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Human whole-body angular momentum (WBAM) during walking typically follows a consistent pattern, making it a valuable indicator of the state of balance. However, calculating WBAM is labor-intensive, where the kinematic data for all body segments is needed, that is, based on a full-body model. In this study, we focused on selecting appropriate segments for estimating sagittal-plane WBAM during both unperturbed and perturbed gaits, which were segments with significant angular momentum contributions. Those major segments were constructed as a simplified model, and the sagittal-plane WBAM based on a simplified model was calculated by combining the angular momenta of the selected segments. We found that the WBAM estimated by seven-segment models, incorporating the head & torso (HT) and all lower limb segments, provided an average correlation coefficient of 0.99 and relative angular momentum percentage of 96.8% and exhibited the most similar sensitivity to external perturbations compared to the full-body model-based WBAM. Additionally, our findings revealed that the rotational angular momenta (RAM) of lower limb segments were much smaller than their translational angular momenta (TAM). The pair-wise comparisons between simplified models with and without RAMs of lower body segments were observed with no significant difference, indicating that RAMs of lower body segments are neglectable. This may further simplify the WBAM estimation based on the seven-segment model, eliminating the need to estimate the angular velocities of lower limb segments. These findings have practical implications for future studies of using inertial measurement units (IMUs) for estimating WBAM, as our results can help reduce the number of required sensors and simplify kinematics measurement., Competing Interests: Declaration of competing interest The authors declare that they have no competing or financial interests., (Copyright © 2024 The Authors. Published by Elsevier B.V. All rights reserved.)

Tongue based robotic interfaces have shown the potential to control assistive robotic devices developed for individuals with severe disabilities due to spinal cord injury. However, current tongue-robotic interfaces require invasive methods such as piercing to attach an activation unit (AU) to the tongue. A noninvasive tongue interface concept, which used a frame integrated AU instead of a tongue attached AU, was previously proposed. However, there is a need for the development of compact one-piece sensor printed circuit boards (PCBs) to enable activation of all inductive sensors. In this study, we developed and tested four designs of compact one-piece sensor PCBs incorporating inductive sensors for the design of a noninvasive tongue-robotic interface. We measured electrical parameters of the developed sensors to detect activation and compared them with a sensor of the current version of the inductive tongue-computer interface (ITCI) by moving AUs with different contact surfaces at the surface of the sensors. Results showed that, the newly developed inductive sensors had higher and wider activation than the sensor of ITCI and the AU with a flat contact surface had 3.5 - 4 times higher activation than the AU with a spherical contact surface. A higher sensor activation can result in a higher signal to noise ratio and thus a higher AU tracking resolution.

Background: Disambiguation of behavioral restitution from compensation is important to better understand recovery of upper limb motor control post-stroke and subsequently design better interventions. Measuring quality of movement (QoM) during standardized performance assays and functional tasks using kinematic and kinetic metrics potentially allows for this disambiguation., Objectives: To identify longitudinal studies that used kinematic and/or kinetic metrics to investigate post-stroke recovery of reaching and assess whether these studies distinguish behavioral restitution from compensation., Methods: A systematic literature search was conducted using the databases PubMed, Embase, Scopus, and Wiley/Cochrane Library up to July 1st, 2020. Studies were identified if they performed longitudinal kinematic and/or kinetic measurements during reaching, starting within the first 6 months post-stroke., Results: Thirty-two longitudinal studies were identified, which reported a total of forty-six different kinematic metrics. Although the majority investigated improvements in kinetics or kinematics to quantify recovery of QoM, none of these studies explicitly addressed the distinction between behavioral restitution and compensation. One study obtained kinematic metrics for both performance assays and a functional task., Conclusions: Despite the growing number of kinematic and kinetic studies on post-stroke recovery, longitudinal studies that explicitly seek to delineate between behavioral restitution and compensation are still lacking in the literature. To rectify this situation, future studies should measure kinematics and/or kinetics during performance assays to isolate restitution and during a standardized functional task to determine the contributions of restitution and compensation.

Objective . Investigation of the night-to-night (NtN) variability of pulse oximetry features in children with suspicion of Sleep Apnea. Approach . Following ethics approval and informed consent, 75 children referred to British Columbia Children's Hospital for overnight PSG were recorded on three consecutive nights, including one at the hospital simultaneously with polysomnography and 2 nights at home. During all three nights, a smartphone-based pulse oximeter sensor was used to record overnight pulse oximetry (SpO2 and photoplethysmogram). Features characterizing SpO2 dynamics and heart rate were derived. The NtN variability of these features over the three different nights was investigated using linear mixed models. Main results . Overall most pulse oximetry features (e.g. the oxygen desaturation index) showed no NtN variability. One of the exceptions is for the signal quality, which was significantly lower during at home measurements compared to measurements in the hospital. Significance . At home pulse oximetry screening shows an increasing predictive value to investigate obstructive sleep apnea (OSA) severity. Hospital recordings affect subjects normal sleep and OSA severity and recordings may vary between nights at home. Before establishing the role of home monitoring as a diagnostic test for OSA, we must first determine their NtN variability. Most pulse oximetry features showed no significant NtN variability and could therefore be used in future at-home testing to create a reliable and consistent OSA screening tool. A single night recording at home should be able to characterize pulse oximetry features in children., (Creative Commons Attribution license.)

Sensing of the interaction forces at fingertips is of great value in assessment and rehabilitation therapy. Current force sensors are not compliant to the fingertip tissue and result in loss of touch sensation of the user. This work shows the development and characterization of a flexible fully-3D-printed piezoresistive shear and normal force sensor that uses the mechanical deformation of the finger tissue. Two prototypes of the sensing structure are evaluated using a finite element model and a measurement setup that applies normal and shear forces up to 10 N on a fingertip phantom placed inside the sensing structure, which is fixed to prevent slippage. Furthermore, the relation between strain (rate) and resistance of the conductive TPU, used for the strain gauges, is characterized. The applied normal and shear force components of the 3D-printed sensing structure can be partly separated. FEM analysis showed that the output of the sensor is largely related to the sensor geometry and location of the strain gauges. Furthermore, the conductive TPU that was used has a negative gauge factor for the strain range used in this study and might cause non-linear behaviors in the sensor output.

3D printing of soft EMG sensing structures enables the creation of personalized sensing structures that can be potentially integrated in prosthetic, assistive and other devices. We developed and characterized flexible carbon-black doped TPU-based sEMG sensing structures. The structures are directly 3D-printed without the need for an additional post-processing step using a low-cost, consumer grade multi-material FDM printer. A comparison between the gold standard Ag/AgCl gel electrodes and the 3D-printed EMG electrodes with a comparable contact area shows that there is no significant difference in the EMG signals' amplitude. The sensors are capable of distinguishing a variable level of muscle activity of the biceps brachii. Furthermore, as a proof of principle, sEMG data of a 3D-printed 8-electrode band are analyzed using a patten recognition algorithm to recognize hand gestures. This work shows that 3D-printed sEMG electrodes have great potential in practical applications.

