Effects of wrist posture and stabilization on precision grip force production and muscle activation patterns.

Most of the power for generating forces in the fingers arises from muscles located in the forearm. This configuration maximizes finger joint range of motion while minimizing finger mass and inertia. The resulting multiarticular arrangement of the tendons, however, complicates independent control of the wrist and the digits. Actuating the wrist impacts sensorimotor control of the fingers and vice versa. The goal of this study was to systematically investigate interactions between isometric wrist and digit control. Specifically, we examined how the need to maintain a specified wrist posture influences precision grip. Fifteen healthy adults produced maximum precision grip force at 11 different wrist flexion/extension angles, with the arm supported, under two conditions: 1) the participant maintained the desired wrist angle while performing the precision grip and 2) a robot maintained the specified wrist angle. Wrist flexion/extension posture significantly impacted maximum precision grip force (P < 0.001), with the greatest grip force achieved when the wrist was extended 30° from neutral. External wrist stabilization by the robot led to a 20% increase in precision grip force across wrist postures. Increased force was accompanied by increased muscle activation but with an activation pattern similar to the one used when the participant had to stabilize their wrist. Thus, simultaneous wrist and finger requirements impacted performance of an isometric finger task. External wrist stabilization can promote increased precision grip force resulting from increased muscle activation. These findings have potential clinical significance for individuals with neurologically driven finger weakness, such as stroke survivors.NEW & NOTEWORTHY We explored the interdependence between wrist and fingers by assessing the influence of wrist posture and external stabilization on precision grip force generation. We found that maximum precision grip force occurred at an extended wrist posture and was 20% greater when the wrist was Externally Stabilized. The latter resulted from amplification of muscle activation patterns from the Self-Stabilized condition rather than adoption of new patterns exploiting external wrist stabilization.

Factors that influence the adoption of rehabilitation technologies: a multi-disciplinary qualitative exploration.

BACKGROUND: Technological innovation is recognised as having the potential to enhance rehabilitation for people with disability. Yet, resistance to, and abandonment of, rehabilitation technology is prevalent and the successful translation of technology into rehabilitation settings remains limited. Therefore, the aim of this work was to develop an in-depth, multi-stakeholder perspective on what influences the adoption of rehabilitation technologies. METHODS: Semi-structured focus groups were conducted as part of a larger research project aiming to facilitate the co-design of a novel neurorestorative technology. Focus group data were analysed using a five-phase hybrid deductive-inductive approach to qualitative data analysis. RESULTS: Focus groups were attended by 43 stakeholders with expertise in one or more of the following fields: people with disability, allied health, human movement science, computer science, design, engineering, ethics, funding, marketing, business, product development, and research development. Six main themes influencing the adoption of technology in rehabilitation were identified: cost beyond the purchase price, benefits to all stakeholders, trust to be earned in technology, ease of technology operation, ability to access technology, and the 'co' in co-design. All six themes were found to be interrelated; in particular, the importance of direct stakeholder engagement in the development of rehabilitation technologies (the 'co' in co-design) was prevalent in all themes. CONCLUSIONS: A range of complex and interrelated factors influence the adoption of rehabilitation technologies. Importantly, many of the issues that have the potential to negatively impact rehabilitation technology adoption may be addressed during development by utilising the experience and expertise of stakeholders who influence its supply and demand. Our findings state that a wider cohort of stakeholders needs to be actively engaged in the development of rehabilitation technologies to better address the factors that contribute to technology underutilisation and abandonment and facilitate better outcomes for people with disability.

Immediate and Long-Term Implications of the COVID-19 Pandemic for People With Disabilities.

Some people with disabilities may have greater risk of contracting COVID-19 or experiencing worse outcomes if infected. Although COVID-19 is a genuine threat for people with disabilities, they also fear decisions that might limit lifesaving treatment should they contract the virus.During a pandemic, health systems must manage excess demand for treatment, and governments must enact heavy restrictions on their citizens to prevent transmission. Both actions can have a negative impact on people with disabilities.Ironically, the sociotechnical advances prompted by this pandemic could also revolutionize quality of life and participation for people with disabilities. Preparation for future disasters requires careful consideration.

