Planar Motion Research Articles

Numerical PMM test in finite depth

This study conducted a numerical planar motion mechanism (PMM) test for a containership, considering the effects of finite depth. An OpenFOAM-based computational fluid dynamics (CFD) approach was employed to conduct the simulations. Before conducting a series of numerical computations, uncertainty analysis for the grid size and time step was performed to ensure the reliability of the computational results. Two PMM tests, static drift and pure yaw, were conducted, and the results were validated against experimental data. The comparison demonstrated good agreement between forces, moments, and hydrodynamic coefficients when compared with both experimental and other computational results. Furthermore, a comparison between a first- and second-order combination model and a first- and third-order combination model revealed that the latter showed better alignment with experimental data in deep water, while the former performed better in shallow water, emphasizing the role of crossflow. This study contributes to understanding the differences in maneuvering performance between deep and shallow water conditions.

Type Synthesis of a Novel Class of One-DOF Multi-Mode Parallel Mechanisms

Abstract Multi-mode parallel mechanisms (PMs) are a class of reconfigurable mechanisms that can switch between different operation modes without the need for disconnection and reassembly. Although a number of multi-DOF multi-mode PMs have been presented in the literature, very few 1-DOF multi-mode PMs have been proposed. This paper deals with the type synthesis of a novel class of 1-DOF multi-mode PMs, which have one 1-DOF translation mode and at least one 1-DOF planar motion mode, using a construction method by leveraging symmetry of mechanisms and merging two multi-mode mechanisms. By inserting a revolute (R) joint into Sarrus-6R like six-joint mechanisms, 1-DOF two-mode two-legged PMs, which are composed of a moving platform and a base connected by one three-joint leg and one four-joint leg, are constructed first. From each 1-DOF two-mode two-legged PM, one can construct a 1-DOF two-mode three-legged PM by adding a third four-joint leg which is the mirror image of the four-joint leg about the plane of motion of the three-joint leg. Subsequently, 1-DOF three- and four-mode three-legged PMs are constructed by merging two 1-DOF multi-mode three-legged PMs. The instantaneous DOF of the above multi-mode PMs in a transition configuration is analyzed using screw theory. This work complements the existing approaches to the type synthesis of multi-mode PMs and hybrid reconfigurable mechanisms.

The Bressesque Surface: Distribution of Screw Pitch

Abstract Presented is an overview of the T-N interpretation of the famous planar Euler–Savary formula. The T-N spatial analog interpretation consists of two components: the established axial component along with a new transverse component. The axial component entails the spatial Euler–Savary relation involving the Disteli axis and motion parallel to the instantaneous screw axis (ISA). The transverse component emulates the classical planar Euler–Savary relation involving motion perpendicular to the ISA. Within the T-N interpretation is an inflection surface together with a family of Bressesque surfaces. Traditionally, a Bresse circle is a planar motion concept defined by points with zero tangential acceleration. Here, the Bressesque surfaces do not consider accelerations akin to the planar scenario. Instead, the Bressesque surfaces are defined as a linear combination of two axes of the inflection surface. These two axes are used to establish a skew axis gear set where the axodes are tangent along a generator of the Bressesque surface. This tangency is the ISA for the gear set. What is new is the screw pitch for each generator of the hyperboloidal Bressesque surface. Two graphs are shown: the first graph is the variation in screw pitch in terms of the ray angle and the second graph is the variation in speed ratio of the skew axes gear set in terms of the ray angle.

Spatiotemporal kinematics during top speed sprinting in male intercollegiate track and field and team sport athletes

ABSTRACT We investigated spatiotemporal kinematics during top speed sprinting and biomechanical running strategies in 98 male intercollegiate athletes from a range of athletic backgrounds in track and field (TF, n = 28) and team sports (TS, n = 70). Participants completed 40 m running trials with sagittal plane motion analyses of high-speed video captured from 30 m to 40 m. Across the entire sample, measures of contact time, step rate, step length, flight length and duty factor (ratio of contact duration to stride duration) were meaningfully correlated with top speed (p < 0.05, 0.51 ≤ |r or ρ| ≤ 0.78). Flight time and contact length were weakly correlated with top speed (p < 0.05, 0.27 ≤ |r or ρ| ≤ 0.34). When comparing sub-groups of Slow TF (n = 14) and Fast TS athletes (n = 22) with similar top speeds (~9.3 m/s), Fast TS athletes clearly demonstrated a more ground-based strategy, with longer ground contact times and contact lengths, shorter flight times and flight lengths, and larger duty factors. Therefore, the results of this study suggest that existing technical models and normative metrics based on data from TF athletes could require modification when evaluating and coaching sprinting performance with TS athletes.

