3D Motion Capture Research Articles

Protocol to record and analyze primate leaping in three dimensions in the wild.

Several studies comparing primate locomotion under lab versus field conditions have shown the importance of implementing both types of studies, as each has their advantages and disadvantages. However, three-dimensional (3D) motion capture of primates has been challenging under natural conditions. In this study, we provide a detailed protocol on how to collect 3D biomechanical data on primate leaping in their natural habitat that can be widely implemented. To record primate locomotion in the dense forest we use modified GoPro Hero Black cameras with zoom lenses that can easily be carried around and set up on tripods. We outline details on how to obtain camera calibrations at greater heights and how to process the collected data using the MATLAB camera calibration app and the motion tracking software DLTdv8a. We further developed a new MATLAB application "WildLeap3D" to generate biomechanical performance metrics from the derived x, y, z coordinates of the leaps. We provide details on how to collect data on support diameter, compliance, and orientation, and combine these with the jumps to study locomotor performance in an ecological context. We successfully reconstructed leaps of wild primates in the 3D space under natural conditions and provided data on four representative leaps. We provide exemplar data on primate velocity and acceleration during a leap and show how our protocol can be used to analyze segmental kinematics. This study will help to make motion capture of freely moving animals more accessible and help further our knowledge about animal locomotion and movement.

Biomechanical Motion Changes in Adjacent and Noncontiguous Segments Following Single-Level Anterior Cervical Discectomy and Fusion: A Computed Tomography-Based 3D Motion Capture Study.

Anterior cervical discectomy and fusion (ACDF) is known to elicit adverse biomechanical effects on immediately adjacent segments; however, its impact on the kinematics of the remaining nonadjacent cervical levels has not been understood. This study aimed to explore the biomechanical impact of ACDF on kinematics beyond the immediate fusion site. We hypothesized that compensatory motion following single-level ACDF is not predictably distributed to adjacent segments due to compensation from noncontiguous levels. Six fresh-frozen cervical spines (C2-T1) underwent fluoroscopic screening and sagittal and coronal reformats from computed tomography scans and were utilized to grade segmental degeneration. Each specimen was tested to 30° of flexion and extension intact and following single-level ACDF at the C5-C6 level. The motions of each vertebral body were tracked using 3-dimensional (3D) motion capture into an inverse kinematics model, facilitating correlations between the 3D reconstruction from computed tomography images and the 3D motion capture data. This model was used to calculate each level's flexion/extension range of motion (ROM). Single-level fusion at the C5-C6 level across all specimens resulted in a significant motion reduction of -6.8° (P = 0.002). No significant change in ROM occurred in the immediate adjacent segments C4-C5 (P = 0.07) or C6-C7 (P = 0.15). Hypermobility was observed in 2 specimens (33%) exclusively in adjacent segments. In contrast, the other 4 spines (66%) displayed hypermobility at noncontiguous segments. Hypermobility occurred in 42% (5/12) of the adjacent segments, 28% (5/18) of the noncontiguous segments, and 50% (3/6) of the cervicothoracic segments. Single-level ACDF impacts ROM beyond adjacent segments, extending to noncontiguous levels. Compensatory motion, not limited to adjacent levels, may be influenced by degenerative changes in noncontiguous segments. Surprisingly, hypermobility may not occur in adjacent segments after ACDF. Overall, the multifaceted biomechanical effects of ACDF underscore the need for a comprehensive understanding of cervical spine dynamics beyond immediate adjacency, and it needs to be taken into consideration when planning single-level ACDF.

Running biomechanical and isokinetic strength differences in masters runners with and without Achilles tendinopathy

ABSTRACT Masters runners are an increasing proportion of the running community. The most significant musculoskeletal changes in runners occur after the age of 50 in addition to changes in injury rates and types, the most common being Achilles tendinopathy (AT). Previous evidence has suggested similarities between risk factors for AT and age-related changes that are focused at the hip and the ankle during the propulsive stage of running. The purpose of this study was to investigate biomechanical and peak torque association to AT in masters runners. Thirty-two masters runners over age 50 with AT (60.31 ± 8.37, n = 16) and without (59.94 ± 4.95 n = 16) were included. 3D motion capture and force plates were used to assess running biomechanics. A motor-driven dynamometer was used to assess isokinetic peak torque production. No significant differences in running biomechanics were found between masters runners with and without AT. Hip peak isokinetic torque production was found to be significantly less in masters runners with AT, but no significant differences in ankle plantarflexion peak isokinetic torque production were found. Masters runners with AT may be able to adapt their running biomechanics and muscular torque production during submaximal running efforts.