Technology-aided assessments of sensorimotor function: current use, barriers and future directions in the view of different stakeholders.

BACKGROUND: There is growing interest in the use of technology in neurorehabilitation, from robotic to sensor-based devices. These technologies are believed to be excellent tools for quantitative assessment of sensorimotor ability, addressing the shortcomings of traditional clinical assessments. However, clinical adoption of technology-based assessments is very limited. To understand this apparent contradiction, we sought to gather the points-of-view of different stakeholders in the development and use of technology-aided sensorimotor assessments. METHODS: A questionnaire regarding motivators, barriers, and the future of technology-aided assessments was prepared and disseminated online. To promote discussion, we present an initial analysis of the dataset; raw responses are provided to the community as Supplementary Material. Average responses within stakeholder groups were compared across groups. Additional questions about respondent's demographics and professional practice were used to obtain a view of the current landscape of sensorimotor assessments and interactions between different stakeholders. RESULTS: One hundred forty respondents from 23 countries completed the survey. Respondents were a mix of Clinicians (27%), Research Engineers (34%), Basic Scientists (15%), Medical Industry professionals (16%), Patients (2%) and Others (6%). Most respondents were experienced in rehabilitation within their professions (67% with > 5 years of experience), and had exposure to technology-aided assessments (97% of respondents). In general, stakeholders agreed on reasons for performing assessments, level of details required, current bottlenecks, and future directions. However, there were disagreements between and within stakeholders in aspects such as frequency of assessments, and important factors hindering adoption of technology-aided assessments, e.g., Clinicians' top factor was cost, while Research Engineers indicated device-dependent factors and lack of standardization. Overall, lack of time, cost, lack of standardization and poor understanding/lack of interpretability were the major factors hindering the adoption of technology-aided assessments in clinical practice. Reimbursement and standardization of technology-aided assessments were rated as the top two activities to pursue in the coming years to promote the field of technology-aided sensorimotor assessments. CONCLUSIONS: There is an urgent need for standardization in technology-aided assessments. These efforts should be accompanied by quality cross-disciplinary activities, education and alignment of scientific language, to more effectively promote the clinical use of assessment technologies. TRIAL REGISTRATION: NA; see Declarations section.

Robot-supported assessment of balance in standing and walking.

Clinically useful and efficient assessment of balance during standing and walking is especially challenging in patients with neurological disorders. However, rehabilitation robots could facilitate assessment procedures and improve their clinical value. We present a short overview of balance assessment in clinical practice and in posturography. Based on this overview, we evaluate the potential use of robotic tools for such assessment. The novelty and assumed main benefits of using robots for assessment are their ability to assess 'severely affected' patients by providing assistance-as-needed, as well as to provide consistent perturbations during standing and walking while measuring the patient's reactions. We provide a classification of robotic devices on three aspects relevant to their potential application for balance assessment: 1) how the device interacts with the body, 2) in what sense the device is mobile, and 3) on what surface the person stands or walks when using the device. As examples, nine types of robotic devices are described, classified and evaluated for their suitability for balance assessment. Two example cases of robotic assessments based on perturbations during walking are presented. We conclude that robotic devices are promising and can become useful and relevant tools for assessment of balance in patients with neurological disorders, both in research and in clinical use. Robotic assessment holds the promise to provide increasingly detailed assessment that allows to individually tailor rehabilitation training, which may eventually improve training effectiveness.

On the assessment of coordination between upper extremities: towards a common language between rehabilitation engineers, clinicians and neuroscientists.

