# Biomechanics of Table Tennis: A Systematic Scoping Review of Playing Levels and Maneuvers
## 4 Discussion
Additionally, a shorter center of pressure in the anterior-posterior direction in higher level players facilitates quicker responses to resume to a neutral position for the next move [3; 28]. However, it should be noted that higher level players exhibited larger ankle RoM during the match which may inherit the risk of ankle sprain [28; 29]. Regarding the methodological quality, more than half of the included studies did not reveal clearly the source of population and sampling method. There was also a lack of blinding. Although blinding the maneuver conditions seemed to be impossible since the participants needed to be acknowledged for the tasks they performed, it could be accomplished by counting successive returns from delivering random serves by the coaches or serving robots [30; 40]. Furthermore, the implementation of a randomized cross-over design across various interventions and maneuvers is necessary to avoid carry-over effects. Future studies can investigate how technologies can improve training outcomes. For instance, augmented reality (AR) technology with different filmed footages of different balls and gaze information can be modulated with artificial intelligence program to simulate the virtual opponent with the matched playing levels. Such simulations would provide a steppingstone towards individualized training solutions. On the other hand, several studies investigated a large number of outcome variables which was not well justified. While a full biomechanical profile with a large number of outcome variables were endeavored, statistical analyses were performed without corrections for multiple or multivariate comparisons. This may fall into the trap of data dredging or p-hacking [52] and those research may confine to exploratory studies [53]. There are some limitations when interpreting our findings. A systematic scoping review covered a vast volume of literature over a topic and thus offered an overview picture within the discipline [21]. However, due to the heterogeneity and breadth of the included studies, the established data framework did not attempt to answer a single research question which shall be put forward by a systematic review. It is also not possible to conduct meta-analysis to estimate overall determinants on playing levels, movement tasks, and equipment because of the diversity of objectives and designs across the included studies. In fact, the amount of literature required for a subset study was insufficient to formulate a focused research question for a traditional systematic review. For example, only two included studies were comparing upper limb kinematics of forehand topspin among different player levels in our review. In other words, it is pragmatically demanding to call for more research to establish the map over biomechanical variables, maneuvers, and playing levels, and reinforce key ideas on the determinants of performance using a unified study design and protocol. Additionally, there was potential publication or language bias since some relevant articles were excluded for being published in Chinese, despite the fact that China is one of the dominating countries in the table tennis sports [16]. Summarizing information from the Chinese literature can enhance the impact of table tennis research but may require considerable effort in screening, translation, and interpretation. Furthermore, we found that there was a lack of literature on backspin maneuvers, longline maneuvers, strikes against sidespin ball, and pen-hold players that warrant further investigations. _Appl. Sci._**2020**, _10_, 5203  
\begin{table}
\begin{tabular}{c c c} \hline \hline
**Author (Year)** & **Outcome Measures** & **Key Findings** \\ \hline \multirow{8}{*}{[PERSON] and [PERSON] (2017) \# [1]} & Time parameters (total time, duration of forward, hit-to-forward end, backward phases, time to reach max velocity (resultant and direction components) of racket; & Forehand stroke \(\downarrow\) total duration than against a spin serve and more power ball.