In order to examine the stroke structural characteristics and stroke effect of young table tennis players, descriptive statistical analysis was conducted on the position and angle changes of upper and lower limb three joints as well as the changes of these variables such as linear velocity and angular velocity of body joints movement, respectively.
Stroke structural characteristics
Position changes of the upper and lower limb three joints movement
The descriptive statistical analysis results of the position changes of the upper and lower limb three joints in the three phases of backspin forehand stroke were shown in Table 2.
For each phase of the backspin forehand stroke, the position changes of the upper limb three joints movement from large to small were right wrist joint, right elbow joint, and right shoulder joint. The position changes of the right wrist joint movement in the three phases of the stroke were: 674.12±128.47 mm in the backswing phase, 910.42±121.30 mm in the forward phase, and 571.59±118.93 mm in the backward phase (Table 2), of which the change in the forward phase was the largest, followed by the backswing phase and, finally, the backward phase.
In the backswing phase of the backspin forehand stroke, the position changes of the lower limb three joints movement from large to small were as followed: right hip joint (209.06±74.65 mm), right knee joint (155.59±124.40 mm), and right ankle joint (120.89±115.77 mm). In the forward phase of the stroke, the position changes of the lower limb three joints movement from large to small were as followed: right knee joint (207.78±104.30 mm), right hip joint (203.80±80.19 mm), and right ankle joint (149.23±152.00 mm). In the backward phase of the stroke, the position changes of the lower limb three joints movement from large to small were as followed: right knee joint (195.98±110.13 mm), right ankle joint (175.68±116.33 mm), and right hip joint (175.00±107.95 mm) (Table 2).
Angle changes of the upper and lower limb three joints movement
The descriptive statistical analysis results of the angle changes of the upper and lower limb three joints in the three phases of backspin stroke with forehand were shown in Table 3.
In the backswing phase of the backspin forehand stroke, the angle changes of the upper limb three joints movement from large to small were as followed: right elbow joint (39.64±27.34。), right wrist joint (32.24±13.86。), and right shoulder joint (16.29±11.01。). In the forward phase of the stroke, the angle changes of the upper limb three joints movement from large to small were as followed: right wrist joint (34.70±15.39。), right elbow joint (33.73±20.41。), and right shoulder joint (23.74±15.90。). In the backward phase of the stroke, the angle changes of the upper limb three joints movement from large to small were as followed: right wrist joint (35.08±14.25。), right elbow joint (29.50±25.06。), and right shoulder joint (21.79±14.61。) (Table 3).
In the backswing phase of the backspin forehand stroke, the angle changes of the lower limb three joints movement from large to small were as followed: right hip joint (81.42±16.07。), right knee joint (28.72±14.12。), and right ankle joint (27.91±9.20。). In the forward phase of the stroke, the angle changes of the lower limb three joints movement from large to small were as followed: right hip joint (126.08±20.21。), right ankle joint (45.51±15.75。), and right knee joint (25.22±17.35。). In the backward phase of the stroke, the angle changes of the lower limb three joints movement from large to small were as followed: right hip joint (50.60±19.58。), right ankle joint (28.70±11.70。), and right knee joint (15.53±12.48。) (Table 3).
Changes of the linear velocity of the upper and lower limb three joints movement
The descriptive statistical analysis results of the changes of the linear velocity of the upper and lower limb three joints movement in the three phases of backspin forehand stroke were shown in Table 4.
For each phase of the backspin forehand stroke, the linear velocity variation of the upper limb three joints movement from large to small was right wrist joint, right elbow joint, and right shoulder joint. The linear velocity changes of the right wrist joint movement in the three phases of the stroke were: 0.96 ±0.46 m/s in the backswing phase, 2.40 ±0.85 m/s in the forward phase, and 0.89±0.40 m/s in the backward phase, of which the change in the forward phase was the largest (Table 4). During the three phases of the whole stroke, the linear velocity of each upper limb joint was increased at first and then decreased at the end. In the backward phase of the stroke, the linear velocity change of the right shoulder joint was the smallest, which had a positive impact on maintaining the stability of the upper body.
In the backswing phase of the backspin forehand stroke, the linear velocity changes of the lower limb three joints were in the following order: right hip joint, right knee joint, right ankle joint, and the largest change of linear velocity was 0.29±0.11 m/s in the right hip joint. In the forward phase, the variation of linear speed of the lower limb three joints was in the following order: right knee joint, right hip joint, and right ankle joint. Among them, the linear speed of the right knee joint was the fastest, which was 0.53±0.24 m/s, and the linear speed of the hip joint was 0.52 ±0.18 m/s, which was close to that of the right knee joint. In the backward phase, the linear velocity variation was in the following order: right knee joint, right hip joint, and right ankle joint, of which the biggest variation was the right knee joint, which was 0.30±0.18 m/s, followed by the right hip joint and right ankle joint (Table 4).
Changes of angular velocity of the upper and lower limb three joints movement
The descriptive statistical analysis results of the changes of angular velocity of the upper and lower limb three joints movement in the three phases of backspin forehand stroke were shown in Table 5.
In the backswing phase of the backspin forehand stroke, the angular velocity changes of the upper limb three joints were in the following order: right elbow joint, right wrist joint, and right shoulder joint, of which the largest change of angular velocity was the right elbow joint (58.61 ±52.03。/s), followed by the right wrist joint (45.10±36.31。/s) and the right shoulder joint (22.68±17.90。/s). In the forward phase, the angular velocity changes of the upper limb three joints were in the following order: right wrist joint (92.48±101.20。/s), right elbow joint (89.11±59.83。/s), and right shoulder joint (63.07±47.17。/s), of which the change of the right wrist joint was the largest. In the backward phase, the angular velocity changes of the upper limb three joints were in the following order: right wrist joint (53.40±66.31。/s), right elbow joint (46.56±42.27。/s), and right shoulder joint (34.90±28.09。/s), of which the change of the right wrist joint was the largest (Table 5).