Well-developed coordination of the upper extremities is critical for function in everyday life. Interlimb coordination is an intuitive, yet subjective concept that refers to spatio-temporal relationships between kinematic, kinetic and physiological variables of two or more limbs executing a motor task with a common goal. While both the clinical and neuroscience communities agree on the relevance of assessing and quantifying interlimb coordination, rehabilitation engineers struggle to translate the knowledge and needs of clinicians and neuroscientists into technological devices for the impaired. The use of ambiguous definitions in the scientific literature, and lack of common agreement on what should be measured, present large barriers to advancements in this area. Here, we present the different definitions and approaches to assess and quantify interlimb coordination in the clinic, in motor control studies, and by state-of-the-art robotic devices. We then propose a taxonomy of interlimb activities and give recommendations for future neuroscience-based robotic- and sensor-based assessments of upper limb function that are applicable to the everyday clinical practice. We believe this is the first step towards our long-term goal of unifying different fields and help the generation of more consistent and effective tools for neurorehabilitation.

Transfemoral amputee recovery strategies following trips to their sound and prosthesis sides throughout swing phase.

BACKGROUND: Recovering from trips is challenging for transfemoral amputees, and attempts often result in falls. Better understanding of the effects of the sensory-motor deficits brought by amputation and the functional limitations of prosthetic devices could help guide therapy and fall prevention mechanisms in prostheses. However, how transfemoral amputees attempt to recover from trips on the sound and prosthesis sides throughout swing phase is poorly understood. METHODS: We tripped eight able-bodied subjects and eight unilateral transfemoral amputees wearing their prescribed prostheses. The protocol consisted of six repetitions of 6 and 4 points throughout swing phase, respectively. We compared recovery strategies in able-bodied, sound side and prosthesis side limbs. The number of kinematic recovery strategies used, when they were used throughout swing phase, and kinematic characteristics (tripped limb joint angles, bilateral trochanter height and time from foot arrest to foot strike) of each strategy were compared across limb groups. Non-parametric statistical tests with corrections for post-hoc tests were used. RESULTS: Amputees used the same recovery strategies as able-bodied subjects on both sound and prosthesis sides, although not all subjects used all strategies. Compared to able-bodied subjects, amputees used delayed-lowering strategies less often from 30-60 % of swing phase on the sound side, and from 45-60 % of swing phase on the prosthesis side. Within-strategy kinematic differences occurred across limbs; however, these differences were not consistent across all strategies. Amputee-specific recovery strategies-that are not used by control subjects-occurred following trips on both the sound and prosthesis sides in mid- to late swing. CONCLUSIONS: Collectively, these results suggest that sensory input from the distal tripped leg is not necessary to trigger able-bodied trip recovery strategies. In addition, the differences between sound and prosthesis side recoveries indicate that the ability of the support leg might be more critical than that of the tripped leg when determining the response to a trip. The outcomes of this study have implications for prosthesis control, suggesting that providing correct and intuitive real-time selection of typical able-bodied recovery strategies by a prosthetic device when it is the tripped and the support limb could better enable balance recovery and avoid falls.

Towards Translation of Novel Neurorehabilitation Systems: A Practical Approach to Usability Testing.

Usability testing is important for the effective translation of neurorehabilitation technologies but is often overlooked and under-reported. The aim of this paper is to present a method of collecting and analyzing usability data, using a think-aloud and semi-structured interview protocol and qualitative analysis techniques. We present a worked case study of this method with a novel neurorehabilitation system that utilizes thought-controlled robotics to partially restore lower-limb function of people with spinal cord injury (SCI). Five male participants (mean age = 32.6 years) with SCI who identified as users of related neurorehabilitation technologies completed the usability study. Video-recorded usability sessions utilized a combination of concurrent and retrospective think-aloud methods as well as semi-structured interviews. Recordings were analyzed to identify verbal and behavioral feedback from participants regarding system performance and acceptability. In total, 538 data points were logged, which were aggregated into 60 usability issues, 44 positive evaluations, and 31 strategies for improvement. The approach undertaken was novel in that we sought to not only capture usability issues but also system elements that were positively evaluated by intended users and strategies for improvement from the perspective of intended users. These observations will be used to inform the further development of the neurorehabilitation system.

End-User Perspectives of the Importance of Rehabilitation Technologies and Related Values for Implementation.

