The cross-step and chasse step are the basic steps of table tennis. This study presents a protocol to investigate the ground reaction force characteristics between cross-step and chasse step during stroke in table tennis. Sixteen healthy male national level 1 table tennis players (Age: 20.75 ± 2.06 years) volunteered to participate in the experiment after understanding the purpose and details of the experiment. All participants were asked to hit the ball into the target zone by cross-step and chasse step, respectively. The ground reaction force in the anterior-posterior, medial-lateral, and vertical directions of the participant was measured by a force platform. The key finding of this study was that: the posterior ground reaction force of cross-step footwork (0.89 ± 0.21) was significantly large (P = 0.014) than the chasse step footwork (0.82 ± 0.18). However, the lateral ground reaction force of cross-step footwork (-0.38 ± 0.21) was significantly lower (P < 0.001) than chasse step footwork (-0.46 ± 0.29) as well as the vertical ground reaction force of cross-step footwork (1.73 ± 0.19) was significantly lower (P < 0.001) than chasse step footwork (1.9 ± 0.33). Based on the mechanism of the kinetic chain, the better lower limb dynamic performance of sliding stroke may be conducive to energy transmission and thus bring gain to the swing speed. Beginners should start from the chasse step to hit the ball technically, and then practice the skill of cross-step.
Table tennis has developed continuously in sports training and competition practice for more than 100 years1. With economic globalization and cultural exchanges, table tennis has developed rapidly in various countries2,3. In Croatia, for example, table tennis is not only played in clubs, but also in universities, schools, and even in dormitories4. For athletes, the establishment of sports analysis is helpful for training and competition5. In table tennis competitions, players need good strategies to try to win the match6. Additionally, footwork is a skill that must be mastered in table tennis, and it is also the basis and one of the key points of table tennis training. The chasse step and cross-step are the basic steps of table tennis7. Every sports skill has a basic mechanical structure. The study of biomechanics is of high interest to the progress and development of table tennis skills. In training and competition, table tennis players find the accurate position through their steps7. Therefore, it is necessary to study the step of table tennis.
There are differences in the step of table tennis players from different regions, with Asian players using steps more frequently than European players both during training and in competition8. During competition, a high-level table tennis player will hit the ball in a shorter time, at a more steady step, and have enough time to hit the next ball9. In table tennis, because of the cross-step hitting action, in most cases it is a technical action to save the ball, leading to the inability to complete the hitting action with high quality. On the contrary, different from cross-step hitting, chasse step hitting is a common technical action, so athletes can better grasp the hitting technical action through practice to ensure the quality of their stroke. A chasse step is when the drive leg (right leg) moves to the right side (toward the ball) and then the left leg follows to move. A cross-step is when the drive leg (right leg) moves to the right side (toward the ball) with a large distance, and the left leg does not move.
Through previous studies, lower limb muscles play an important role in table tennis performance10. Table tennis has similarities with tennis moves. There are differences in the driving stability of lower limbs of tennis players with different levels of serving skill11. Table tennis involves knee flexion and asymmetrical torsion of the trunk12. In order to improve the skills of table tennis players, attention should be paid to the rotation of the pelvis13. When playing forehand loop, excellent table tennis players have a better sole control ability14. High-level table tennis players can better control the plantar pressure deviation, increase the inner and outer pressure deviation, and reduce the front and back pressure deviation15. Compared with a straight shot, a diagonal shot has a greater knee extension during the swing16. Table tennis service technology is diverse and has complex biomechanical characteristics. Compared with standing serves, squatting serves require higher lower-limb drive17. Compared with beginners, elite athletes are more flexible in their stride in cross-step exercises7.
In light of the above, with the increasing progress of science and the continuous development of table tennis skills, more and more players and researchers have joined table tennis, which requires high-quality biomechanical research to support the sport. However, due to the complexity of table tennis, it is difficult for researchers to measure the biomechanics1. There are few studies on the biomechanics of the lower limbs of table tennis. The purpose of this study was to measure the ground reaction force of elite college table tennis players in the movement of the racket lead and swing in chasse step and cross-step. The ground reaction force data of the two steps are compared. The first hypothesis of this study is that the chasse step and cross-step have different ground reaction force characteristics. The ground reaction force of chasse step and cross-step is used to obtain the kinetic data of two kinds of steps, which provides guidance and suggestions for table tennis players.
