Optoelectronic Motion Capture System Research Articles

Kinematics of the Tennis Serve Using an Optoelectronic Motion Capture System: Are There Correlations between Joint Angles and Racket Velocity?

The serve is the most important stroke in tennis. It is a complex gesture consisting of numerous rotations with a wide amplitude, which are important to manage for performance. The aim of this study was to investigate whether correlations exist between joint kinematic parameters and racket velocity. A quantitative kinematics analysis of four ranked players (two boys and two girls) was carried out using an optoelectronic system composed of 10 cameras (150 Hz). Five flat serves per player were analyzed. Eighty-two markers were located across the 15 body segments and on the racket. A descriptive statistical analysis including a correlation analysis was carried out between joint angles and racket kinematic parameters (vertical position, velocity, and acceleration) during the cocking and acceleration phases. Ten very high (0.7 < r < 0.9) and three almost perfect (r > 0.9) correlations were found. Shoulder and hip axial rotations, knee flexion, and trunk extension were correlated linearly with racket vertical position and velocity during the cocking phase. For the acceleration phase, elbow flexion, trunk flexion/extension, and trunk axial rotation were linked to racket kinematics. Some of these parameters showed differences between slow and fast serves. These parameters, which are involved in transmitting ball velocity, are important to consider for tennis players and coaches in training programs, education, and performance enhancement.

The Flexion Relaxation Phenomenon in Patients with Radiculopathy and Low Back Pain: A Cross-Sectional Study.

Although the measurements of the lumbar spine and pelvic flexion have shown that subjects with radiculopathy exhibited greater decreases of motion when compared with subjects with low back pain, there is still a lack of evidence regarding the changes in flexion relaxation ratio in patients with radiculopathy. The aims of this study were to investigate the flexion relaxation ratio and flexion of the lumbar spine and pelvis in subjects with low back pain (LBP) and LBP with radiculopathy (LBPR) in comparison with healthy subjects (CG-control group). A total of 146 participants were divided in three groups: LBP patients (54 males; 21 females); LBPR patients (26 males; 11 females); and CG subjects (16 males; 18 females). The lumbar spine and pelvis flexion was recorded using optoelectronic motion capture system. The electrical activity of the erector spinae muscles was assessed by surface electromyography during flexion-extension movements. Comparisons between groups were made using one-way ANOVA tests and Mann-Whithney U test with the level of statistical significance at 0.05. The lumbar and pelvic flexion and electromyography of the erector spinae muscle showed significant differences between LBP and LBPR patients compared to CG. Patients LBPR showed significantly smaller angles of lumbar and pelvic flexion compared to LBP patients and CG. An increase in the erector spinae muscle activity during flexion was also observed in patients with radiculopathy. The increased muscular activity of the erector spinae is related to the reduced flexion of the lumbar spine in order to protect the lumbar spine structure. Measurements of trunk, lumbar spine and pelvic flexion, and the flexion relaxation ratio may allow us to predict better outcomes or responsiveness to treatment of LBPR patients in the future.

Analysis of the obstetrician's posture and movements during a simulated forceps delivery

BackgroundThe objective of this study was to identify and qualify, by means of a three-dimensional kinematic analysis, the postures and movements of obstetricians during a simulated forceps birth, and then to study the association of the obstetricians’ experience with the technique adopted.MethodFifty-seven volunteer obstetricians, 20 from the Limoges and 37 from the Poitiers University hospitals, were included in this multi-centric study. They were classified into 3 groups: beginners, intermediates, and experts, beginners having performed fewer than 10 forceps deliveries in real conditions, intermediates between 10 and 100, and experts more than 100. The posture and movements of the obstetricians were recorded between December 2020 and March 2021 using an optoelectronic motion capture system during simulated forceps births. Joint angles qualifying these postures and movements were analysed between the three phases of the foetal traction. These phases were defined by the passage of a virtual point associated with the forceps blade through two anatomical planes: the mid-pelvis and the pelvic outlet. Then, a consolidated ascending hierarchical classification (AHC) was applied to these data in order to objectify the existence of groups of similar behaviours.ResultsThe AHC distinguished four different postures adopted when crossing the first plane and three different traction techniques. 48% of the beginners adopted one of the two raised posture, 22% being raised without trunk flexion and 26% raised with trunk flexion. Conversely, 58% of the experts positioned themselves in a “chevalier servant” posture (going down on one knee) and 25% in a “squatting” posture before initiating traction. The results also show that the joint movement amplitude tends to reduce with the level of expertise.ConclusionForceps delivery was performed in different ways, with the experienced obstetricians favouring postures that enabled observation at the level of the maternal perineum and techniques reducing movement amplitude. The first perspective of this work is to relate these different techniques to the traction force generated. The results of these studies have the potential to contribute to the training of obstetricians in forceps delivery, and to improve the safety of women and newborns.