Automating Video-Based Two-Dimensional Motion Analysis in Sport? Implications for Gait Event Detection, Pose Estimation, and Performance Parameter Analysis.

Two-dimensional (2D) video is a common tool used during sports training and competition to analyze movement. In these videos, biomechanists determine key events, annotate joint centers, and calculate spatial, temporal, and kinematic parameters to provide performance reports to coaches and athletes. Automatic tools relying on computer vision and artificial intelligence methods hold promise to reduce the need for time-consuming manual methods. This study systematically analyzed the steps required to automate the video analysis workflow by investigating the applicability of a threshold-based event detection algorithm developed for 3D marker trajectories to 2D video data at four sampling rates; the agreement of 2D keypoints estimated by an off-the-shelf pose estimation model compared with gold-standard 3D marker trajectories projected to camera's field of view; and the influence of an offset in event detection on contact time and the sagittal knee joint angle at the key critical events of touch down and foot flat. Repeated measures limits of agreement were used to compare parameters determined by markerless and marker-based motion capture. Results highlighted that a minimum video sampling rate of 100 Hz is required to detect key events, and the limited applicability of 3D marker trajectory-based event detection algorithms when using 2D video. Although detected keypoints showed good agreement with the gold-standard, misidentification of key events-such as touch down by 20 ms resulted in knee compression angle differences of up to 20°. These findings emphasize the need for de novo accurate key event detection algorithms to automate 2D video analysis pipelines.

Robust Methods for Assessing the Characteristics of Locomotor Activity Based on Markerless Video Capture Data

Introduction. Analysis of locomotor activity is essential in a number of biomedical and pharmacological research designs, as well as environmental monitoring. The movement trajectories of biological objects can be represented by time series exhibiting a complex multicomponent structure and non-stationary dynamics, thus limiting the effectiveness of conventional correlation and spectral time series analysis methods. Recordings obtained using markerless technologies are typically characterized by enhanced noise levels, including both instrumental noise and anomalous errors associated with false estimates of the location of the points of interest, as well as gaps in the trajectories, promoting an urgent need in the development of robust methods to assess the characteristics of locomotor activity.Aim. Development of robust methods for assessing the characteristics of locomotor activity capable of efficient processing of noisy recordings obtained by markerless video-based motion capture systems.Materials and methods. In order to assess the characteristics of locomotor activity, the relative movements of body parts of laboratory animals were analyzed using the stability metrics of the mutual dynamics of their trajectories, their relative delays, as well as the relative duration of the recording fragments when relatively stable mutual dynamics could be observed. The local maxima of the cross-correlation function of two body fragments, the minima of the standard deviation of the difference between their Hilbert phases, as well as their relative delays, were used as the metrics of mutual dynamics.Results. The considered phase metrics were shown to explicitly reflect changes in locomotor activity, while the assessment of time delays using phase metric was shown to be prone to periodic error. The above limitation could be largely overcome using the correlation metrics, assuming that phase and correlation metrics could be combined.Conclusion. The proposed robust methods provide stable estimates of the characteristics of locomotor activity based on markerless video capture recordings, altogether increasing the efficiency of diagnostic procedures and assessment of the therapeutic effect during rehabilitation.

Validity of Inertial Measurement Unit (IMU Sensor) for Measurement of Cervical Spine Motion, Compared with Eight Optoelectronic 3D Cameras Under Spinal Immobilization Devices.