This study was approved by The Human Ethics Committee of Ningbo University, China. Written informed consent was obtained from all subjects after they were told about the goal, details, requirements, and experimental procedures of the table tennis experimental.
1. Laboratory preparation for table tennis
- Insert the USB dongle into the PC's parallel port and open the motion-capture infrared cameras and analog-to-digital converter.
NOTE: In this laboratory, the force platform (sampling frequency of 1000 Hz) is used together with the motion acquisition system, and the data collected by the force platform was displayed and preliminarily analyzed through the same system. The default sampling frequency of the force platform is 1000 Hz.
- Double-click the software icon on the desktop to open the tracking software.
NOTE: Before opening the software, remove all obstacles in the experimental environment and clean the ground.
- Every camera node will show a green light if the hardware connection is true. When the indicator light of all cameras is green, select eight cameras in the Local System.
- Click on Camera in the Perspective window and adjust the Strobe Intensity as 0.95-1, Gain to times 1 (x1), Threshold as 0.2-0.4, Minimum Circularity Ratio as 0.5, Grayscale Mode to Auto, as well as Max Blob Height to 50.
- Place the T correction rack in the center of the shooting area, and select eight cameras in the system. Using a 2D model, confirm that the camera can discern T correction and that there are no noise points.
- Place the T correction rack in the center of the camera area. Click on the System Preparation, the L - Frame drop-down list, and select 5 Marker Wand & L - Frame. Then, click on the Start button under the AimMX cameras option.
- Select the System preparation button, and click on the Start button in the Calibrate MX Camera section in the Tool pane. Then, wave the T-wand in the capture range. When the blue light on the infrared camera stops flashing, stop the action.
- Observe the progress bar until the calibration process is complete at 100% and returns to 0%. At the same time, observe the error of the image. When the error of the image is less than 0.3, continue the following operation.
- Place the T-shaped correction frame in the center of the moving area to ensure that the axis direction is consistent with the boundary direction of the force platform.
- Select the Start button under the Set Volume Origin section in the Tool pane.
2. Participants' preparation
NOTE: Sixteen healthy male national level 1 table tennis players volunteered to participate in the experiment (Ages: 20.75 ± 2.06year; Height: 173.25 ± 6.65 cm; Weight: 66.50 ± 14.27 kg; Training Year: 12.50 ± 2.08 year). All of them belong to the Ningbo University table tennis team. Before the formal start of the experiment, the details and process of the experiment were briefly explained to the participants again, and the written informed consent of the participant who met the conditions of the experiment were obtained.
- Select participants that are right-handed, have the right leg as dominant, and are in good physical health, free of any form of lower limb disease or injury in the last 6 months. A total of 16 male participants who met the experimental conditions were included in this experiment. The demographic information of participants is shown in Table 1.
NOTE: Because there are few left-handed racket users, it was easier to find enough right-handed racket users to participate in this experiment.
- Ask all participants to fill out a questionnaire related to fitness.
NOTE: Questions include: Have you had a history of table tennis competition? How often do you take part in table tennis training in a week? Have you suffered any lower-limb disorders and injuries in the last 6 months?
- Ensure that all participants wear professional table tennis match shoes as well as identical t-shirts and tight-fitting pants. Have all participants use the same professional table tennis racket.
- Give each participant 5 min to adapt to the experimental environment and 15 min to warm up with light running on the professional treadmill and stretching. Due to the short duration of the experiment, restrict subjects from eating and drinking during the formal experiment in order to keep them in a stable state.
NOTE: Participants first completed a 5 min jog at an adaptive speed on the lab's professional running table, followed by a 5 min stretch of their lower limb muscles. Finally, they practiced table tennis footwork technique for 5 min. After completing the warm-up task, the participants were given 2 min to adjust their state. The formal data collection began.
3. Static calibration
- Click on the Data Management button on the toolbar.
- Click on the New Database tab on the toolbar, click on the Location, and then import the description of the trial. Select Clinical Template and click on the Create button.
- Select the name of the database created in the Open Database window. Then, click on the green New Patient Category button, the yellow New Patient button, and the gray New Session button to create experimental information in the newly opened screen.
- Click on Subjects to create a New Subject data set in the Nexus main pane.
- Click on the Start button in the Subject Capture section to create a static model. Click on the Stop button when the image frames are at 140-200 to finish the establishment of the static model.
