Objective measures of rollator user stability and device loading during different walking scenarios.

Walking aids are widely used by older adults, however, alarmingly, their use has been linked to increased falls-risk, yet clinicians have no objective way of assessing user stability. This work aims to demonstrate the application of a novel methodology to investigate how the type of walking task, the amount of body weight supported by the device (i.e., device loading), and task performance strategy affect stability of rollator users. In this context, ten users performed six walking tasks with an instrumented rollator. The combined stability margin "SM" was calculated, which considers user and rollator as a combined system. A Friedman Test was used to investigate the effects of task on SM and a least-squares regression model was applied to investigate the relationship between device loading and SM. In addition, the effects of task performance strategy on SM were explored. As a result, it was found that: the minimum SM for straight line walking was higher than for more complex tasks (p<0.05); an increase in device loading was associated with an increase in SM (p<0.05); stepping up a kerb with at least 1 rollator wheel in ground contact at all times resulted in higher SM than lifting all four wheels simultaneously. Hence, we conclude that training should not be limited to straight line walking but should include various everyday tasks. Within person, SM informs on which tasks need practicing, and which strategy facilitates stability, thereby enabling person-specific guidance/training. The relevance of this work lies in an increase in walking aid users, and the costs arising from fall-related injuries.

Methods for the Real-World Evaluation of Fall Detection Technology: A Scoping Review.

Falls in older adults present a major growing healthcare challenge and reliable detection of falls is crucial to minimise their consequences. The majority of development and testing has used laboratory simulations. As simulations do not cover the wide range of real-world scenarios performance is poor when retested using real-world data. There has been a move from the use of simulated falls towards the use of real-world data. This review aims to assess the current methods for real-world evaluation of fall detection systems, identify their limitations and propose improved robust methods of evaluation. Twenty-two articles met the inclusion criteria and were assessed with regard to the composition of the datasets, data processing methods and the measures of performance. Real-world tests of fall detection technology are inherently challenging and it is clear the field is in its infancy. Most studies used small datasets and studies differed on how to quantify the ability to avoid false alarms and how to identify non-falls, a concept which is virtually impossible to define and standardise. To increase robustness and make results comparable, larger standardised datasets are needed containing data from a range of participant groups. Measures that depend on the definition and identification of non-falls should be avoided. Sensitivity, precision and F-measure emerged as the most suitable robust measures for evaluating the real-world performance of fall detection systems.

Skill assessment in upper limb myoelectric prosthesis users: Validation of a clinically feasible method for characterising upper limb temporal and amplitude variability during the performance of functional tasks.

Upper limb myoelectric prostheses remain challenging to use and are often abandoned. A proficient user must be able to plan/execute arm movements while activating the residual muscle(s), accounting for delays and unpredictability in prosthesis response. There is no validated, low cost measure of skill in performing such actions. Trial-trial variability of joint angle trajectories measured during functional task performance, linearly normalised by time, shows promise. However, linear normalisation of time introduces errors, and expensive camera systems are required for joint angle measurements. This study investigated whether trial-trial variability, assessed using dynamic time warping (DTW) of limb segment acceleration measured during functional task performance, is a valid measure of user skill. Temporal and amplitude variability of forearm accelerations were determined in (1) seven myoelectric prosthesis users and six anatomically-intact controls and (2) seven anatomically-intact subjects learning to use a prosthesis simulator over repeated sessions. (1): temporal variability showed clear group differences (p<0.05). (2): temporal variability considerably increased on first use of a prosthesis simulator, then declined with training (both p<0.05). Amplitude variability showed less obvious differences. Analysing forearm accelerations using DTW appears to be a valid low-cost method for quantifying movement quality of upper limb prosthesis use during goal-oriented task performance.

Feasibility study of a take-home array-based functional electrical stimulation system with automated setup for current functional electrical stimulation users with foot-drop.

