Angular Acceleration Research Articles

Robust Path-Following Control for AUV under Multiple Uncertainties and Input Saturation

In this paper, a robust path-following control strategy is proposed to deal with the path-following problem of the underactuated autonomous underwater vehicle (AUV) with multiple uncertainties and input saturation, and the effectiveness of the proposed control strategy is verified by semi-physical simulation experiments. Firstly, the control laws are constructed based on the traditional backstepping method; the multiple uncertainties are treated as lumped uncertainties, which can be estimated and eliminated by the employed extended state observers (ESOs). In addition, the influence of input saturation can be compensated by the designed auxiliary dynamic compensators. Secondly, to simplify controller design and address the “complexity explosion”, two command filters are used to obtain the estimated value of the unknown sideslip angular velocity and the desired yaw angular acceleration, respectively. Finally, the superiority and robustness of the proposed control strategy are verified through computer simulation. A semi-physical simulation experiment platform is built based on the NI Compact cRIO-9068 and PLC S7-1200 to further demonstrate the effectiveness of the proposed control strategy.

Head Injuries Induced by Tennis Ball Impacts: A Computational Study

Abstract Head injuries induced by tennis ball impacts are computationally studied. The impact of a two-piece tennis ball on a human head is simulated by using an established full body model and a newly constructed tennis ball model. The new tennis ball model is validated against existing experimental data. The frontal impact of a tennis ball on a human head at a velocity of 25 m/s is first studied as the baseline case. The effects of the impact location, velocity, and angle as well as the ball spinning are then examined. It is revealed that the lateral impact results in a higher risk of head injury than the frontal and crown impacts. In addition, it is found that the impact force and von Mises stress in the skull, the intracranial pressure and first principal strain in the brain, and the translational and rotational accelerations at the center of gravity of the head all increase with the increase of the impact velocity. Moreover, the normal (90-deg) impact has the highest risk of head injury, which is followed by the 60-deg, 45-deg and 30-deg impacts. Further, it is observed that the spinning of the tennis ball has insignificant effects on the head response. The simulation results show that there will be no skull fracture or mild brain injury in the baseline case. However, traumatic brain injuries may occur after the impact velocity exceeds 40 m/s. The findings of the current study provide new insights into the risks of head injuries induced by tennis ball impacts.

Inflow-velocity and rotational effects on revolving and translating wings

An aspect ratio 9.5 rectangular wing is articulated in revolving and translating motions at a 45° angle of incidence and Reynolds number Re=O(300). The effects of rotational (Coriolis and centripetal) accelerations and relative inflow velocity profile on vorticity transport within the leading-edge vortex (LEV) system are independently investigated. For the range of displacements studied (180° rotation and corresponding translational displacement), a stably attached leading-edge vortex (LEV) is observed when rotational accelerations and/or a linearly varying inflow velocity profile is present; however, the inflow velocity profile has a stronger effect on stability of the LEV. LEV vorticity magnitude and lift are significantly augmented when both factors are included (i.e., the full revolving wing case). Vorticity transport analyses are conducted in a planar control region two chords from the axis of rotation, where LEV stability is typically observed on revolving wings at high incidence and at an equivalent spanwise position in the translating case. The fully revolving wing case exhibits a substantially larger leading-edge shear-layer vorticity flux than the other cases, whereas Coriolis tilting makes little contribution to regulation of LEV strength. A correlation is found between the spanwise convective flux and tilting flux contributions in all cases. Decomposition of the spanwise convective flux term demonstrates that the two phenomena are kinematically linked and, together, define a new out-of-plane convective flux term that captures the essence of the spanwise convective flux. The role of this term and the effect of rotational accelerations on it are examined.