Accuracy validation of a wearable IMU-based gait analysis in healthy female

ObjectiveThe aim of this study was to assess the accuracy and test-retest reliability of a wearable inertial measurement unit (IMU) system for gait analysis in healthy female compared to a gold-standard optoelectronic motion capture (OMC) system.MethodsIn our study, we collected data from 5 healthy young females. Participants were attached with markers from both the OMC system and the IMU system simultaneously. Data was collected when participants walked on a 7 m walking path. Each participant performed 50 repetitions of walking on the path. To ensure the collection of complete gait cycle data, a gait cycle was considered valid only if the participant passed through the center of the walking path at the same time that the OMC system detected a valid marker signal. As a result, 5 gait cycles that met the standards of the OMC system were included in the final analysis. The stride length, cadence, velocity, stance phase and swing phase of the spatio-temporal parameters were included in the analysis. A generalized linear mixture model was used to assess the repeatability of the two systems. The Wilcoxon rank-sum test for continuous variables was used to compare the mean differences between the two systems. For evaluating the reliability of the IMU system, we calculated the Intra-class Correlation Coefficient (ICC). Additionally, Bland-Altman plots were used to compare the levels of agreement between the two systems.ResultsThe measurements of Spatio-temporal parameters, including the stance phase (P = 0.78, 0.13, L-R), swing phase (P = 0.78, 0.13, L-R), velocity (P = 0.14, 0.13, L-R), cadence (P = 0.53, 0.22, L-R), stride length (P = 0.05, 0.19, L-R), by the IMU system and OMC system were similar. Which suggested that IMU and OMC systems could be used interchangeably for gait measurements. The intra-rater reliability showed an excellent correlation for the stance phase, swing phase, velocity and cadence (Intraclass Correlation Coefficient, ICC > 0.9) for both systems. However, the correlation of stride length was poor (ICC = 0.36, P = 0.34, L) to medium (ICC = 0.56, P = 0.22, R). Additionally, the measurements of IMU systems were repeatable.ConclusionsThe results of IMU system and OMC system shown good repeatability. Wearable IMU system could analyze gait data accurately. In particular, the measurement of stance phase, swing phase, velocity and cadence showed excellent reliability. IMU system provided an alternative measurement to OMC for gait analysis. However, the measurement of stride length by IMU needs further consideration.

The Traffic Light System: A user-friendly alternative for gait data representation

BackgroundInstrumented gait analysis is an established procedure in biomechanical assessment, requiring specially-trained analysts to interpret the complex graphical output generated. Research questionDoes a new method of visual representation of lower limb kinematic gait analysis data provide a reliable and valid method of interpretation of biomechanical data for healthcare professionals? MethodsAn innovative system based on the Traffic Lights System (TLS) was developed. Simulated abnormal gait was captured using a 16-camera optoelectronic motion capture system, and the results were presented in both the Traditional Graphical System (TGS) format and the new TLS. An online form was filled by health professionals who attempted to interpret normal and abnormal motion in the joints presented in the 2 output formats. ResultsOut of 26 raters, 18 preferred the new system because of its user-friendliness and its ease of interpretation. 2 raters preferred the TGS, with one of these raters clarifying that the preference is due to colour blindness. For intra-rater reliability, 2 trained raters provided a second response for the TGS (Cronbach’s Alpha ranging between 0.733 and 0.918), whilst the TLS resulted in Cronbach’s Alpha between 0.817 and 1.00 amongst 3 untrained raters. The Fleiss Multi-rater Kappa Test demonstrated low inter-rater reliability amongst raters in the TGS, whereas the overall Fleiss Multi-rater Kappa values of the TLS surpassed the TGS in all 3 studies. SignificanceThis study showed that whilst trained health professionals have high intra-rater reliability in interpreting traditional gait analysis results, those professionals inexperienced in the system, do not always comprehend the complex graphs generated by the system when presenting gait analysis data. When these graphs are transformed into coloured outputs representing the extent of the movement, the TLS has demonstrated high validity and high intra- and inter-rater reliability, significantly exceeding those of the TGS, especially in untrained health professionals.

