Glen Cooper

Inertial sensor-based knee flexion/extension angle estimation

A new method for estimating knee joint flexion/extension angles from segment acceleration and angular velocity data is described. The approach uses a combination of Kalman filters and biomechanical constraints based on anatomical knowledge. In contrast to many recently published methods, the proposed approach does not make use of the earths magnetic field and hence is insensitive to the complex field distortions commonly found in modern buildings. The method was validated experimentally by calculating knee angle from measurements taken from two IMUs placed on adjacent body segments. In contrast to many previous studies which have validated their approach during relatively slow activities or over short durations, the performance of the algorithm was evaluated during both walking and running over 5 minute periods. Seven healthy subjects were tested at various speeds from 1 to 5 mile/h. Errors were estimated by comparing the results against data obtained simultaneously from a 10 camera motion tracking system (Qualysis). The average measurement error ranged from 0.7 degrees for slow walking (1 mph) to 3.4 degrees for running (5 mph). The joint constraint used in the IMU analysis was derived from the Qualysis data. Limitations of the method, its clinical application and its possible extension are discussed.

Is stair descent in the elderly associated with periods of high centre of mass downward accelerations

When descending stairs bodyweight becomes supported on a single limb while the forwards-reaching contralateral limb is lowered in order to make contact with the step below. This is associated with lowering of the centre of mass (CoM), which in order to occur in a controlled manner, requires increased ankle and knee joint torque production relative to that in overground walking. We have previously shown that when descending steps or stairs older people operate at a higher proportion of their maximum eccentric capacity and at, or in excess of the maximum passive reference joint range of motion. This suggests they have reduced and/or altered control over their CoM and we hypothesised that this would be associated with alterations in muscle activity patterns and in the CoM vertical acceleration and velocity profiles during both the lowering and landing phases of stair descent. 15 older (mean age 75 years) and 17 young (mean age 25 years) healthy adults descended a 4-step staircase, leading with the right limb on each stair, during which CoM dynamics and electromyographic activity patterns for key lower-limb muscles were assessed. Maximum voluntary eccentric torque generation ability at the knee and ankle was also assessed. Older participants compared to young participants increased muscle co-contraction relative duration at the knee and ankle of the trailing limb so that the limb was stiffened for longer during descent. As a result older participants contacted the step below with a reduced downwards CoM velocity when compared to young participants. Peak downwards and peak upwards CoM acceleration during the descent and landing phases respectively, were also reduced in older adults compared to those in young participants. In contrast, young participants descended quickly onto the step below but arrested their downward CoM velocity sooner following landing; a strategy that was associated with longer relative duration lead-limb plantar flexor activity, increased peak upwards CoM acceleration, and a reduced landing duration. These results suggest that a reduced ability to generate high eccentric torque at the ankle in the forward reaching limb is a major factor for older participants adopting a cautious movement control strategy when descending stairs. The implications of this CoM control strategy on the incidences of falling on stairs are discussed.

The use of hydrogel as an electrode-skin interface for electrode array FES applications

Functional electrical stimulation is commonly used to restore function in post-stroke patients in upper and lower limb applications. Location of the electrodes can be a problem hence some research groups have begun to experiment with electrode arrays. Electrode arrays are interfaced with a thin continuous hydrogel sheet which is high resistivity to reduce transverse currents between electrodes in the array. Research using electrode arrays has all been conducted in a laboratory environment over short time periods but it is suspected that this approach will not be feasible over longer time periods due to changes in hydrogel resistivity. High resistivity hydrogel samples were tested by leaving them in contact with the skin over a seven day period. The samples became extremely conductive with resistivities reaching around 10-50 Ωm. The effect of these resistivity changes was studied using finite element analysis to solve for the stationary current quasi-static electric field gradient in the tissue. Electrical stimulation efficiency and focality were calculated for both a high and low resistivity electrode-skin interface layer at different tissue depths. The results showed that low resistivity hydrogel produced significant decreases in stimulation efficiency and focality compared to high resistivity hydrogel.