Despite the increased availability of rehabilitation technologies (such as robotics) and evidence to support their use, their adoption is still limited in practice. To begin to address this issue, we sought to better understand the perspectives of end-users regarding the implementation of rehabilitation technologies through an online survey. Fifty unique responses across Client (e.g., people with disability and carers), Allied Health (e.g., occupational and physical therapists, podiatrists, psychologists, dieticians, audiologists, exercise physiologists), and Medical (i.e., physicians and nurses) groups were analyzed. Respondents considered rehabilitation technologies to be important (median across groups of 9 out of 10). Across groups, value statements related to the implementation of rehabilitation technologies ranked from most to least important related to: benefits of technology to its intended end-user with disability, practical use of technologies, the technologies themselves (e.g., innovative, established, stand-alone), and their impact on health professionals or the health system as a whole. There were similarities and differences in ranking within and across end-user groups. The prioritization of statements indicates where development efforts can be focused to address end-user goals, and disparity in results across groups supports rich stakeholder engagement during rehabilitation technology development.

Electronic Assistive Technology to Support Memory Function After Traumatic Brain Injury: A Systematic Review of Efficacy and User Perspectives.

Abstract Rapid technology advances have led to diverse assistive technology (AT) options for use in memory rehabilitation after traumatic brain injury (TBI). This systematic review aimed to evaluate the efficacy of electronic AT for supporting phases of memory in daily life after TBI. A secondary aim was to examine user perspectives on the utility of AT and factors influencing uptake or use. A systematic search of PsycINFO, MEDLINE, Cumulative Index of Nursing and Allied Health Literature (CINAHL), Excerpta Medica database (Embase), Scopus, and Cochrane Library was conducted from database inception to June 13, 2022, to identify eligible studies. Methodological quality was assessed by two independent reviewers. Nineteen eligible articles involving a total of 311 participants included four randomized controlled trials (RCTs; Class I), five single-case experimental designs (Class II), and 10 pre-post group (n > 10) or single-case studies without experimental control (Class III). Three Class I studies, two Class II studies and eight Class III studies supported the efficacy of AT for supporting memory functioning. Treatment fidelity was not examined in any study. There was the most empirical support for the efficacy of AT for facilitating retrieval and execution phases of memory (i.e., supported by 6/9 studies) with external support to encode memory intentions or pre-programmed reminders. Further controlled studies are needed to determine whether outcomes vary according to individuals' level of independence with use (e.g., self-initiated vs. pre-programmed reminders) and to examine user characteristics and design features influencing uptake and effectiveness. Greater involvement of end-users with brain injury in the design and evaluation of AT features is also recommended to enhance usability and uptake in daily life.

A technology-focused service within a rehabilitation setting: exploring the experiences and current technology demands of people with disabilities.

PURPOSE: To understand and combat the challenges in taking up and implementing technology in rehabilitation settings, the HabITec Lab, a clinical service focused on technology, was piloted for 12-months within a tertiary hospital. This article reports on its preliminary impacts as a clinical service and on clients, including the types of assistive technology (AT) in demand. MATERIALS AND METHODS: Referral and administrative data from 25 individuals who attended the HabITec Lab were collated and analysed using descriptive statistics. For those who attended more than once (n = 12), goal attainment was assessed using the Modified Goal Attainment Measure (MGAM). Post-intervention semi-structured interviews were completed with participants to understand their experience at the HabITec Lab. Interviews were analysed using thematic analysis. RESULTS: Most attendees (92%) were undergoing inpatient rehabilitation following a spinal cord injury (SCI). The majority (73%) of goals related to improving entertainment and connection. All participants who completed the MGAM showed improved goal attainment following their HabITec Lab attendance. Qualitative data highlighted appreciation for the service and suggestions for its future. CONCLUSIONS: This study revealed a high level of demand for support to use AT amongst individuals with SCI, particularly consumer-grade smart devices that could assist communication. This finding may have been influenced by the impacts of the COVID-19 pandemic and frequent lockdowns during this period. This study indicated that the HabITec Lab was able to address important goals for attendees, but also illuminate a new future and trigger enthusiasm about future goals. Attendance was liberating, but resourcing barriers were frustrating.IMPLICATIONS FOR REHABILITATIONDedicated socio-technological spaces such as HabITec are an important way to provide access to expertise and develop consumer knowledge of technology not adequately addressed elsewhere in the rehabilitation continuum.Access to technological support for individuals in the inpatient setting facilitates access to technology in the present and capacity building to foster ongoing use of technology in the future.Dedicated socio-technological spaces should be adequately resourced, funded, staffed and promoted to ensure optimal outcomes.Access to Smart devices within the inpatient rehabilitation setting is critical for people with spinal cord injury to foster communication with family, friends and communities.