Interlimb Coordination during Double Support Phase of Gait in People with and without Stroke

This study aims to identify differences between participants with and without stroke regarding the ipsilesional and contralesional lower limbs kinematics, kinetics, muscle activity and their variability during double support phase of gait. Eleven post-stroke and thirteen healthy participants performed 10 gait trials at a self-selected speed while being monitored by an optoelectronic motion capture system, two force plates and an electromyographic system. The following outcomes were evaluated during the double support: the time and the joint position; the external mechanical work on the centre of mass; and the relative electromyographic activity. Both, contralesional/ipsilesional and dominant/non-dominant of participants with and without stroke, respectively, were evaluated during double support phase of gait in trailing or leading positions. The average value of each parameter and the coefficient of variation of the 10 trials were analysed. Post-stroke participants present bilateral decreased mechanical work on the centre of mass and increased variability, decreased contralesional knee and ankle flexion in trailing position, increased ipsilesional knee flexion in leading position and increased variability. Increased relative muscle activity was observed in post-stroke participants with decreased variability. Mechanical work on the centre of mass seems to be the most relevant parameter to identify interlimb coordination impairments in post-stroke subjects.

Mechanical work and energy of sit-to-stand and stand-to-sit transitions performed with traditional and dynamic office chair designs.

Adherence to sit-stand workstation usage has been shown to decrease post-intervention, with the reported reasons related to fatigue, cumbersome workstation adjustments, and focus. To characterize the mechanical work and total energy required to perform transitions from a traditional office chair and a dynamic chair designed specifically for sit-stand workstations. The whole-body, thigh, and shank centre-of-mass (CoM) were evaluated. Fifteen participants (8 male; 7 female) performed three intermittent sit-to-stand and stand-to-sit transitions from the traditional and dynamic chairs. Kinematic data of the trunk, pelvis, and lower extremities were collected using an optoelectronic motion capture system and triaxial accelerometers. The change in total energy and work between the sitting and standing postures were evaluated for each CoM point. Lumbar spine range-of-motion was further assessed between chair conditions. Chair designs facilitated opposite work and energy responses for a given transition. Transitions performed from the dynamic chair reduced the work and total energy of the whole-body CoM, by ±8.5J and ±214.6J (p < 0.001), respectively. The work and energy of the thigh CoM differed within transitions (p < 0.001), but the positive and negative components were similar between chairs (work =±0.18J, energy =±0.55J). The dynamic chair increased the total energy (±38.3J, p < 0.001) but not the work of the shank CoM (±1.1J, p≥0.347). The required mechanical work and energy of sit-to-stand and stand-to-sit transitions was modified by chair design. These outcomes have the potential to address identified reasons for the disuse of sit-stand workstations.

Level of Agreement between the MotionMetrix System and an Optoelectronic Motion Capture System for Walking and Running Gait Measurements

