###### Abstract  
The topspin forehand is the most frequent and effective shot in top-level table tennis matches. The present study assesses the biomechanical differences in the topspin forehand stroke technique when the incoming ball is in different rotations. Eight national level-1 male table tennis athletes (176.6 \(\pm\) 4.8 cm, 70.8 \(\pm\) 6.6 kg, 20.9 \(\pm\) 2.4 yr) performed two kinds of techniques--topspin forehand strokes against topspin (AT) and against backspin (AB) balls, respectively. The kinematic parameters of their bodies and rackets were calculated. Meanwhile, the force plates analyzed their lower limb moments through inverse dynamics. Paired \(t\)-test and non-parametric paired \(t\)-test mapping were used to assess the differences between the two conditions. Their center of gravity (COG) vertical distance, elbow flexion, thorax-pelvis flexion, and knee flexion angles had significant differences during the stroke phase (\(p\) < 0.05). The moment of the racket-side hip rotation and ankle dorsiflexion showed significant differences during the stroke phase (\(p\) < 0.05). The racket velocity, angle, and trajectories showed significant differences at characteristic moments (\(p\) < 0.05). This study revealed the different topspin forehand stroke techniques in table tennis, even though the two movements look similar. Compared with AT strokes, the athletes kept a straight elbow and lower center of gravity than they did during the stroke phase of AB strokes. They increased the distance of the racket trajectory and velocity to meet the incoming ball with a backspin, especially in the vertical direction. This detailed information is necessary for beginners to improve the efficiency of their forehand topspin technique, especially in strokes against incoming balls with different rotations. 3D motion analysis; table tennis; topspin forehand; shot techniques; kinematic; kinetic acronyms: article  
A Comparative Biomechanical Analysis of Topspin Forehand against Topspin and Backspin in Table Tennis  
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Footnote 1: email: [EMAIL_ADDRESS] (C.M. ); [EMAIL_ADDRESS] (T.L. ); [EMAIL_ADDRESS] (X.L. );  
[EMAIL_ADDRESS] (Z.L. ); [EMAIL_ADDRESS] (Z.L. );  
luzijun@smu. However, as [PERSON] concluded, \"not only must you learn to loop, but you must learn to return the loop\" [12]. The incoming ball's condition (e.g., rotation, velocity, and path) also affects the athlete's stroke technique. For example, generating a higher topspin rate and initial speed while serving could reduce the opponent's preparation time [13]. Meanwhile, [PERSON] and [PERSON] compared the topspin forehand against a ball without rotation and with backspin. They concluded that the athletes performed the motion with the longest racket distance when they stroke against the backspin balls [4]. However, few studies have examined the differences between the topspin forehand stroke against topspin (AT) and against backspin (AB) incoming balls, which might provide more practical information for learners. In addition, the kinematic parameters of the racket are also important for the topspin forehand. However, the racket speed has been widely examined [14; 15; 16]. More recently, [PERSON] and his colleagues accessed the racket position during the topspin forehand drive [9]. They suggested that athletes need to increase the racket height to improve its effectiveness during the stroke [9]. In addition, the racket angle at the ball-racket impact point during the topspin forehand may also affect the stroke effectiveness [8]. However, to the best of our knowledge, these studies failed to further compare the incoming balls under different conditions or analyze the process from the perspective of the racket. For the preceding reasons, this study aims to compare the kinematic differences in the topspin forehand stroke between AT and AB incoming balls. Not only did we focus on the kinematics of the trunk and racket-side arm, but the racket angles, velocity, and trajectory were also evaluated.