The ability to access and assess technique of world-class athletes in-competition has long eluded sport biomechanists due to the constraints of 3-dimensional marker-based motion capture systems. Encouragingly, the advent of video-based markerless motion analysis offers the opportunity for unobtrusive capture of sporting performances in-competition. This narrative review explores the progression of markerless systems from laboratory-like to in-competition analysis. It first explores the accuracy of markerless motion analysis for joint kinematics in dynamic and sporting movements. Next, its utility in competition is explored with ways to validate these in-competition set-ups. Existing in-competition set-ups offer a viable foundation for skeletal tracking but still requires rigorous validation. Tennis is proposed as an example where the current in-competition infrastructure may support high-fidelity motion analysis. On top of the advanced hardware (i.e. camera configurations) that has been heavily invested in, software optimization methods proposed in computer vision research (i.e. enhancing data processing efficiency, expanding and refining training datasets with anatomically-accurate labelling and sport-specific data, and increasing the quantity and types of keypoints detected), can potentially improve its accuracy for in-competition analysis. Ultimately, a markerless system rigorously validated under real-world constraints can bridge the gap between accessing and assessing world-class sporting performances for sport biomechanics.

This study aimed to assess whether training to increase knee flexion during the tennis serve improves performance and to explore the associated biomechanical changes across the body. Twenty junior tennis players were randomly allocated into control (standard in-season training) and training groups (received training to increase knee flexion during serve). Inertial sensors tracked full body and racket kinematics during five serves performed in pre- and post-training assessments. Racket velocity, impact height, and lower- and upper-body kinematics were compared. Training increased serve knee flexion by 31° (p < 0.001), leading to a 1.38 km/h increase racket velocity (p = 0.036) without affecting impact height (p = 0.331). Additionally, training increased: range of front leg knee extension (MD = 23.46°, p < 0.001) and extension velocity (MD = 54.28°/s, p = 0.008), hip range of motion (front: MD = 53.60°/s, p = 0.003; back: MD = 57.28°/s, p = 0.015), pelvis upward velocity (MD = 0.27 m/s, p < 0.001), and trunk contralateral flexion velocity (MD = 23.18°/s, p = 0.025). No main effects were found for shoulder internal rotation (p = 0.304) and elbow extension (p = 0.214) velocities. No changes were observed in the control group other than a decreased trunk contralateral flexion velocity (MD = -28.98°/s, p = 0.007). Specific training can, therefore, increase serve knee flexion. This study highlights that specific training to increase knee flexion can enhance serve performance by increasing racket velocity, without increasing upper limb joint contribution.

Drive volley is one of the essential backhand stroke technique trends seen in recent women’s tennis competitions. Although movements of the drive volley and groundstroke are similar, activation of the internal muscles vary due to different incoming ball conditions. Most previous studies only focused on the groundstroke, however. The current study investigates the different muscle activation patterns in the upper extremity muscle during the two-handed backhand drive volley as well as the groundstroke for female tennis players. Ten elite female tennis players were measured in the muscle activation of the flexor carpi radialis (FCR), extensor carpi radialis (ECR), biceps brachii (BB), and triceps brachii (TB) from both upper extremities. Racket-head speed at impact, swing duration of each phase, and racket-head average velocity in both strokes were also recorded. Significant differences were found between the drive volley and groundstroke in the velocity profile of racket tip, swing duration of each phase (preparation, early follow-through, and late follow-through), activation patterns of upper extremity muscles, and flexor/ extensor ratios of wrist and elbow in both upper extremities. Different racket trajectory strategies were also observed between the two strokes, with greater horizontal racket velocity recorded in the groundstroke but greater vertical velocity in the drive volley. ECR and TB muscle activation during the drive volley preparation phase was greater than the groundstroke when completing a quicker backswing. In the early acceleration phase, the greater FCR leading arm activation in the drive volley assisted wrist stabilization in preparation for impact. In the late follow-through phase, less TB leading arm activity and higher ECR trailing arm activity in the drive volley showed more forward compression movement in racket contact with the ball. As it is essential for the drive volley to complete a quicker backswing and to increase shot efficiency at the end of the forward movement, coaches should consider the two strokes’ muscle activation and technique differences to enhance specific techniques and fitness training programs.