Minimal solver for relative pose estimation under planar motion

Minimal solver for relative pose estimation under planar motion

SECEC Grammont Award 2024: The critical role of posture adjustment for range of motion simulation in reverse total shoulder arthroplasty preoperative planning.

The objective of this study was to compare simulated range of motion (ROM) for reverse total shoulder arthroplasty (rTSA) with and without adjustment for scapulothoracic orientation in a global reference system. We hypothesized that values for simulated ROM in preoperative planning software with and without adjustment for scapulothoracic orientation would be significantly different. A statistical shape model of the entire humerus and scapula was fitted into ten shoulder CT scans randomly selected from 162 patients who underwent rTSA. Six shoulder surgeons independently planned a rTSA in each model using prototype development software with the ability to adjust for scapulothoracic orientation, the starting position of the humerus, as well as kinematic planes in a global reference system simulating previously described posture types A, B, and C. ROM with and without posture adjustment was calculated and compared in all movement planes. All movement planes showed significant differences when comparing protocols with and without adjustment for posture. The largest mean difference was seen in external rotation, being 62° (SD 16°) without adjustment compared to 25° (SD 9°) with posture adjustment (p < 0.001), with the highest mean difference being 49° (SD 15°) in type C. Mean extension was 57° (SD 18°) without adjustment versus 24° (SD 11°) with adjustment (p < 0.001) and the highest mean difference of 47° (SD 18°) in type C. Mean abducted internal rotation was 69° (SD 11°) without adjustment versus 31° (SD 6°) with posture adjustment (p < 0.001), showing the highest mean difference of 51° (SD 11°) in type C. The present study demonstrates that accounting for scapulothoracic orientation has a significant impact on simulated ROM for rTSA in all motion planes, specifically rendering vastly lower values for external rotation, extension, and high internal rotation. The substantial differences observed in this study warrant a critical re-evaluation of all previously published studies that examined component choice and placement for optimized ROM in rTSA using conventional preoperative planning software.

Can we reliably assess spine movement quality in clinics? A comparison of systems to evaluate reliability of spine movement quality in a healthy population

Inertial measurement units (IMUs) have the potential to facilitate a large influx of spine movement and neuromuscular control data to stratify low back pain (LBP) diagnosis and care; however, uncertainties related to validity and reliability are preventing widespread use and acceptance. This study evaluated the concurrent validity of Xsens DOT IMUs relative to gold-standard optical motion capture equipment, and compared within- and between-day reliability of both systems to track spine range of motion (ROM) and movement quality (MQ) by evaluating intraclass correlation coefficients (ICC), standard error of measurement (SEM), coefficient of variation (CV), and minimum detectable difference (MDD). ROM was evaluated during planar ROM movements, and local dynamic stability (LDS; λmax), mean absolute relative phase (MARP) and deviation phase (DP) were estimated from repetitive trunk flexion at 3 speeds, in 15 healthy controls. Results show no statistically significant differences between systems for all metrics, and ICCs ≥ 0.86; therefore, validity was confirmed for tracking primary axis ROM and MQ. IMU data revealed that absolute (C7, T12, and S1) and relative (thoracic, lumbar, and total) ROM was the most reliable metric, followed by λmax, DP, and MARP. Reliability was similar between systems, suggesting that the poorer between-day reliability (higher SEM and CV, lower ICC) observed is attributable to movement variability and sensor placement rather than equipment error. MDDs provide thresholds to researchers and clinicians for identifying change in MQ. Further standardization of evaluated movements/metrics, and patient subgrouping are suggested to improve reliability assessments and refine MDDs in future work.