Markerless motion capture systems (MCS) have been developed as an alternative solution to overcome the limitations of 3D MCS as they provide a more practical and efficient setup process given, among other factors, the lack of sensors attached to the body. However, this might affect the accuracy of the measures recorded. Thus, this study is aimed at evaluating the level of agreement between a markerless MSC (i.e., MotionMetrix) and an optoelectronic MCS (i.e., Qualisys). For such purpose, 24 healthy young adults were assessed for walking (at 5 km/h) and running (at 10 and 15 km/h) in a single session. The parameters obtained from MotionMetrix and Qualisys were tested in terms of level of agreement. When walking at 5 km/h, the MotionMetrix system significantly underestimated the stance and swing phases, as well as the load and pre-swing phases (p &lt; 0.05) reporting also relatively low systematic bias (i.e., ≤ −0.03 s) and standard error of the estimate (SEE) (i.e., ≤0.02 s). The level of agreement between measurements was perfect (r &gt; 0.9) for step length left and cadence and very large (r &gt; 0.7) for step time left, gait cycle, and stride length. Regarding running at 10 km/h, bias and SEE analysis revealed significant differences for most of the variables except for stride time, rate and length, swing knee flexion for both legs, and thigh flexion left. The level of agreement between measurements was very large (r &gt; 0.7) for stride time and rate, stride length, and vertical displacement. At 15 km/h, bias and SEE revealed significant differences for vertical displacement, landing knee flexion for both legs, stance knee flexion left, thigh flexion, and extension for both legs. The level of agreement between measurements in running at 15 km/h was almost perfect (r &gt; 0.9) when comparing Qualisys and MotionMetrix parameters for stride time and rate, and stride length. The agreement between the two motion capture systems varied for different variables and speeds of locomotion, with some variables demonstrating high agreement while others showed poor agreement. Nonetheless, the findings presented here suggest that the MotionMetrix system is a promising option for sports practitioners and clinicians interested in measuring gait variables, particularly in the contexts examined in the study.

Two-Dimensional Mechanical Model of Human Stability in External Force-Caused Fall

The paper proposes a two-dimensional model of human stability. The model allows for gaining data on forces and moments of forces being the effect of musculoskeletal interactions of body parts at human joints. The necessary input data are registered with the use of an optoelectronic motion capture system, two force plates, and a dynamometer. The latter measures the magnitude of the external force that is randomly applied to cause a backward fall. Therefore, the position of the participant’s body during the experiment, the external force used to cause the fall, and the ground reaction forces are known. The model proposed has the structure of a closed kinematic chain with one loop and two open subchains and uses the Euler–Newton approach to analyse the motion. In addition to external loads, linear and angular accelerations are also needed. To calculate those, we used a variant of approximation. This consists in carrying out a simultaneous approximation of a given function and its first and second derivatives in the subintervals that shift along the whole data range. The experiments conducted include two activities while maintaining a state of equilibrium and the fall itself. This gives the basis for examining whether the internal forces and moments at human joints differ significantly in both these states. The results and conclusions are discussed in the final part of the paper.

On the Kinematics of the Forward-Facing Venetian-Style Rowing Technique

This work presents a qualitative and quantitative pilot study which explores the kinematics of Venetian style forward-facing standing rowing as practised by able-bodied competitive athletes. The technique, made famous by the gondoliers, was replicated in a biomechanics laboratory by a cohort of four experienced rowers who compete in this style at National Level events in Malta. Athletes were marked with reflective markers following the modified Helen Hayes model and asked to row in a manner which mimics their on-water practise and recorded using a Vicon optoelectronic motion capture system. Data collected were compared to its equivalent using a standard sliding-seat ergometer as well as data collated from observations of athletes rowing on water, thus permitting the documentation of the manner of how this technique is performed. It was shown that this rowing style is characterised by rather asymmetric and complex kinematics, particularly upper-body movements which provides the athlete with a total-body workout involving all major muscle groups working either isometrically, to provide stability, or actively.

Smile Reanimation with Masseteric-to-Facial Nerve Transfer plus Cross-Face Nerve Grafting in Patients with Segmental Midface Paresis: 3D Retrospective Quantitative Evaluation