Establishing the normative and comparative needs of assistive technology provision in Queensland from the agency and funding scheme perspective.

BACKGROUND AND AIMS: Assistive technology services and devices support the participation and inclusion of people living with disability. In Australia, the regulatory bodies, agencies and schemes that manage assistive technology provision are governed by national and / or state-based Acts and Legislation. This study examined the assistive technology sector from the perspective of the regulatory bodies, agencies and schemes. DESIGN AND METHODS: Regulatory bodies, agencies and schemes that manage funding for assistive technology in Australia were identified by the research team. A website audit reviewed publicly available documents and information. Semi-structured interviews with representatives from the agencies and schemes were audio-recorded and transcribed verbatim. FINDINGS: The audit (n =17) found that the range and level of information publicly available was variable. The availability of assistive technology for driving and transport, design and building for access and safety, and mobility was most often promoted. The qualitative findings (n = 11) indicated variability and challenges within four themes: operationalising the legislation; internal assistive technology processes; reasonable and necessary; and risks in the assistive technology pathway. CONCLUSIONS: Regulatory bodies, agencies and schemes are critical to the effectiveness of the sector. The findings identified opportunities for the organisations to review how internal processes are communicated publicly, and for the sector to address the perceived risks related to health professional availability, knowledge and skills, and limited accessibility to trial assistive technology. Subsequent studies explored the perspectives of the assistive technology advisors and suppliers and the recipients of assistive technology services and devices.

An undignified disaster reality for Australians with disability.

The United Nations Convention on the Rights of Persons with Disabilities and the Sendai Framework for Disaster Risk Management establish the importance of ensuring the equitable protection of human rights in disaster planning, relief, and recovery. However, internationally and within Australia, the reality is one of indignity, human rights violations, and corruption. Australia is living in a perpetual state of crisis, following 3years of environmental and health disaster events. Vulnerable Australian citizens, especially people with disability, are at a great risk of human rights violations and may have restricted access to resilience-building resources that would enable them to recover. Embedding dignity into disaster management and recovery can safeguard human rights and improve outcomes for people with disability.

Knee Compliance Reduces Peak Swing Phase Collision Forces in a Lower-Limb Exoskeleton Leg: A Test Bench Evaluation.

Powered lower limb exoskeletons are a viable solution for people with a spinal cord injury to regain mobility for their daily activities. However, the commonly employed rigid actuation and pre-programmed trajectories increase the risk of falling in case of collisions with external objects. Compliant actuation may reduce forces during collisions, thus protecting hardware and user. However, experimental data of collisions specific to lower limb exoskeletons are not available. In this work, we investigated how a variable stiffness actuator at the knee joint influences collision forces transmitted to the user via the exoskeleton. In a test bench experiment, we compared three configurations of an exoskeleton leg with a variable stiffness knee actuator in (i) compliant or (ii) stiff configurations, and with (iii) a rigid actuator. The peak torque observed at the pelvis was reduced from 260.2 Nm to 116.2 Nm as stiffness decreased. In addition, the mechanical impulse was reduced by a factor of three. These results indicate that compliance in the knee joint of an exoskeleton can be favorable in case of collision and should be considered when designing powered lower limb exoskeletons. Overall, this could decrease the effort necessary to maintain balance after a collision, and improved collision handling in exoskeletons could result in safer use and benefit their usefulness in daily life.

Estimating Movement Smoothness From Inertial Measurement Units.