Practical 6-DoF Manoeuvring Simulation of a BB2 Submarine Near the Free Surface

It is necessary to predict the manoeuvring performance of a submarine accurately at the early design stage for its safe and effective operations. In this paper, the practical 6-DoF simulation models of an X-form stern plane submarine operating near the free surface are proposed. A 1/15 scaled model of ‘BB2 submarine’ is constructed, the captive model tests are performed in a towing tank of Korea Research Institute of Ships and Ocean Engineering (KRISO) at the full-scale depths, 30, 15.4 (snorkel depth), and 4.5 metres (surfaced depth). Resistance and propulsion tests are performed at the deepest depth, 30 metres. The vertical planar motion mechanism (PMM) tests including the forced rolling motions are also carried out at the depth of 30 metres. The horizontal PMM tests are conducted at three kinds of depths, respectively. The depth-varying horizontal plane coefficients in the model are identified, and the coefficients which are little influenced by the depths are treated as the constant values for the practical purpose. Some of velocity coupled terms are approximated by using the added mass coefficients on the assumption that the viscous components are negligible. In addition, the resistance increases, vertical suction forces and moments are measured in the straight-ahead tests with varying the submergence depths. The free surface effects are considered as the exponential function terms in the proposed models. Based on the present tests and the previous studies about the free surface effects on the submerged bodies, it is practically assumed that the free surface effects are exponentially decayed with the depths, and are already negligible when the submergence depth is 30 metres, approximately three times the hull depth. Horizontal and vertical plane manoeuvring motions as well as the neutral flights are simulated with the control plane deflections less than 15 degrees. The present simulations are in good agreements with existing free-running model test results.

A Compact and Cost-Effective Gait Simulator to Advance Prosthesis Development with Reduced Reliance on Human Subject Testing: Development, Validation and Application

Gait simulators play a crucial role in assessing the performance of physical prototypes of prosthetic knees, validating numerical simulation findings, and reducing dependency on user trials during prosthesis development. However, their practical application is limited because of substantial capital investment required for sophisticated high degrees-of-freedom (DOF) system development on one side and insufficient DOF for accurate simulation on the other. In this study, we evaluated the minimum DOF of thigh segment that a gait simulator should have to test the performance of prosthetic knees in a cost-effective manner. Initially, numerical simulations of swing phase of prosthetic leg with IITM polycentric knee (IPK) using 3D gait data and with different arrested DOF of the thigh were performed to identify the essential DOF of gait simulator. By comparing different cases of arrested DOF with the six-DOF ideal case, it was revealed that only sagittal plane movements, namely flexion-extension, vertical translation, and horizontal translation, are sufficient to test prosthetic knees. Subsequently, a compact and modular gait simulator was developed. Hardware-in-loop simulations of the IPK using the gait simulator were used to demonstrate its effectiveness in assessing the performance of prosthetic knees, which validated the ability of the IPK to extend completely without an extension assist before heel contact. Additionally, it was exposed that the IPK's extension stop needs redesigning to effectively absorb the impact energy when the knee extends completely before heel contact. These findings emphasize the significance of a cost-effective gait simulator in prosthesis development and reduce dependency on user trials.

Comparison Between InterCriteria and Correlation Analyses over sEMG Data from Arm Movements in the Horizontal Plane

InterCriteria analysis (ICrA) and two kinds of correlation analyses, Pearson (PCA) and Spearman (SCA), were applied to surface electromyography (sEMG) signals obtained from human arm movements in the horizontal plane. Ten healthy participants performed ten movements, eight of which were cyclic. Each cyclic movement (CM) consisted of flexion and extension phases with equal duration (10 s, 6 s, 2 s, and 1 s) and two 5 s rest poses between them. The CMs were performed with and without an added load of 0.5 kg on the wrists of the participants. The sEMG signals from six different muscles or separate muscle heads (m. deltoideus pars clavicularis, m. deltoideus pars spinata, m. brachialis, m. anconeus, m. biceps brachii, and m. triceps brachii long head) were recorded and used to compare the results of the ICrA, PCA, and SCA. All three methods found identical consonance pairs for the flexion and extension CM phases. Additionally, PCA detected two more consonance pairs in the extension phases. In this investigation, ICrA, PCA, and SCA were proven to be reliable tools when applied separately or in combination for sEMG data. These three methods are appropriate for researching arm movements in the horizontal plane and experimental protocol revision.

In-plane orientational motions of the functional groups of molecules at the air/water interface by time-resolved vibrational sum frequency generation.