The assessment of cervical spine motion is critical for out-of-hospital patients who suffer traumatic spinal cord injuries, given the profound implications such injuries have on individual well-being and broader public health concerns. 3D Optoelectronic systems (BTS SmartDX) are standard devices for motion measurement, but their price, complexity, and size prevent them from being used outside of designated laboratories. This study was designed to evaluate the accuracy and reliability of an inertial measurement unit (IMU) in gauging cervical spine motion among healthy volunteers, using a 3D optoelectronic motion capture system as a reference. Twelve healthy volunteers participated in the study. They underwent lifting, transferring, and tilting simulations using a long spinal board, a Sked stretcher, and a vacuum mattress. During these simulations, cervical spine angular movements-including flexion-extension, axial rotation, and lateral flexion-were concurrently measured using the IMU and an optoelectronic device. We employed the Wilcoxon signed-rank test and the Bland-Altman plot to assess reliability and validity. A single statistically significant difference was observed between the two devices in the flexion-extension plane. The mean differences across all angular planes ranged from -1.129° to 1.053°, with the most pronounced difference noted in the lateral flexion plane. Ninety-five percent of the angular motion disparities ascertained by the SmartDX and IMU were less than 7.873° for the lateral flexion plane, 11.143° for the flexion-extension plane, and 25.382° for the axial rotation plane. The IMU device exhibited robust validity when assessing the angular motion of the cervical spine in the axial rotation plane and demonstrated commendable validity in both the lateral flexion and flexion-extension planes.

Four-quadrant propeller hydrodynamic performance mapping for improving ship motion predictions

On the path toward fully autonomous sea vessels, forecasting a ship’s exact velocity and position during its route plays a crucial role in dynamic positioning, target tracking, and autopilot operations of the unmanned body navigating toward predetermined locations. This paper addresses the prediction of the operational performance of a free-running submarine advancing in a straight route (in surge motion). Along with the forward advancing vessel (straight-ahead motion) the study covers all possible scenarios of ship’s surge, including crash-ahead, crash-back, and astern motions. Conventional maneuvering models cannot handle motions other than forward advancement due to the absence of propeller data in all four quadrants of hydrodynamic performance map. This study proposes an approach for predicting submarine performance in all these surge conditions by utilizing four-quadrant propeller performance and resistance test data. We developed an in-house code, SMot4QP, to simulate ship speed and position in the time domain. We obtained satisfying results for the straight-ahead and crash-ahead motions, while the crash-back and astern maneuvers require further refinement due to propeller wake interaction with the hull. The proposed method is capable of predicting the motions of all types of vessels using the ship’s resistance and four-quadrant propeller test results. Thus, SMot4QP offers a fast and robust alternative to computationally expensive free-running self-propulsion simulations for operational performance prediction in broader naval applications.

Poster 171: Comparative Analysis of Kinetic Variables Between Different Pitch Types in Professional Baseball Pitchers

