# Biomechanics of Table Tennis: A Systematic Scoping Review of Playing Levels and Maneuvers
## 3 Results
### Ball and Racket Performance  
Eight included studies examined the effects of ball and racket mechanics as well as serve techniques on table-tennis performance [1; 2; 24; 25; 26; 33; 35; 37], and some of these studies also compared the influences of different handworks [1; 2] and playing levels [24; 25]. Common variants included the type of ball spin [1; 2; 33; 35; 37; 39] and the spin rate [24; 25]. Moreover, seven included studies investigated ball, racket, and serve as outcome measures instead of variants [31; 38; 40; 41; 42; 43; 44; 45]. Figure 2: A scoping review map summarizing: (**a**) types of forehand and backhand maneuvers; (**b**) types of serves (as variant) to hit back; (**c**) map of dependent variables comparing the number of studies between topics on maneuvers and playing levels; (**d**) body of context (independent variables), the n-values in the interior circle denote number of studies with multiple independent variables between or within the factors stated on the exterior circle; (**e**) direction of strike; and (**f**) shake-hand vs pen-hold. Ball speed, accuracy, and repeatability were suggested to be the key indicators of playing level. Ball speed and accuracy were significantly correlated with player ranking in a competition [43]. Higher-level players produced higher ball speed and accuracy, which could be due to significantly shorter duration and variability of duration in the forward swing phase [31; 32; 38; 41]. However, [PERSON] and [PERSON] [24] found that racket speed at impact was not significantly different between playing levels (advanced vs. intermediate), although players with higher-level can rotate the trunk effectively to produce a greater racket acceleration at ball impact. Yet, [PERSON] and [PERSON] [24] imposed a stringent significance level using a Bonferroni correction. Similarly, [PERSON] et al. [40] found that while there was only a slight difference in ball speed comparing higher and lower-level players, players with higher-level demonstrated higher accuracy of ball target placement and made fewer errors in training and competition. On the other hand, inexperienced players showed higher inconsistency in ball speed and accuracy during within- and between-day trials [43]. Compared to the intermediate players, advanced players showed smaller variance of joint angle that affected the racket vertical angle during forehand topspin stroke [41]. Furthermore, a lower variability in the racket orientation and movement direction could be the reason for more successful returns and higher accuracy of the ball bounce location [38]. An uncontrolled manifold analysis suggested that higher-level players exploited higher degree of redundancy to maintain a similar racket angle at ball impact [41]. In brief, higher-level players exhibited higher accuracy and reproducibility on ball and racket mechanics but may not necessarily produce higher ball speed than lower-level players. Compared to the topspin serves, returning backspin serves demonstrated significantly higher resultant and vertical racket velocities at ball impact [35; 37], which could be contributed greatly by the wrist extension [35]. A possible explanation for this is that backspin serves tend to be treated back-low owing to the spin, resulting in a greater upward velocity of the shoulder joint center [37]. Moreover, peak shoulder torques in all directions, as well as elbow valgus torques, were significantly larger against backspin, in addition to the peaks of upper trunk right axial rotation and extension velocities [37]. Returning a spinning ball also alters the moving distance and velocity of the racket in the upward-downward direction, as compared to an ordinary stroke or a stroke with higher power. Hitting back a backspin serve could be more demanding than a topspin serve. In addition, biomechanical differences between returning light and heavy backspin serves were assessed by two included articles from the same research group [24; 25].