OBJECTIVE: To investigate the feasibility of unsupervised community use of an array-based automated setup functional electrical stimulator for current foot-drop functional electrical stimulation (FES) users. DESIGN: Feasibility study. SETTING: Gait laboratory and community use. PARTICIPANTS: Participants (N=7) with diagnosis of unilateral foot-drop of central neurologic origin (>6mo) who were regular users of a foot-drop FES system (>3mo). INTERVENTION: Array-based automated setup FES system for foot-drop (ShefStim). MAIN OUTCOME MEASURES: Logged usage, logged automated setup times for the array-based automated setup FES system and diary recording of problems experienced, all collected in the community environment. Walking speed, ankle angles at initial contact, foot clearance during swing, and the Quebec User Evaluation of Satisfaction with Assistive Technology version 2.0 (QUEST version 2.0) questionnaire, all collected in the gait laboratory. RESULTS: All participants were able to use the array-based automated setup FES system. Total setup time took longer than participants' own FES systems, and automated setup time was longer than in a previous study of a similar system. Some problems were experienced, but overall, participants were as satisfied with this system as their own FES system. The increase in walking speed (N=7) relative to no stimulation was comparable between both systems, and appropriate ankle angles at initial contact (N=7) and foot clearance during swing (n=5) were greater with the array-based automated setup FES system. CONCLUSIONS: This study demonstrates that an array-based automated setup FES system for foot-drop can be successfully used unsupervised. Despite setup's taking longer and some problems, users are satisfied with the system and it would appear as effective, if not better, at addressing the foot-drop impairment. Further product development of this unique system, followed by a larger-scale and longer-term study, is required before firm conclusions about its efficacy can be reached.

Visuomotor behaviours when using a myoelectric prosthesis.

BACKGROUND: A recent study showed that the gaze patterns of amputee users of myoelectric prostheses differ markedly from those seen in anatomically intact subjects. Gaze behaviour is a promising outcome measures for prosthesis designers, as it appears to reflect the strategies adopted by amputees to compensate for the absence of proprioceptive feedback and uncertainty/delays in the control system, factors believed to be central to the difficulty in using prostheses. The primary aim of our study was to characterise visuomotor behaviours over learning to use a trans-radial myoelectric prosthesis. Secondly, as there are logistical advantages to using anatomically intact subjects in prosthesis evaluation studies, we investigated similarities in visuomotor behaviours between anatomically intact users of a trans-radial prosthesis simulator and experienced trans-radial myoelectric prosthesis users. METHODS: In part 1 of the study, we investigated visuomotor behaviours during performance of a functional task (reaching, grasping and manipulating a carton) in a group of seven anatomically intact subjects over learning to use a trans-radial myoelectric prosthesis simulator (Dataset 1). Secondly, we compared their patterns of visuomotor behaviour with those of four experienced trans-radial myoelectric prosthesis users (Dataset 2). We recorded task movement time, performance on the SHAP test of hand function and gaze behaviour. RESULTS: Dataset 1 showed that while reaching and grasping the object, anatomically intact subjects using the prosthesis simulator devoted around 90% of their visual attention to either the hand or the area of the object to be grasped. This pattern of behaviour did not change with training, and similar patterns were seen in Dataset 2. Anatomically intact subjects exhibited significant increases in task duration at their first attempts to use the prosthesis simulator. At the end of training, the values had decreased and were similar to those seen in Dataset 2. CONCLUSIONS: The study provides the first functional description of the gaze behaviours seen during use of a myoelectric prosthesis. Gaze behaviours were found to be relatively insensitive to practice. In addition, encouraging similarities were seen between the amputee group and the prosthesis simulator group.

Automated detection of instantaneous gait events using time frequency analysis and manifold embedding.

Accelerometry is a widely used sensing modality in human biomechanics due to its portability, non-invasiveness, and accuracy. However, difficulties lie in signal variability and interpretation in relation to biomechanical events. In walking, heel strike and toe off are primary gait events where robust and accurate detection is essential for gait-related applications. This paper describes a novel and generic event detection algorithm applicable to signals from tri-axial accelerometers placed on the foot, ankle, shank or waist. Data from healthy subjects undergoing multiple walking trials on flat and inclined, as well as smooth and tactile paving surfaces is acquired for experimentation. The benchmark timings at which heel strike and toe off occur, are determined using kinematic data recorded from a motion capture system. The algorithm extracts features from each of the acceleration signals using a continuous wavelet transform over a wide range of scales. A locality preserving embedding method is then applied to reduce the high dimensionality caused by the multiple scales while preserving salient features for classification. A simple Gaussian mixture model is then trained to classify each of the time samples into heel strike, toe off or no event categories. Results show good detection and temporal accuracies for different sensor locations and different walking terrains.

Simulating acceleration from stereophotogrammetry for medical device design.