To support stroke survivors in activities of daily living, wearable soft-robotic gloves are being developed. An essential feature for use in daily life is detection of movement intent to trigger actuation without substantial delays. To increase efficacy, the intention to grasp should be detected as soon as possible, while other movements are not detected instead. Therefore, the possibilities to classify reach and grasp movements of stroke survivors, and to detect the intention of grasp movements, were investigated using inertial sensing. Hand and wrist movements of 10 stroke survivors were analyzed during reach and grasp movements using inertial sensing and a Support Vector Machine classifier. The highest mean accuracies of 96.8% and 83.3% were achieved for single- and multi-user classification respectively. Accuracies up to 90% were achieved when using 80% of the movement length, or even only 50% of the movement length after choosing the optimal kernel per person. This would allow for an earlier detection of 300-750ms, but at the expense of accuracy. In conclusion, inertial sensing combined with the Support Vector Machine classifier is a promising method for actuation of grasp-supporting devices to aid stroke survivors in activities of daily living. Online implementation should be investigated in future research.

Background: Patients with acute respiratory failure may develop respiratory acidosis. Metabolic compensation by bicarbonate production or retention results in posthypercapnic alkalosis with an increased arterial bicarbonate concentration. The hypothesis of this study was that elevated plasma bicarbonate levels decrease respiratory drive and minute ventilation., Methods: In an intervention study in 10 healthy subjects the ventilatory response using a hypercapnic ventilatory response (HCVR) test was assessed, before and after administration of high dose sodium bicarbonate. Total dose of sodiumbicarbonate was 1000 ml 8.4% in 3 days., Results: Plasma bicarbonate increased from 25.2 ± 2.2 to 29.2 ± 1.9 mmol/L. With increasing inspiratory CO 2 pressure during the HCVR test, RR, V t , Pdi, EAdi and V E increased. The clinical ratio ΔV E /ΔP et CO 2 remained unchanged, but Pdi, EAdi and V E were significantly lower after bicarbonate administration for similar levels of inspired CO 2 ., Conclusion: This study demonstrates that in healthy subjects metabolic alkalosis decreases the neural respiratory drive and minute ventilation, as a response to inspiratory CO 2 ., (Copyright © 2018 The Authors. Published by Elsevier B.V. All rights reserved.)

Introduction: Soft-robotic gloves have been developed to enhance grip to support stroke patients during daily life tasks. Studies showed that users perform tasks faster without the glove as compared to with the glove. It was investigated whether it is possible to detect grasp intention earlier than using force sensors to enhance the performance of the glove., Methods: This was studied by distinguishing reach-to-grasp movements from reach movements without the intention to grasp, using minimal inertial sensing and machine learning. Both single-user and multi-user support vector machine classifiers were investigated. Data were gathered during an experiment with healthy subjects, in which they were asked to perform grasp and reach movements., Results: Experimental results show a mean accuracy of 98.2% for single-user and of 91.4% for multi-user classification, both using only two sensors: one on the hand and one on the middle finger. Furthermore, it was found that using only 40% of the trial length, an accuracy of 85.3% was achieved, which would allow for an earlier prediction of grasp during the reach movement by 1200 ms., Conclusions: Based on these promising results, further research will be done to investigate the possibility to use classification of the movements in stroke patients., Competing Interests: The author(s) declared no potential conflicts of interest with respect to the research, authorship, and/or publication of this article.

Monitoring physical activities during post-stroke rehabilitation in daily life may help physicians to optimize and tailor the training program for patients. The European research project INTERACTION (FP7-ICT-2011-7-287351) evaluated motor capabilities in stroke patients during the recovery treatment period. We developed wearable sensing platform based on the sensor fusion among inertial, knitted piezoresistive sensors and textile EMG electrodes. The device was conceived in modular form and consists of a separate shirt, trousers, glove, and shoe. Thanks to the novel fusion approach it has been possible to develop a model for the shoulder taking into account the scapulo-thoracic joint of the scapular girdle, considerably improving the estimation of the hand position in reaching activities. In order to minimize the sensor set used to monitor gait, a single inertial sensor fused with a textile goniometer proved to reconstruct the orientation of all the body segments of the leg. Finally, the sensing glove, endowed with three textile goniometers and three force sensors showed good capabilities in the reconstruction of grasping activities and evaluating the interaction of the hand with the environment, according to the project specifications. This paper reports on the design and the technical evaluation of the performance of the sensing platform, tested on healthy subjects.

Background and Aim: Several studies have shown that feedback in upper-leg prostheses is possible, but slow or difficult to interpret. In this study, electrotactile and auditive error-based feedback, only giving feedback when an undesired event occurs, were tested for its use in upper-leg prosthesis when provided during a perturbation., Technique: A total of nine healthy subjects walked on a prosthetic simulator which was disturbed at the end of the swing phase. They received either no feedback, electrotactile feedback, or auditive feedback at the time of the perturbation., Discussion: The reaction time of the subjects only improved by 40 ms when using auditory feedback, compared to the no-feedback condition. No changes in reaction time were found in the electrotactile feedback condition. Considering perturbation detection was not taken into account in this study, this improvement is not enough for practical applications in upper-leg prosthesis., Clinical Relevance: Many transfemoral amputees are insecure about their prosthesis, are afraid of falling, or actually fall. Providing feedback specifically during a perturbation may prevent them from falling, or at least give them a chance to react., (© The International Society for Prosthetics and Orthotics 2014.)

Objective: In spinal cord stimulation, anodes tend to have a strong effect over the area of dorsal column (DC) activation, when configured as both longitudinal guarded cathodes (LGCs) and transverse tripoles (TTs). Inclusion of a small spacing step (LGC+) in the center-center (C-C) spacing of the LGC can be an efficient method to study the local effects around the electrode. The primary aim of this computer modeling study is to investigate if enhanced DC recruitment is achieved when anodal currents in TT and LGC combinations (both LGC and LGC+) are increased up to 30% with respect to the cathodal current. Secondly, the merits of anodal intensification (AI) are evaluated by comparing the DC recruitment areas (S(RA)) and energy consumption (EDT ) of LGC+ with AI, against stimulation using an LGC without AI., Materials and Methods: The commercially available LGC and LGC+, with 4.0 and 4.5 mm C-C, respectively, were modeled on a single percutaneous lead at the low-thoracic vertebral region (T10-T12). Transverse tripolar stimulation (TTS) was modeled on triple percutaneous leads., Results: TTS with 10% AI recruited a smaller S(RA) as compared with TTS with no AI. AI of LGC and LGC+ resulted in increasing SRAs respectively to that of LGC and LGC+ without AI. Also, AI of LGC+ recruited a larger S(RA) and usage range (UR) at lower E(DT) compared with that of LGC without AI., Conclusions: AI of TTS is not advantageous. LGC and LGC+ with AI allow additional DC stimulation, which may increase the likelihood of activating fibers inaccessible with conventional programming. LGC+ with AI can be more efficient than LGCs without AI, as a larger SRA and UR is achieved at lower EDT ., (© 2013 International Neuromodulation Society.)