In the backswing phase of the backspin forehand stroke, the angular velocity changes of the lower limb three joints were in the following order: right hip joint, right ankle joint, and right knee joint, of which the largest change of angular velocity was the right hip joint (115.41±42.00。/s), followed by the right ankle joint (39.15±16.74。/s) and the right knee joint (37.85±17.15。/s). In the forward phase, the angular velocity changes of the upper limb three joints were in the following order: right hip joint (327.63±65.17。/s), right ankle joint (120.05±47.78。/s), and right knee joint (65.52±46.60。/s), of which the change of the right hip joint was the largest. In the backward phase, the angular velocity of the right hip joint was the largest (76.98±33.11。/s), followed by the right ankle joint (44.75±22.23。/s) and, finally, the right knee joint (24.49±21.29。/s) (Table 5).
Time duration of the three phases of backspin stroke with forehand
The descriptive statistical analysis results of the time duration of the three phases of players’ backspin stroke with forehand were shown in Table 6.
The time duration of the three phases of players’ backspin stroke with forehand was 92.98 ±28.10 frames in the backswing phase, 47.18 ±8.55 frames in the forward phase, and 82.39±22.84 frames in the backward phase, respectively. During the whole stroke, the backswing phase’s time duration was the longest, followed by the backward phase and the forward phase, which made the body fully expanded to make a good preparation for the stroke and good preparation for the next stroke (Table 6).
Stroke effect of backspin stroke with forehand
The descriptive statistical analysis results of the stroke effect (ball speed, spin speed, and placement) of players’ backspin forehand stroke were shown in Table 7.
The ball speed of players’ backspin stroke with forehand was 10.34 ± 2.09 m/s, the spin speed was 106.78 ±17.29 r/s, and the placement score was 2.93 ±1.33 points (table 7). According to the placement score, the young players had a general ability to control the placement of backspin forehand stroke (mainly in the 40*40cm corner area).
Correlation analysis between stroke structural characteristics and stroke effect
Pearson bivariate correlations were calculated to examine the relationships between the stroke structural characteristics and stroke effect. These results were presented in Table 8.
As shown, there was a significantly negative correlation between the time duration of the backswing phase and the ball speed (r = -0.403, p < 0.01) and spin speed (r = -0.244, p = 0.027), respectively. The longer the backswing time, the closer the coming ball to the body, and the more difficult for players to return the ball, which makes the stroke effect reduced. There was a significantly negative correlation between the time duration of the forward phase and the ball speed (r = -0.390, p < 0.01), spin speed (r = -0.369, p < 0.01), and placement (r = -0.270, p = 0.014), respectively. There was also a significantly negative correlation between the time duration of the backward phase and the ball speed (r = -0.272, p = 0.013).
The linear velocity of right wrist joint was positively correlated with ball speed (r = 0.298, p < 0.01) and spin speed (r = 0.238, p = 0.031), and had no significant correlation with the placement of the stroke (r = -0.022, p = 0.847). As the final power transfer point of the upper body when striking the ball, the linear speed of the right wrist joint has a positive impact on the ball speed and spin speed of the stroke. The linear speed of the right elbow joint was positively correlated with the spin speed of the stroke (r = 0.227, p = 0.040), and had no significant correlation with the ball speed (r = 0.212, p = 0.056) and placement of the stroke (r = -0.096, p = 0.392). The linear speed of the right shoulder joint and right hip joint had no significant correlations with the ball speed, spin speed, and placement of the stroke (all p > 0.05), respectively. The linear speed of the right knee joint had a significantly negative correlation with the spin speed of the stroke (r = -0.255, p = 0.021), and had no significant correlation with the ball speed (r = -0.124, p = 0.268) and placement of the stroke (r = 0.082, p = 0.462). The linear velocity of right ankle joint had no significant correlation with the placement (r = -0.019, p = 0.869), but had a significantly negative correlation with the ball speed (r = -0.369, p < 0.01) and spin speed (r = -0.430, p < 0.01), respectively.
The angular velocity of right elbow joint had a significantly positive correlation with the ball speed of the stroke (r = 0.219, p = 0.013) and spin speed (r = 0.172, p = 0.048), and had no significant correlation with the placement (r = -0.018, p = 0.870). The angular velocity of the right wrist joint and right shoulder joint had no significant correlation with the ball speed, spin speed, and placement of the stroke (all p > 0.05), respectively. The angular velocity of the right hip joint had no significant correlation with the placement of the stroke (r = 0.175, p = 0.115), however, it had a significantly positive correlation with the ball speed (r = 0.427, p < 0.01) and spin speed (r = 0.277, p = 0.012), respectively. The angular velocity of the right knee joint had a significantly negative correlation with the placement of the stroke (r = -0.246, p = 0.026), and had no significant correlation with the ball speed (r = -0.197, p = 0.077) and spin speed (r = -0.150, p = 0.177), respectively. The angular velocity of the right ankle joint had a significantly positive correlation with the ball speed of the stroke (r = 0.443, p < 0.01), and had no significant correlation with the spin speed (r = 0.217, p = 0.050) and placement (r = 0.102, p = 0.360), respectively.