When designing a medical device based on lightweight accelerometers, the designer is faced with a number of questions in order to maximize performance while minimizing cost and complexity: Where should the inertial unit be located? How many units are required? How is performance affected if the unit is not correctly located during donning? One way to answer these questions is to use position data from a single trial, captured with a nonportable measurement system (e.g., stereophotogrammetry) to simulate measurements from multiple accelerometers at different locations on the body. In this paper, we undertake a thorough investigation into the applicability of these simulated acceleration signals via a series of interdependent experiments of increasing generality. We measured the dynamics of a reference coordinate frame using stereophotogrammetry over a number of trials. These dynamics were then used to simulate several "virtual" accelerometers at different points on the body segment. We then compared the simulated signals with those directly measured to evaluate the error under a number of conditions. Finally, we demonstrated an example of how simulated signals can be employed in a system design application. In the best case, we may expect an error of 0.028 m/s2 between a derived virtual signal and that directly measured by an accelerometer. In practice, however, using centripetal and tangential acceleration terms (that are poorly estimated) results in an error that is an order of magnitude greater than the baseline. Furthermore, nonrigidity of the limb can increase error dramatically, although the effects can be reduced considerably via careful modeling. We conclude that using simulated signals has definite benefits when an appropriate model of the body segment is applied.

Movement variability in stroke patients and controls performing two upper limb functional tasks: a new assessment methodology.

BACKGROUND: In the evaluation of upper limb impairment post stroke there remains a gap between detailed kinematic analyses with expensive motion capturing systems and common clinical assessment tests. In particular, although many clinical tests evaluate the performance of functional tasks, metrics to characterise upper limb kinematics are generally not applicable to such tasks and very limited in scope. This paper reports on a novel, user-friendly methodology that allows for the assessment of both signal magnitude and timing variability in upper limb movement trajectories during functional task performance. In order to demonstrate the technique, we report on a study in which the variability in timing and signal magnitude of data collected during the performance of two functional tasks is compared between a group of subjects with stroke and a group of individually matched control subjects. METHODS: We employ dynamic time warping for curve registration to quantify two aspects of movement variability: 1) variability of the timing of the accelerometer signals' characteristics and 2) variability of the signals' magnitude. Six stroke patients and six matched controls performed several trials of a unilateral ('drinking') and a bilateral ('moving a plate') functional task on two different days, approximately 1 month apart. Group differences for the two variability metrics were investigated on both days. RESULTS: For 'drinking from a glass' significant group differences were obtained on both days for the timing variability of the acceleration signals' characteristics (p = 0.002 and p = 0.008 for test and retest, respectively); all stroke patients showed increased signal timing variability as compared to their corresponding control subject. 'Moving a plate' provided less distinct group differences. CONCLUSION: This initial application establishes that movement variability metrics, as determined by our methodology, appear different in stroke patients as compared to matched controls during unilateral task performance ('drinking'). Use of a user-friendly, inexpensive accelerometer makes this methodology feasible for routine clinical evaluations. We are encouraged to perform larger studies to further investigate the metrics' usefulness when quantifying levels of impairment.

An instance-based algorithm with auxiliary similarity information for the estimation of gait kinematics from wearable sensors.

Wearable human movement measurement systems are increasingly popular as a means of capturing human movement data in real-world situations. Previous work has attempted to estimate segment kinematics during walking from foot acceleration and angular velocity data. In this paper, we propose a novel neural network [GRNN with Auxiliary Similarity Information (GASI)] that estimates joint kinematics by taking account of proximity and gait trajectory slope information through adaptive weighting. Furthermore, multiple kernel bandwidth parameters are used that can adapt to the local data density. To demonstrate the value of the GASI algorithm, hip, knee, and ankle joint motions are estimated from acceleration and angular velocity data for the foot and shank, collected using commercially available wearable sensors. Reference hip, knee, and ankle kinematic data were obtained using externally mounted reflective markers and infrared cameras for subjects while they walked at different speeds. The results provide further evidence that a neural net approach to the estimation of joint kinematics is feasible and shows promise, but other practical issues must be addressed before this approach is mature enough for clinical implementation. Furthermore, they demonstrate the utility of the new GASI algorithm for making estimates from continuous periodic data that include noise and a significant level of variability.

Falls and gait characteristics among older persons with peripheral neuropathy.

OBJECTIVE: To prospectively determine the frequency and circumstances of falls in older persons with peripheral neuropathy and to identify gait characteristics on smooth and irregular surfaces associated with falls in this same population. DESIGN: This was a descriptive and observational study of a prospective group cohort. Spatial and temporal gait measures on smooth and irregular surfaces, as well as basic demographic and clinical data, were obtained in 20 older persons with peripheral neuropathy. Falls and fall-related injuries were then prospectively determined for 1 yr. RESULTS: Thirteen of 20 (65%) subjects fell, and 6 of 20 (30%) subjects sustained a fall-related injury during the year of observation. Of the 76 reported falls, 69 (90.8%) were associated with a surface abnormality (irregular or slick). Gait measures on the smooth surface did not distinguish between fall groups. On the irregular surface, however, step-time variability tended to be higher for those subjects who fell than for those who did not (89 +/- 29 vs. 64 +/- 26 msecs, respectively; P = 0.077) and for those who were injured from a fall compared with those who were not injured (101 +/- 21 vs. 71 +/- 29 msecs, respectively; P = 0.038). CONCLUSIONS: Older patients with peripheral neuropathy have a high rate of falls, and these falls are often associated with walking on irregular surfaces. Gait analysis on an irregular surface may be superior to that on a smooth surface for detecting fall risk in this patient population.