Objectives: The persistent high rates of elbow injuries among professional baseball pitchers indicates a critical gap in our understanding of how a pitch influences load on the elbow. Traditionally, research has examined the maximum value of various kinetics experienced at the throwing arm during a pitch, especially elbow varus torque. The maximum elbow varus torque has been used as a surrogate for potential elbow injury; however, the elbow injury epidemic has still persisted. It is possible that analysis focused on only the maximum value misses the total load experienced on the throwing arm. Therefore, the purpose of this study was to investigate different metrics to evaluate elbow stress, including maximum elbow varus torque, elbow loading rate, and cumulative varus torque between different pitch types. By evaluating these aspects of elbow stress, our study aims to uncover previously overlooked kinetic variables that might be potential contributors to elbow injuries, bridging the gap between existing kinetic analyses and the persistent high injury rates. Methods: Data from a cohort of 41 professional baseball pitchers were utilized for this analysis (188 ± 6 cm; 91.9 ± 8.2 kg). Pitchers threw a series of fastball, changeup, and curveball pitches (fastball: 10 ± 3 pitches, changeup: 3 ± 1 pitches, curveball: 4 ± 1 pitches) captured using a 3D motion capture system (480 Hz). Kinetic variables were calculated for each pitch, including maximum elbow varus torque, loading torque rate (measured as the derivative of the varus torque curve), and cumulative elbow varus torque (measured as the area under the elbow varus torque curve). A linear mixed effects model was employed to examine within player associations between pitch type and ball velocity, maximum elbow varus torque, loading torque rate, and cumulative elbow varus torque. Statistical significance was set at p<0.01. Results: Our findings reveal that the fastball pitch created greater loading on the elbow compared to the change up and curveball pitches (Table 1). Pitchers threw their fastball with increased ball velocity (40.3 ± 0.6 m/s) compared to throwing their changeup (36.6 ± 0.5 m/s) and curveball (33.7±0.5 m/s) (p<0.001). Maximum elbow varus torque was also greater in the fastball pitch (93.7 ± 3.3 N∙m) compared to the changeup pitch (84.1 ± 2.4 N∙m) and curveball (91.0 ± 2.3 N∙m) (p<0.001); the curveball pitch had greater maximum torque compared to changeup pitches (p<0.001). The loading rate was 15% lower for the changeup pitch (690.0 ± 49.4 N∙m/s) (p<0.001) and 6% lower for the curveball (753.6 ± 60.3 N∙m/s) compared to the fastball (820.1 ± 72.2 N∙m/s) (p<0.001). The cumulative elbow varus torque for the fastball was 4% greater than the changeup pitch (2996.9 ± 92.9 vs 2894.1 ± 84.1 N∙m) and 7% greater than the curveball pitch (2996.9 ± 92.9 vs 2797.2 ± 85.8 N∙m) (p<0.001). Conclusions: This study reveals the importance of considering pitch type when evaluating kinetic variables in professional baseball pitchers. The observed differences in elbow varus torque, loading rate, and other kinematic metrics between fastball, changeup, and curveball pitches highlights the need for a comprehensive understanding of biomechanical variations associated with different pitch types. These findings have implications for optimizing pitcher training programs, injury prevention strategies, and player management. By unraveling the intricate connections between kinetic variables and pitch types, this research contributes to advancing the biomechanical knowledge within the field of orthopedics and sports science.

Disturbance observer based adaptive heading control for unmanned surface vehicle with event‐triggered and signal quantization

SummaryThis article delves into the adaptive heading tracking control of unmanned surface vehicle (USV) by incorporating an event‐triggered mechanism and signal quantization. The primary objective is to save communication resources while alleviating the burden of signal transmission. To address time‐varying external perturbations inherent in the control system, a disturbance observer is employed for precise estimation. Additionally, a linear model is introduced to delineate the procedure of quantization. By furnishing the controller with purpose‐designed quantized control input, the adaptive tracking control system can effectively track desired input without requiring any prior knowledge of the quantized parameters. The article substantiates its claims by demonstrating the system's stability in the absence of quantization considerations and the bounded nature of quantization errors through a series of presented lemmas. Further, the stability of the USV heading control system, integrated with an event‐triggered mechanism and signal quantization, is proofed in accordance with Lyapunov stability theory. Finally, the proposed strategy's efficacy and practical applicability are validated through experimental simulations.

Egocentric 3D Skeleton Learning in a Deep Neural Network Encodes Obese-like Motion Representations.

Obesity is a growing health concern, mainly caused by poor dietary habits. Yet, accurately tracking the diet and food intake of individuals with obesity is challenging. Although 3D motion capture technology is becoming increasingly important in healthcare, its potential for detecting early signs of obesity has not been fully explored. In this research, we used a deep LSTM network trained with individual identity (identity-trained deep LSTM network) to analyze 3D time-series skeleton data from mouse models with diet-induced obesity. First, we analyzed the data from two different viewpoints: allocentric and egocentric. Second, we trained various deep recurrent networks (e.g., RNN, GRU, LSTM) to predict the identity. Lastly, we tested whether these models effectively encode obese-like motion representations by training a support vector classifier with the latent features from the last layer. Our experimental results indicate that the optimal performance is achieved when utilizing an identity-trained deep LSTM network in conjunction with an egocentric viewpoint. This approach suggests a new way to use deep learning to spot health risks in mouse models of obesity and should be useful for detecting early signs of obesity in humans.