Contributory Factors to Unsteadiness During Walking Up and Down Stairs in Patients With Diabetic Peripheral Neuropathy

OBJECTIVE Although patients with diabetic peripheral neuropathy (DPN) are more likely to fall than age-matched controls, the underlying causative factors are not yet fully understood. This study examines the effects of diabetes and neuropathy on strength generation and muscle activation patterns during walking up and down stairs, with implications for fall risk. RESEARCH DESIGN AND METHODS Sixty-three participants (21 patients with DPN, 21 diabetic controls, and 21 healthy controls) were examined while walking up and down a custom-built staircase. The speed of strength generation at the ankle and knee and muscle activation patterns of the ankle and knee extensor muscles were analyzed. RESULTS Patients with neuropathy displayed significantly slower ankle and knee strength generation than healthy controls during stair ascent and descent (P < 0.05). During ascent, the ankle and knee extensor muscles were activated significantly later by patients with neuropathy and took longer to reach peak activation (P < 0.05). During descent, neuropathic patients activated the ankle extensors significantly earlier, and the ankle and knee extensors took significantly longer to reach peak activation (P < 0.05). CONCLUSIONS Patients with DPN are slower at generating strength at the ankle and knee than control participants during walking up and down stairs. These changes, which are likely caused by altered activations of the extensor muscles, increase the likelihood of instability and may be important contributory factors for the increased risk of falling. Resistance exercise training may be a potential clinical intervention for improving these aspects and thereby potentially reducing fall risk.

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

OBJECTIVEnTo 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.nnnDESIGNnFeasibility study.nnnSETTINGnGait laboratory and community use.nnnPARTICIPANTSnParticipants (N=7) with diagnosis of unilateral foot-drop of central neurologic origin (>6mo) who were regular users of a foot-drop FES system (>3mo).nnnINTERVENTIONnArray-based automated setup FES system for foot-drop (ShefStim).nnnMAIN OUTCOME MEASURESnLogged 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.nnnRESULTSnAll 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.nnnCONCLUSIONSnThis study demonstrates that an array-based automated setup FES system for foot-drop can be successfully used unsupervised. Despite setups 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.

Enhancing public involvement in assistive technology design research

Abstract Purpose: To appraise the application of accepted good practice guidance on public involvement in assistive technology research and to identify its impact on the research team, the public, device and trial design. Methods: Critical reflection and within-project evaluation were undertaken in a case study of the development of a functional electrical stimulation device. Individual and group interviews were undertaken with lay members of a 10 strong study user advisory group and also research team members. Results: Public involvement was seen positively by research team members, who reported a positive impact on device and study designs. The public identified positive impact on confidence, skills, self-esteem, enjoyment, contribution to improving the care of others and opportunities for further involvement in research. A negative impact concerned the challenge of engaging the public in dissemination after the study end. Conclusions: The public were able to impact significantly on the design of an assistive technology device which was made more fit for purpose. Research team attitudes to public involvement were more positive after having witnessed its potential first hand. Within-project evaluation underpins this case study which presents a much needed detailed account of public involvement in assistive technology design research to add to the existing weak evidence base. Implications for Rehabilitation The evidence base for impact of public involvement in rehabilitation technology design is in need of development. Public involvement in co-design of rehabilitation devices can lead to technologies that are fit for purpose. Rehabilitation researchers need to consider the merits of active public involvement in research.

86 Human Tendon Deformation: Is It Greatest At Regions Of Smallest Cross-sectional Area?

Introduction Long tendons such as the human Achilles vary considerably in cross-sectional area (CSA) along their length.1 If a constant force is assumed to act along the tendon, regions of smaller CSA will be subject to greater stresses and may undergo larger deformations. This study aimed to determine whether regional variations in tendon CSA cause changes in tendon deformation. Methods We studied nine males (mean age 25 years) free from tendon injury or pathology. Magnetic resonance imaging of the lower leg was performed at rest and during isometric plantarflexions at 10, 20 and 30% of the maximum voluntary contraction (MVC) torque. The Achilles and gastrocnemius tendon CSAs were measured along their length (21 scans; Figure 1) during the four contraction levels. Tendon CSA was compared at each corresponding anatomical level between four contraction levels (rest, 10, 20 and 30% of MVC). Data were analysed using a repeated measures analysis of variance and post-hoc testing. *denotes significantly (p < 0.01) different from rest. SOL MTJ = soleus myo-tendinous junction. Results At 10% of MVC, CSAs were significantly smaller throughout the gastrocnemius tendon compared to those at rest, but there were no significant differences in the Achilles tendon CSAs (Figure 1A). At 20% and 30% of MVC, the gastrocnemius tendon CSAs remained significantly smaller throughout its length (Figure 1B and C). At 20% of MVC only the most proximal CSA of the Achilles tendon was significantly smaller compared to that at rest (Figure 1B). At 30% of MVC, CSAs in the proximal region (5 scans) of the Achilles tendon were significantly smaller compared to those at rest (Figure 1C). Abstract 86 Figure 1 Cross-sectional area (CSA) of the Achilles and gastrocnemius tendons at rest and during contraction at (A) 10%, (B) 20% and (C) 30% of plantarflexion maximum voluntary contraction (MVC) Discussion Reductions in tendon CSA as a result of tensile loading applied by muscle contraction were assumed to represent regional-specific longitudinal elongations, i.e. as the tendon is stretched it becomes thinner. Contrary to our initial hypothesis, the largest deformations did not occur in the region of smallest tendon CSA, but were instead tendon-specific with greater deformations in the gastrocnemius compared to the Achilles tendon. This occurred despite presumably lower forces acting on the gastrocnemius tendon, which suggests a reduced stiffness and modulus in the gastrocnemius tendon compared to the Achilles. Acknowledgements EPSRCs Bridging the Gaps funding. Reference 1 Magnusson, Kjaer. Eur J Appl Physiol. 2003;90:549–553