Mechanism Balancing Taxonomy

The balancing of mechanisms consists in distributing their moving masses, inertias, and elastic components in order to achieve key mechanical properties, such as the elimination of the shaking forces and moments exported onto their supporting structure or the insensitivity of the mechanism to gravity and to the motions of its chassis. This article introduces a new refined systematic taxonomy for the classification of multi-degree-of-freedom (DoF) 3-dimensional passively balanced mechanisms. The taxonomy is composed of 15 distinct types – compared to only 4 types described in the literature. Each type is provided with its definition, the necessary conditions to be satisfied, the list of resulting mechanical properties, and a 1-DoF mechanism example. This taxonomy applies to mechanisms subject to gravity and mounted onto fixed or mobile chassis undergoing linear and angular accelerations, and, newly, also angular velocities. It is represented as a 4-set Venn diagram built on 4 primary balancing types: static, force, moment, and a newly introduced inertial invariance. This theoretical work allows for a refined categorization of the broad spectrum of balanced mechanisms while alleviating some inconsistencies observed in the existing literature.

Closed Loop Vector Formulation in Eulers Complex Numbers for Multi Loop Planar Mechanisms With N bars A Novel Modeling Approach and Algorithm

This paper presents a novel iterative algorithm incorporated in a user-friendly GUI for modeling the kinematics of multiple looped N-bar closed-loop mechanisms. Past research works have used custom coding or expensive commercial software to analyze the mechanisms of specific applications. The proposed algorithm focuses on kinematics and offers a quick, easy-to-use, cost-effective solution to analyze a wide range of generic mechanisms, reducing the need for custom coding and lowering computational costs. The algorithm employs algebraic equations, such as solving complex closed-loop vector equations using the Euler form of complex numbers, to simulate and derive the unknowns necessary to characterise any generic closed-loop mechanism. The Python code implemented in the algorithm adapts to various scenarios by utilising available information on the position, velocity, and acceleration variables of the mechanisms. The simulation tool can display real-time color contour plots (RGB color scale) for linear and angular velocities and accelerations, simulate mechanisms with multiple loops and switch configurations, and find inverse mechanisms. The approach for solving multiple loop problems and the algorithm utilized to solve the configurations, methods, equations used and GUI features implementation are all described in this study. The case study considered for a four-bar mechanism indicates a strong agreement between the results obtained from the proposed kinematics-based simulator and ANSYS software. These results demonstrate the simulator’s effectiveness in providing low-cost and user-friendly simulation results for various generic mechanisms involving multiple interconnected loops.

Evolution of Rotational Motion of the Planet Earth under the Influence of Internal Dissipative Forces

The influence of internal dissipation on the rotational motion of the Earth in the gravitational field of the Sun and Moon is studied within the model of M.A. Lavrentiev. The averaged equations of second approximation describing the evolution of the Earth’s rotation axis and the magnitude of its angular velocity are obtained. The dependence of the rate of evolution on the values of the model parameters is studied. Phase trajectories of the evolutionary process are constructed for different parameter values. It is shown that the observed drift of the Earth’s magnetic poles can be explained within the framework of a mechanical model by the angular acceleration of the Earth.

Characterization of Traumatic Brain Injury in a Gyrencephalic Ferret Model Using the Novel Closed Head Injury Model of Engineered Rotational Acceleration (CHIMERA).

Traumatic brain injury (TBI) results from mechanical force to the brain and leads to a series of biochemical responses that further damage neurons and supporting cells. Clinically, most TBIs result from an impact to the intact skull, making closed head TBI pre-clinical models highly relevant. However, most of these closed head TBI models use lissencephalic rodents, which may not transduce biomechanical load in the same manner as gyrencephalic humans. To address this translational gap, this study aimed to characterize acute axonal injury and microglial responses in ferrets-the smallest gyrencephalic mammal. Injury was induced in male ferrets (Mustela furo; 1.20-1.51 kg; 6-9 months old) with the novel Closed Head Injury Model of Engineered Rotational Acceleration (CHIMERA) model. Animals were randomly allocated to either sham (n = 4), a 22J (joules) impact (n = 4), or a 27J impact (n = 4). Axonal injury was examined histologically with amyloid precursor protein (APP), neurofilament M (RMO 14.9) (RMO-14), and phosphorylated tau (AT180) and the microglial response with ionized calcium-binding adaptor molecule 1 at 24 h post-injury in gray and white matter regions. Graded axonal injury was observed with modest increases in APP and RMO-14 immunoreactivity in the 22J TBI group, mostly within the corpus callosum and fornix and more extensive diffuse axonal injury encompassing gray matter structures like the thalamus and hypothalamus in the 27J group. Accompanying microglial activation was only observed in the 27J group, most prominently within the white matter tracts in response to the larger amounts of axonal injury. The 27J, but not the 22J, group showed an increase in AT180 within the base of the sulci post-injury. This could suggest that the strain may be highest in this region, demonstrating the different responses in gyrencephalic compared to lissencephalic brains. The CHIMERA model in ferrets mimic many of the histopathological features of human closed head TBI acutely and provides a promising model to investigate the pathophysiology of TBI.

