Automated Service Height Fault Detection Using Computer Vision and Machine Learning for Badminton Matches.

In badminton, accurate service height detection is critical for ensuring fairness. We developed an automated service fault detection system that employed computer vision and machine learning, specifically utilizing the YOLOv5 object detection model. Comprising two cameras and a workstation, our system identifies elements, such as shuttlecocks, rackets, players, and players' shoes. We developed an algorithm that can pinpoint the shuttlecock hitting event to capture its height information. To assess the accuracy of the new system, we benchmarked the results against a high sample-rate motion capture system and conducted a comparative analysis with eight human judges that used a fixed height service tool in a backhand low service situation. Our findings revealed a substantial enhancement in accuracy compared with human judgement; the system outperformed human judges by 3.5 times, achieving a 58% accuracy rate for detecting service heights between 1.150 and 1.155 m, as opposed to a 16% accuracy rate for humans. The system we have developed offers a highly reliable solution, substantially enhancing the consistency and accuracy of service judgement calls in badminton matches and ensuring fairness in the sport. The system's development signifies a meaningful step towards leveraging technology for precision and integrity in sports officiation.

Inter-Unit Consistency and Validity of 10-Hz GNSS Units in Straight-Line Sprint Running.

The present study aimed to investigate the inter-unit consistency and validity of multiple 10-Hz Catapult Global Navigation Satellite System (GNSS) units in measuring straight-line sprint distances and speeds. A total of 13 participants performed one 45.72-m linear sprint at maximum effort while wearing all eight GNSS units at once. Total run distance and peak speed recorded using GNSS units during the sprint duration were extracted for analysis. Sprint time and peak speed were also obtained from video recordings as reference values. Inter-unit consistency was assessed using intraclass correlation coefficients (ICC) and standard errors of measurements (SEM). For a validity test, one-sample t-tests were performed to compare each GNSS unit's distance with the known distance. Additionally, Wilcoxon signed-rank tests were performed to compare each unit's peak speed with the reference peak speed measured using video analysis. Results showed poor inter-unit consistency for both distance (ICC = 0.131; SEM = 8.8 m) and speed (ICC = 0.323; SEM 1.3 m/s) measurements. For validity, most units recorded a total distance (44.50 m to 52.69 m) greater than the known distance of 45.72 m and a lower peak speed (7.25 (0.51) m/s) than the video-based reference values (7.78 (0.90) m/s). The present findings demonstrate that there exist variations in distance and speed measurements among different units of the same GNSS system during straight-line sprint running. Practitioners should be aware of the window of errors associated with GNSS measurements and interpret the results with caution. When making comparisons over a season, players should wear the same unit every time if logistically possible.

Measuring Upper Limb Kinematics of Forehand and Backhand Topspin Drives with IMU Sensors in Wheelchair and Able-Bodied Table Tennis Players.

To better understand the biomechanics of para-table tennis players, this study compared the shoulder, elbow, and wrist joint kinematics among able-bodied (AB) and wheelchair players in different classifications. Nineteen participants (AB, n = 9; classification 1 (C1), n = 3; C2, n = 3; C3, n = 4) executed 10 forehand and backhand topspin drives. Shoulder abduction/adduction, elbow flexion/extension, wrist extension/flexion, respective range of motion (ROM), and joint patterns were obtained using inertial measurement unit (IMU) sensors. The results showed clear differences in upper limb kinematics between the able-bodied and wheelchair players, especially in the elbow and wrist. For the para-players, noticeable variations in techniques were also observed among the different disability classes. In conclusion, wheelchair players likely adopted distinct movement strategies compared to AB to compensate for their physical impairments and functional limitations. Hence, traditional table tennis programs targeting skills and techniques for able-bodied players are unsuitable for para-players. Future work can investigate how best to customize training programs and to optimize movement strategies for para-players with varied types and degrees of impairment.

Application of Instrumented Paddles in Measuring On-Water Kinetics of Front and Back Paddlers in K2 Sprint Kayaking Crews of Various Ability Levels.

This study used instrumented paddles to obtain on-water kinetic variables of two-seater (K2) crews during sprint kayaking. A total of 74 male kayakers of various ability levels (national team: 9, recreational club: 38, school team: 27) comprising 39 K2 crews were recruited. Both the front and back paddlers were provided with an instrumented paddle to perform 200-m maximal effort paddling in a reservoir. Force, power, and temporal variables were extracted from the paddle data. Difference among groups were compared using a factorial Analysis of Variance. Results showed that the force, power, and temporal characteristics of the front and back paddlers were similar during maximal effort sprint kayaking. Proficient kayakers produced greater kinetic outputs than less proficient kayakers, while the coordination strategy based on timing differences at key events between the two crew members in a K2 boat was similar across ability levels. These data can be useful for coaches, sport scientists, and athletes in planning and monitoring the training.