Inertial measurement units (IMUs) are increasingly used to estimate movement quality and quantity to the infer the nature of motor behavior. The current literature contains several attempts to estimate movement smoothness using data from IMUs, many of which assume that the translational and rotational kinematics measured by IMUs can be directly used with the smoothness measures spectral arc length (SPARC) and log dimensionless jerk (LDLJ-V). However, there has been no investigation of the validity of these approaches. In this paper, we systematically evaluate the use of these measures on the kinematics measured by IMUs. We show that: (a) SPARC and LDLJ-V are valid measures of smoothness only when used with velocity; (b) SPARC and LDLJ-V applied on translational velocity reconstructed from IMU is highly error prone due to drift caused by integration of reconstruction errors; (c) SPARC can be applied directly on rotational velocities measured by a gyroscope, but LDLJ-V can be error prone. For discrete translational movements, we propose a modified version of the LDLJ-V measure, which can be applied to acceleration data (LDLJ-A). We evaluate the performance of these measures using simulated and experimental data. We demonstrate that the accuracy of LDLJ-A depends on the time profile of IMU orientation reconstruction error. Finally, we provide recommendations for how to appropriately apply these measures in practice under different scenarios, and highlight various factors to be aware of when performing smoothness analysis using IMU data.

Biomechanics of Ankle Ligament Reconstruction: A Cadaveric Study to Compare Stability of Reconstruction Techniques Using 1 or 2 Fibular Tunnels.

BACKGROUND: Anatomic lateral ankle ligament reconstruction has been proposed for patients with chronic ankle instability. A reliable approach is a reconstruction technique using an allograft and 2 fibular tunnels. A recently introduced approach that entails 1-fibular tunnel reconstruction might reduce the risk of intraoperative complications and ultimately improve patient outcome. HYPOTHESIS: We hypothesized that both reconstruction techniques show similar ankle stability (joint laxity and stiffness) and are similar to the intact joint condition. STUDY DESIGN: Controlled laboratory study. METHODS: A total of 10 Thiel-conserved cadaveric ankles were divided into 2 groups and tested in 3 stages-intact, transected, and reconstructed lateral ankle ligaments-using either the 1- or the 2-fibular tunnel technique. To quantify stability in each stage, anterior drawer and talar tilt tests were performed in 0°, 10°, and 20° of plantarflexion (anterior drawer test) or dorsiflexion (talar tilt test). Bone displacements were measured using motion capture, from which laxity and stiffness were calculated together with applied forces. Finally, reconstructed ligaments were tested to failure in neutral position with a maximal applicable torque in inversion. A mixed linear model was used to describe and compare the outcomes. RESULTS: When ankle stability of intact and reconstructed ligaments was compared, no significant difference was found between reconstruction techniques for any flexion angle. Also, no significant difference was found when the maximal applicable torque of the 1-tunnel technique (9.1 ± 4.4 N·m) was compared with the 2-tunnel technique (8.9 ± 4.8 N·m). CONCLUSION: Lateral ankle ligament reconstruction with an allograft using 1 fibular tunnel demonstrated similar biomechanical stability to the 2-tunnel approach. CLINICAL RELEVANCE: Demonstrating similar stability in a cadaveric study and given the potential to reduce intraoperative complications, the 1-fibular tunnel approach should be considered a viable option for the surgical therapy of chronic ankle instability. Clinical randomized prospective trials are needed to determine the clinical outcome of the 1-tunnel approach.

A framework for closing the loop between human experts and computational algorithms for the assessment of movement disorders.

Clinical assessment of abnormal neuromechanics is typically performed by manipulation of the affected limbs; a process with low inter- and intra-rater reliability. This paper aims at formalizing a framework that closes the loop between a clinician's expertise and computational algorithms, to enhance the clinician's diagnostic capabilities during physical manipulation. The framework's premise is that the dynamics that can be measured by manipulation of a limb are distinct between movement disorders. An a priori database contains measurements encoded in a space called the information map. Based on this map, a computational algorithm identifies which probing motions are more likely to yield distinguishing information about a patient's movement disorder. The clinician executes this movement and the resulting dynamics, combined with clinician input, is used by the algorithm to estimate which of the movement disorders in the database are most probable. This is recursively repeated until a diagnosis can be confidently made. The main contributions of this paper are the formalization of the framework and the addition of the information map to select informative movements. The establishment of the framework provides a foundation for a standardized assessment of movement disorders and future work will aim at testing the framework's efficacy.