The influence of particle density and diameter on the interactions between the finite-size particles and the turbulent channel flow

Understanding the influence of different particle parameters on the two-way interactions between the particles and wall-bounded turbulence is important in many natural phenomena and engineering applications. In this work, particle-resolved direct simulation of particle-laden turbulent channel flow is performed based on the mesoscopic lattice Boltzmann method (LBM), and the particle–fluid interface is treated using the interpolated bounce back scheme. The friction Reynolds number (Reτ) of the single phase turbulent channel flow is 180, and the particle volume fraction is fixed at 1%. Three particle–fluid density ratios and three particle diameters are considered, and five particle-laden simulations are performed to investigate the influence of particle density and diameter on the interactions between the particles and the carrier turbulence. Results show that the streamwise velocity of the solid phase is larger than that of the fluid phase in the near-wall region, and the velocity difference between the two phases decreases with increasing particle density, but increases with increasing particle diameter. The probability density functions (PDFs) of particle velocity and angular velocity depend on the distance between the particles and the wall, but the PDFs of particle acceleration and angular acceleration are not spatially dependent. The distribution of particle Reynolds number follows the Gamma distribution within the buffer region and viscous sublayer. The solid phase concentration is high in the near-wall region, and the largest solid-phase concentration in this region occurs in the case with particles of intermediate density. Particles with different parameters would lead to different modulation to the carrier flow. Then, two aspects of the turbulence modulation are explored, i.e., the streamwise velocity and the turbulent kinetic energy (TKE). The presence of finite-size particles typically increases the streamwise velocity in the near-wall region and reduce the streamwise velocity outside this region. The trend is similar for TKE, but the TKE attenuation mainly occurs in the buffer region. The modulation to the streamwise velocity is analyzed using the streamwise momentum balance equation. It is found that the streamwise velocity modulation is dominated by the weighted Reynolds stress, but the different modulation in the near-wall region is due to the difference in weighted particle-induced stress, whereas the different modulation outside the near-wall region is due to the change in weighted Reynolds stress. Through TKE budget analysis, it is found that the enhancement of the total TKE source in the viscous sublayer increases with increasing particle density and diameter and the attenuation of total TKE source in the buffer region increases with increasing particle density and diameter, which is consistent with the TKE modulation for different cases.

The interrelationship between lower limb movement, muscle activity, and joint moment during half squat and gait

