Investigation of high-speed badminton racket kinematics by motion capture

The kinematics of a badminton racket during a smash stroke was observed in this study with the purpose of investigating stroke dynamics and racket behaviour. Motion capture measurements of the racket during several smash strokes performed by three players of different skill levels indicated a clear increase in racket velocity at impact with increasing skill level. Variations between translational and rotational contributions to the impact speed could also be seen between the players. The advanced player produced a much higher peak angular velocity and also relied much less on translation, with a translational velocity of only 8% of the total velocity versus the 20% for the recreational player. It is proposed that, as an alternative to shuttlecock speeds, racket head speed measurements can be used as an indicator of performance, and can also provide some insight into the interaction between the racket and player.     

Measurement of badminton racket deflection during a stroke

The compliance of a badminton racket is an important design consideration, which can be better understood by studying the deflection behaviour of the racket during a stroke. Deflection can be measured using direct methods, such as motion capture or high speed video, or by indirect methods, which then require a mathematical model in order to calculate the deflections from indirect measures. Indirect methods include strain gauges and accelerometers. Here, racket deflection is measured directly using motion capture and compared with deflections calculated from strain gauge data using a beam model. While the elastic behaviour is better calculated from strains than measured by motion capture, it is not possible to extract the whole motion of the racket from strain data. Motion capture is therefore also necessary to determine the rigid body velocity, in order to put the elastic velocity (as calculated from strains) in perspective.     

Kinematics of table tennis topspin forehands: effects of performance level and ball spin

Abstract

The purpose of this study was to investigate whether performance level and ball spin affect arm and racket kinematics of the table tennis topspin forehand. Nine advanced and eight intermediate male table tennis players hit topspin forehands against light and heavy backspins. Five high-speed video cameras were used to record their strokes at 200 fps. Contributions of joint rotations to the racket speed, the racket kinematics at ball impact, the time required for racket acceleration and the maximum slope of the racket speed-time curve (s _max) were determined. The advanced players showed a significantly larger contribution of lower trunk axial rotation to the racket speed at impact and a significantly larger value of s_max, and tended to require a less time for racket acceleration than the intermediate players. The racket speed at impact was not significantly different between the two player groups. The players adjusted the racket face angle rather than the inclination of the racket path at impact to the different ball spins. The results suggest that the ability to accelerate the racket in less time in the topspin forehand against backspin balls may be an important factor that affects the performance level.     

The kinematic differences between skill levels in the squash forehand drive,volley and drop strokes

ABSTRACT

Knowledge of the kinematic differences that separate highly skilled and less-skilled squash players could assist the progression of talent development. This study compared trunk, upper-limb and racket kinematics between two groups of nine highly skilled and less-skilled male athletes for forehand drive, volley and drop strokes. A 15-camera motion analysis system recorded three-dimensional trajectories, with five shots analysed per participant per stroke. The highly skilled group had significantly (p < 0.05) larger forearm pronation/supination range-of-motion and wrist extension angles at impact than the less-skilled. The less-skilled group had a significantly more “open” racket face and slower racket velocities at impact than the highly skilled. Rates of shoulder internal rotation, forearm pronation, elbow extension and wrist flexion at impact were greater in the drive stroke than in the other strokes. The position of the racket at impact in the volley was significantly more anterior to the shoulder than in the other strokes, with a smaller trunk rotation angular velocity. Players used less shoulder internal/external rotation, forearm pronation/supination, elbow and wrist flexion/extension ranges-of-motions and angular velocities at impact in the drop stroke than in the other strokes. These findings provide useful insights into the technical differences that separate highly skilled from less-skilled players and provide a kinematic distinction between stroke types.     