NOTE: The participants were asked to stand on a force platform during the experiment. They were asked to maintain a stable posture with their hands folded and raised on their chest, looking ahead, and their feet shoulder-width apart.
4. Dynamic trials
- As shown in Figure 1, place the table tennis table and ball basket in the experimental environment to ensure that the subjects have enough space to execute two kinds of footwork.
NOTE: The table tennis table and balls are up to the standards of professional events.
- Ask the participant to hold the ready position, When the experimenter gives the start command, ask the coach to serve the table tennis balls to the first and final impact area, respectively.
- Before the formal experiment begins, give the participants enough time to get accustomed to this position through practice.
- Ask the participants to start on the left side of the table, about half a meter away from the table. Then, ask them to hit the first and second served ball by forehand with maximum force and return to the ready position after finishing the second stroke task.
- Ask the participants to first use the chasse step footwork to complete 5 successful strokes, and then use the cross-step footwork to complete 5 successful strokes.
- In the software, click on the Capture button in the pressure platform to start the recording and click on the Stop button to end the recording. Repeat five times for each participant.
NOTE: If the shot is not within the range of the target area, or if the subject's right foot is not fully on the force platform, the measurement will be re-taken.
- Double-click on the trial name in the Data Management window. Click on the Reconstruct Pipeline and Labels buttons in the toolbar to display the experiment demonstration.
- In the Perspective window, move the blue triangle on the time bar to intercept the desired time interval.
- Select the Dynamic Plug-in Gait that is in the Subject Calibration pane. Click on the Start button to run and export the data.
6. Statistical analysis
- Analyze all data using professional statistical software. Run the Shapiro-Wilks tests to check the normal distribution for all variables.
- Use a paired t-test to compare kinetics characteristics of chasse step footwork and cross-step footwork during table tennis stroke.
- Set the significance level at p < 0.05. The results are presented as the mean ± the standard deviation throughout the text unless otherwise stated.
As shown in Figure 2 and Table 2, the posterior ground reaction force of the cross-step footwork (0.89 ± 0.21) was significantly larger (P = 0.014) compared with the chasse step footwork (0.82 ± 0.18). However, the lateral ground reaction force of cross-step footwork (-0.38 ± 0.21) was significantly lower (P < 0.001) than the chasse step footwork (-0.46 ± 0.29). Additionlly, the vertical ground reaction force of cross-step footwork (1.73 ± 0.19) was significantly lower (P < 0.001) than the chasse step footwork (1.9±0.33). No differences were observed between the medial or anterior ground reaction forces between the cross-step and the chasse step footwork during stroke in table tennis (P > 0.05).
Figure 1: Experiment setup Please click here to view a larger version of this figure.
Figure 2: The ground reaction force in the posterior, anterior, medial, lateral, and vertical directions. Please click here to view a larger version of this figure.
|Participants (n)||Ages (years)||Height (cm)||Weight (kg)||Training Year (years)|
Table 1: The participant demographic information table.
|Ground Reaction Force||Cross-Step Footwork Mean±SD||Chasse Step Footwork Mean±SD||P-value|
Table 2: The ground reaction force information of chasse step footwork and cross-step footwork in three planes during stroke in table tennis. Significant differences between the chasse step footwork and cross-step footwork are denoted with an asterisk (*). BW means multiple of body weight.
The aim of this study is to investigate the ground reaction force characteristics between cross-step and chasse steps during stroke in table tennis. The key findings of this study are stated here. The anterior ground reaction force of cross-step footwork was significantly larger than the chasse step footwork. The lateral ground reaction force of cross-step footwork was significantly lower than the chasse step footwork. The vertical ground reaction force of cross-step footwork was significantly lower than the chasse step footwork.
Marsan et al. (2020) showed that Newton's second law could be a good estimation method for the ground reaction force value except for peak ground reaction forces18. In the results of this study, the displayed value of the ground reaction force is close to the value of the measurement observed by Marsan et al. (2020). This further supports the results of this study. A perfect stroke requires coordination of the whole body. The control of footwork patterns requires a coordinated sequence of body parts interacting with each other, and the optimal activation of all links is defined as the "kinetic chain"11,19,20. The lower limbs, as the starting point of the kinetic chain, transfer the best-activated energy from the lower limbs to the upper limbs through the continuous movement of the kinetic chain9,21. These include the integrity of the body when hitting the ball, as well as more full transmission of the lower limb kinetic chain.