Joint moment is the resultant force of limb movements. However, estimation methods for joint moments using surface electromyography frequently use joint angles instead of limb angles. The limb angle in joint moment estimation using electromyography could clarify the effects of muscle activity on the limbs: acceleration, deceleration, or stabilization. No study has quantified the comprehensive relationship between limb movement, muscle activity, and joint moment. This study aimed to determine the influencing factors for ankle-joint moment and knee-joint moment in the sagittal plane among muscle activities and parameters related to limb movements during half squat and gait. This study included 29 healthy adults (16 female participants, 21.1 ± 2.09 years). Using inertial measurement units, thigh, shank, and foot inclination angles and angular accelerations were calculated as the parameters of limb movements. Muscle activations of the biceps femoris long head, rectus femoris, gastrocnemius, and tibialis anterior were measured. Ankle joint moment and knee-joint moment were measured using a three-dimensional motion capture system and two force plates. Regression models showed high accuracy in measuring ankle-joint moment during a half squat and gait (R2f = 0.92, 0.97, respectively) and knee-joint moment during a half squat (R2f = 0.98), but not knee-joint moment during gait (R2f = 0.63). However, only a maximum of five parameters were selected from muscle activities and limb angular information. Tibialis anterior and gastrocnemius activity were the largest contributors to ankle-joint moment during a half squat and gait, respectively, while muscle activities were not directly reflected in the knee-joint moment during either movement. Consideration of the interrelationships among limb movement, muscle activity, and joint moment is required when adjusting joint movements according to the target and aim of the therapeutic interventions.

Thermal characterization of an interior permanent magnet electric motor

An engineering approach for thermal characterization of an interior permanent magnet electric motor (EM) with a specific aim to identify the interdependency between its mean coil temperature and the maximum component temperatures at the conditions with constant and variable loads/speeds is proposed. For specifying the convective thermal boundary condition between stator and rotor that spins at variable speeds/directions, an experimental study aimed at devising the empirical heat transfer correlation for the Taylor-Couette airflow with varying rotating speed/direction is performed. It is firstly revealed that the responsive air-gap heat convection to angular acceleration follows the characteristic of a single-degree-of-freedom (SDOF) dynamic system. Along with the heat transfer correlation for the unsteady Taylor-Couette airflow, the nonhomogeneous thermal conductivity model that considers the orthogonality effect of the bent coiled winding at its two axial ends is integrated with an iteration scheme for calculating the air bulk temperature in an entrapped air chamber. The favorable experimental validation with the maximum discrepancies between predicted and measured component temperatures less than 7 % in steady and unsteady running conditions affirms the accuracy of the proposed simulation model. At a rotating speed of 4800 rev/min and power output of 1688 W, the maximum-to-mean temperature differences of stator winding, magnetic stripe, and steel sheet of stator reach respectively 6.75 °C, 3.21 °C, and 6.94 °C. Particularly, all the maximum component temperatures are well correlative with the mean temperature of the stator winding at the various steady/unsteady operating conditions. This finding extends the application of lumped thermal network analysis that predicts the averaged components’ temperatures; and enables the on-line monitoring for the maximum component temperatures using a mean stator-winding temperature as the controlling factor.

Efficacy of Guardian Cap Soft-Shell Padding on Head Impact Kinematics in American Football: Pilot Findings.

Sport-related concussion prevention strategies in collision sports are a primary interest for sporting organizations and policy makers. After-market soft-shell padding purports to augment the protective capabilities of standard football helmets and to reduce head impact severity. We compared head impact kinematics [peak linear acceleration (PLA) and peak rotational acceleration (PRA)] in athletes wearing Guardian Cap soft-shell padding to teammates without soft-shell padding. Ten Division I college football players were enrolled [soft-shell padding (SHELL) included four defensive linemen and one tight end; non-soft-shell (CONTROL) included two offensive linemen, two defensive linemen, and one tight end]. Participants wore helmets equipped with the Head Impact Telemetry System to quantify PLA (g) and PRA (rad/s2) during 14 practices. Two-way ANOVAs were conducted to compare log-transformed PLA and PRA between groups across helmet location and gameplay characteristics. In total, 968 video-confirmed head impacts between SHELL (n = 421) and CONTROL (n = 547) were analyzed. We observed a Group x Stance interaction for PRA (F1,963 = 7.21; p = 0.007) indicating greater PRA by SHELL during 2-point stance and lower PRA during 3- or 4-point stances compared to CONTROL. There were no between-group main effects. Protective soft-shell padding did not reduce head impact kinematic outcomes among college football athletes.

Dynamic strain fields of the mouse brain during rotation.