Evaluating Gesture Generation in a Large-scale Open Challenge: The GENEA Challenge 2022

This article reports on the second GENEA Challenge to benchmark data-driven automatic co-speech gesture generation. Participating teams used the same speech and motion dataset to build gesture-generation systems. Motion generated by all these systems was rendered to video using a standardised visualisation pipeline and evaluated in several large, crowdsourced user studies. Unlike when comparing different research articles, differences in results are here only due to differences between methods, enabling direct comparison between systems. The dataset was based on 18 hours of full-body motion capture, including fingers, of different persons engaging in a dyadic conversation. Ten teams participated in the challenge across two tiers: full-body and upper-body gesticulation. For each tier, we evaluated both the human-likeness of the gesture motion and its appropriateness for the specific speech signal. Our evaluations decouple human-likeness from gesture appropriateness, which has been a difficult problem in the field. The evaluation results show some synthetic gesture conditions being rated as significantly more human-like than 3D human motion capture. To the best of our knowledge, this has not been demonstrated before. On the other hand, all synthetic motion is found to be vastly less appropriate for the speech than the original motion-capture recordings. We also find that conventional objective metrics do not correlate well with subjective human-likeness ratings in this large evaluation. The one exception is the Fréchet gesture distance (FGD), which achieves a Kendall’s tau rank correlation of around -0.5. Based on the challenge results we formulate numerous recommendations for system building and evaluation.

1D1-2 Validation of a Joint Moment Analysis Method measured by Markerless Motion Capture

1D1-2 Validation of a Joint Moment Analysis Method measured by Markerless Motion Capture

Mapping the Behavioral Signatures of Shank3b Mice in Both Sexes

Autism spectrum disorders (ASD) are characterized by social and repetitive abnormalities. Although the ASD mouse model with Shank3b mutations is widely used in ASD research, the behavioral phenotype of this model has not been fully elucidated. Here, a 3D-motion capture system and linear discriminant analysis were used to comprehensively record and analyze the behavioral patterns of male and female Shank3b mutant mice. It was found that both sexes replicated the core and accompanied symptoms of ASD, with significant sex differences. Further, Shank3b heterozygous knockout mice exhibited distinct autistic behaviors, that were significantly different from those those observed in the wild type and homozygous knockout groups. Our findings provide evidence for the inclusion of both sexes and experimental approaches to efficiently characterize heterozygous transgenic models, which are more clinically relevant in autistic studies.

Lower Limb Muscle Activation in Young Adults Walking in Water and on Land

Previous research has shown that exercise interventions requiring increased activation of the tibialis anterior (TA), the primary ankle dorsiflexor, can improve walking performance in individuals with foot drop. Correspondingly, heightened drag forces experienced during walking performed in water may augment TA activation during the swing phase of gait, potentially leading to improved walking gait on land. Therefore, this study aimed to compare surface electromyographic (sEMG) activation in the TA and medial gastrocnemius (GM) during gait performed in water versus on land. Thirty-eight healthy, recreationally active young adults, comprising 18 females and 20 males, participated in the study. Each participant completed 2 min walking trials under five conditions: land 2.5 mph, land 3.5 mph, water 2.5 mph, water 3.5 mph, and water 3.5 mph with added jet resistance. Stride kinematics were collected using 2-dimensional underwater motion capture. TA and GM, muscle activation magnitudes, were quantified using sEMG root-mean-square (RMS) amplitudes for both the swing and stance phases of walking. Additionally, TA and GM co-activation (Co-A) indices were estimated. Two-way within-subjects repeated measures analyses of variance were used to evaluate the main effects of and interactions between the environment and walking speed. Additionally, paired sample t-tests were conducted as a secondary analysis to investigate differences between walking in water at 3.5 mph with and without added jet resistance. Main effects and interactions were observed across various stride kinematics and sEMG measures. Notably, TA sEMG RMS during the swing phase of walking gait performed at 2.5 mph was 15% greater in water than on land (p < 0.001). This effect increased when walking gait was performed at 3.5 mph (94%; p < 0.001) and when jet resistance was added to the 3.5 mph condition (52%; p < 0.001). Furthermore, TA Co-A was increased during the stance phase of gait in water compared to on land (p < 0.001), while GM Co-A was reduced during the swing phase (p < 0.001). The findings of this study offer compelling evidence supporting the efficacy of aquatic treadmill walking as a potential treatment for individuals suffering from foot drop. However, further research is needed to evaluate whether a causal relationship exists between heightened TA activation observed during aquatic treadmill walking and improvements in voluntary dorsiflexion during gait.