Adaptive Regulation in a Stable Performance Environment: Trial-To-Trial Consistency in Cue Sports Performance.

This study aimed to investigate individual trial-to-trial performance in three tests to define adaptive regulation as a key feature of expertise in nine-ball. Thirty-one male players were assigned into the low-skilled (n = 11), intermediate (n = 10), or high-skilled groups (n = 10). The power control, cue alignment, and angle tests were selected to assess participants' ability to control the power applied in shots, strike the ball straight, and understand the ball paths, respectively. Error distance and correction of error distance were identified for each shot using 2D video analysis. Results of one-way analysis of variance showed that the high-skilled group performed better in two out of the three tests than the other two groups (p = .010 for the cue alignment test; p = .002 for the angle test). However, the adaptation effect represented by the decreased error distances across trials was not observed. Pearson correlation revealed only a few significant correlations between the error distance and its correction within each participant in all tests (p < .05), and hence, the hypothesis that "low correction happened after small error and vice versa" is not supported.

Computer simulation on the cueing movements in cue sports: a validation study.

Background: Simulation models have been applied to analyze daily living activities and some sports movements. However, it is unknown whether the current upper extremity musculoskeletal models can be utilized for investigating cue sports movements to generate corresponding kinematic and muscle activation profiles. This study aimed to test the feasibility of applying simulation models to investigate cue sports players' cueing movements with OpenSim. Preliminary muscle forces would be calculated once the model is validated. Methods: A previously customized and validated unimanual upper extremity musculoskeletal model with six degrees of freedom at the scapula, shoulder, elbow, and wrist, as well as muscles was used in this study. Two types of cueing movements were simulated: (1) the back spin shot, and (2) 9-ball break shot. Firstly, kinematic data of the upper extremity joints were collected with a 3D motion capture system. Using the experimental marker trajectories of the back spin shot on 10 male cue sports players, the simulation on the cueing movements was executed. The model was then validated by comparing the model-generated joint angles against the experimental results using statistical parametric mapping (SPM1D) to examine the entire angle-time waveform as well as t-tests to compare the discrete variables (e.g., joint range of motion). Secondly, simulation of the break shot was run with the experimental marker trajectories and electromyographic (EMG) data of two male cue sports players as the model inputs. A model-estimated muscle activation calculation was performed accordingly for the upper extremity muscles. Results: The OpenSim-generated joint angles for the back spin shot corresponded well with the experimental results for the elbow, while the model outputs of the shoulder deviated from the experimental data. The discrepancy in shoulder joint angles could be due to the insufficient kinematic inputs for the shoulder joint. In the break shot simulation, the preliminary findings suggested that great shoulder muscle forces could primarily contribute to the forward swing in a break shot. This suggests that strengthening the shoulder muscles may be a viable strategy to improve the break shot performance. Conclusion: It is feasible to cater simulation modeling in OpenSim for biomechanical investigations of the upper extremity movements in cue sports. Model outputs can help better understand the contributions of individual muscle forces when performing cueing movements.

Crossover gait in running and measuring foot inversion angle at initial foot strike: a front-view video analysis approach.

Introduction: Foot inversion angle at initial foot strike is associated with various running-related injuries. Traditionally, video analysis of foot inversion angle has been accomplished by positioning a camera to record from the back view, but complications arise when a crossover gait obscures the area of measurement. This study aims to investigate the viability of measuring foot inversion angles at initial foot strike of running from the front view as an alternative to using the back view in 2D video analysis. Methods: Forty-four healthy runners (20 females, 24 males) ran at their self-selected speeds on a treadmill with their gait recorded from front and back camera views. Foot inversion angles at initial foot strike were analyzed using Kinovea. A 2 × 2 (Camera × Foot) ANOVA with repeated measures was performed on the foot inversion angle data. Subsequently, correlation and linear regression were performed to determine the relationship between the back and front-view measurements. Results: Thirteen runners (29.5%) displayed crossover gait within 18 gait cycles. ANOVA revealed a significant main effect on Camera (p < .001) only, where foot inversion angle was greater from the front camera view. Correlation analysis showed a significant positive correlation between the front and back camera views (r = 0.388, p < .001). Regression analyses yielded an equation, y = 0.42 + 0.53 x, where y and x were the foot inversion angle measured from the back and front camera views, respectively. Discussion: With a linear regression conversion equation, front-view foot inversion angles at initial foot strike can be used to determine rearfoot inversion angles when crossover gait obstructs the back camera view.