Facial paresis involves functional and aesthetic problems with altered and asymmetric movement patterns. Surgical procedures and physical therapy can effectively reanimate the muscles. From our database, 10 patients (18–50 years) suffering from unilateral segmental midface paresis and rehabilitated by a masseteric-to-facial nerve transfer combined with a cross-face facial nerve graft, followed by physical therapy, were retrospectively analyzed. Standardized labial movements were measured using an optoelectronic motion capture system. Maximum teeth clenching, spontaneous smiles, and lip protrusion (kiss movement) were detected before and after surgery (21 ± 13 months). Preoperatively, during the maximum smile, the paretic side moved less than the healthy one (23.2 vs. 28.7 mm; activation ratio 69%, asymmetry index 18%). Postoperatively, no differences in total mobility were found. The activity ratio and the asymmetry index differed significantly (without/with teeth clenching: ratio 65% vs. 92%, p = 0.016; asymmetry index 21% vs. 5%, p = 0.016). Postoperatively, the mobility of the spontaneous smiles significantly reduced (healthy side, 25.1 vs. 17.2 mm, p = 0.043; paretic side 16.8 vs. 12.2 mm, p = 0.043), without modifications of the activity ratio and asymmetry index. Postoperatively, the paretic side kiss movement was significantly reduced (27 vs. 19.9 mm, p = 0.028). Overall, the treatment contributed to balancing the displacements between the two sides of the face with more symmetric movements.

Indoor Visual-Based Localization System for Multi-Rotor UAVs.

Industry 4.0, smart homes, and the Internet of Things are boosting the employment of autonomous aerial vehicles in indoor environments, where localization is still challenging, especially in the case of close and cluttered areas. In this paper, we propose a Visual Inertial Odometry localization method based on fiducial markers. Our approach enables multi-rotor aerial vehicle navigation in indoor environments and tackles the most challenging aspects of image-based indoor localization. In particular, we focus on a proper and continuous pose estimation, working from take-off to landing, at several different flying altitudes. With this aim, we designed a map of fiducial markers that produces results that are both dense and heterogeneous. Narrowly placed tags lead to minimal information loss during rapid aerial movements while four different classes of marker size provide consistency when the camera zooms in or out according to the vehicle distance from the ground. We have validated our approach by comparing the output of the localization algorithm with the ground-truth information collected through an optoelectronic motion capture system, using two different platforms in different flying conditions. The results show that error mean and standard deviation can remain constantly lower than , so not degrading when the aerial vehicle increases its altitude and, therefore, strongly improving similar state-of-the-art solutions.

Transcranial direct current stimulation (tDCS) modulates motor execution in a limb reaching task.

The majority of human activities show a trade-off between movement speed and accuracy. Here we tested 16 participants in a quick pointing action after 20 minutes (2 mA) of transcranial direct current stimulation (tDCS) delivered at the supplementary motor area in a single-blind crossover design study for testing the feedforward components in the control of action. tDCS stimuli were delivered in three randomized sessions of stimulations as anodal, cathodal and sham as a control. The task performed pre- and post-tDCS stimulation, was to point as fast and as precise as possible with the big toe to targets having different sizes (2 and 8 cm; Width) and positioned at different distances (20 and 60 cm; Distance). An optoelectronic motion capture system was used to collect the kinematics of movement. The result indicates that individuals after receiving anodal stimulation decreased their movement time and increased their movement speed, while the opposite happened after receiving a cathodal stimulation. The scarcity of studies in this area invites us to plan a research that aims at the trade-off especially in the clinical settings.

Validity and repeatability of a new inertial measurement unit system for gait analysis on kinematic parameters: Comparison with an optoelectronic system

Inertial measurement unit (IMU) systems are offering promising alternatives to optoelectronic systems for measuring human movement. The objective of this study was to assess the validity of a new inertial measurement system, iSen STT-IWS sensors, with reference to the optoelectronic motion capture system OptiTrack. 22 young participants performed three minutes of treadmill walking at different speeds. Hip, knee and ankle joint angles in the sagittal plane were compared between the two systems. Accuracy and repeatability of iSen IMU measures was evaluated with the Root Mean Square Deviation (RMSD) and Lin’s Concordance Correlation (LCC). A good to tolerable Isen measures’ accuracy was found (RMSD < 10°, LCC > 0.75) and reliability decreased with walking speed. Results indicated excellent test–retest repeatability of the inertial system (Intraclass correlation (ICC) > 0.75). Sagittal kinematic gait estimation using the iSen IMU system can be reliably used for clinical purposes on older adults.

A Deep Learning Approach for Gait Event Detection from a Single Shank-Worn IMU: Validation in Healthy and Neurological Cohorts.