Skeleton Cluster Tracking for robust multi-view multi-person 3D human pose estimation

The multi-view 3D human pose estimation task relies on 2D human pose estimation for each view; however, severe occlusion, truncation, and human interaction lead to incorrect 2D human pose estimation for some views. The traditional “Matching-Lifting-Tracking” paradigm amplifies the incorrect 2D human pose into an incorrect 3D human pose, which significantly challenges the robustness of multi-view 3D human pose estimation. In this paper, we propose a novel method that tackles the inherent difficulties of the traditional paradigm. This method is rooted in the newly devised “Skeleton Pooling-Clustering-Tracking (SPCT)” paradigm. It initiates a 2D human pose estimation for each perspective. Then a symmetrical dilated network is created for skeleton pool estimation. Upon clustering the skeleton pool, we introduce and implement an innovative tracking method that is explicitly designed for the SPCT paradigm. The tracking method refines and filters the skeleton clusters, thereby enhancing the robustness of the multi-person 3D human pose estimation results. By coupling the skeleton pool with the tracking refinement process, our method obtains high-quality multi-person 3D human pose estimation results despite severe occlusions that produce erroneous 2D and 3D estimates. By employing the proposed SPCT paradigm and a computationally efficient network architecture, our method outperformed existing approaches regarding robustness on the Shelf, 4D Association, and CMU Panoptic datasets, and could be applied in practical scenarios such as markerless motion capture and animation production.

A Contemporary analysis of tackle height: Implications for head injury risk and tackler technique in Rugby Union

Rugby tackles pose significant head injury risks, raising concerns for players' well-being. Despite advocating for lower tackle heights for safety, limited research exists explaining how tackle height influences head characteristics and tackler technique. This study aimed to investigate the effects of two tackle heights, aligned with recent law changes in the community game, on head and joint kinematics for both tackler and the ball carrier. To strengthen ecological validity, innovative techniques were employed, including markerless motion capture and Inertial Measurement Units (IMUs), for tracking of the tackler's joint kinematics and head accelerations until ground contact, addressing a key limitation in previous research. Ethical approval was granted by Cardiff Metropolitan University. Ten male participants (mean ± SD age: 22 ± 3 years, stature: 184 ± 10 cm, mean mass: 94 ± 15 kg) alternated between tackler and ball carrier roles, executing upper and lower body tackles. Theia3D markerless motion capture software (Theia3Dv2022.1.0.2309, Theia Markerless, Inc., Kingston, ON, Canada) and Vicon IMeasureU Blue Trident dual-G IMUs measured tackle height's impact on head and joint kinematics. Discrete joint angles at key events and continuous joint angles normalised from 0% at Step 1 to 100% at Contact were exported. Peak head accelerations and continuous normalised head acceleration data were exported. Statistical analyses included a paired t-test for discrete joint angle data and the Wilcoxon Rank Sum Test for peak linear and angular accelerations. Cohen’s d and effect sizes were calculated for respective analyses. One-dimensional statistical parametric mapping (SPM) and one-dimensional statistical non-parametric mapping (SnPM) facilitated statistical differences across continuous variables of interest. Significant increases (P < 0.05) were noted in ball carriers' inertial head kinematics in the upper body tackle, while no such distinctions were observed for tacklers. The low tackle condition consistently exhibited substantial reductions in bilateral hip flexion, particularly during contact (Effect size; lead: −1.866; rear: −1.977). Lumbopelvic flexion significantly decreased in each event for the low tackle condition, with the largest effect size during contact (−3.91). These findings underscore the heightened inertial loading with higher tackles, indicating an elevated risk of head injury, despite current tackle height regulations. The adjustments made by the tackler in response to varying tackle heights are not evident in knee flexion. Increased knee flexion during the preparatory phase could alleviate the necessity for such a flexed lumbopelvic angle. This study, utilising innovative techniques, highlights the potential for more ecologically valid approaches to biomechanical research in rugby tackling.