Mouse models are used to better understand brain injury mechanisms in humans, yet there is a limited understanding of biomechanical relevance, beginning with how the murine brain deforms when the head undergoes rapid rotation from blunt impact. This problem makes it difficult to translate some aspects of diffuse axonal injury from mouse to human. To address this gap, we present the two-dimensional strain field of the mouse brain undergoing dynamic rotation in the sagittal plane. Using a high-speed camera with digital image correlation measurements of the exposed mid-sagittal brain surface, we found that pure rotations (no direct impact to the skull) of 100-200rad/s are capable of producing complex strain fields that evolve over time with respect to rotational acceleration and deceleration. At the highest rotational velocity tested, the largest tensile strains (≥ 21% elongation) in selected regions of the mouse brain approach strain thresholds previously associated with axonal injury in prior work. These findings provide a benchmark to validate the mechanical response in biomechanical computational models predicting diffuse axonal injury, but much work remains in correlating tissue deformation patterns from computational models with underlying neuropathology.

Detection accuracy of target accelerations based on vortex electromagnetic wave in keyhole space

The influence of the longitudinal acceleration and the angular acceleration of detecting target based on vortex electromagnetic waves in keyhole space are analyzed. The spectrum spreads of different orbital angular momentum (OAM) modes in different non-line-of-sight situations are simulated. The errors of target accelerations in detection are calculated and compared based on the OAM spectra spreading by using two combinations of composite OAM modes in the keyhole space. According to the research, the effects about spectrum spreads of higher OAM modes are more obvious. The error in detection is mainly affected by OAM spectrum spreading, which can be reduced by reasonably using different combinations of OAM modes in different practical situations. The above results provide a reference idea for investigating keyhole effect when vortex electromagnetic wave is used to detect accelerations.

Modification of an IMU Based System for Analyzing Hand Kinematics During Activities of Daily Living

The hand of a human being is the most commonly utilized body part in daily activities. Assessing the functional capability is highly challenging and important in medical applications purposes. This research aims to design and implement a sensor-based system for function assessment and movements analysis of the hand by calculating the angular velocity, acceleration and magnetic field for the joints of the fingers during the daily activities. The proposed system was applied to two groups of volunteers: The first group consisted of seven males, whereas the second group consisted of seven females, and the results were taken by calculating the acceleration, angular velocity, magnetic field during activities of daily living (ADL). This study showed the system is important in hand movement and control function evaluation. The thumb and index fingers have similar pitch orientations while interacting, while the middle finger employs a distinct range. Yaw variables are less noticeable, but the variation in roll angles between fingers is.

Determination of the dynamics of the wheel of a mobile machine

A sensor, which consists of a three-axis accelerometer, a gyroscope, and a magnetometer, has been developed to determine the dynamics of the wheel of a mobile machine. The sensor is connected to a microcontroller, which transmits the received data via a 2.4 GHz channel. It is mounted coaxial to the center of the wheel. At the first processing stage, the accelerometer, gyroscope, and magnetometer data values are adjusted. The corrected accelerations and angular velocities signal are processed using a Butterworth filter. Filter Madgwick determines the angles of orientation of the sensor in space. In the next step, we remove the centrifugal component from the accelerations. Next, the gravitational component is subtracted from the accelerations, and its real value is obtained. The speed of the wheel is obtained by integrating accelerations. The Kalman filter processes the angular velocities, acceleration, and velocities. The measurement noise covariance matrix and the evaluation process matrix are calculated based on sensor errors. The results of experimental studies of the proposed method and sensor for determining the wheel dynamics of mobile machines on tractors with a 4x4 wheel arrangement were carried out. The sensors were installed on all wheels of the tractor. The developed wheel dynamics sensor allows us to determine the slippage of the engines of a mobile machine. This method of determining slipping is entirely accurate and does not require intervention in the design of the machine. The determination of the speed of rotation of the wheels of a mobile machine is based on the determination of the angular speed of rotation, which is measured with a gyroscope and accelerometer located in the center of the wheel of a mobile machine. Keywords: sensor, dynamics, wheel, mobile car, filter.