Perceiving the affordance of string tension for power strokes in badminton: Expertise allows effective use of all string tensions

Abstract

Affordances mean opportunities for action. These affordances are important for sports performance and relevant to the abilities developed by skilled athletes. In racquet sports such as badminton, different players prefer widely different string tension because it is believed to provide opportunities for effective strokes. The current study examined whether badminton players can perceive the affordance of string tension for power strokes and whether the perception of affordance itself changed as a function of skill level. The results showed that string tension constrained the striking performance of both novice and recreational players, but not of expert players. When perceptual capability was assessed, perceptual mode did not affect perception of the optimal string tension. Skilled players successfully perceived the affordance of string tension, but only experts were concerned about saving energy. Our findings demonstrated that perception of the affordance of string tension in badminton was determined by action abilities. Furthermore, experts could adjust the action to maintain a superior level of performance based on the perception of affordance.     

Evaluation of elite table tennis players' technique effectiveness

Abstract

This study constructed a technique effectiveness evaluation formula for table tennis players based on the relationship between the scoring rate and usage rate of techniques and established the evaluation criteria through the examination of 224 matches of the world's top 35 players. It also built a competition performance formula with the score difference theory for the exploration of the correlation between player technique effectiveness and competition performance. The results showed the three indices – the technique effectiveness of the first and third strokes (TE_1,3), the second and fourth strokes (TE_2,4) and the after fourth strokes (TE_>4) – could help better evaluate the technique effectiveness of elite players. The comparative analysis of Chinese elite table tennis players and players from other countries and regions revealed that Chinese players as a whole were “excellent” in all the examined techniques except in the male's “first and third strokes”; while players from other countries and regions were overall “general”. The case analysis of two world top players further indicated that correlation analysis of technique effectiveness and competition performance could help identify the technique indices highly correlated with player competition performance.     

Science and the major racket sports: a review

The major racket sports include badminton, squash, table tennis and tennis. The growth of sports science and the commercialization of racket sports in recent years have focused attention on improved performance and this has led to a more detailed study and understanding of all aspects of racket sports. The aim here, therefore, is to review recent developments of the application of science to racket sports. The scientific disciplines of sports physiology and nutrition, notational analysis, sports biomechanics, sports medicine, sports engineering, sports psychology and motor skills are briefly considered in turn. It is evident from these reviews that a great deal of scientific endeavour has been applied to racket sports, but this is variable across both the racket sports and the scientific disciplines. A scientific approach has helped to: implement training programmes to improve players' fitness; guide players in nutritional and psychological preparation for play; inform players of the strategy and tactics used by themselves and their opponents; provide insight into the technical performance of skills; understand the effect of equipment on play; and accelerate the recovery from racket-arm injuries. Racket sports have also posed a unique challenge to scientists and have provided vehicles for developing scientific methodology. Racket sports provide a good model for investigating the interplay between aerobic and anaerobic metabolism and the effect of nutrition, heat and fatigue on performance. They have driven the development of mathematical solutions for multi-segment interactions within the racket arm during the performance of shots, which have contributed to our understanding of the mechanisms of both performance and injury. They have provided a unique challenge to sports engineers in relation to equipment performance and interaction with the player. Racket sports have encouraged developments in notational analysis both in terms of analytical procedures and the conceptualization of strategy and tactics. Racket sports have provided a vehicle for investigating fast interceptive actions, hand-eye coordination and perception-action coupling in the field of motor control. In conclusion, science has contributed considerably to our knowledge and understanding of racket sports, and racket sports have contributed to science by providing unique challenges to researchers.     

The kinematic differences between accurate and inaccurate squash forehand drives for athletes of different skill levels

ABSTRACT

To maintain the accuracy of squash shots under varying conditions, such as the oncoming ball’s velocity and trajectory, players must adjust their technique. Although differences in technique between skilled and less-skilled players have been studied, it is not yet understood how players vary their technique in a functional manner to maintain accuracy under varying conditions. This study compared 3-dimensional joint and racket kinematics and their variability between accurate and inaccurate squash forehand drives of 9 highly skilled and 9 less-skilled male athletes. During inaccurate shots, less-skilled players hit the ball with a more open racket, demonstrating a difference in this task-relevant parameter. No joint kinematic differences were found for accuracy for either group. Coordinated joint rotations at the elbow and wrist both displayed a “zeroing-in” effect, whereby movement variability was reduced from the initiation of propulsive joint rotation to a higher consistency at ball-impact; potentially highlighting the “functionality” of the variability prior to the impact that enabled consistent task-relevant parameters (racket orientation and velocity) under varying conditions. Further, highly skilled players demonstrated greater consistency of task-relevant parameters at impact than less-skilled players. These findings highlight the superior ability of highly skilled players to adjust their technique to achieve consistent task-relevant parameters and a successful shot.     