What causes a crossover step when walking on uneven ground? A study in healthy young women.

We hypothesized that, during gait, the perturbation caused by stepping on a 1.2-cm high protuberance with the medial forefoot would not only alter stance foot kinematics and kinetics, but also alter subsequent step location and timing, even to the point of causing a crossover step. Twelve healthy young women performed at least three flat surface and three perturbation trials while walking along a level walkway. To obstruct visual monitoring of their upcoming foot placement they used both hands to carry a large tray in front of their abdomen. Kinematic data from optoelectronic markers and force plate data were recorded at 50 and 100Hz, respectively. The results showed that the medial forefoot perturbation significantly decreased the net ankle eversion moment (p<0.001) and increased the maximum inversional foot acceleration (p=0.007). Step width (SW) and time (ST) of the post-perturbation recovery step were significantly decreased compared with normal steps (p=0.002 and 0.049, respectively). The maximum inversional foot acceleration correlated negatively with SW and ST of the recovery step (both p=0.001). Finally, four of 36 (12%) recovery steps were crossover steps. We conclude that a medial forefoot perturbation results in an increased inversional acceleration of the stance foot followed by a decrease in recovery SW and ST. In some cases, a medial forefoot perturbation can result in a crossover step, an extreme form of a narrow recovery step.

Gait analysis in a challenging environment differentiates between fallers and nonfallers among older patients with peripheral neuropathy.

OBJECTIVE: To identify differences in gait based on fall history among a group of older subjects with peripheral neuropathy (PN) in 2 environments: standard (SE) (smooth surface, normal lighting) and challenging (CE) (irregular surface, low lighting). DESIGN: Observational, case-control study of PN subjects with and without a history of falling in the previous year. SETTING: A biomechanical laboratory. PARTICIPANTS: Forty-two subjects (mean age, 64.7+/-9.8 y; 20 [47.6%] women), including 22 (52.4%) with a history of at least 1 fall in the previous year. INTERVENTION: Subjects walked in the SE and CE while kinematic data were obtained. MAIN OUTCOME MEASURES: Step width variability, step time variability, step width-to-step length ratio, step length, and step time and speed (with step length and speed normalized for height) in the SE and CE. RESULTS: In the SE, gait parameters of subjects with and without a history of falls did not differ significantly. However, in the CE, subjects with a history of falls had increased step time variability (P=.001). Moreover, significant interactions between environment and fall status were identified: in the CE, subjects with a history of falls had greater increases in step time variability (P=.010) and step width-to-step length ratio (P=.009) and greater decreases in step length (P=.007) and speed (P=.045) than did subjects with no fall history. CONCLUSIONS: Analysis of gait in the CE and adjustment to the CE from the SE effectively identified gait characteristics associated with falls in an older PN population, whereas analysis of gait in the SE did not. PN-associated gait dysfunction is more sensitively detected on an irregular rather than on a flat surface.

Effects of surface irregularity and lighting on step variability during gait: a study in healthy young and older women.

Relatively few studies have examined how uneven surfaces affect human gait. To study this, along with the effects of advancing age and low light conditions, we measured step width and step time variability, as well as comfortable gait speed, in 12 healthy young women (YW) and 12 healthy older women (OW) as they walked at a comfortable speed along a 10-m walkway. Ten trials were completed for each cell of a 2 x 2 factorial design: (1) flat surface with regular lighting; (2) flat surface with low lighting; (3) irregular surface with regular lighting; and (4) irregular surface with low lighting. Effects of surface type, incident lighting, and age on gait parameters were tested via repeated measures ANOVA. Surface type significantly affected step width variability (P < 0.001) and step time variability (P < 0.001). Light level showed no significant effect on any of the gait parameters. One significant age group difference was found: step width variability was significantly greater in OW than YW (P = 0.010). We conclude that the irregular surface had a greater effect on the gait variability of healthy OW than on that of healthy YW.

Influence of an irregular surface and low light on the step variability of patients with peripheral neuropathy during level gait.