Design and Characterization of an Exoskeleton for Perturbing the Knee During Gait.

OBJECTIVE: An improved understanding of mechanical impedance modulation in human joints would provide insights about the neuromechanics underlying functional movements. Experimental estimation of impedance requires specialized tools with highly reproducible perturbation dynamics and reliable measurement capabilities. This paper presents the design and mechanical characterization of the ETH Knee Perturbator: an actuated exoskeleton for perturbing the knee during gait. METHODS: A novel wearable perturbation device was developed based on specific experimental objectives. Bench-top tests validated the device's torque limiting capability and characterized the time delays of the on-board clutch. Further tests demonstrated the device's ability to perform system identification on passive loads with static initial conditions. Finally, the ability of the device to consistently perturb human gait was evaluated through a pilot study on three unimpaired subjects. RESULTS: The ETH Knee Perturbator is capable of identifying mass-spring systems within 15% accuracy, accounting for over 95% of the variance in the observed torque in 10 out of 16 cases. Five-degree extension and flexion perturbations were executed on human subjects with an onset timing precision of 2.52% of swing phase duration and a rise time of 36.5 ms. CONCLUSION: The ETH Knee Perturbator can deliver safe, precisely timed, and controlled perturbations, which is a prerequisite for the estimation of knee joint impedance during gait. SIGNIFICANCE: Tools such as this can enhance models of neuromuscular control, which may improve rehabilitative outcomes following impairments affecting gait and advance the design and control of assistive devices.

An adaptive and robust online method to predict gait events.

Accurate timing of interventions during the gait cycle are critical for optimal efficacy of assistive devices, e.g., to reduce the metabolic cost of walking. However, timing control generally relies on methods that can neither account for changes in the stride duration over time due to different walking speeds, nor reject isolated abnormal strides, which could be caused by stumbling or obstacle avoidance for example. In order to address these issues, a method, named the Gait Phase Estimator (GPE), is proposed to predict temporal gait events and stride duration. Predictions are based on the weighted forward moving-average of stride duration. Prediction performance in steady-state walking, robustness to stride disturbances, and adaptation to speed changes were evaluated in an experiment with three subjects walking on a treadmill at three different speeds. Results suggest that, on average, the GPE produces better predictions than a predefined estimate. On top, it automatically adapts to changes in speed, while offering the benefit of robustness to irregular strides unlike a conventional moving-average. Thus, the proposed GPE has the potential to improve and greatly simplify the process of obtaining stride duration estimates, which could benefit gait-assistive devices and experimental protocols.

Trip recovery strategies following perturbations of variable duration.

Appropriately responding to mechanical perturbations during gait is critical to maintain balance and avoid falls. Tripping perturbation onset during swing phase is strongly related to the use of different recovery strategies; however, it is insufficient to fully explain how strategies are chosen. The dynamic interactions between the foot and the obstacle may further explain observed recovery strategies but the relationship between such contextual elements and strategy selection has not been explored. In this study, we investigated whether perturbation onset, duration and side could explain strategy selection for all of swing phase. We hypothesized that perturbations of longer duration would elicit lowering and delayed-lowering strategies earlier in swing phase than shorter perturbations. We developed a custom device to trip subjects multiple times while they walked on a treadmill. Seven young, healthy subjects were tripped on the left or right side at 10% to 80% of swing phase for 150 ms, 250 ms or 350 ms. Strategies were characterized by foot motion post-perturbation and identified by an automated algorithm. A multinomial logistic model was used to investigate the effect of perturbation onset, side, and the interaction between duration and onset on recovery strategy selection. Side perturbed did not affect strategy selection. Perturbation duration interacted with onset, limiting the use of elevating strategies to earlier in swing phase with longer perturbations. The choice between delayed-lowering and lowering strategies was not affected by perturbation duration. Although these variables did not fully explain strategy selection, they improved the prediction of strategy used in response to tripping perturbations throughout swing phase.