A biomechanical comparison of the topspin and backspin forehand approach shots in tennis

Three‐dimensional (3‐D) high‐speed cinematographic techniques were used to record topspin and backspin forehand approach shots hit down‐the‐line by high‐performance players. The direct linear transformation (DLT) technique was used in the 3‐D space reconstruction from 2‐D images recorded via laterally placed phase‐locked cameras operating at 200 Hz. A Mann‐Whitney U‐test was calculated for the different aspects of the topspin and backspin shots to test for significance (P<0.05).

A significant difference was recorded between topspin and backspin shots in the angle of the racket at the completion of the backswing. The racket was taken 0.48 rad past a line drawn perpendicular to the back fence for topspin trials, but only rotated 0.86 rad from a line parallel to the net in the backspin shot. Maximum racket velocities occurred prior to impact and were significantly higher in topspin (26.5 m s‐¹) compared to backspin (16.6 m s^‐1) trials. This resulted in the topspin trials recording a significantly higher ball velocity compared to backspin trials (27.6 m s^‐1 vs 21.7 m s^‐1). Pre‐impact racket trajectories revealed that in topspin shots the racket moved on an upward path of 0.48 rad while in backspin shots it moved down at an angle of 0.34 rad. In the topspin trials impact occurred significantly further forward of the front foot than in backspin shots (0.26 m vs 0.05 m) while the angle of the racket was the same for both strokes (0.14 rad behind a line parallel to the net). The mean angle of the racket‐face at impact was inclined backwards by 0.11 rad for backspin strokes and rotated forward by 0.13 rad for topspin strokes. Angles of incidence and reflection of the impact between the ball and the court showed that backspin trials had larger angles of incidence and reflection than topspin strokes.     

Measurement error associated with the SAGIT/Squash computer tracking software

Abstract

The velocities and distances covered by players during competition serve as a basis for planning fitness regimes according to the specific demand of the sport. The techniques used to calculate these movement parameters have ranged from human judgements to technological solutions such as GPS and computer vision. This paper evaluates the accuracy of a computerized motion tracking system (SAGIT/Squash) that uses computer vision methods on video captured via a fixed single camera located centrally above the court. Digital images were processed automatically with operator supervision so that any tracking errors could be rectified and manual tagging of all shots added. Four separate experiments were used to assess the error associated with tracking adult players' velocities and positions with respect to the court floor. Experiment 1 involved players standing still in different areas of the court. The tracking software was found to be more accurate when a player was stood in the centre of the court (1.33 m · min^?1 error) than in the corners (2.61 m · min^?1 error), predominately due to systematic errors (e.g. calibration). Experiment 2 was conducted in the same manner as Experiment 1 except that the players vigorously swung a racket around their body continuously. This resulted in 15 times the error found in Experiment 1 for the distance covered during 1 min. However, this is an unrealistic estimate of the true error when assessing matches, as during matches the racket is only swung approximately 35% of the time. Experiment 3 involved a player running at different speeds around a rectangular path on the court. The resultant trajectory, as captured by the software, was compared using different Gaussian smoothing equations of kernel widths 0.25 s, 0.5 s, and 1 s. The best solution (0.5 s) resulted in the most accurate trajectory, although the difference in distance calculated between the different equations was negligible. Experiment 4 used the 0.5-s smoothing equation to assess the tracking accuracy for a player running at a relatively steady speed in a more realistic circular trajectory. The trajectory of the pixel image was shown to have a smaller radius than the reference trajectory at increased speeds, due to the tendency of the player to lean over when negotiating a circular path. The error associated with the distance covered over 1 min was shown to range between 1.33 and 21 m depending on the nature and position of the player's movements. Values, typically somewhere in this range, are likely to be evident during typical use of this software.     