Patients with peripheral neuropathy (PN) report greater difficulty walking on irregular surfaces with low light (IL) than on flat surfaces with regular lighting (FR). We tested the primary hypothesis that older PN patients would demonstrate greater step width and step width variability under IL conditions than under FR conditions. Forty-two subjects (22 male, 20 female: mean +/- S.D.: 64.7 +/- 9.8 years) with PN underwent history, physical examination, and electrodiagnostic testing. Subjects were asked to walk 10 m at a comfortable speed while kinematic and force data were measured at 100 Hz using optoelectronic markers and foot switches. Ten trials were conducted under both IL and FR conditions. Step width, time, length, and speed were calculated with a MATLAB algorithm, with the standard deviation serving as the measure of variability. The results showed that under IL, as compared to FR, conditions subjects demonstrated greater step width (197.1 +/- 40.8 mm versus 180.5 +/- 32.4 mm; P < 0.001) and step width variability (40.4 +/- 9.0 mm versus 34.5 +/- 8.4 mm; P < 0.001), step time and its variability (P < 0.001 and P = 0.003, respectively), and step length variability (P < 0.001). Average step length and gait speed decreased under IL conditions (P < 0.001 for both). Step width variability and step time variability correlated best under IL conditions with a clinical measure of PN severity and fall history, respectively. We conclude that IL conditions cause PN patients to increase the variability of their step width and other gait parameters.

A comparison of gait characteristics between older women with and without peripheral neuropathy in standard and challenging environments.

OBJECTIVES: To compare gait patterns in older women with and without peripheral neuropathy (PN) in standard (smooth surface, normal lighting) and challenging environments (CE) (irregular surface, low lighting). DESIGN: Observational, controlled study of 24 subjects. SETTING: Biomechanical research laboratory. PARTICIPANTS: Twenty-four older women, 12 with PN and 12 without PN (mean age +/- standard deviation =67.1 +/- 7.9 and 70.2 +/- 4.3, respectively). MEASUREMENTS: Gait parameters and, in the 12 PN subjects, neuropathy severity. RESULTS: The CE was associated with increases in step width, step-width variability, step-width range, step width-to-step length ratio, step time and step-time variability, and decreases in step length and speed. The PN subjects demonstrated a greater step width-to-step length ratio and step time and shorter step length and slower speed than the control subjects. In adapting to the CE, the PN subjects demonstrated greater increases in step width-to-step length ratio and step-time variability and a greater decrease in step length than did the control subjects. In the standard environment, only one gait parameter correlated with PN severity, whereas in the CE, four gait parameters did so. CONCLUSION: The subjects demonstrated a gait that was slower, less efficient, and more variable temporally and in the frontal plane in the CE. Control and PN subjects demonstrated similar variability in medial-lateral step placement in the CE but at the cost of speed and efficiency for the PN subjects. Because the CE magnified gait differences between the two groups of subjects and caused gait changes in the PN subjects that correlated with PN severity, the CE may offer improved resolution for detecting gait abnormalities.

Interventions improve gait regularity in patients with peripheral neuropathy while walking on an irregular surface under low light.

OBJECTIVES: To determine which, if any, of three inexpensive interventions improve gait regularity in patients with peripheral neuropathy (PN) while walking on an irregular surface under low-light conditions. DESIGN: Observational. SETTING: University of Michigan Biomechanics Research Laboratory. PARTICIPANTS: Forty-two patients with PN (20 women), mean age+/-standard deviation=64.5+/-9.7. INTERVENTIONS: A straight cane, touch of a vertical surface, or semirigid ankle orthoses. MEASUREMENTS: Step-width variability and range, step-time variability, and speed. RESULTS: Subjects demonstrated significantly less step-width variability (mean=41.0+/-1.5, 36.9+/-1.6, 37.2+/-1.3, and 35.9+/-1.5 mm for baseline, cane, orthoses, and vertical surface, respectively; P<.0001) and range (182.7+/-7.4, 163.7+/-8.3, 164.3+/-7.4, 154.3+/-6.9 mm for baseline, cane, orthoses and vertical surface, respectively; P=.0006) with each of the interventions than under baseline conditions. Step-time variability significantly decreased with use of the orthoses and vertical surface but not the cane (P=.0001). Use of a cane, but not orthoses or vertical surface, was associated with decreased speed (0.79+/-0.03, 0.73+/-0.03, 0.79+/-0.03, 0.80+/-0.03 m/s for baseline, cane, orthoses, and vertical surface, respectively; P=.0001). CONCLUSION: Older patients with PN demonstrate improved spatial and temporal measures of gait regularity with the use of a cane, ankle orthoses, or touch of a vertical surface while walking under challenging conditions. The decreased speed and stigma associated with the cane and uncertain availability of a vertical surface suggest that the ankle orthoses may be the most practical intervention.