The objective of the INTERACTION Eu project is to develop and validate an unobtrusive and modular system for monitoring daily life activities, physical interactions with the environment and for training upper and lower extremity motor function in stroke subjects. This paper describes the development and preliminary testing of the project sensing platform made of sensing shirt, trousers, gloves and shoes. Modular prototypes were designed and built considering the minimal set of inertial, force and textile sensors that may enable an efficient monitoring of stroke patients. The single sensing elements are described and the results of their preliminary lab-level testing are reported.

In this study we determined if detection of the onset of gait initiation in transfemoral amputees can be useful for voluntary control of upper leg prostheses. From six transfemoral amputees inertial sensor data and EMG were measured at the prosthetic leg during gait initiation. First, initial movement was detected from the inertial sensor data. Subsequently it was determined whether EMG could predict initial movement before detection based on the inertial sensors with comparable consistency as the inertial sensors. From the inertial sensors the initial movement can be determined. If the prosthetic leg leads, the upper leg accelerometer data was able to detect initial movement best. If the intact leg leads the upper leg gyroscope data performed best. Inertial sensors at the upper leg in general showed detections at the same time or earlier than those at the lower leg. EMG can predict initial movement up to a 138 ms in advance, when the prosthetic leg leads. One subject showed consistent EMG onset up to 248 ms before initial movement in the intact leg leading condition. A new method to detect initial movement from inertial sensors was presented and can be useful for additional prosthetic control. EMG measured at the prosthetic leg can be used for prediction of gait initiation when the prosthetic leg is leading, but for the intact leg leading condition this will not be of additional value., (Copyright © 2013 Elsevier B.V. All rights reserved.)

Most modern intelligent knee prosthesis use dampers to modulate dynamic behavior and prevent excessive knee flexion, but they dissipate energy and do not assist in knee extension. Energy efficient variable stiffness control (VSA) can reduce the energy consumption yet effectively modulate the dynamic behavior and use stored energy during flexion to assist in subsequent extension. A principle design of energy efficient VSA in a prosthetic knee is proposed and analyzed for the specific case of rejection of a disturbed stance phase. The concept is based on the principle that the output stiffness of a spring can be changed without changing the energy stored in the elastic elements of the spring. The usability of this concept to control a prosthetic knee is evaluated using a model. Part of the stance phase of the human leg was modeled by a double pendulum. Specifically the rejection of a common disturbance of transfemoral prosthetic gait, an unlocked knee at heel strike, was evaluated. The ranges of spring stiffnesses were determined such that the angular characteristics of a normal stance phase were preserved, but disturbances could also be rejected. The simulations predicted that energy efficient VSA can be useful for the control of prosthetic knees., (Copyright © 2012 IPEM. Published by Elsevier Ltd. All rights reserved.)

Gait initiation in transfemoral amputees (TFA) is different from non-amputees. This is mainly caused by the lack of stability and push-off from the prosthetic leg. Adding control and artificial push-off to the prosthesis may therefore be beneficial to TFA. In this study the feasibility of real-time intention detection of gait initiation was determined by mimicking the TFA situation in non-amputees. EMG and inertial sensor data was measured in 10 non-amputees. Only data available in TFA was used to determine if gait initiation can be predicted in time to control a transfemoral prosthesis to generate push-off and stability. Toe-off and heel-strike of the leading limb are important parameters to be detected, to control a prosthesis and to time push-off. The results show that toe-off and heel-strike of the leading limb can be detected using EMG and kinematic data in non-amputees 130-260 ms in advance. This leaves enough time to control a prosthesis. Based on these results we hypothesize that similar results can be found in TFA, allowing for adequate control of a prosthesis during gait initiation., (Copyright © 2012 Elsevier B.V. All rights reserved.)

Many of the currently available myoelectric forearm prostheses stay unused because of the lack of sensory feedback. Vibrotactile and electrotactile stimulation have high potential to provide this feedback. In this study, performance of a grasping task is investigated for different hand opening feedback conditions on 15 healthy subjects and validated on three patients. The opening of a virtual hand was controlled by a scroll wheel. Feedback about hand opening was given via an array of eight vibrotactile or electrotactile stimulators placed on the forearm, relating to eight hand opening positions. A longitudinal and transversal orientation of the array and four feedback conditions were investigated: no feedback, visual feedback, feedback through vibrotactile or electrotactile stimulation, and addition of an extra stimulator for touch feedback. No influence of array orientation was shown for all outcome parameters (duration of the task, the percentage of correct hand openings, the mean position error, and the percentage deviations up to one position). Vibrotactile stimulation enhances the performance compared to the nonfeedback conditions. The addition of touch feedback further increases the performance, but at the cost of an increased duration. The same effects were found for the patient group, but the task duration was around 25% larger.

Objective:   In spinal cord stimulation, neurosurgeons increasingly tend to implant dual leads. Dual leads (longitudinal bipole/tripole) provide medio-lateral control over the recruited dorsal column (DC) area by steering the injected cathodal currents. However, the DC recruited area is suboptimal when dual aligned leads straddling the midline programmed as longitudinal guarded cathodes (+-+) are used instead of a single lead placed over the spinal cord midline with the same configuration. As a potential improvement, an additional third lead between the two aligned leads is modeled to maximize the medio-lateral extent of the DCs at the low-thoracic vertebral region (T10-T12)., Methods and Materials:   The University of Twente Spinal Cord Stimulation software (UT-SCS) is used in this modeling study. Longitudinal guarded cathodes were modeled on the low-thoracic vertebral region (T10-T12) using percutaneous triple lead configurations. The central lead was modeled over the spinal cord midline and the two lateral leads were modeled at several transverse distances to the midline lead. Medio-lateral field steering was performed with the midline lead and the second lead on each side to achieve constant anodal current ratios and variable anodal current ratios., Results:   Reducing the transverse lead separation resulted in increasing the depths and widths of the recruited DC area. The triple lead configuration with the least transverse separation had the largest DC recruited area and usage range. The maximum DC recruited area (in terms of both depth and width) was always found to be larger under variable anodal current ratio than constant anodal current ratio conditions., Conclusions:   Triple leads programmed to perform as longitudinal guarded cathodes provide more postoperative flexibility than single and dual leads in covering a larger width of the low-thoracic DCs. The transverse separation between the leads is a major determinant of the area and distribution of paresthesia., (© 2011 International Neuromodulation Society.)

