3D Motion Capture Research Articles

The effect of age and bracing on vehicle occupant responses during sled-simulated evasive swerving

Objective Bracing can reduce adult occupants’ out-of-position postures, but it is unclear if this finding can be extended to child occupants. We investigated the effect of bracing, and age on the motion of vehicle occupants of different ages during sled-simulated pre-crash maneuvers. Methods Forty seatbelt restrained subjects (9–40 y.o.) experienced sled simulated evasive swerving maneuvers during a brace condition, where subjects actively brace before the maneuver onset, and an unbraced condition. A 3D motion capture system, electromyography (EMG), and seatbelt load cells captured head and trunk kinematics, muscle activation, and seat belt reaction forces, respectively. The effects of age and bracing on peak lateral head and trunk displacement were examined with Mixed Effects Model (p ≤ 0.05). Results In the braced condition, all subjects had reduced normalized peak head (0.09 ± 0.05) and trunk (0.11 ± 0.05) displacements compared to the unbraced condition (Head: 0.14 ± 0.06, Trunk: 0.17 ± 0.07) (p < 0.05). For the into-the-belt direction in the unbraced condition, children showed the smallest peak head and trunk displacement of all age groups (p < 0.01) while teens had the greatest peak head and trunk displacement compared to all other age groups (p < 0.02). Similar trends were found in the out-of-the-belt direction in the unbraced condition (p < 0.01). In the unbraced condition, all occupants showed greater shoulder seat belt reaction loads than the braced condition (unbraced 1.6–2.7 N/kg, braced 1.0–1.4 N/kg). Children also showed greater neck muscle activation (50–64% MVIC) compared to other muscles and older occupants regardless of the bracing condition or direction of motion. Conclusion Bracing reduced out-of-position postures across all ages. In the unbraced condition, children move less than teens and adults due to greater activation in the neck muscles. In the unbraced condition, teens showed the greatest motion, potentially due to their developing neuromotor control transitioning to a more mature stage. Across all age groups in the unbraced condition, occupants relied more heavily on the seat belt to maintain their position rather than their muscles to brace, suggesting the importance of good seatbelt-torso interaction in unbraced occupants.

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.

The effect of reclined seat-back angles on the LODC with and without a belt-positioning booster during far-side lateral-oblique impacts

Objective In frontal crashes belt-positioning boosters (BPB) may prevent submarining when the seatback is reclined. It is unclear if the BPB can also mitigate injuries in far-side lateral-oblique crashes in reclined conditions, where current restraints are less effective in reducing lateral excursion. This study aimed to understand reclined child injury risk during lateral-oblique impacts, with and without a booster seat, by using the Large Omni-Directional Child (LODC) test device. Methods The LODC was tested in nine lateral-oblique impact (80° from frontal) sled tests (target 31.3 km/h, duration 58 ms maximum, peak acceleration 21 g). Three seatback angles (25°, 45°, and 60°) with and without the BPB were compared on a production passenger seat with an integrated seatbelt. The LODC moved toward the buckle side during the far-side lateral-oblique impact. Abdominal pressure (left and right), seatbelt loads, anterior superioriliac spine (ASIS) forces, and pelvis lateral rotation were examined. The LODC head and knee excursions were extracted from a 3D-motion capture system. Results In the reclined noBPB condition, peak abdominal pressures on the buckle side reached up to 186 kPa and the ASIS forces demonstrated an early (∼ 50 ms) peak and a subsequent drop in the reclined noBPB conditions, suggesting that the belt slid into the abdomen. With the BPB, peak pelvis lateral rotation was greater than in the noBPB conditions but decreased with increasing reclined seatback angles (BPB: 31° to 36.5° vs no-BPB: −5° to −4.6°). Peak lap belt forces were greater in the reclined noBPB conditions (4.8-4.9 kN) compared to all conditions with the BPB (2.9-3.2 kN). The greatest lateral head excursion was observed in the BPB 25° condition (895 mm) and the lowest in the noBPB 45° condition (748 mm). Conclusions The BPB may prevent the lap belt intrusion into the abdomen in reclined configurations in far side lateral-oblique impacts. The greater pelvis lateral rotation and head displacement with the BPB may lead to contact with other rear-seated occupants and/or vehicle structures, although motion decreased with the BPB as the reclined seatback angle increased. This suggests that reclined seats may help reduce BPB-seated children’s lateral excursion in far-side lateral-oblique impacts.