The lateral ground reaction force of the chasse step hitting movement is significantly greater than the action of the cross-step hitting movement. Lam et al. (2019) observed the same results. The maximum horizontal force of the side-step was significantly higher than the one-step22. The chasse step hitting technique can be mastered by athletes through practice, and the cross-step hitting technique has great variability compared with the chasse step hitting action. Therefore, with a lot of practice of the chasse step hitting, the lower limb kinetic chain transmission of the players could be more complete and smoother, so that the swing of hitting the ball in the process of the push force is more complete. The flow of the kinetic chain is conducive to an energy transfer from the lower limb to the upper limb, considerably influencing racket and ball speed in racket sports22,23,24,25. In general, in terms of the lateral ground reaction force, the chasse step hitting ball is higher than the cross-step hitting ball, which again confirms the results of this study regarding the vertical ground reaction force. Due to the variability and immediacy of the cross-step, the cross-step hitting technique cannot fully complete the swing action. Therefore, a greater push is required as a compensatory mechanism in the anterior direction. To compensate, the cross-step exhibits a greater anterior ground reaction force than the chasse step hitting technique. Shimokawa et al. (2020) investigated a similar result in the tennis forehand groundstroke. The peak anterior-posterior ground reaction force plays an influential role in affecting forehand post-impact ball speed26. However, a greater anterior ground reaction force may cause the center of gravity not to return to the initial position in time, thus affecting the beginning of the next movement. In the practical application of training and competition, athletes and coaches attempt to master the ability to control the center of gravity during cross-step footwork. Beginners should start from the chasse step footwork to hitting the ball. When the player has mastered the ability to control the center of gravity while hitting the ball, they can further learn to use the cross-step footwork.
There are several critical steps in the protocol. Firstly, the subject needs to accurately step on the center position of the force measuring table when executing the two footwork, to ensure that the ground reaction force data of the subject can be collected completely and accurately. Any data where the foot is placed outside the platform should be eliminated. Secondly, during the execution of the experiment, in order to accurately collect data, athletes need to execute actions after hearing the "start" command. The same experimenter is responsible for issuing the command. Third, in the process of data post-processing, the interpretation of the subjects' movements should be extremely rigorous.
The main limitations of this study were that the whole experiment was a real match environment as this will affect the practical application of the results of this study. Secondly, in this study, only the ground reaction force information of the two footsteps in the swing stage was measured. In future further research, experimental data should be collected in a situation that is as close to a real competitive environment as possible and the ground reaction force information of the racket lead stage should also be collected together.
By comparing the ground reaction force of two footwork techniques, the anterior ground reaction force of the cross-step footwork was significantly larger than the chasse step. The cross-step footwork is often used to recover the ball from a large distance, which may be a result of the timeliness of the cross-step. The time to return to the initial position changed the center of gravity and influenced the beginning of the next action. Athletes and coaches should pay attention to using cross-step footwork and having good control over the center of gravity to avoid moving the weight forward too much and affect the next movement. At the same time, the player should adjust their step as soon as possible after the cross-step stroke to prepare for the next movement. The lateral and vertical ground reaction force of the chasse step was significantly larger than the cross-step footwork. The chasse step is an action that the athlete can learn through training to hit the ball. Enhancing the driving force of the lower limbs and optimizing the transmission of the lower limb power chain could increase the speed and power of the swing.
No potential conflict of interest was reported by the authors.
This work was supported by the National Natural Science Foundation of China (No. 81772423). The authors would like to thank the table tennis players who participated in this study.
|14 mm Diameter Passive Retro-reflective Marker||Oxford Metrics Ltd., Oxford, UK||n=22|
|Double Adhesive Tape||Oxford Metrics Ltd., Oxford, UK||For fixing markers to skin|
|Force Platform||Advanced Mechanical Technology, Inc.||Measure ground reaction force|
|Motion Tracking Cameras||Oxford Metrics Ltd., Oxford, UK||n= 8|
|T-Frame||Oxford Metrics Ltd., Oxford, UK||-|
|Valid Dongle||Oxford Metrics Ltd., Oxford, UK||Vicon Nexus 1.4.116|
|Vicon Datastation ADC||Oxford Metrics Ltd., Oxford, UK||-|
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