The movements of molecules at interfaces and surfaces are restricted by their asymmetric environments, leading to anisotropic orientational motions. In this work, in-plane orientational motions of the -C=O and -CF3 groups of coumarin 153 (C153) at the air/water interface were measured using time-resolved (TR) vibrational sum frequency generation (SFG). The in-plane orientational time constants of the -C=O and -CF3 groups of C153 are found to be 41.5 ± 8.2 and 36.0 ± 4.5ps. These values are over five-times faster than that of 198 ± 15ps for the permanent dipole of the whole C153molecule at the interface, which may indicate that the two groups experience different interfacial friction in the plane. These differences could also be the result of the permanent dipole of C153 being almost five times those of the -C=O and -CF3 groups. The difference in orientational motions reveals the microscopic heterogeneous environment that molecules experience at the interface. While the interfacial dynamics of the two functional groups are similar, our TR-SFG experiments allowed the quantification of the in-plane dynamics of individual functional groups for the first time. Our experimental findings about the interfacial molecular motion have implications for molecular rotations, energy transfer, and charge transfer at material interfaces, photocatalysis interfaces, and biological cell/membrane aqueous interfaces.

A novel spine tester TO GO.

Often after large animal experiments in spinal research, the question arises-histology or biomechanics? While biomechanics are essential for informed decisions on the functionality of the therapy being studied, scientists often choose histological analysis alone. For biomechanical testing, for example, flexibility, specimens must be shipped to institutions with special testing equipment, as spine testers are complex and immobile. The specimens must usually be shipped frozen, and, thus, biological and histological investigations are not possible anymore. To allow both biomechanical and biological investigations with the same specimen and, thus, to reduce the number of required animals, the aim of the study was to develop a spine tester that can be shipped worldwide to test on-site. The "Spine Tester TO GO" was designed consisting of a frame with three motors that initiate pure moments and rotate the specimen in three motion planes. A load cell and an optical motion tracking system controlled the applied loads and measured range of motion (ROM) and neutral zone (NZ). As a proof of concept, the new machine was validated and compared under real experimental conditions with an existing testing machine already validated employing fresh bovine tail discs CY34 (n = 10). The new spine tester measured reasonable ROM and NZ from hysteresis curves, and the ROM of the two testing machines formed a high coefficient of determination R 2 = 0.986. However, higher ROM results of the new testing machine might be explained by the lower friction of the air bearings, which allowed more translational motion. The spine tester TO GO now opens up new opportunities for on-site flexibility tests and contributes hereby to the 3R principle by limiting the number of experimental animals needed to obtain full characterization of spine units at the macroscopic, biomechanical, biochemical, and histological level.

Relative pose estimation from panoramic images using a hybrid neural network architecture

Camera-based relative pose estimation (RPE) localizes a mobile robot given a view at the current position and an image at a reference location. Matching the landmarks between views is critical to localization quality. Common challenges are appearance changes, for example due to differing illumination. Indirect RPE methods extract high-level features that provide invariance against appearance changes but neglect the remaining image data. This can lead to poor pose estimates in scenes with little detail. Direct RPE methods mitigate this issue by operating on the pixel level with only moderate preprocessing, but invariances have to be achieved by different means. We propose to attain illumination invariance for the direct RPE algorithm MinWarping by integrating it with a convolutional neural network for image preprocessing, creating a hybrid architecture. We optimize network parameters using a metric on RPE quality, backpropagating through MinWarping and the network. We focus on planar movement, panoramic images, and indoor scenes with varying illumination conditions; a novel dataset for this setup is recorded and used for analysis. Our method compares favourably against the previous best preprocessing method for MinWarping, edge filtering, and against a modern deep-learning-based indirect RPE pipeline. Analysis of the trained hybrid architecture indicates that neglecting landmarks in a direct RPE framework can improve estimation quality in scenes with occlusion and few details.

Experimental study on enhancing pedestrian efficiency and crowd safety with regular sound under open boundaries

Abstract We empirically investigated the impact of regular sound on planar pedestrian movement in open boundary environments, a rarely studied topic. Participants walked to regular sound with different tempos (70 BPM vs. 100 BPM) and types (monotone vs. periodic ‘tick-tack’ rhythm). We found that regular sounds at 100 BPM, close to the normal walking pace, improve pedestrian efficiency. They reduce passing time by 8.41% and increase average flow by 9.50%. This efficiency enhancement is lower compared to single-file experiment with periodic boundaries, where reaching a high-density jammed phase is easier. Additionally, this efficiency enhancement from sound is reduced by unstable step synchronization under open boundaries and turning behavior. Regular sound significantly improves crowd safety in turning areas, where congestion levels (Cls) and crowd danger (Cd) are highest. Cls decrease by 8.27% with the 100 BPM monotone, and Cd decreases by 19.1% with the 100 BPM periodic rhythm. Operationally, regular sounds at 100 BPM can be used to guide pedestrian flow smoothly and effectively in crowd management.