Carbon outclasses wood in racket paddles: Ratings of expert and intermediate tennis players

Abstract

Wooden racket paddles were modified with rubber and carbon fibre laminates and their differences tested in terms of flexural, damping, and coefficient of restitution properties. Four rackets types were designed: a wood reference, wood with rubber, carbon fibre 0°, and carbon fibre 90°. Seven expert and eight intermediate tennis players tested the rackets. To determine which of the four rackets suited the players best, we asked the players to compare the rackets two by two. After each pair tested, participants had to fill out a 4-item questionnaire in which different aspects of the rackets' performance were judged. The most preferred racket was the 0° carbon fibre racket, followed by the 90° carbon fibre racket, the wood racket and, finally, the 1-mm rubber racket. Thus, rackets with the highest stiffness, least damping, and highest coefficient of restitution were the most preferred. Interestingly, although experts and intermediate players overall judged the rackets in very similar ways according to force, vibration, and control, they were sensitive to quite different physical characteristics of the rackets.     

An investigation into the power point in tennis

This paper investigates the nature of the power point in tennis. A series of static racket impacts and a polynomial fit were used to simulate four different racket shots with increasing amounts of angular velocity—identifying the true ‘power point’ for each shot. A rigid body model was used to define the ‘ideal point’ for each shot—the impact point which theoretically yields maximum outbound ball velocity. Comparing theory with experiment revealed that the ‘ideal point’ is most accurate for impacts around the racket’s node point (the rigid body model does not account for frame vibration). Previous research has shown that tennis players aim to strike the node point of the racket. The concept of the ideal point has potential in tuning the weight distribution of a racket to a player’s shot type. If the ‘ideal point’ exists at the racket node point for a player’s typical forehand shot, then outbound ball velocities can be maximised.     

A kinematic comparison between long-line and cross-court top spin forehand in competitive table tennis players

ABSTRACT

The aim of the present study was to compare the biomechanical characteristics of the table tennis top spin shot when played cross-court (CC) or long-line (LL) in competitive table tennis players. Seven national level players respectively completed 10 long-line and 10 cross-court top spin shots responding to a standard ball machine. A stereophotogrammetric system was used to track body segments while executing the motion. Significantly more flexed right knee and elbow angles were measured at the moment of maximum velocity of the racket (MMV) in LL. In addition, significantly greater angles between the feet and the table and between the shoulders and the table at the MMV, indicated more pronounced rotation angles of the lower upper and upper-body in LL compared to CC with respect to the table. A higher inclination of the racket at the MMV was found in LL. The elbow flexion and the racket inclination may be associated to the direction of the shot. The present findings show that kinematic differences exist between the LL and the CC topspin forehand in competitive table tennis players. Coaches should be aware of these differences to adopt the optimal teaching strategies and to reproduce proper joint angles during training.     

A three-dimensional analysis of the contributions of upper limb joint movements to horizontal racket head velocity at ball impact during tennis serving

In this study, we examined the relationship between upper limb joint movements and horizontal racket head velocity to clarify joint movements for developing racket head speed during tennis serving. Sixty-six male tennis players were videotaped at 200 Hz using two high-speed video cameras while hitting high-speed serves. The contributions of each joint rotation to horizontal racket velocity were calculated using vector cross-products between the angular velocity vectors of each joint movement and relative position vectors from each joint to the racket head. Major contributors to horizontal racket head velocity at ball impact were shoulder internal rotation (41.1%) and wrist palmar flexion (31.7%). The contribution of internal rotation showed a significant positive correlation with horizontal racket head velocity at impact (r = 0.490, P < 0.001), while the contribution of palmar flexion showed a significant negative correlation (r = ? 0.431, P < 0.001). The joint movement producing the difference in horizontal racket head velocity between fast and slow servers was shoulder internal rotation, and angular velocity of shoulder internal rotation must be developed to produce a high racket speed.     