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 &lt; 0.001). This effect increased when walking gait was performed at 3.5 mph (94%; p &lt; 0.001) and when jet resistance was added to the 3.5 mph condition (52%; p &lt; 0.001). Furthermore, TA Co-A was increased during the stance phase of gait in water compared to on land (p &lt; 0.001), while GM Co-A was reduced during the swing phase (p &lt; 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 &lt; 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 &amp; 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 &lt;0.3; P&gt;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.

Accuracy, Validity, and Reliability of Markerless Camera-Based 3D Motion Capture Systems versus Marker-Based 3D Motion Capture Systems in Gait Analysis: A Systematic Review and Meta-Analysis.

(1) Background: Marker-based 3D motion capture systems (MBS) are considered the gold standard in gait analysis. However, they have limitations for which markerless camera-based 3D motion capture systems (MCBS) could provide a solution. The aim of this systematic review and meta-analysis is to compare the accuracy, validity, and reliability of MCBS and MBS. (2) Methods: A total of 2047 papers were systematically searched according to PRISMA guidelines on 7 February 2024, in two different databases: Pubmed (1339) and WoS (708). The COSMIN-tool and EBRO guidelines were used to assess risk of bias and level of evidence. (3) Results: After full text screening, 22 papers were included. Spatiotemporal parameters showed overall good to excellent accuracy, validity, and reliability. For kinematic variables, hip and knee showed moderate to excellent agreement between the systems, while for the ankle joint, poor concurrent validity and reliability were measured. The accuracy and concurrent validity of walking speed were considered excellent in all cases, with only a small bias. The meta-analysis of the inter-rater reliability and concurrent validity of walking speed, step time, and step length resulted in a good-to-excellent intraclass correlation coefficient (ICC) (0.81; 0.98). (4) Discussion and conclusions: MCBS are comparable in terms of accuracy, concurrent validity, and reliability to MBS in spatiotemporal parameters. Additionally, kinematic parameters for hip and knee in the sagittal plane are considered most valid and reliable but lack valid and accurate measurement outcomes in transverse and frontal planes. Customization and standardization of methodological procedures are necessary for future research to adequately compare protocols in clinical settings, with more attention to patient populations.

Gamified learning experience based on digital media and the application of virtual teaching robots in dance teaching

The research aims to explore the application of gamified learning experience based on digital media and virtual teaching robots in dance teaching. A virtual teaching robot system is designed, which combines technologies such as 3D motion capture, pose calculation, loss function constraint, and similarity matching. Through methods such as bone orientation, digital media audio-visual synchronization, and analysis of robot motion effects, virtual teaching robots have been able to present dance movements. Integrating virtual teaching robots into the teaching process through gamified learning methods. By introducing elements such as tasks, challenges, and rewards into learning, it is possible to stimulate students’ interest and enthusiasm in learning, and improve learning outcomes. The application of digital media based virtual teaching robots in dance teaching has a good effect. The overall structure of the system is reasonable, and the application of virtual reality technology allows students to learn dance firsthand. Through the analysis of skill teaching effectiveness and comprehensive teaching effectiveness, it was found that students have better participation and learning outcomes when learning dance through virtual teaching robots. The implementation of this system can enhance students’ learning enthusiasm and effectiveness, providing a new way for innovation in dance teaching.

Validation of OpenCap: A low-cost markerless motion capture system for lower-extremity kinematics during return-to-sport tasks

Low-cost markerless motion capture systems offer the potential for 3D measurement of joint angles during human movement. This study aimed to validate a smartphone-based markerless motion capture system’s (OpenCap) derived lower extremity kinematics during common return-to-sport tasks, comparing it to an established optoelectronic motion capture system. Athletes with prior anterior cruciate ligament reconstruction (12–18 months post-surgery) performed three movements: a jump-landing-rebound, single-leg hop, and lateral-vertical hop. Kinematics were recorded concurrently with two smartphones running OpenCap’s software and with a 10-camera, marker-based motion capture system. Validity of lower extremity joint kinematics was assessed across 437 recorded trials using measures of agreement (coefficient of multiple correlation: CMC) and error (mean absolute error: MAE, root mean squared error: RMSE) across the time series of movement. Agreement was best in the sagittal plane for the knee and hip in all movements (CMC > 0.94), followed by the ankle (CMC = 0.84–0.93). Lower agreement was observed for frontal (CMC = 0.47–0.78) and transverse (CMC = 0.51–0.6) plane motion. OpenCap presented a grand mean error of 3.85° (MAE) and 4.34° (RMSE) across all joint angles and movements. These results were comparable to other available markerless systems. Most notably, OpenCap’s user-friendly interface, free software, and small physical footprint have the potential to extend motion analysis applications beyond conventional biomechanics labs, thus enhancing the accessibility for a diverse range of users.