The validation of inertial measurement units in upper limb movement during wheelchair activity

Introduction: 3D motion capture is accepted to be the gold standard approach to all data collection for the production of accurate data, however, in recent literature the ecological validity of 3D systems has come into question. This has brought about the use of Inertial measurement units (IMU’s) and the investigation into their accuracy in enabling accurate real life scenario data collection. The depth of research on IMU’s in wheelchair data collection is limited, and at current there is limited attempts at a validation in comparison to an established data collection software. This research aims to validate basic upper body motions seen within wheelchair propulsion in an attempt to identify the current limitations of IMU’s. Methods: numerous IMU placements and calibration stances were investigated for the collection of elbow flexion and shoulder flexion. IMU’s for elbow flexion were placed at the wrist and central on the forearm. For shoulder flexion the IMU was placed 1 cm above the elbow joint. During the calibration phase, standing anatomical position with thumbs forwards, palms outwards, bent elbow and straight arms outwards at 90° for elbow and shoulder flexion, respectively. For both shoulder and elbow flexion, the participant started at a neutral position and moved through to 90° of flexion and returned to starting position. Quintic was used as the validated software. Results: the wrist placed IMU determined elbow flexion more accurately than the forearm placed IMU. Range of motion for both shoulder and elbow flexion were well calculated within several degrees when using the anatomical thumbs forwards calibration pose; with 99.97 and 89.69°, respectively compared to 88.48 and 97.32°. However, the degree of elbow flexion was overestimated with a difference of 27.78°, with the IMU being 91.11° and quintic being 63.33°. Similar results were also seen for the prediction of elbow flexion during the starting phase with a difference of 26.58°. Discussion: with range of motion accurately calculated in comparison to quintic, and shoulder flexion maximum and minimum values also being similar when segment angle was calculated. Then the differences are likely due to error in the calculation of joint angle using a calculation of global coordinate system from the IMU coordinate system during data processing. Therefore, future research should target alternate approaches to data processing in order to reduce the errors seen.

Using inertial measurement units to estimate ground reaction force and knee angular velocity during decelerations

Despite undergoing anterior cruciate ligament (ACL) reconstruction, athletes continue to present altered ground reaction force (GRF) and knee angular velocities (AV) for 6-24 months as they return to highly demanding tasks such as rapid decelerations (Schmitt et al., 2015, Med Sci Sports Ex, 47, 1426). In-field identification of GRF and knee AV during such deceleration tasks is challenging due to the laboratory restrictions of force platforms and 3D motion capture. Therefore, the use of inertial measurement units (IMU) has been suggested as an appropriate alternative to estimate such variables in the field (Pratt & Sigward, 2018. Sensors, 3460). The study aimed to establish whether IMU-derived measures can be used to estimate GRF and knee AV that are indicative of ACL injury risk during decelerations. Following ethical approval from the Cardiff Metropolitan Ethics Committee, ten male team-sport athletes performed five maximal decelerations at three approach speeds (100, 85, and 70% relative to maximal attainable speed), for a total of fifteen trials per athlete. GRF and kinematics were measured using four Kistler force platforms and Theia3D markerless motion capture. Pearson’s correlation coefficient was used to determine the relationship between IMeasureU Blue Trident IMUs mounted at the thigh or shank and vertical GRF, horizontal GRF, and knee AV during the first step of deceleration. A measure was considered field-viable if a very large significant correlation (r ≥ 0.7; P ≤ 0.05) was observed. At approach speeds of 85 and 70%, shank AV had a very large significant correlation (r = 0.79, 0.76; P = 0.001, 0.01, respectively) to vertical GRF, a moderate to large significant correlation to horizontal GRF (r = 0.46, 0.51; P = 0.04, 0.02, respectively), and a moderate significant correlation to knee AV (r =0.46, 0.40; P = 0.004, 0.02, respectively). At 100% approach speeds, shank AV had no significant correlation to GRF (r <0.3; P>0.05) and a moderate correlation to knee AV (r = 0.40; P = 0.02). This study was the first to find a strong association between shank AV and vertical GRF for whole-body decelerations at 85 and 70% approach speeds. This supports the use of IMUs in sport-specific settings (e.g., football pitches) to better quantify vertical GRF deficits during decelerations. This can further enhance in-field monitoring of GRF deficits and better assess athletes' readiness to return to sport following ACL reconstruction. However, alternative methods are required to accurately estimate horizontal GRFs and knee AV in the field.