Quasi-two-dimensional dispersions of Brownian particles with competitive interactions: phase behavior and structural properties.

Competing short-range attractive (SA) and long range repulsive (LR) particle interactions can be used to describe three-dimensional charge-stabilized colloid or protein dispersions at low added salt concentrations, as well as membrane proteins with interaction contributions mediated by lipid molecules. Using Langevin dynamics (LD) simulations, we determine the generalized phase diagram, cluster shapes and size distributions of a generic quasi-two-dimensional (Q2D) dispersion of spherical SALR particles confined to in-plane motion inside a bulk fluid. The SA and LR interaction parts are modelled by a generalized Lennard-Jones potential and a screened Coulomb potential, respectively. The microstructures of the detected equilibrium and non-equilibrium Q2D phases are distinctly different from those observed in three-dimensional (3D) SALR systems, by exhibiting different levels of hexagonal ordering. We discuss a thermodynamic perturbation theory prediction for the metastable binodal line of a reference system of particles with SA interactions only, which in the explored Q2D-SALR phase diagram region separates cluster from non-clustered phases. The transition from the high-temperature (small SA) dispersed fluid (DF) phase to the lower-temperature equilibrium cluster (EC) fluid phase is characterised by a low-wavenumber peak height of the static structure factor (corresponding to a thermal correlation length of about twice the particle diameter) featuring a distinctly smaller value (≈1.4) than in 3D SALR systems. With decreasing temperature (increasing SA), the cluster morphology changes from disk-like shapes in the equilibrium cluster phase, to double-stranded anisotropic hexagonal cluster segments formed in a cluster-percolated (CP) gel-like phase. This transition can be quantified by a hexagonal order parameter distribution function. The mean cluster size and coordination number of particles in the CP phase are insensitive to changes in the attraction strength.

Efficient Data Collection Strategy for Modeling the Dynamics of Floating Robotic Vehicles Using Neural Networks

As the hydrodynamic model of a surface vehicle is highly nonlinear and of high dimension, an extensive set of experiments is required to estimate the parameters of the model. Typically, the dynamic behavior of a surface vehicle is investigated through experimental tests such as planar motion mechanisms or free running tests in specialized test facilities. However, the cost of such tests is very high, and it is challenging to design effective and efficient test conditions, especially when the model is represented by numerous parameters such as neural networks. In this paper, we propose an efficient data collection strategy for modeling the dynamics of a floating robotic vehicle using neural networks. For generalized modeling, it is important to collect diverse data by exploring all the reachable state space of the vehicle. To achieve this, a data collection policy is built based on sampling-based planning toward reducing the uncertainty of the neural network-based model. The proposed method allows for collecting more comprehensive data than other commonly used random-based data collection policies. We show experimentally that the proposed method enables more accurate modeling of both fully actuated and under-actuated floating robotic vehicles, as demonstrated by the effective execution of various tasks.

Neural network and layer-wise relevance propagation reveal how ice hockey protective equipment restricts players' motion.

Understanding the athlete's movements and the restrictions incurred by protective equipment is crucial for improving the equipment and subsequently, the athlete's performance. The task of equipment improvement is especially challenging in sports including advanced manoeuvres such as ice hockey and requires a holistic approach guiding the researcher's attention toward the right variables. The purposes of this study were (a) to quantify the effects of protective equipment in ice hockey on player's performance and (b) to identify the restrictions incurred by it. Twenty male hockey players performed four different drills with and without protective equipment while their performance was quantified. A neural network accompanied by layer-wise relevance propagation was applied to the 3D kinematic data to identify variables and time points that were most relevant for the neural network to distinguish between the equipment and no equipment condition, and therefore presumable result from restrictions incurred by the protective equipment. The study indicated that wearing the protective equipment, significantly reduced performance. Further, using the 3D kinematics, an artificial neural network could accurately distinguish between the movements performed with and without the equipment. The variables contributing the most to distinguishing between the equipment conditions were related to the upper extremities and movements in the sagittal plane. The presented methodology consisting of artificial neural networks and layer-wise relevance propagation contributed to insights without prior knowledge of how and to which extent joint angles are affected in complex maneuvers in ice hockey in the presence of protective equipment. It was shown that changes to the equipment should support the flexion movements of the knee and hip and should allow players to keep their upper extremities closer to the torso.