The aim of this modeling study is to determine the influence of electrode alignment of transverse tripoles on the paresthesia coverage of the pain area in spinal cord stimulation, using a percutaneous triple-lead approach. Transverse tripoles, comprising a central cathode and two lateral anodes, were modeled on the low-thoracic vertebral region (T10-T12) using percutaneous triple-lead configurations, with the center lead on the spinal cord midline. The triple leads were oriented both aligned and staggered. In the staggered configuration, the anodes were offset either caudally (caudally staggered) or rostrally (rostrally staggered) with respect to the midline cathode. The transverse tripolar field steering with the aligned and staggered configurations enabled the estimation of dorsal column fiber thresholds (I(DC)) and dorsal root fiber thresholds (I(DR)) at various anodal current ratios. I(DC) and I(DR) were considerably higher for the aligned transverse tripoles as compared to the staggered transverse tripoles. The aligned transverse tripoles facilitated deeper penetration into the medial dorsal columns (DCs). The staggered transverse tripoles always enabled broad and bilateral DC activation, at the expense of mediolateral steerability. The largest DC recruited area was obtained with the rostrally staggered transverse tripole. Transverse tripolar geometries, using percutaneous leads, allow for selective targeting of either medial or lateral DC fibers, if and only if the transverse tripole is aligned. Steering of anodal currents between the lateral leads of the staggered transverse tripoles cannot target medially confined populations of DC fibers in the spinal cord. An aligned transverse tripolar configuration is strongly recommended, because of its ability to provide more post-operative flexibility than other configurations.

In this paper a new concept to identify environmental loads during the interaction with the human body by sensing interface forces and movement is proposed. Mass and spring loads were moved by hand over a fixed height difference. Kinematic and kinetic quantities were measured between the hand and the load using an instrumented handle. Force was measured using a force transducer module, movement was measured using an accelerometer and rate gyroscope. Under the condition that the human body was actively generating force at the load, while the load was passive, the dynamic characteristics of the load could be estimated. The estimated parameter values were compared to their specified values and appeared to be accurate within 4% for both mass and spring loads.

In this study vibrotactile stimulation of the upper leg and its usability for feedback was tested. Three experiments were performed on ten healthy subjects using pager motors. The first experiment was to test the perception of the vibration at different frequencies and at different locations of the upper leg. The second experiment tested the ability of subjects to estimate location and number of stimuli in an array. In addition it was evaluated whether simultaneous or sequential stimulation is better interpretable. Thirdly the habituation of the vibration was determined. The experiments showed that vibrotactile stimulation is well perceived and can be useful in providing feedback on the upper leg. Further experiments are needed to determine the effectiveness of vibrotactile stimulation for feedback in trans-femoral prostheses.

User acceptance of myoelectric forearm prostheses is currently low. Awkward control, lack of feedback, and difficult training are cited as primary reasons. Recently, researchers have focused on exploiting the new possibilities offered by advancements in prosthetic technology. Alternatively, researchers could focus on prosthesis acceptance by developing functional requirements based on activities users are likely to perform. In this article, we describe the process of determining such requirements and then the application of these requirements to evaluating the state of the art in myoelectric forearm prosthesis research. As part of a needs assessment, a workshop was organized involving clinicians (representing end users), academics, and engineers. The resulting needs included an increased number of functions, lower reaction and execution times, and intuitiveness of both control and feedback systems. Reviewing the state of the art of research in the main prosthetic subsystems (electromyographic [EMG] sensing, control, and feedback) showed that modern research prototypes only partly fulfill the requirements. We found that focus should be on validating EMG-sensing results with patients, improving simultaneous control of wrist movements and grasps, deriving optimal parameters for force and position feedback, and taking into account the psychophysical aspects of feedback, such as intensity perception and spatial acuity.

The possibility of gathering reliable information about movement characteristics during activities of daily living holds particular appeal for researchers. Data such as this could be used to analyze the performance of individuals undergoing rehabilitation and to provide vital information on whether or not there is an improvement during a neurorehabilitation protocol. Wearable devices are particularly promising toward this aim, because they can be used in unstructured environments (e.g., at home). Recently, two different approaches in this area have become very popular and show promising performance: the use of inertial sensors together with advanced algorithms (e.g., Kalman filters) and the development of e-textile, in which the sensing technology is directly embroidered into the garment worn by the user.

Purpose: Vagus nerve stimulation (VNS) for medically refractory epilepsy can give hoarseness due to stimulation of the recurrent laryngeal nerve. For a group of VNS-therapy users this side-effect interferes severely with their daily activities. Our goal was to investigate the severity of intra-operative VNS-related vocal fold contraction at different pulse widths and current output parameters. We investigated electromyographic and morphometric alterations on the vocal folds during VNS., Methods: Vocal fold EMG experiments were conducted intra-operatively during the implantation of a VNS system. During surgery the VNS pulse generator was programmed to stimulate at different pulse durations. At each pulse width the EMG-threshold current was determined by electrical stimulation of the vagus nerve with increasing stimulation currents. Laryngostroboscopic examination was performed after surgery to analyze the effects of spontaneous stimulation on the larynx., Results: The vocal fold EMG and morphodynamic changes in the larynx have been analyzed in eight patients. In all patients left vocal fold EMG-threshold was between 0.25 and 0.50 mA. Pulse duration had little influence on the EMG-threshold level. Vocal fold EMG saturation levels were reached between 0.75 and 1.00 mA. Video stroboscopic monitoring showed that stimulation induced an adductory spasm of either the ipsilateral vocal fold or the vestibular fold, and was present remarkably irrespective of the presence of hoarseness., Conclusions: VNS causes pronounced effects on the vocal folds even at low stimulation amplitudes. At therapeutic levels even at the lowest stimulation pulse durations, the vocal fold contract, however, this does not necessarily give hoarseness., (Copyright 2010 Elsevier B.V. All rights reserved.)