Background: There is a range of magneto-inertial measurement unit (MIMU) systems commercially available, however sensor specifications and fusion methods vary considerably between manufacturers. Such variability can influence the concurrent validity of MIMUs relative to reference standard measurement devices. Different MIMUs have been compared during static or low-velocity conditions, with higher-velocity movements assessed in robotic-based studies. However, there is a need for the concurrent validity of higher-velocity movements to be established in human-based studies. Research question: This study aimed to assess the concurrent validity of two commercial MIMU systems (Noraxon and Xsens), relative to a 'gold-standard' retro-reflective motion capture system, when measuring trunk angles during uni-planar range of motion (ROM) and cricket bowling, which involves high-speed, multi-planar movements. Methods: For this criterion-based validity study, both MIMU systems incorporated comparable sensor specificaotions and employed Kalman filter sensor fusion algorithms. The MIMU based angles were compared with angles derived from concurrently captured three-dimensional retro-reflective data for 10 fast-medium bowlers. Statisotical parametric mapping and root mean squared differences (RMSD) were computed for both MIMU systems. Results: One-dimensional statistical parametric mapping showed no significant differences for angles from both MIMU systems when compared with retro-reflective based angle outputs. The MIMU systems produced ROM RMSDs between 1.4 +/- 1.0. and 2.6 +/- 1.5.. One system displayed RMSDs between 4.6 +/- 1.4. and 7.4 +/- 1.9. during bowling, indicating functionally relevant differences to retro-reflective derived angles. There were some small but statistically significant differences in RMSDs between the MIMU systems. Significance: MIMU-based angle accuracy is poorer during high-speed, multi-planar movement than uni-planar tasks. Comparable MIMU systems can produce varying measurements during ROM and bowling tasks. It is likely that varying sample rates and sensor fusion algorithm parameters contributed to the differences.

Magneto-inertial measurement unit (MIMU) systems allow calculation of simple sensor-to-sensor Euler angles, though this process does not address sensor-to-segment alignment, which is important for deriving meaningful MIMU-based kinematics. Functional sensor-to-segment calibrations have improved concurrent validity for elbow and knee angle measurements but have not yet been comprehensively investigated for trunk or sport-specific movements. This study aimed to determine the influence of MIMU functional calibration on thorax and lumbar joint angles during uni-planar and multi-planar, sport-specific tasks. It was hypothesised that functionally calibrating segment axes prior to angle decomposition would produce smaller differences than a non-functional method when both approaches were compared with concurrently collected 3D retro-reflective derived angles. Movements of 10 fast-medium cricket bowlers were simultaneously recorded by MIMUs and retro-reflective motion capture. Joint angles derived from four different segment definitions were compared, with three incorporating functionally defined axes. Statistical parametric mapping and root mean squared differences (RMSD) quantified measurement differences one-dimensionally and zero-dimensionally, respectively. Statistical parametric mapping found no significant differences between MIMU and retro-reflective data for any method across bowling and uni-planar trunk movements. The RMSDs for the functionally calibrated methods and non-functional method were not significantly different. Functional segment calibration may be unnecessary for MIMU-based measurement of thorax and lumbar joint angles.

Delivering a cricket ball with a wrist-spin (WS) bowling technique is considered one of the game's most difficult skills. Limited biomechanical information exists for WS bowlers across skill levels. The purpose of this study was to compare biomechanical, isokinetic strength and anthropometric measures between elite (12) and pathway bowlers (eight). Data were collected using a motion analysis system, dynamometer and a level-two anthropometrist. A regression analysis identified that performance was best explained by increased wrist radial deviation torque and longitudinal axis rotational moments at the shoulder and wrist. From back foot impact (BFI) to ball release (BR), elite bowlers rotated their trunks less, experienced less trunk deceleration resulting in a more front-on position and increased pelvis rotation angular velocity. They also displayed an increased shoulder internal rotation moment as the upper arm moved from external into internal rotation and was a major contributor in the subsequent differences observed in the distal segments of the bowling limb. Anthropometric differences were observed at the wrist and finger joints and may be used to form the basis for talent identification programmes. This study highlights the important contribution to bowling performance of the musculature responsible for producing long axis rotations of the bowling limb.