Influence of expertise level on techniques of applying top and back spins in cue sports.

This study compared the kinematics of upper body and cue stick among players of various skill levels when performing back spin and top spin shots. Twenty-eight male cue sports players were assigned to the novice (n = 10), intermediate (n = 9), or skilled groups (n = 9). The back spin and top spin tests were administrated while kinematic data were recorded using a 3D motion capture system. The results revealed greater upper limb joint ranges of motions (all p < 0.05), maximum angular velocities (all p < 0.05), and cue tip speed in the back spin than top spin shots (p < 0.001). None of joint kinematic or shot performance variables investigated was significantly different among the three skill levels (all p > 0.05). For the head movement, the novice group exhibited greater anteroposterior displacement than the skilled group (p = 0.020). In conclusion, except for the head movement, the upper body and cue stick kinematics did not significantly differ among players with varied skill levels. Greater joint ranges of motions and angular velocities were required to generate a faster cue tip speed for the back spin shots when compared with the top spin shots.

Functional versus conventional strength and conditioning programs for back injury prevention in emergency responders.

Back pain and back-related injuries are common complaints among emergency responders. The purpose of this study was to compare the effectiveness of two strength and conditioning programs in improving back muscle characteristics and disabilities in emergency responders (firefighters/paramedics). Participants (n = 24) were randomized into two groups to complete 16 weeks of supervised exercise intervention: 1) Functional training used unilateral movements that mimicked the asymmetrical nature of emergency operations, 2) Conventional training performed bilaterally loaded exercises. Outcome measures were maximum isometric back extension strength, passive muscle stiffness, lumbar extensor fatigability, and revised Oswestry Low Back Pain Questionnaire. A mixed model Analysis of Variance with repeated measures was performed to compare the difference over time and between groups. While the training effects were similar between groups, both programs improved isometric back extension strength (+21.3% functional, +20.3% conventional, p < 0.001, ηp 2 = 0.625) and lumbar extensor muscle fatigability (+17.4% functional, +9.5% conventional, p = 0.009, ηp 2 = 0.191). Bilateral symmetry in muscle stiffness was improved as indicated by reduction in symmetry index (-7.1% functional, -11.8% conventional, p = 0.027, ηp 2 = 0.151). All self-reported pain and disability scores fell within the category of "minimum functional limitation" throughout the intervention and 6-month follow-up periods. For frontline firefighters and paramedics, both functional and conventional strength training are effective for improving back muscle characteristics.

Development of new 9-ball test protocols for assessing expertise in cue sports.

BACKGROUND: This study aimed to develop new test protocols for evaluating 9-ball expertise levels in cue sports players. METHODS: Thirty-one male 9-ball players at different playing levels were recruited (recreational group, n = 8; university team, n = 15; national team, n = 8). A 15-ball test was administered to indicate overall performance by counting the number of balls potted. Five skill tests (power control, cue alignment, angle, back spin, and top spin) were conducted to evaluate specific techniques by calculating error distances from pre-set targets using 2D video analysis. RESULTS: Intra-class correlation analyses revealed excellent intra-rater and inter-rater reliability in four out of five skill tests (ICC > 0.95). Significant between-group differences were found in 15-ball test performance (p <  0.001) and absolute error distances in the angle (p <  0.001), back spin (p = 0.006), and top spin tests (p = 0.045), with the recreational group performing worst while the national team performing best. Greater inter-trial variability was observed in recreational players than the more skilled players (p <  0.005). CONCLUSIONS: In conclusion, the 9-ball test protocols were reliable and could successfully discriminate between different playing levels. Coaches and researchers may employ these protocols to identify errors, monitor training, and rank players.

Can a Good Break Shot Determine the Game Outcome in 9-Ball?

This study aimed to quantify the break shot characteristics and identify their significance in predicting the game outcomes in 9-ball tournaments. The break shots of 275 frames (241 men's, 34 women's) of professional tournaments were analyzed from two aspects: (1) cue ball position, represented by the distance between the cue ball and the table center, and (2) ball distribution, indicated by the standard deviation of Voronoi cell areas determined from all remaining balls on the table. Spearman correlation and binary logistic regression were utilized to identify associations and to predict the frame outcomes, respectively. Results showed that the more balls falling into the pockets during the break, the more clustered the remaining balls (r s = 0.232, p < 0.001). The closer the cue ball ending toward the table center, the more balls potted in the visit immediately after the break (r s = -0.144, p = 0.027). Neither cue ball position nor ball distribution could predict table clearance or winning of a frame. In conclusion, pocketing more balls during the break is associated with more clustered balls remaining on the table. Parking the cue ball near the table center after the break can facilitate potting more balls immediately after.