The Effect of Motorcycle Helmet Type on Head Response in Oblique Impact

In Malaysia, riding motorcycles is a popular mode of transportation, particularly in urban areas where traffic congestion is prevalent. Additionally, motorcycles are relatively affordable and have low fuel consumption, which makes them an attractive option for many. Per Malaysian traffic laws, riders must wear helmets while riding. As a result, various brands and types of helmets are available for purchase. However, with the increasing popularity of online shopping platforms, many individuals opt to purchase helmets online despite the uncertain quality control of these products. This study aims to assess the effectiveness of three different types of motorcycle helmets in protecting the head from injury. The helmet types evaluated in this unbiased study include full-face, open-face, and half-coverage helmets. The head injury predictors used in this study include Peak Linear Acceleration (PLA), Peak Rotational Acceleration (PRA), Head Injury Criterion (HIC), and Brain Injury Criterion (BrIC). Each helmet was subjected to an impact in a controlled environment using a 6-kg cylinder attached to a pendulum arm, with the impact directed at the front of the helmet at a speed of approximately 6 m/s. Full-face and open-face helmets performed exceptionally well in terms of linear parameters (PLA and HIC). The PLA and HIC of half-coverage helmets are nearly 70% and 50% higher than full-face and open-face helmets. All helmets perform poorly against rotational impact (PRA and BrIC). This shows that helmet design needs to be improved to enhance protection against rotational impact. This study represents the first case study in Malaysia to gather mechanical head injury data comparing the protective performance of different helmet types under both linear and rotational impact. These findings may provide a more accurate understanding of helmet performance in protecting against head injuries.

Assessing the association between on-field heading technique and head impact kinematics in a cohort of female youth soccer players

ABSTRACT There is concern that exposure to soccer headers may be associated with neurological sequelae. Training proper heading technique represents a coachable intervention that may reduce head acceleration exposure. The objective was to assess relationships between heading technique and head kinematics in female youth soccer players. Fourteen players (mean age = 14.4 years) wore instrumented mouthpieces during practices and games. Headers were reviewed by three raters to assign a technique score. Mixed models and LASSO regression evaluated associations of technique with peak linear acceleration (PLA), rotational acceleration (PRA), rotational velocity (PRV), and head impact power ratio (HIP Ratio) while adjusting for session type and ball delivery. Two hundred eighty-nine headers (n = 212 standing, n = 77 jumping) were analyzed. Technique score (p = 0.043) and the technique score – session type interaction (p = 0.004) were associated with PRA of standing headers, whereby each 10-unit increase in technique score was associated with an 8.6% decrease in PRA during games but a 5.1% increase in PRA during practices. Technique was not significantly associated with any other kinematic metrics; however, peak kinematics tended to decrease as technique score increased. LASSO regression identified back extension and shoulder/hip alignment as important predictors of peak kinematics. Additional research on heading technique and head acceleration is recommended.

Time-energy-jerk optimal trajectory planning for high-speed parallel manipulator based on quantum-behaved particle swarm optimization algorithm and quintic B-spline

This paper presents a technique for multi-node trajectory planning for high-speed parallel manipulators that optimizes the execution time, energy consumption and jerk (the time derivative of the acceleration of the manipulator joints) to improve working efficiency, decrease energy consumption, dampen vibration and ensure mechanism protection. Initially, an improved quintic B-spline interpolation model is proposed, incorporating additional jerk boundary constraints to dampen residual vibrations at the start and end of the trajectory. Subsequently, the time-energy-jerk optimization model is formulated, with the maximum angular velocity, acceleration, and jerk serving as constraints. The normalized parameter of the B-spline curve is considered to divide the whole model into two submodels. In the first submodel, the satisfaction function is proposed to convert energy and jerk indices into one comprehensive objective for optimization with the quantum-behaved particle swarm optimization (QPSO) algorithm. Time parameters are to be decided as decision variables, regardless of kinematic constraints and execution time. In the second submodel, the optimal time parameters obtained in the first submodel are used as input arguments, and the optimal execution time is determined with respect to the kinematic constraints. The simulation results on a planar parallel manipulator show that the proposed method achieves an efficient trajectory, which is energy-saving and possesses reduced vibration. Application of the comprehensive trajectory generated by the proposed method, rather than the classical method, enhances the maximum productivity of the fast pick-and-place operation to 155 picks per minute from 97 picks/min. This improvement is accomplished by using less energy and reducing vibration.