This study aimed to develop a 2-dimensional (2D) video screening tool capable of predicting an athlete's peak 3-dimensional (3D) knee moments during unplanned sidestepping. 2D video-based kinematic measures were simultaneously captured with 3D peak knee moments for 30 female field hockey players (15 junior, 15 senior). Intra- and intertester repeatability of 2D kinematic measures was performed. Then, linear regression models were used to model 3D knee moments from 2D kinematic variables utilizing 80% of the sample (n=24). Regression equations were then validated on the remaining 20% of the sample (n=6). Angular 2D measures had good-excellent intra- (ICC=0.936-0.998) and intertester (ICC=0.662-0.949) reliability. Displacement measures had poor-excellent intra- (ICC=0.377-0.539) and inter-tester (ICC=0.219-0.869) reliability. Significant independent predictors of peak knee moments were dynamic knee valgus, knee flexion angle at foot strike, trunk flexion range of motion (ROM), trunk lateral flexion, hip abduction and knee flexion ROM (P<0.05). Regression equations generated from these models effectively predicted peak knee extension, valgus and internal rotation moments (i. e., were not different from measured values P>0.05, ES<0.4) in the 20% subsample. 2D video-based measurements of an athlete's full body kinematics during unplanned sidestepping provide a reliable, specific, sensitive and cost-effective means for screening female team sport athletes.

ABSTRACT Purpose Anterior cruciate ligament (ACL) injury prevention programs have been shown to have mixed success in reducing injury rates, raising the question whether these programs are effectively targeting biomechanical mechanisms of injury. The current study examined the efficacy of a biomechanically informed ACL injury prevention training program in reducing injury risk and injury incidence and investigated its effect on athletic performance. Participants Twenty-six elite female field hockey players participated in this study. Methods Athletes participated in a 2-yr injury prevention training program. Injury incidence (i.e., lower limb and ACL) and athletic performance (i.e., strength, speed, and aerobic power) were measured during a control season and after two intervention seasons. Biomechanical ACL injury risk factors were recorded during unplanned sidestepping at baseline and after intensive (9 wk: 4 × 20 min·wk −1 ) and maintenance (16 wk: 3 × 10 min·wk −1 ) training phases for a subset of athletes ( n = 17). Results Training was effective in reducing ACL and lower limb injury incidence after the 2-yr program, where zero ACL injuries occurred after implementation (vs 0.4 per 1000 player hours in the control year). High-risk athletes reduced their peak knee valgus moments by 30% ( P = 0.045) and demonstrated improvements in desirable muscle activation strategies after intensive training. The majority of benefits elicited in intensive training were retained during the maintenance phase. One-repetition max strength, beep test scores, and sprint times improved or were maintained over the 2-yr intervention period. Conclusions Biomechanically informed injury prevention training was successful in reducing both biomechanical ACL injury risk factors and ACL injury incidence while maintaining and/or improving athletic performance. It is important to consider the biomechanical mechanisms of injury when designing injury prevention programs.

The purpose of this study was to compare performance variables and upper body kinematics between cohorts of pathway (illegal and legal action) and elite level (legal) finger-spin (FS) bowlers. Results indicated that pathway illegal bowlers created significantly more ball angular velocity compared with bowlers of the same level, reaching levels of elite level bowlers. These differences are driven by various upper body kinematic differences at the trunk, elbow and wrist. This research highlights that when bowling with an illegal action, a possible performance benefit exists, reinforcing the current illegal action laws (this rule of the sport does matter).