Quantifying the traverse: a comprehensive kinematic analysis of climbing technique

Biomechanical analysis plays a pivotal role in enhancing performance and preventing injuries in rock climbing. Despite a recent increase in popularity, there remains a lack of research quantifying full-body movements, resulting in uncertainty regarding biomechanical demands and variability. It should be noted that there is a scarcity of data in climbing research to quantify optimal techniques, particularly for traverses. This study aims to address this gap by examining the demands of a traverse in a controlled setting using Vicon marker-based three-dimensional (3D) motion capture. Fourteen experienced climbers (32 ± 13 years, 70 ± 9 kg) with varying skill levels (intermediate to advanced) and climbing backgrounds (sport climbing, trad climbing and bouldering) completed a two-minute standardised traverse on a custom-built Lattice circuit (2440 × 2440 × 1220 mm). A twelve-camera (200 Hz, Vantage) motion analysis system (Vicon, Motion Systems Ltd. Oxford, United Kingdom) acquired kinematic data. Retroreflective markers were attached to anatomical landmarks of the upper and lower body. The trials were preceded by a 10-minute self-selected warmup. This data will be analysed to assess the degree of inter-participant variability, observing if there is the possibility of quantifying an optimal traversing technique. Intra-participant variability will be assessed, to measure the effect of fatigue on the climbing movement. Previous literature has alluded to the possibility of fatigue increasing the use of the legs when climbing as compensation. Comparing the beginning of the traverse to the end, data should further substantiate this claim. This research will offer insights into the kinematic demands of rock climbing, laying the groundwork for further studies on a larger scale to assess the possibility of optimising technique, performance, and injury strategies. This study contributes to bridging the vast gap between biomechanical research and practical applications in the climbing community, facilitating a more evidence-based approach to performance.

How athletes’ biomechanical running characteristics effect running economy during the use of running shoes with and without carbon inserts

To maximise running economy (RE), shoe manufacturers placed carbon plates within the midsole of shoes. Shoe technology research is limited on understanding the variability of individual responses to carbon-plated shoes and how these responses vary across running velocities. Little research on same shoe characteristics with and without a stiff element has been completed. This study aimed to investigate how running shoes with carbon versus without a carbon composite stiff element alter individual running biomechanics and the metabolic cost of running. Ethical approval was gained from Cardiff Metropolitan University Ethics Committee. Ten male athletes (69 ± 9 kg; 174 ± 4 cm; 28 ± 9 years) completed two submaximal incremental treadmill runs. One test was completed in a shoe without carbon (C1), the other test was completed in carbon shoes (C2), the order of testing for each shoe were randomised. Running velocity started at 9 km/h and increased by 1 km/h every four mins, blood lactate samples were taken after every stage. Once 4 mmol·L−1 (OBLA; the second lactate turn point) had been reached one more stage was completed. Gas exchange was analysed throughout the whole test. The first 15 s of the final 2 minutes of each stage was recorded using Theia3D markerless motion capture software (Theia3Dv2022.1.0.2309, Theia Markerless, Inc., Kingston, ON, Canada). Data were analysed in 4 stages, the initial stage, pre-OBLA, OBLA and post-OBLA. Physiology data were averaged over the final two mins of each stage. Discrete joint angles were taken from each stage, and an average of the 15 s recording was taken for spatiotemporal measure. Data were analysed using a four-way repeat measures ANOVA, to show individual differences. Non-parametric data were analysed using Wilcoxon signed-rank test. Hedges g calculations were completed to calculate effect size (ES). Results showed significant increase in flight time (FT; P = 0.04, ES = 0.20) in the pre-OBLA stage when using C2. Metatarsophalangeal joint (MTP) dorsiflexion showed significant increase during the initial stage in C2 (P = 0.05, ES = 0.8), and ankle dorsiflexion had significant increase in the post-OBLA stage in C2 (P = 0.03, ES = 0.2). The were no significant differences present in the physiology data. Across the physiological, spatiotemporal and kinematics, high dispersions around the mean were exhibited. Findings suggest that to improve RE, mechanical and spatiotemporal changes need to be present when using C2. Further findings show carbon shoes elicit highly individual responses to both RE and mechanics of running.