Deep-Learning-Based Recovery of Missing Optical Marker Trajectories in 3D Motion Capture Systems.

Motion capture (MoCap) technology, essential for biomechanics and motion analysis, faces challenges from data loss due to occlusions and technical issues. Traditional recovery methods, based on inter-marker relationships or independent marker treatment, have limitations. This study introduces a novel U-net-inspired bi-directional long short-term memory (U-Bi-LSTM) autoencoder-based technique for recovering missing MoCap data across multi-camera setups. Leveraging multi-camera and triangulated 3D data, this method employs a sophisticated U-shaped deep learning structure with an adaptive Huber regression layer, enhancing outlier robustness and minimizing reconstruction errors, proving particularly beneficial for long-term data loss scenarios. Our approach surpasses traditional piecewise cubic spline and state-of-the-art sparse low rank methods, demonstrating statistically significant improvements in reconstruction error across various gap lengths and numbers. This research not only advances the technical capabilities of MoCap systems but also enriches the analytical tools available for biomechanical research, offering new possibilities for enhancing athletic performance, optimizing rehabilitation protocols, and developing personalized treatment plans based on precise biomechanical data.

Combining IMU With Acoustics for Head Motion Tracking Leveraging Wireless Earphone

Combining IMU With Acoustics for Head Motion Tracking Leveraging Wireless Earphone

Calibrationless monocular vision musculoskeletal simulation during gait

With computer vision technology and prediction of ground reaction forces (GRF), a previous study performed markerless motion capture and musculoskeletal simulation with two smartphones (OpenCap). A recent approach can reconstruct 3D human motion from a single video without calibration and it may further simplify the motion capture process. However it has not been combined with musculoskeletal simulation and the validity is unclear. Therefore, the purpose of this study was to determine the validity of the musculoskeletal simulation using a monocular vision approach. An open-source dataset that contains motion capture and video data during gait from 10 healthy participants was used. Human motion reconstruction with the skinned human (SMPL) model was performed on each video. Virtual marker data was generated by extracting the position data from the SMPL skin vertices. Inverse kinematics, GRF prediction (only for monocular vision approach), inverse dynamics and static optimization were performed using a musculoskeletal model for experimental motion capture data and the generated virtual markers from videos. Mean absolute errors (MAE) between motion capture based and monocular vision based simulation outcomes were calculated. The MAE were 8.4° for joint angles, 5.0 % bodyweight for GRF, 1.1 % bodyweight*height for joint moments and 0.11 for estimated muscle activations from 16 muscles. The entire MAE was larger but some were comparable to OpenCap. Using the monocular vision approach, motion capture and musculoskeletal simulation can be done with no preparations and is beneficial for clinicians to quantify the daily gait assessment.

A novel tool for characterising upper limb function in progressive multiple sclerosis through kinematic assessment

IntroductionCurrent upper limb assessment methods in MS rely on measuring duration in tasks like the nine-hole peg test (9HPT). Kinematic techniques may provide a more useful measure of functional change in clinical and research practice. The aim of this study was to assess upper limb function prospectively in people with progressive MS using a kinematic 3D motion capture system and compare with current measures. Methods42 people with progressive MS (PwPMS) and 15 healthy controls reached-and-grasped different objects whilst recorded by a kinematic assessment system. 9HPT, Expanded Disability Status Scale (EDSS), and patient reported outcome measures (PROs) were collected. All measures were taken at baseline for PwPMS and controls, and again at six months for PwPMS. ResultsRelative to controls, PwPMS had significantly longer reaction (0.11 s, p < 0.05) and reach (0.25 s, p < 0.05) times. PwPMS took longer to pick-up (0.34 s, p < 0.05), move (0.14 s, p < 0.05), and place (0.18 s, p < 0.05) objects. PwPMS had lower peak velocities when reaching (7.4 cm/s, p < 0.05) and moving (7.3 cm/s, p < 0.05) objects. Kinematic assessment demonstrated consistent differences between PwPMS with mild and severe upper limb dysfunction as defined by PROs, which were not captured by 9HPT or EDSS in this group. PwPMS demonstrated altered grip apertures profiles, as measured by their ability to complete individual parts of the reach and grasp task, between the baseline and follow-up timepoints. ConclusionsWe have created and tested a novel upper limb function assessment tool which has detected changes and characteristics in hand function, not currently captured by the EDSS and 9HPT.