With advances in technology, scientists are now able to more accurately measure elbow displacement changes during the cricket bowling action. This has led to the realization that the majority of bowlers undergo some degree of elbow extension during the forward swing phase of bowling. Consequently, the International Cricket Council were obliged to revise the once zero tolerance for elbow extension threshold to a 15° range. However, it is still not understood if bowling with >15° of elbow extension aids performance or alters other kinematic movements. The purpose of this study was to compare performance and technique measures between legal and illegal finger‐spin bowlers. Data were collected from 48 pathway and elite bowlers using a 22‐camera motion analysis system. Results indicated that the ball velocity and revolutions at ball release of pathway bowlers with illegal actions showed no significant difference and were similar to elite legal bowlers. Technique differences were also identified, with illegal bowlers being more front‐on, forcing a reliance on increased elbow flexion and supination to impart effective ball kinematics at ball release. The performance benefit of greater ball velocity and revolutions is obtained when finger‐spin bowlers deliver the ball with more than the allowable 15° of elbow extension, thus reinforcing the validity of the current bowling laws. To counteract bowling with an illegal action, it is recommended that a more side‐on technique at back foot impact and rotating the trunk through to the point of ball release will assist bowlers in reducing undesirable elbow extension levels.

This study investigates the inter-tester repeatability of an upper limb direct kinematic (ULDK) model specifically for the reporting of elbow flexion-extension (FE) during overhead sporting movements, such as cricket bowling. The ULDK model consists of an upper arm and a forearm connected with a 6° of freedom elbow joint. The ULDK model was assessed for inter-tester repeatability by calculating elbow FE during cricket bowling in two sessions, with unique testers applying the kinematic marker set in each session. Analysis of both elbow FE time-varying waveforms (statistical parametric mapping = 0% time different) and extracted discrete events (no statistical differences, strong correlations > 0.9) support that this model is inter-tester repeatable at assessing elbow FE within the context of cricket bowling. This model is recommended as a framework in future studies for measuring elbow kinematics during other overhead sporting tasks, with recommendations for further participant-specific considerations.

Magnetic and inertial measurement units (MIMUs) may provide an accessible, three-dimensional, in-field alternative to laboratory-restricted marker-based motion capture. Existing upper limb MIMU models have predominantly been validated with low-velocity motion and their suitability for use with sport-based movements remains relatively untested. We propose a MIMU system approach to enable the estimation of anatomically meaningful and participant-specific elbow kinematics with considerations for use with cricket bowling. A novel standardised elbow reference posture of 90 degrees flexion and 0 deg pronation, and functional definition of elbow joint axes of rotation calibrated the MIMU method model before it was validated across three experiments: (1) simple elbow rotations with a mechanical linkage; (2) low-velocity elbow rotations in human participants; and (3) low-medium velocity sport-based movements in human participants. The proposed MIMU method demonstrated high elbow kinematic measurement agreement when compared with a criterion measure across all three conditions. However, during experiment 3, sensor components neared their measurement capacity and the MIMU method elbow flexion measurement variability increased. We conclude that the proposed MIMU method can estimate anatomically referenced, participant-specific joint angles, however, the hardware specifications of currently available systems may limit application in high-velocity/acceleration situations, preventing the measurement of cricket bowling in-field for now.

Identifying lumbar injury risk amongst cricket bowlers is a challenge to those involved in the sport. Bowling technique injury risk factors concerning thoracic and pelvic motion have been identified by previous research that used three-dimensional (3D) retroreflective (RR) motion analysis. Inertial measurement units (IMUs) are considered a feasible and more portable means of 3D motion analysis. However, the validity of IMU measurement of thorax and pelvis movement during bowling has not yet been fully determined. This study aimed to achieve this by comparing concurrent IMU and RR angle outputs. Results suggest that when RR coordinate systems are aligned with the IMUs’ there are no significant differences in cricket bowling relevant angle outputs. However, some differences arise when IMUs are compared to the anatomically derived RR angle outputs typically used in 3D analysis.

