally (Malagoli Lanzoni et al., 2014). These results show a difference between the tactical game plan of junior and senior category regarding receive. In particular, it seems that senior players would limit the first topspin on push of the opponent using short receive or in alternative use flip to take initiative earlier.
Instead, junior players prefer to push long in order to take advantage of minor consistency of junior's topspin that can result in higher number of direct errors and because of the low effectiveness that permit a counterattack or an active block with a good percentage of success.
In particular, for the receive behavior during the developmental process, the coach should encourage players to train and use different solutions in order to avoid the long push. Also, sometimes it is not the best tactic solution in relation to the opponent. Young players could be encouraged to limit the long push receive. Also, it seems that in their category could be the best tactic solution. The return to a serve is one the most important shots in table tennis (Muster, 1999).
Some potential limitations of this study need to be mentioned. With 25 matches per age category, the selected sample is relatively small. Thus, although respecting the selected criteria in match selection, a single player who might be participating in 5/25 matches might have a bigger influence on the results than other players and could skew the statistics, especially if that certain player is often performing rare serving/receives. Another potential limitation could be the identification of the correct placement of the ball with the 9-area system, that shows a good inter and intra-operator reliability, but multiply the evaluation of the operator on the certain consistencies.

Conclusion
The results of the study demonstrated that significant differences are present between the junior and senior female category.
The consistency of strokes and higher physical capacity seems to be fundamental to enhance their performance.
Moreover, the biggest difference was registered in the receiving game. This might be a consequence of a possible different general game plan of senior players and might be important parameters when evaluating junior players if they are ready to face the senior category. Considering that the transition from junior to senior category is influenced by a high number of factors, coaches should be aware of the future technical, tactical and physical demands that the senior level requires.
Junior players (especially in last years in junior category) should be addressed in training to focus on the aspects where their game plan differs from senior behavior.
Certainly, more research is needed to confirm the assumptions formulated on the results of this paper and in particular to assess the role of serve and receive capacity in predicting future success of junior players.
Moreover, future research could also involve the Asian players, where junior players will be supposed to become the future Top 10 players of the World.

STATEMENT
In their statements, the authors confirmed the absence of any conflict of interest.