Air pistol shooting: upper limb muscle activation between training and simulated competition.

Heightened stress during air pistol competitions may impair shooters' abilities to maintain gun stability, resulting in inferior performance. This study aimed to compare the pre-trigger muscle activation levels of upper muscles in 10-m air pistol shooters between training and simulated competition conditions. Seven sub-elite shooters from the Singapore National Youth Air Pistol Team shot 30 shots in a training versus simulated competition condition in randomised orders on separate days. Muscle activation for the forearm and shoulder muscles, namely extensor carpi radialis, flexor carpi ulnaris, anterior deltoid, and posterior deltoid, were recorded using electromyography (EMG). Shooting performance was evaluated by total shot scores. Stress level was monitored via heart rate and the Mental Readiness Form-3. No statistically significant differences were found in EMG, performance, or stress-related variables between conditions, although moderate-to-large effect sizes were observed in some muscle activation and self-reported stress indicators. Analysis of individual performances using smallest worthwhile change showed that two participants improved under the simulated competition condition, while two declined, and three remained unaffected. In conclusion, sub-elite youth air pistol shooters were able to exhibit good neuromuscular control under high anxiety situations and thus their performance was largely unaffected.

A Clinician-Free Method Using Top-View Photography for Screening and Monitoring Hallux Valgus.

BACKGROUND: Hallux valgus is a progressive foot deformity that commonly affects middle-aged women. The aim of this study was to develop a novel method using only top-view photographs to assess hallux valgus severity. METHODS: A top-view digital photograph was taken of each foot of 70 female participants. Two straight lines were drawn along the medial edge of the great toe and forefoot, and the included angle (termed bunion angle) was measured using a free software program. Each foot was also assessed by a clinician using the Manchester scale as no (grade 1), mild (grade 2), moderate (grade 3), or severe (grade 4) deformity. RESULTS: The mean bunion angles of the 140 feet were 6.7°, 13.5°, and 16.2° for Manchester grades 1, 2, and 3, respectively (no foot was in grade 4). The reliability was excellent for both intrarater (intraclass correlation coefficient [ICC] = 0.93-0.95) and interrater (ICC = 0.90) assessments. Receiver operating characteristic curves determined the optimal bunion angle cutoff value for screening hallux valgus to be 9°, which gives 89.2% sensitivity and 74.2% specificity. CONCLUSIONS: The bunion angle is a reliable, clinician-free method that can potentially be integrated into a smartphone app for easy and inexpensive self-assessment of hallux valgus.

The Role of Vision in Maintaining Stroke Synchronization in K2 Crew-Boat Kayaking.

This study investigated the role of vision in maintaining stroke synchronization in crew-boat sprint kayaking. Sixteen sprint kayakers from a national team were paired into eight two-seater (K2) crews. Each crew paddled at high intensity with the back paddler's eyes open or closed in a randomized order. Using video analysis, stroke synchronization was quantified by the timing offsets between the front and back paddlers at four key positions of the stroke. All crews could paddle continuously without capsize or stopping under both visual conditions. In the absence of vision, neither 200-m performance time (p = 0.23, d = 0.47, small effect size) nor stroke rate (p = 0.41, d = 0.31, small effect size) was severely affected. There were no significant effects of vision on stroke synchronization offsets between the front and back paddlers across all key positions (all p > 0.05). Highly skilled paddlers likely relied on the kinesthetic perception to maintain the boat synchronization when visual information was not available.

Effects of the imperfect interface and piezoelectric/piezomagnetic stiffening on the SH wave in a multiferroic composite.

Studied in the present work is the propagation of SH wave in a cylindrically multiferroic composite consisting of a piezoelectric layer and a piezomagnetic central cylinder. It is assumed that the interface in the composite is damaged mechanically, magnetically or electrically. The dispersion relations of SH wave are obtained for two kinds of electric-magnetic boundary conditions at the free surface, and then the phase velocity is calculated numerically. Parametric studies on the phase velocity yield three main conclusions. (a) The mechanical imperfection may remarkably reduce the phase velocity, depending on the combination of the values of the wavenumber and the thickness ratio. (b) The magneto-electrical imperfection has no obvious effect on the phase velocity in any cases. (c) The piezoelectric and piezomagnetic stiffening can increase the phase velocity.