An Inertial Gait Phase Detection system was developed to replace heel switches and footswitches currently being used for the triggering of drop foot stimulators. A series of four algorithms utilising accelerometers and gyroscopes individually and in combination were tested and initial results are shown. Sensors were positioned on the outside of the upper shank. Tests were performed on data gathered from a subject, sufferer of stroke, implanted with a drop foot stimulator and triggered with the current trigger, the heel switch. Data tested includes a variety of activities representing everyday life. Flat surface walking, rough terrain and carpet walking show 100% detection and the ability of the algorithms to ignore non-gait events such as weight shifts. Timing analysis is performed against the current triggering method, the heel switch. After evaluating the heel switch timing against a reference system, namely the Vicon 370 marker and force plates system. Initial results show a close correlation between the current trigger detection and the inertial sensor based triggering algorithms. Algorithms were tested for stairs up and stairs down. Best results are observed for algorithms using gyroscope data. Algorithms were designed using threshold techniques for lowest possible computational load and with least possible sensor components to minimize power requirements and to allow for potential future implantation of sensor system.

One of the neuropsychological deficits that can result from a stroke is the neglect phenomenon. Neglect has traditionally been assessed with paper-and-pencil tasks, which are administered within the reaching space of a person. The purpose of this explorative study is to investigate whether it is possible to assess neglect in the extrapersonal space based on the performance of acute stroke patients, chronic stroke patients and healthy elderly in orientation and exploration tasks when immersed in a three-dimensional (3D)-virtual environment. Six able-bodied healthy elderly and 12 stroke patients (six subacute and six chronic) participated in this explorative cross-sectional study. Neglect was assessed by means of the 3D neglect test. Different parameters were measured at two challenge levels with increasing difficulty. In the easiest level significant differences between the groups were found for total time spent in the test, mean response time left field of vision, and mean response time in the left field of vision of the left virtual reality environment. Differences in search patterns showed that subacute stroke patients had a much more fuzzy search pattern in scanning the environment than healthy elderly and chronic stroke patients. With respect to the more difficult level results showed significant differences between healthy elderly and the total group of stroke patients. The results of this study suggest that a 3D neglect test by means of virtual reality has the potential to detect and measure unilateral neglect.

This article presents a stimulation control method using a uniaxial gyroscope measuring angular velocity of the shank in the sagittal plane, to control functional electrical stimulation of the triceps surae to improve push-off of stroke subjects during gait. The algorithm is triggered during each swing phase of gait when the angular velocity of the shank is relatively high. Subsequently, the start of the stance phase is detected by a change of sign of the gyroscope signal at approximately the same time as heel strike. Stimulation is triggered when the shank angle reaches a preset value since the beginning of stance. The change of angle is determined by integrating angular velocity from the moment of change of sign. The results show that the real-time reliability of stimulation control was at least 95% for four of the five stroke subjects tested, two of which were 100% reliable. For the remaining subject, the reliability was increased from 50% found during the experiment, to 99% during offline processing. Our conclusion is that a uniaxial gyroscope on the shank is a simple, more reliable alternative to the heel switch for the purpose of restoring push-off of stroke subjects during gait.

Through recent studies, the role of proprioceptors in reactions to perturbations during gait has been finally somewhat better understood. The input from spindle afferents has been investigated with tendon taps, vibration and other forms of muscle stretches, including some resembling natural perturbations (stumbling, slips, and ankle inversions). It was found that activation of spindle afferents produces short-latency response (SLR), consistent with a fast spinal pathway. These reflexes induce relatively minor activation in the stretched muscles. A central question is whether stretch reflexes can occur for stimuli that are quite remote. Thus, a new study was made to examine whether foot sole vibration is able to elicit reflex responses in upper-leg muscles, for example by conduction of vibrations throughout the whole leg. SLR responses were indeed found not only in lower- but also in upper-leg muscles. Similarly during stumbling, SLR are observed throughout the whole limb, although the primary perturbation occurs at foot level. After the SLR, much stronger activations usually occur, with latencies (85 or 120ms) well below those seen in voluntary contractions. These late responses are much more selective and presumably linked to the maintenance of stability. The role of the I(b) afferents from the Golgi tendon organs (GTO) is less clear. From animal work, it is known that these afferents are very sensitive to active muscle contraction and that they play a role in providing reinforcing feedback to extensors during the stance phase. The available evidence supports this notion in humans but lack of selective activation methods precludes more conclusive confirmation.

Objective: To explore the effects of electrical stimulation performed by an anode, a cathode or a bipole positioned over the motor cortex for chronic pain management., Methods: A realistic 3D volume conductor model of the human precentral gyrus (motor cortex) was used to calculate the stimulus-induced electrical field. The subsequent response of neural elements in the precentral gyrus and in the anterior wall and lip of the central sulcus was simulated using compartmental neuron models including the axon, soma and dendritic trunk., Results: While neural elements perpendicular to the electrode surface are preferentially excited by anodal stimulation, cathodal stimulation excites those with a direction component parallel to its surface. When stimulating bipolarly, the excitation of neural elements parallel to the bipole axis is additionally facilitated. The polarity of the contact over the precentral gyrus determines the predominant response. Inclusion of the soma-dendritic model generally reduces the excitation threshold as compared to simple axon model., Conclusions: Electrode polarity and electrode position over the precentral gyrus and central sulcus have a large and distinct influence on the response of cortical neural elements to stimuli., Significance: Modeling studies like this can help to identify the effects of electrical stimulation on cortical neural tissue, elucidate mechanisms of action and ultimately to optimize the therapy.

In order to evaluate the impact of neuromuscular disorders affecting the upper extremities, the functional use of the arm need to be evaluated during daily activities. A system suitable for measuring arm kinematics should be ambulatory and not interfere with activities of daily living. A measurement system based on miniature accelerometers and gyroscopes is adequate because the sensors are small and do not suffer from line of sight problems. A disadvantage of such sensors is the cumulative drift around the vertical and the problems with aligning the sensor with the segment. A method that uses constraints in the elbow to measure the orientation of the lower arm with respect to the upper arm is described. This requires a calibration method to determine the exact orientation of each of the sensors with respect to the segment. Some preliminary measurements were analyzed and they indicated a strong reduction in orientation error around the vertical. It seemed that the accuracy of the method is limited by the accuracy of the sensor to segment calibration.