The effects of player grip on the dynamic behaviour of a tennis racket

The aim of this article is to characterise the extent to which the dynamic behaviour of a tennis racket is dependent on its mechanical characteristics and the modulation of the player’s grip force. This problem is addressed through steps involving both experiment and modelling. The first step was a free boundary condition modal analysis on five commercial rackets. Operational modal analyses were carried out under “slight”, “medium” and “strong” grip force conditions. Modal frequencies and damping factors were then obtained using a high-resolution method. Results indicated that the dynamic behaviour of a racket is not only determined by its mechanical characteristics, but is also highly dependent on the player’s grip force. Depending on the grip force intensity, the first two bending modes and the first torsional mode frequencies respectively decreased and increased while damping factors increased. The second step considered the design of a phenomenological hand-gripped racket model. This model is fruitful in that it easily predicts the potential variations in a racket’s dynamic behaviour according to the player’s grip force. These results provide a new perspective on the player/racket interaction optimisation by revealing how grip force can drive racket dynamic behaviour, and hence underlining the necessity of taking the player into account in the racket design process.     

Relative Strenuousness of Selected Sports as Performed by Women

Abstract

Women participants in archery, badminton, basketball, bowling, golf, hockey, Softball, tennis, and volleyball were tested to determine the relative strenuousness of these sports. The subjects' heart beats were telemetered during participation in each sport, and estimates of their ventilation and oxygen uptake for each activity were determined from data collected in the laboratory.

Mean heart rates, oxygen uptake and VO₂ per kilogram of body weight were calculated for each subject in each sport. Comparisons were made to determine which activities demanded the greatest energy expenditure.

Heart rates ranging from a mean of 85 beats/min. in bowling to a mean of 185 beats/min. for the roving player in basketball were recorded. The energy expenditure of the roving player in basketball was similar to that of the center halfback in hockey; these two positions required a significantly greater O₂ uptake than the positions tested in all other sports. Play in these positions was classified as heavy activity.

The non-roving positions of forward and guard in basketball, badminton, tennis, Softball (pitcher), and volleyball were rated as moderate activity. Golf, archery, and bowling were categorized as light activity in terms of energy expenditure.     

Effect of the racket mass and the rate of strokes on kinematics and kinetics in the table tennis topspin backhand

The purpose of this study was to investigate the effect of the racket mass and the rate of strokes on the kinematics and kinetics of the trunk and the racket arm in the table tennis topspin backhand. Eight male Division I collegiate table tennis players hit topspin backhands against topspin balls projected at 75 balls · min^?1 and 35 balls · min^?1 using three rackets varying in mass of 153.5, 176 and 201.5 g. A motion capture system was used to obtain trunk and racket arm motion data. The joint torques of the racket arm were determined using inverse dynamics. The racket mass did not significantly affect all the trunk and racket arm kinematics and kinetics examined except for the wrist dorsiflexion torque, which was significantly larger for the large mass racket than for the small mass racket. The racket speed at impact was significantly lower for the high ball frequency than for the low ball frequency. This was probably because pelvis and upper trunk axial rotations tended to be more restricted for the high ball frequency. The result highlights one of the advantages of playing close to the table and making the rally speed fast.     

Movements with greater trunk accelerations and their properties during badminton games

Abstract

This study aimed to elucidate the movements requiring greater trunk accelerations and its frequencies during badminton games, and compare the acceleration components among such movements. Trunk acceleration was measured using a triaxial accelerometer during badminton games. The moments that generated >4 G resultant acceleration were extracted, and movements consistent with the extracted moments were identified. We calculated the extracted movement ratio and frequency and compared the resultant, mediolateral, vertical and anteroposterior accelerations between the top five extracted movements. There were 1,342 movements that generated >4 G [mean, 7.72 (95% confidence interval, 7.31–8.14) cases/min]. The top five movements were lunging during underhand strokes with the dominant hand side leg, landing after overhand strokes on the dominant and non-dominant hand side leg, and cutting from a split step using the dominant and non-dominant hand side leg. Landing on the dominant hand side leg had a greater resultant acceleration than the other movements and had the greatest impact during the badminton game. Lunging during underhand strokes on the dominant hand side leg had greater mediolateral acceleration than the other movements. These results reflected the properties of badminton.