A novel trajectory planning method for robotic deburring of automotive castings considering adaptive weights

Robotic deburring of automotive castings with irregular geometry poses a great challenge to trajectory planning, as this operation highly determines the machining efficiency and quality consistency. To address the limitation of the existing trajectory planning methods applicable for automotive castings, in this paper a novel trajectory planning method is presented by considering the adaptive weights. Based on the interval mutation rate, LS-gradient (Line Surface-gradient) and stiffness performance, an adaptive weight function is constructed at first to quantify the path complexity as well as the required robot stability during deburring. Then, the robot trajectory is generated by using a cubic polynomial, which aims primarily at the continuous angular acceleration without sudden impacts on the joint angles. Next, by taking the machining efficiency and machining stability as the objective functions, an adaptive weight-based trajectory planning model is established for accurate control of the robot trajectory, and this model is further solved by the evolutionary COVIDOA algorithm which is not easy to fall into local optimum. Finally, comparative experiments on robotic deburring of automotive engine flywheel shell with four diverse paths are conducted under three conditions: machining without trajectory planning algorithm, machining with fixed weight-based trajectory planning algorithm, and machining with adaptive weight-based trajectory planning algorithm. The experimental results demonstrate the effectiveness of the proposed algorithm in terms of machining adaptability and machining effects. The novel trajectory planning method also can effectively enhance both the machining efficiency and machining stability, and shows great application potential in robotic deburring of automotive castings.

A novel biomechanical indicator for impaired ankle dorsiflexion function during walking in individuals with chronic stroke

BackgroundAnkle dorsiflexion function during swing phase contributes to foot clearance and plays an important role in walking ability post-stroke. Commonly used biomechanical measures such as foot clearance and ankle joint excursion have limited ability to accurately evaluate impaired dorsiflexor function. Research questionCan ankle angular velocity and acceleration be used as reliable measurers of dorsiflexion function in post-stroke gait? MethodsUsing linear regression and Pearson’s correlation we retrospectively compared peak ankle angular velocity (AωP), peak ankle angular acceleration (AαP), peak dorsiflexion angle (DFAP) and peak foot clearance (FCLP) as direct measures for swing phase dorsiflexor function in 60 chronic stroke survivors. Intraclass correlation coefficient (ICC) analysis was used for test-retest reliability of AωP and AαP. ResultsLinear regression models revealed that AωP, AαP, DFAP, FCLP had a significant relationship (p < 0.05) with impaired dorsiflexion function. AαP and DFAP accounted for the most variance of dorsiflexion function. AωP, AαP, FCLP, correlated significantly with all clinical outcome measures of walking ability. DFAP had a positive correlation only with FMA-LE. Post-hoc William’s t-tests, used to compare the magnitude of difference between two non-independent correlations, revealed that the correlation between all clinical measures and DFAP were significantly weaker than with AωP and AαP. Correlation between FMA-LE and FCLP was weaker than with AωP and AαP. Excellent test-retest reliability for both AωP (ICC = 0.968) and AαP (ICC = 0.947) was observed. SignificanceThese results suggest that DFAP may only be associated with dorsiflexion function during non-task specific isolated movements, but not during walking. FCLP is associated with dorsiflexion function and walking ability measures but not as strongly as AωP and AαP possibly because FCLP is influenced by contribution from hip and knee joint movements. Therefore, AωP and AαP are reliable measures and represent dorsiflexion function more accurately than DFAP, and FCLP.