Objective  To compare the technical performance of different percutaneous lead types for spinal cord stimulation. Methods  Using the ut-scs software (University of Twente's spinal cord stimulation), lead models having similar characteristics such as the 3487A PISCES-Quad (PQ), 3887 PISCES-Quad Compact (PC), 3888 PISCES-Quad Plus (PP) (Medtronic Inc., Minneapolis, MN), and the AB SC2108 (AB) (Advanced Bionics Corp., Valencia, CA) were simulated in monopolar and tripolar (guarded cathode) combinations on a single lead, placed just outside the dorsal dura mater and both centered on the spinal cord midline, and at 1 mm lateral. The influence of displacing a lead dorsally in the epidural fat was examined as well. Finally, dual leads both aligned and offset were modeled. Several parameters were calculated to allow a quantitative comparison of the performances. Results  When programmed as a guarded cathode, the AB lead recruits nerve fibers in an ~25% larger dorsal column area than the PQ. However, the AB has an ~160% higher energy consumption. The performance of the PC is between the AB and PQ, whereas the PP is suitable only for dorsal root stimulation. Displacing a single lead off midline or dorsally decreases its ability to recruit fibers in the dorsal columns. Similarly, dual lead combinations are less capable when compared to single lead centered on the spinal cord midline just outside the dura mater. Conclusions  Complex pain syndromes are treated best with lead having a small contact spacing, being programmed as a tripole (guarded cathode) and centered on the spinal cord midline just outside the dura mater. This is because dorsal column fiber recruitment is more extensive than with any other combinations, including dual leads. Improved recruitment of dorsal column fibers is accompanied by increased energy consumption.

In the medical field, there is a need for small ambulatory sensor systems for measuring the kinematics of body segments. Current methods for ambulatory measurement of body orientation have limited accuracy when the body moves. The aim of the paper was to develop and validate a method for accurate measurement of the orientation of human body segments using an inertial measurement unit (IMU). An IMU containing three single-axis accelerometers and three single-axis micromachined gyroscopes was assembled in a rectangular box, sized 20 x 20 x 30 mm. The presented orientation estimation algorithm continuously corrected orientation estimates obtained by mathematical integration of the 3D angular velocity measured using the gyroscopes. The correction was performed using an inclination estimate continuously obtained using the signal of the 3D accelerometer. This reduces the integration drift that originates from errors in the angular velocity signal. In addition, the gyroscope offset was continuously recalibrated. The method was realised using a Kalman filter that took into account the spectra of the signals involved as well as a fluctuating gyroscope offset. The method was tested for movements of the pelvis, trunk and forearm. Although the problem of integration drift around the global vertical continuously increased in the order of 0.50 degrees s(-1), the inclination estimate was accurate within 3 degrees RMS. It was shown that the gyroscope offset could be estimated continuously during a trial. Using an initial offset error of 1 rad s(-1), after 2 min the off-set error was roughly 5% of the original offset error. Using the Kalman filter described, an accurate and robust system for ambulatory motion recording can be realised.

The surface electromyographic (SEMG) signal obtained during gait is often presented as the SEMG profile, the average SEMG activation pattern during one gait cycle. A disadvantage of this method is that it omits the step-to-step variability of the timing of the muscle activation patterns that might be relevant information as a performance measure of motor control and balance. In this paper, a method was used in which every step in the gait cycle could be analysed with respect to the timing of the muscle activation. For this purpose, the approximated generalised likelihood (AGLR) algorithm was implemented and tested. Results of the simulations show that the AGLR was much more accurate than a standard threshold criterion. Timing parameters could be calculated from a SEMG recording during gait and a measure for symmetry and coordination could be extracted. The amplitude distribution within and outside defined bursts is also presented to avoid the less precise classification into on and off patterns.

A three dimensional inertial sensing system for measuring foot movements during gait is proposed and tested. It can form the basis for an automated tuning system for a two-channel implantable drop-foot stimulator. The foot orientation and position during the swing phase of gait can be reconstructed on the basis of three-dimensional measurement of acceleration and angular velocity, using initial and final conditions during mid-stance. The foot movements during gait of one stroke person using the implanted two-channel stimulator were evaluated for several combinations of stimulation parameters for both channels. The reconstructed foot movements during gait in this person indicated that the channel stimulating the deep peroneal nerve contributes mainly to dorsiflexion and provides some reduction of inversion seen without stimulation, while the channel activating the superficial peroneal nerve mainly provides additional reduction of inversion. This agrees with anatomical knowledge about the function of the muscles activated by both branches of the peroneal nerve. The inertial sensor method is expected to be useful for the clinical evaluation of foot movements during gait supported by the two-channel drop-foot stimulator. Furthermore, it is expected to be applicable for the automated balancing of the two stimulation channels to ensure optimal support of gait.

The objective of this study was to test myoelectrically controlled functional electrical stimulation of the same muscle (AutoMCS) on patients with either stroke or spinal cord injury. The paretic anterior tibialis (TA) muscle was stimulated with an amplitude controlled continuously by the volitional myoelectric signal from the same muscle. Surface electrodes were used and volitional myoelectric signals were extracted by analog/digital signal processing techniques. Isometric dorsiflexion torque of the foot was displayed on a screen and the subjects were asked to track a sinusoidal curve. Subjects with dropped foot, as a result of a stroke (CVA, n = 9) or spinal cord lesion (SCI, n = 4), performed tests without and then with AutoMCS applied to the muscle. Subjects were their own control and tracking tests without and with AutoMCS. Changes in torque range, tracking delay, and tracking control accuracy have been evaluated. A significant (p < 0.05) increase of dorsiflexion torque by AutoMCS was found. An immediate carryover effect was seen in one stroke subject. The analysis of the tracking control showed only little loss of controllability with the system. We conclude that for selected subjects this method can instantly increase the muscle force of the anterior tibialis without significantly compromising tracking control or tracking delay.

Interaction of electrocutaneous stimulation with an impaired human motor control system may result in unstable reflex loops causing excessive spastic reactions. These contractions are usually excluded from analysis since the presence of spasm is one of the criteria commonly applied for discarding a contraction. They may, however, provide interesting information on the nature of spasticity. The dorsiflexor muscles of four SCI subjects were activated by means of surface electrical stimulation and the isometric ankle moment was measured. Short bursts of constant stimulation frequency at seven different frequencies (8, 12, 16, 20, 25, 33, 50 Hz) triggered spastic reactions in all subjects. The onset times of spastic activity during an electrically elicited contraction shortened with increased stimulation frequency. A stimulation burst may also have a spasticity reduction effect on a subsequent burst, indicating potential short term therapeutic effects of stimulation on spasticity in isometric conditions.

Biomechatronics concerns the interdisciplinary field of interaction with the human neuromuscular-skeletal system with the objective to assist impaired human motor control. In this field technology is developed that integrates neuroscience, robotics, interface and sensor technology, dynamic systems and control theory. The primary issue in this field concerns the concepts of assisting impaired human motor function. The secondary, derived, issue concerns possible methods of interfacing with the human body at all hierarchical levels of the human motor system. The application of motor assist systems may serve several goals: it can take over part of the affected motor control, enable the physiological motor system to perform the desired function or aid in training the impaired physiological system. The progress in these issues are reviewed and their potential implications for assistance of the impaired human motor system are discussed.