Validation of upper extremity kinematics using Markerless motion capture

Movement research has typically been performed using three-dimensional (3D) marker-based motion capture, which is considered the “gold-standard” for biomechanical assessment. However, limitations exist due to the lack of portability, extensive preparation for data collection, marker placement training, error due to marker movement, and possible skin irritation due to marker adhesives. There is inherent error due to motion artifact stemming from skin movement and differences in marker placement between testers. Markerless motion capture systems are emerging as a new method of kinematic assessment. These methods require little preparation and there is no need to alter participant clothing. Markerless motion capture has also been validated for the lower extremity in healthy older adults during gait. However, it has not been validated for other populations or for the assessment of upper extremity (UE) motion. Therefore, the purpose of this study was to examine differences in calculated UE kinematics between marker-based and a markerless motion capture system. Participants attended two data collection sessions. Marker-based and markerless motion capture data was collected simultaneously while participants completed the Box and Blocks test (BBT). Kinematic and spatiotemporal data from both systems was exported using identical time series to ensure the same conditions for comparisons. Intraclass Correlation Coefficients (ICCs) were calculated to determine between session reliability for both systems on range of motion and peak joint angular data to ensure movement variability was not affecting measurement consistency. ICCs and Bland Altman statistics were also calculated between the systems. Root mean square deviation (RMSD) values were determined between demeaned UE joint angles for the two systems to examine movement pattern differences. The resulting between-session ICCs for each system showed that the markerless system shared similar reliability during this task as the marker-based system, further supporting the effect of variability on between-session reliability. Between-system ICCs resulted in good (0.7<ICC<0.9) to excellent (ICC>0.9) agreement. Bland Altman results confirmed the existence of measurement bias between the systems. RMSD values for all UE joint angles were found to be less than 6°. Overall, the results from this study support the use of markerless motion capture in clinical settings to examine upper extremity biomechanics in children.

3D octopus kinematics of complex postures: Translation to long, thin, soft devices and their potential for clinical use.

Octopuses are capable of complex arm movements. Unfortunately, experimental barriers and lack of a robust analysis method made it difficult to quantify the three-dimensional (3D) kinematics of soft, flexible bodies, such as the octopus arm. This information is not only crucial for understanding the posture of the animal's arm but also for the development of similarly designed soft, flexible devices. The primary goal of this work was to create a method to comprehensively quantify complex, 3D postures of octopus (Octopus Bimaculoides) arms in a manner that is conducive and translatable to octopus arm-inspired devices for health monitoring and rehabilitation. In this study, 3D underwater motion capture was used to collect kinematic data on both live octopuses and disembodied arms that still had neural activity. A new method was developed to define how arm curvature and regional segments were oriented relative to each other in 3D. This included identification of the bend within a segment along with the computation of the relative orientation between segments, thus permitting the complete quantification of complex arm motions. By comparing vector-based and radius of curvature-based approaches to magnitude of curvature, it was clear that the vector-based approach was less dependent on the length of a segment and that its reported ranges of motion were translatable for outcome measures associated with clinical use. The new approach for the relative orientation of each segment of the octopus arm resulted in the capability of describing the octopus arm in many unique postures, such as straight, simple bending, and complex bending as it utilized the three rotational angles. This method and its application to octopus arms will yield new information that can be used to better communicate and track not only octopus arm movements but in the development of complex, segmented, soft-bodied devices that can be used in health monitoring and rehabilitation.

The applicability of markerless motion capture for clinical gait analysis in children with cerebral palsy

The aim of this comparative, cross-sectional study was to determine whether markerless motion capture can track deviating gait patterns in children with cerebral palsy (CP) to a similar extent as marker-based motion capturing. Clinical gait analysis (CGA) was performed for 30 children with spastic CP and 15 typically developing (TD) children. Marker data were processed with the Human Body Model and video files with Theia3D markerless software, to calculate joint angles for both systems. Statistical parametric mapping paired t-tests were used to compare the trunk, pelvis, hip, knee and ankle joint angles, for both TD and CP, as well as for the deviation from the norm in the CP group. Individual differences were quantified using mean absolute differences. Markerless motion capture was able to track frontal plane angles and sagittal plane knee and ankle angles well, but individual deviations in pelvic tilt and transverse hip rotation as present in CP were not captured by the system. Markerless motion capture is a promising new method for CGA in children with CP, but requires improvement to better capture several clinically relevant deviations especially in pelvic tilt and transverse hip rotation.