The purpose of this study was to assess the sensitivity of wrist joint velocity to manipulations of knee joint flexion–extension kinematic waveforms through the use of a forward kinematic approach. The bowling kinematics of twelve male cricket pace bowlers were entered into a forward kinematic model using MATLAB software. Participants‘ knee joint flexion-extension kinematics were manipulated in two ways: 1) offset by ± 20° and 2) amplified by a factor of ± 2. Both manipulations led to increases in resultant wrist joint velocity at the time of ball release. An offset of 20° extension increased wrist joint velocity by 5.6% whereas an amplification factor of 2 increased wrist joint velocity by 29.9%. These results support the notion that a flexor-extender knee joint technique is ideal for cricket pace bowlers.

Spin bowling plays a fundamental role within the game of cricket yet little is known about the initial ball kinematics in elite and pathway spin bowlers or their relationship to performance. Therefore, the purpose of this study was to record three-dimensional ball kinematics in a large and truly high level cohort of elite and pathway finger-spin (FS) and wrist-spin (WS) bowlers, identifying potential performance measures that can be subsequently used in future research. A 22-camera Vicon motion analysis system captured retro-reflective markers placed on the seam (static) and ball (dynamic) to quantify ball kinematics in 36 FS (12 elite and 24 pathway) and 20 WS (eight elite and 12 pathway) bowlers. Results indicated that FS bowlers delivered the ball with an increased axis of rotation elevation, while wrist-spin bowlers placed greater amounts of revolutions on the ball. It also highlighted that ball release (BR) velocity, revolutions and velocity/revolution index scores for both groups and seam stability for FS bowlers, and seam azimuth angle and spin axis elevation angle for WS bowlers, were discriminators of playing level. As such these variables could be used as indicators of performance (i.e. performance measures) in future research.

Background: Lumbar spine injury is a multi-factorial problem involving workload management, technique, musculoskeletal factors, growth and development. From a biomechanical view increased magnitudes of spinal axial torsion, lateral flexion and loading have been associated with stress injuries to the lumbar spine. The “crunch factor” – the instantaneous product of lateral flexion and axial rotational velocity – is an intuitive aetiology for lumbar spine injury across sports such as golf, tennis, javelin and cricket. The aim of this study was to assess the “crunch factor” in relation to the incidence of lumbar spine injuries in a cohort of cricket fast bowlers, a population well known to suffer lumbar spine injuries.

Background Exercise-based training programmes are commonly used to prevent sports injuries but programme effectiveness within community men's team sport is largely unknown. Objective To present the intention-to-treat analysis of injury outcomes from a clustered randomised controlled trial in community Australian football. Methods Players from 18 male, non-elite, community Australian football clubs across two states were randomly allocated to either a neuromuscular control (NMC) (intervention n=679 players) or standard-practice (control n=885 players) exercise training programme delivered as part of regular team training sessions (2× weekly for 8-week preseason and 18-week regular-season). All game-related injuries and hours of game participation were recorded. Generalised estimating equations, adjusted for clustering (club unit), were used to compute injury incidence rates (IIRs) for all injuries, lower limb injuries (LLIs) and knee injuries sustained during games. The IIRs were compared across groups with cluster-adjusted Injury Rate Ratios (IRRs). Results Overall, 773 game injuries were recorded. The lower limb was the most frequent body region injured, accounting for 50% of injuries overall, 96 (12%) of which were knee injuries. The NMC players had a reduced LLI rate compared with control players (IRR: 0.78 (95% CI 0.56 to 1.08), p=0.14.) The knee IIR was also reduced for NMC compared with control players (IRR: 0.50 (95% CI 0.24 to 1.05), p=0.07). Conclusions These intention-to-treat results indicate that positive outcomes can be achieved from targeted training programmes for reducing knee and LLI injury rates in men's community sport. While not statistically significant, reducing the knee injury rate by 50% and the LLI rate by 22% is still a clinically important outcome. Further injury reductions could be achieved with improved training attendance and participation in the programme.