The purpose of this study was to investigate the force-frequency relationships and the post-tetanic twitch potentiation as a function of joint angle (i.e. muscle length) in human skeletal muscles under isometric conditions. The dorsiflexor muscles of healthy subjects were stimulated at different ankle joint angles by means of constant frequency bursts at seven submaximal frequencies (50, 33, 25, 20, 16, 12, 8 Hz) with a duration of two seconds. Particular attention has been focused on the stability of recruitment in the range of joint angles examined. The results show that moment-frequency curves of human dorsiflexors change as a function of ankle angle: especially for the lower stimulation frequency range (8, 12, 16, 20 Hz), the normalized moment increases from dorsiflexion to plantar flexion (i.e. with increasing muscle length) resulting in a leftward shift of the normalized moment-frequency curves. Post-tetanic twitch potentiation is shown to be ankle joint dependent as well.

Objective: To reduce the triceps surae stretch reflex by electrical stimulation of the deep peroneal nerve., Design: Intervention study., Setting: Research institution., Participants: Sample of convenience of 10 spastic stroke individuals., Intervention: After the deep peroneal nerve was stimulated between 0.9 and 4 times tibialis anterior motor threshold, the triceps surae was stretched to elicit a reflex., Main Outcome Measure: The triceps surae stretch reflex was quantified by the amplitude of the reflex electromyography (EMG) in soleus and medial gastrocnemius muscles and mean ankle moment. Paired t test and the Wilcoxon signed rank test (p < .05) were used to evaluate the effect of conditioning stimulation., Results: The soleus stretch reflex EMG was reduced significantly (p < .001) by stimulating the deep peroneal nerve to 25%+/-6% (standard error) of the unconditioned value (relaxed triceps surae). The optimal interval between stimulation and stretch was 141+/-15 msec. The velocity threshold increased significantly (p = .006) from a median value of 8 degrees per second to 33 degrees per second and the area under the stretch velocity/stretch reflex relation decreased significantly (p < .001) (soleus EMG)., Conclusions: The stretch reflex of relaxed triceps surae in persons with spastic stroke can be extensively reduced by stimulating the deep peroneal nerve at several times motor threshold of the tibialis anterior.

Objectives. To investigate the feasibility of inhibiting the stretch reflex of the soleus muscle by a conditioning stimulus applied to the deep peroneal nerve in spastic stroke participants during the early swing phase of gait. Materials and Methods. This study investigated the effect of an electrical conditioning stimulus applied to the deep peroneal nerve on the magnitude at the peak of the soleus stretch reflex in the early swing phase of gait in six spastic stroke participants. Results. Five of the six participants showed a reduced stretch reflex of more than 80%. On average (n= 4), it was shown that maximal inhibition occurred at a conditioning-test interval of 114 ms and had a magnitude of more than 90% (p < 0.05). For all five participants investigated, there was a significant reduction in the sensitivity of the soleus stretch reflex after conditioning (p < 0.02). Conclusions. It is concluded that the inhibition of the soleus stretch reflex with an electrical conditioning stimulus applied to the deep peroneal nerve is feasible in the early swing phase of walking. This shows a potential for being used in the rehabilitation of walking by spastic stroke persons.

Finite state control is an established technique for the implementation of intention detection and activity co-ordination levels of hierarchical control in neural prostheses, and has been used for these purposes over the last thirty years. The first finite state controllers (FSC) in the functional electrical stimulation of gait were manually crafted systems, based on observations of the events occurring during the gait cycle. Subsequent systems used machine learning to automatically learn finite state control behaviour directly from human experts. Recently, fuzzy control has been utilised as an extension of finite state control, resulting in improved state detection over standard finite state control systems in some instances. Clinical experience over the last thirty years has been positive, and has shown finite state control to be an effective and intuitive method for the control of functional electrical stimulation (FES) in neural prostheses. However, while finite state controlled neural prostheses are of interest in the research community, they are not widely used outside of this setting. This is largely due to the cumbersome nature of many neural prostheses which utilise externally mounted gait sensors and FES electrodes. FES-based control of movement has been subject to the constraints of artificial sensor and FES actuator technologies. However, continued advances in natural sensors and implanted multi-channel stimulators are broadening the boundaries of artificial control of movement, driving an evolutionary process towards increasingly human-like control of FES-based gait rehabilitation systems.

A new orthosis (SEPRIX) which combines user friendliness with low energy cost of walking has been developed and will be subject to a clinical comparison with conventional hip-knee-ankle-foot orthoses. In designing such comparative trials it was considered it may be worthwhile to use previous clinical studies as practical examples. A literature search was conducted in order to select all comparative trials which have studied two walking systems (hip-knee-ankle-foot orthoses) for patients with a complete thoracic lesion. Study population, intervention, study design, outcome measurement and statistical analyses were examined. Statistical power was calculated where possible. Of 12 selected studies, 7 were simple A-B comparisons, 2 A-B comparisons with a replication, 2 cross-over trials and 1 nonrandomised parallel group design, the last of which was considered internally invalid due to severe confounding by indication. All A-B comparisons were considered internally invalid as well, since they have not taken into account that a comparison of two orthoses requires a control for aspecific effects (like test effects) which may cause a difference. Statistical power could only be examined in 4 studies and the highest statistical power achieved in one study was 47%. It is concluded that statistical power was too low to be able to detect differences. Even analysis through interval estimation showed that the estimation of the difference was too imprecise to be useful. Since the majority of the surveyed papers have reported small studies (of only 4-6 patients), it is assumed that lack of statistical power is a more general problem. Three possibilities are discussed in order to enhance statistical power in comparative trials, i.e. multicentre studies, statistical pooling of results and improving the efficiency of study design by means of interrupted time series designs.

Objective: To determine the validity and reproducibility of heart rate (HR) and crutch force measurements to estimate energy expenditure during paraplegic walking. Usefulness of these outcome measures in comparative trials was assessed in terms of responsiveness., Design: Cross-sectional validity was determined using one single (first) measurement. Longitudinal validity as well as reproducibility were calculated using repeated measurements., Setting: Oxygen uptake and HR during steady state as well as axial crutch load were measured at subjects' self-selected walking speeds., Patients: Ten subjects with thoracic-level spinal cord injury were included in the study. All subjects had considerable experience with ambulation in the advanced reciprocating gait orthosis (ARGO)., Main Outcome Measures: Oxygen uptake (VO2, mL/min) and oxygen cost (EO2, mL/m) were used as criterion standards. Crutch peak force (CPF), crutch force time integral (CFTI), HR, and physiological cost index (PCI) were used to estimate energy expenditure., Results: The PCI was found to be sensitive to detect differences between sessions in criterion standard (r = .86). Smallest detectable difference (ie, point where difference exceeds measurement error) ranged from approximately 15% for CPF to 33.7% and 41.8% for EO2 and PCI, respectively., Conclusions: Although PCI is expected to be a valid measure for within-patient differences in VO2, responsiveness was lower compared to EO2 and CPF. The limited number of patients who can be included in studies on paraplegic locomotion requires reproducible outcome measures. Therefore, CPF and EO2 are advocated in favor of PCI.