Many algorithms use 3D accelerometer and/or gyroscope data from inertial measurement unit (IMU) sensors to detect gait events (i.e., initial and final foot contact). However, these algorithms often require knowledge about sensor orientation and use empirically derived thresholds. As alignment cannot always be controlled for in ambulatory assessments, methods are needed that require little knowledge on sensor location and orientation, e.g., a convolutional neural network-based deep learning model. Therefore, 157 participants from healthy and neurologically diseased cohorts walked 5 m distances at slow, preferred, and fast walking speed, while data were collected from IMUs on the left and right ankle and shank. Gait events were detected and stride parameters were extracted using a deep learning model and an optoelectronic motion capture (OMC) system for reference. The deep learning model consisted of convolutional layers using dilated convolutions, followed by two independent fully connected layers to predict whether a time step corresponded to the event of initial contact (IC) or final contact (FC), respectively. Results showed a high detection rate for both initial and final contacts across sensor locations (recall , precision ). Time agreement was excellent as witnessed from the median time error (0.005 s) and corresponding inter-quartile range (0.020 s). The extracted stride-specific parameters were in good agreement with parameters derived from the OMC system (maximum mean difference 0.003 s and corresponding maximum limits of agreement (−0.049 s, 0.051 s) for a confidence level). Thus, the deep learning approach was considered a valid approach for detecting gait events and extracting stride-specific parameters with little knowledge on exact IMU location and orientation in conditions with and without walking pathologies due to neurological diseases.

Differences in the Glenohumeral Joint before and after Unilateral Breast Cancer Surgery: Motion Capture Analysis.

After mastectomy, women might lose mobility and develop kinematic changes in the shoulder. The objective of this research was to compare the kinematics of the glenohumeral joint in women, before and after unilateral breast cancer surgery. This was a longitudinal study with a pre- and post-evaluation design; in total, 15 Mexican women who had a mastectomy for breast cancer and who received a physical therapy program after surgery were evaluated. Flexion–extension and abduction–adduction movements of the glenohumeral joint were evaluated (15 days before and 60 days after mastectomy). For the kinematic analysis of the glenohumeral joint, an optoelectronic motion capture system was used to monitor 41 reflective markers located in anatomical landmarks. There was no significant difference in the range of motion of the glenohumeral joint when comparing pre- and post-mastectomy, flexion–extension (p = 0.138), and abduction–adduction (p = 0.058). Furthermore, patients who received chemotherapy (53%) before mastectomy were more affected (lower range of motion) than those who did not receive it. There were no significant differences in the kinematics of the glenohumeral joint after mastectomy in this group of patients who received a physical therapy program after surgery. Moreover, patients who received chemotherapy treatment before breast cancer surgery tended to have a lower range of motion than those who did not receive it. Therefore, it is necessary for the physical rehabilitation team to attend to these patients even before the mastectomy.

Margins of stability and trunk coordination during Nordic walking

Although it has already been demonstrated that Nordic walking has some peculiar biomechanical features with respect to walking, the effects on balance and trunk coordination are still unknown. Our aim here was to compare margins of stability, hip stabilizer muscle activation and scapular-pelvis coordination (mean and variability of continuous relative phase) between walking and two different pole walking techniques (observational design). Eleven Nordic walking instructors were asked to walk at 5.5 km·h−1 on a flat treadmill while 1) walking, 2) Nordic walking and 3) pole walking with just elbow flexion–extension motion allowed and constrained shoulder motion (elbow technique). The 3D movements of limbs and poles were measured by an optoelectronic motion capture system, and gluteus medius activation was measured through surface electromyography. Both techniques using poles show larger mediolateral margins of stability and similar anterior-posterior margins of stability in comparison with walking (p < 0.001). The larger mediolateral margin of stability using poles (conditions 2 and 3) is accompanied by greater trunk coordination stability (greater continuous relative phase variability) than walking. Although the Nordic walking (condition 2) technique results in a similar range of scapular and pelvis transverse rotation, the general pattern of scapular-pelvis coordination was temporally delayed by approximately 20% of the gait cycle in relation to other conditions (1 and 3). In conclusion, Nordic walking provides enhanced mediolateral support and coordination stability of trunk compared with walking, suggesting that it could be proposed as a safer exercise modality than walking.

Validation of the Perception Neuron system for full-body motion capture.

