# Kinematic Analysis of the Racket Position during the Table Tennis Top Spin Forehand Stroke
## 4 Discussion  
This study aimed to compare the height of the racket with respect to the floor between two different types of shots (CC vs. LL). We hypothesized that the height of the racket with respect to the floor was different in CC and LL top spin forehand executions, respectively. We also hypothesized that the inclination of the racket at the moment of maximum racket velocity (racket-ball impact) was different, comparing the two executions. A limited number of studies have evaluated the height of the racket in the top spin forehand stroke [1,2], and all studies have only assessed CC shots. A previous study [2] analyzed the relative temporal structures of the rotative and striking top spin strokes and defined the range of movements along the anterior-posterior and vertical axes. The results showed that the racket covered the same horizontal distance in both rotative and striking top spin. On the contrary, a difference in vertical range was detected between the two shots. Indeed, the amplitude and localization of the key points (start, end of preparation, impact and end of movement) were different according to the players and the stroke used. [PERSON] and [PERSON] [1] investigated the racket kinematics at ball impact, and the ball height at impact was measured as the distance between the racket and the floor. They did not show any significant effect of participants performance level on the racket kinematics and ball speed after impact. On the contrary, advanced players adjusted racket/ball impact height to the different spins, 0.988 \(\pm\) 0.072 m and 1.034 \(\pm\) 0.037 m, against light and heavy spin, respectively. Theoretically, players can adjust parameters such as the racket speed, the direction of the racket path, the racket face angle and the height of the impact point, to properly play different shots [1]. [PERSON] and [PERSON] [1] also measured the speed of the racket at impact \begin{table}
\begin{tabular}{c c c c} \hline \multirow{2}{*}{**Variable**} & **CC** & **LL** & \multirow{2}{*}{\(p\)} \\  & **(Mean \(\pm\) SD)** & **(Mean \(\pm\) SD)** & \\ \hline H-Min (m) & 0.53 \(\pm\) 0.12 & 0.53 \(\pm\) 0.13 & 0.82 \\ H-Min-norm (\%) & 30.0 \(\pm\) 7.2 & 30.1 \(\pm\) 7.6 & 0.82 \\ H-RT (m) & 0.60 \(\pm\) 0.09 & 0.61 \(\pm\) 0.09 & 0.64 \\ H-RT-norm (\%) & 33.9 \(\pm\) 5.9 & 34.2 \(\pm\) 5.9 & 0.64 \\ H-MMV (m) & 1.08 \(\pm\) 0.05 & 1.09 \(\pm\) 0.05 & 0.62 \\ H-MMV-norm (\%) & 61.0 \(\pm\) 3.3 & 61.3 \(\pm\) 3.4 & 0.62 \\ H-Max (m) & 1.63 \(\pm\) 0.08 & 1.62 \(\pm\) 0.08 & 0.56 \\ H-Max-norm (\%) & 91.9 \(\pm\) 4.7 & 91.6 \(\pm\) 5.2 & 0.56 \\ Rx-MMV (\({}^{\circ}\)) & \(-\)154.1 \(\pm\) 13.2 & \(-\)155.8 \(\pm\) 9.1 & 0.77 \\ Ry-MMV (\({}^{\circ}\)) & 29.8 \(\pm\) 2.5 & 30.4 \(\pm\) 1.6 & 0.79 \\ Rz-MMV (\({}^{\circ}\)) & 148.6 \(\pm\) 6.6 * & 161.8 \(\pm\) 5.3 & 0.00 \\ Max Racket velocity (m/s) & 13.94 \(\pm\) 0.67 & 13.79 \(\pm\) 0.58 & 0.54 \\ \hline \end{tabular}
\end{table} 
Table 1: Mean SD values of the examined kinematic variables in both the CC and LL conditions. CC = cross-court; LL = long-line. * \(p\) \(<\) 0.05.  
comparing advanced and intermediate players, against light- and heavy-spin, respectively. The racket speed at impact was not significantly different between the two player groups but they showed higher speed values compared to the present investigation (i.e., 19.6 \(\pm\) 1.1 vs. 13.9 \(\pm\) 0.7 m/s). This information suggests that players need a lowest maximum speed of the racket to play a top spin forehand against no-spin compared with a top spin forehand against backspin, respectively. However, the results of the present investigation show no difference for some of the measured kinematic variables (H-Min, H-RT, H-MMV, and H-Max) between the two different executions (CC and LL), and does not support our first hypothesis. Racket motion, in terms of the height of the racket at the key points, seems to show a stereotypical movement pattern and a similar execution between the two considered shots.