The normal human gait cycle is divided into two phases, namely, stance and swing. The objective of stance is to provide support, stability and propulsion and that of swing is to provide ground clearance and limb advancement. Knee flexion is essential during swing to lift the foot off the ground for limb advancement. The complex mechanisms involved in producing limb advancement can produce excessive knee flexion at faster walking speeds. Under these circumstances the shank needs to be decelerated to reduce the amount of knee flexion. It is assumed that rectus femoris (RF) is active for a very short period at the beginning of the swing phase (Perry J. Gait Analysis-Normal and Pathological Gait. Slack Incorporated, USA, 1992; Scott L, Ringwelsky D, Carroll N. Transfer of rectus femoris: effects of transfer site on moment arms about the knee and hip. J Biomech 27;1994:1201-1211) and the amount of this activation is proportional to the walking speed and thus to the generated knee moment and the angular acceleration of the lower limb segments. However, there is very little evidence to support these assumptions. The objective of this study was to study this relationship. Quantified electromyogram of RF and vastus lateralis (VL), using surface electrodes, were examined, body mounted kinematic sensors such as seismic accelerometers and gyroscopes were used to measure segments' angular accelerations and the net muscular knee torque calculated from the kinematics of the segments at various speeds. The results showed that RF and VL work independent of each other during the initial swing phase. The amount of RF activity is clearly related to walking speed. The muscle activity increases with increasing walking speed. The relationship between the angular acceleration of the shank and the amount of RF activity is linear. The active knee moment, as a function of the shank's angular acceleration, shows the same high correlation to the EMG signal of RF.

Artificial motor control systems may reduce the handicap of motor impaired individuals. Sensors are essential components in feedback control of these systems and in the information exchange with the user. The objective of this paper is to give an overview of the applications of sensors in the artificial control of human mobility. These applications may either require an accurate estimate of the measured physical quantities or can be based on learning the relation between sensory information and control actions by example. Actual use of sensors in artificial motor control systems requires that the user experienced complexity of the system is not increased, while improving the repeatable and flexible functioning of the system. Therefore, the sensors need to be integrated with the mechanical part of the artificial support system or implanted, the information exchange between sensor and controller should be wireless and automatic in-use calibration is a desired feature.

Objective: To determine speed dependence of crutch force and oxygen uptake, and to discuss the implications of differences in self-selected walking speed between orthoses in a comparative trial., Design: Cross-sectional comparison., Setting: Treadmill experiments and gait laboratory experiments were performed at five and three different imposed walking speeds, respectively., Patients: Five paraplegic subjects with lesions between T9 and T12 were included. All subjects had experience with ambulation using the advanced reciprocating gait orthosis (ARGO) as well as walking on a treadmill., Main Outcome Measures: Crutch force time integral (CFTI), crutch peak force on stance and swing side (CPFstance and CPFswing), oxygen uptake (VO2), oxygen cost (EO2)., Results: VO2, EO2, and CFTI were strongly dependent on walking speed. CPFstance and CPFswing were less dependent. However, depending on the clinically relevant difference that should be detected in a comparative trial, the peak forces can still be confounded by walking speed., Conclusion: CFTI, CPFswing, VO2, and EO2 should be adjusted for walking speed if differences in walking speed between orthoses are found, but this correction is relevant only if there is no effect modification. Such modification (different slopes between orthoses) cannot be excluded for the studied outcome measures. In addition, because determination of effect modification is difficult in small studies, standardization of walking speed, by means of a three-point design, is recommended.

Background and Purpose: In this study, the validity and reliability of measurements obtained with an "Activity Monitor" (AM) were examined. The instrument is designed to monitor ambulatory activity by use of accelerometer signals, and it detects several activities associated with mobility (standing, sitting, lying, transitions, movement-related activities)., Subjects: Four men with a transtibial amputation and 4 men without a transtibial amputation participated., Methods: The subjects performed normal daily activities, during which accelerations were measured and videotape recording were made (reference method). Validity was assessed by calculating agreement scores between the AM output and the videotape recordings and by comparing the number of transitions and the duration of activities determined by both methods., Results: The overall agreement between the AM output and the videotape recordings was 90%. Other agreement scores, in addition to the determination of the number of transitions and the duration of activities, were generally within a range of error of 0% to 10%., Conclusion and Discussion: The reliability and validity of the AM measurements appeared to be good, which supports its potential use in rehabilitation and physical therapy. [Bussmann HBJ, Reuvekamp PJ, Veltink PH, et al. Validity and reliability of measurements obtained with an "Activity Monitor" in people with and without a transtibial amputation.

This special section is about the control of electrical stimulators to restore standing functions to paraplegics. It addresses several important topics regarding the interactions of the intact central nervous systems (CNS) with the artificial control system. The topics are as follows: how paraplegics use their arms to help themselves stand up with functional electrical stimulation (FES); the user-driven artificial control of FES-supported standing up; a controller which is promising for the control of sitting down; the application of reinforcement machine learning for the controllers of standing up; arms-free standing with voluntary upper body balancing and artificially controlled ankle stiffness; and cognitive feedback in balancing. This Commentary introduces the papers in this section and relates them to earlier research.

A low-level, closed-loop controller for FES-assisted standing up and sitting down is described. If, for able-bodied individuals, when standing up and sitting down, the knee angular velocity is plotted against knee angle, consistent phase-plane trajectories are produced. The bang-bang controller uses a model of this trajectory as a switching curve. The design rationale for the controller was the desire to avoid injuries that might occur if knee-locking on standing up and seat-contact on sitting down are not adequately controlled. This switching curve controller (SCC) was incorporated within a hierarchical, finite state control scheme, with electrical stimulation applied bilaterally to the knee extensors. The SCC was tested in a pilot study on a female volunteer with paraplegia (T5/6 ASIA A) and evaluated against an unramped, open-loop controller (OLC). The vertical hand forces and knee angles were measured. The subject was able to achieve standing up and sitting down safely using both controllers. For standing up, the SCC was not found to offer any quantifiable advantages over the OLC and was found to increase the hand force by 8.4%. In contrast, for sitting down the SCC was found to reduce the knee angular velocities as the subject approached the seat by 27%, demonstrating a safer, softer landing.