Effect of adapted dance program on gait in adults with cerebral palsy: a pilot study.

The gait function in adults with cerebral palsy (CP) deteriorates rapidly with age. Dance has been used as an effective intervention to improve balance, postural control, and gait. This study aimed to investigate the feasibility and effects of an adapted dance program (ADP) on the gait in adults with CP. The ADP, which consists of floor and barre workouts, was designed to be adapted for individuals with CP. Ten female adults with spastic diplegic CP (mean age 52.3 ± 6.34, Gross Motor Function Classification System level II) participated in this study. Outcome measures, examined using 3D gait analysis, included spatiotemporal gait parameters and the Gait Deviation Index (GDI) based on nine kinematic variables in all planes of motion. To assess feasibility, we conducted post-questionnaires and a group interview. The ADP, each lasting 90 min, was held twice per week for 12 weeks. A statistically significant improvement was observed in GDI (Δ5.74 points, p = 0.014), with a large effect size (d = 0.76). Foot off (Δ-0.72%), first double support (Δ-0.2%), second double support (Δ1.5%), and single support (Δ0.64%) showed no significant differences. Step length (Δ1.48 cm), cadence (Δ3.95 steps/min), and walking speed (Δ6.41 cm/s) tended to increase, though the differences were not statistically significant. Participants expressed high levels of physical and emotional satisfaction, suggesting a need for early intervention. The ADP may improve gait patterns in adults with spastic diplegic CP. The feasibility results indicated that the ADP is suitable for adults with spastic diplegic CP. This study provides evidence for improvement in gait patterns through dance, which has not been reported in previous dance studies on individuals with CP, offering additional information on the benefits of dance.

Design and analysis of a thick-panel origami-inspired soft crawling robot with multiple locomotion patterns

Abstract Due to the flexibility obtained through both materials and structures, soft robots have wide potential applications in complicated internal and external environments. This paper presents a new soft crawling robot with multiple locomotion patterns that integrate inchworm motion and various turning motions. First, the conceptual design of the proposed robot is presented by introducing thick-panel origami into the synthesis of a crawling robot, resulting in a Waterbomb-structure-inspired hybrid mechanism. Second, all locomotion patterns of the robot are precisely described and analyzed by screw theory in an algebraic manner, which include inchworm motion, restricted planar motion, quantitative turning motion, and marginal exploration motion. Then, the output motion parameter for each locomotion pattern is analytically modeled as a function of the robotic dimensional parameters, and the robot can thus be designed and controlled in a customized way for the expected output motion. Finally, the theoretical analysis and derivations are validated by simulation and physical prototype building, which lay the foundations for the design and manufacture of small-scale soft crawling robots with precise output motions in a complex planar environment.

Assessing the Reliability and Validity of Inertial Measurement Units to Measure Three-Dimensional Spine and Hip Kinematics During Clinical Movement Tasks

Inertial measurement units (IMUs) provide benefits over the traditional optoelectronic motion capture (OMC) systems in measuring kinematics for the low back pain population. The reliability and validity of IMUs to quantify three-dimensional motion for multiple hip/spine segments have not been systematically evaluated. The purpose of this study was to determine the repeated-measures reliability and concurrent validity of an IMU system for measuring the three-dimensional spine/hip kinematics in six common movement assessments. Seventeen participants (32.3 (14.7) years; 11 female) performed two trials each of six range-of-motion assessments while fitted with four IMUs (T1/T2, T12/L1, L5/S1, and femur). The IMUs showed good–excellent reliability for most of the movements in the primary plane and poor–moderate reliability in the non-primary planes. The IMU and OMC systems showed generally good–excellent agreement in the primary plane and RMSE values between 3.03° and 15.75°. The removal of outliers based on the Bland–Altman analysis resulted in RMSE values between 2.44° and 10.30°. The system agreement in the non-primary planes was generally poor–moderate, and the RMSE values ranged from 2.19° to 45.88°. Anomalies in the proprietary sensor fusion algorithm or calibration may have contributed to the large RMSE values, highlighting the importance of assessing data for physiological relevance. The results suggest that these IMUs may be best suited for population-based studies measuring movement in the primary plane and point toward the need for the development of more robust approaches for broader implementation.