Recent advancements in Inertial Measurement Units (IMUs) offers the possibility of its use as a cost effective and portable alternative to traditional optoelectronic motion capture systems in analyzing biomechanical performance. One such commercially available IMU is the Perception Neuron motion capture system (PNS). The accuracy of the PNS had been tested and was reported to be a valid method for assessing the upper body range of motion to within 5° RMSE. However, testing of the PNS was limited to upper body motion involving functional movement within a single plane. Therefore, the purpose of this study is to further validate the Perception Neuron system with reference to a conventional optoelectronic motion capture system (VICON) through the use of dynamic movements (e.g., walking, jogging and a multi-articular sports movement with object manipulation) and to determine its feasibility through full-body kinematic analysis. Validation was evaluated using Pearson's R correlation, RMSE and Bland-Altman estimates. Present findings suggest that the PNS performed well against the VICON motion analysis system with most joint angles reporting a RMSE of < 4° and strong average Pearson's R correlation of 0.85, with the exception of the shoulder abduction/adduction where RMSE was larger and Pearson's R correlation at a moderate level. Bland-Altman analysis revealed that most joint angles across the different movements had a mean bias of less than 10°, except for the shoulder abduction/adduction and elbow flexion/extension measurements. It was concluded that the PNS may not be the best substitute for traditional motion analysis technology if there is a need to replicate raw joint angles. However, there was adequate sensitivity to measure changes in joint angles and would be suitable when normalized joint angles are compared and the focus of analysis is to identify changes in movement patterns.

The WGD-A Dataset of Assembly Line Working Gestures for Ergonomic Analysis and Work-Related Injuries Prevention.

This paper wants to stress the importance of human movement monitoring to prevent musculoskeletal disorders by proposing the WGD—Working Gesture Dataset, a publicly available dataset of assembly line working gestures that aims to be used for worker’s kinematic analysis. It contains kinematic data acquired from healthy subjects performing assembly line working activities using an optoelectronic motion capture system. The acquired data were used to extract quantitative indicators to assess how the working tasks were performed and to detect useful information to estimate the exposure to the factors that may contribute to the onset of musculoskeletal disorders. The obtained results demonstrate that the proposed indicators can be exploited to early detect incorrect gestures and postures and, consequently to prevent work-related disorders. The approach is general and independent on the adopted motion analysis system. It wants to provide indications for safely performing working activities. For example, the proposed WGD can also be used to evaluate the kinematics of workers in real working environments thanks to the adoption of unobtrusive measuring systems, such as wearable sensors through the extracted indicators and thresholds.

An Innovative Sensor Fusion Algorithm for Motion Tracking With On-Line Bias Compensation: Application to Joint Angles Estimation in Yoga

Magnetic Inertial Measurement Units (MIMUs) represent an increasingly used technology in the field of human motion. However, their applications are strongly affected by magnetic disturbances and poor calibration, which could determine inaccurate attitude estimations. Thus, Inertial Measurement Units (IMUs), relying exclusively on accelerometers and gyroscopes, could be used as an alternative to MIMUs for motion tracking, avoiding the negative effect of magnetic disturbances. Unfortunately, gyroscope signals are characterized by several error sources, among which gyroscope bias, whose variations due to environmental factors and temporal instability strongly affect the attitude estimation accuracy. Aim of the present work is to propose a novel sensor fusion algorithm for IMU-based applications that embodies an adaptive on-line bias capture module. The accuracy of the proposed filter was tested on ten expert yoga practitioners during the execution of a sun salutation sequence. The right upper limb joint angles were estimated and their accuracy assessed in terms of Mean Absolute Error (MAE) and Pearson’s correlation coefficient by comparison with an optoelectronic motion capture system. The achieved worst-case accuracy was 5.59, 6.75 and 3.49 degrees for the wrist, elbow and shoulder joints respectively. The accuracy of the algorithm is further confirmed by the high values of the Pearson’s correlation coefficients between IMUs and OMC angles, which were greater than 0.91, 0.92 and 0.98 respectively for the three considered joints. The proposed algorithm can thus be considered as a promising tool for attitude estimation in those contexts when magnetic interferences cannot be monitored and, thus, adequately compensated.