In vivo measurement of the biomechanical properties of plantar soft tissues under simulated gait conditions

Background In vivo biomechanical properties of plantar soft tissues have been assessed via manual indentation using simplified loading profiles [1], or in gait, with low image resolution/capture rates [2]. Since plantar soft tissue properties are highly rate dependent [3] these methods are potentially inadequate. The Soft Tissue Response Imaging Device (STRIDE) permits functionally relevant loading profiles to be applied to the plantar tissues.

A device for characterising the mechanical properties of the plantar soft tissue of the foot

The plantar soft tissue is a highly functional viscoelastic structure involved in transferring load to the human body during walking. A Soft Tissue Response Imaging Device was developed to apply a vertical compression to the plantar soft tissue whilst measuring the mechanical response via a combined load cell and ultrasound imaging arrangement. Accuracy of motion compared to input profiles; validation of the response measured for standard materials in compression; variability of force and displacement measures for consecutive compressive cycles; and implementation in vivo with five healthy participants. Static displacement displayed average error of 0.04 mm (range of 15 mm), and static load displayed average error of 0.15 N (range of 250 N). Validation tests showed acceptable agreement compared to a Houndsfield tensometer for both displacement (CMC > 0.99 RMSE > 0.18 mm) and load (CMC > 0.95 RMSE < 4.86 N). Device motion was highly repeatable for bench-top tests (ICC = 0.99) and participant trials (CMC = 1.00). Soft tissue response was found repeatable for intra (CMC > 0.98) and inter trials (CMC > 0.70). The device has been shown to be capable of implementing complex loading patterns similar to gait, and of capturing the compressive response of the plantar soft tissue for a range of loading conditions in vivo.

Testing a mechanical protocol to replicate impact in walking footwear

Impact testing is commonly undertaken to quantify the shock absorption characteristics of footwear. The current widely reported mechanical testing method mimics the vertical heel velocity at touchdown and effective mass of the lower limb recorded in running. This therefore results in a greater impact energy than would be expected at touchdown in walking. Despite this mismatch, the methodology is utilised to quantify the shock absorption properties of running and walking footwear alike. The current work modifies the mechanical testing methodology to replicate the kinematics, specifically the vertical heel velocity, identified in walking footwear. Kinematic and kinetic data was collected for 13 subjects walking in four different styles of footwear used for walking (trainer, oxford shoe, flip-flop and triple-density sandal). The kinematic data was utilised to quantify heel velocity at touchdown and accelerometer and force plate data was utilised to estimate the effective mass of the lower limb. When walking in the toe-post style footwear significantly faster vertical heel velocity toward the floor was recorded compared to barefoot and the other footwear styles (Figure u200b(Figure11 for example flip-flop: 0.36±0.05m.s-1 compared to trainer: 0.18±0.06m.s-1). The mechanical protocol was adapted by altering the mass and drop height from 10.6-17.3 kg and 2-7 mm, compared to the original protocol of 8.45 kg dropped from 50 mm. As expected, the adapted mechanical protocol produced significantly lower peak force and accelerometer values than the ASTM protocol (p <.001). These values more closely resembled those recorded in walking. The mean difference between the human and modified protocol was 12.7±17.5% (p<.001) for peak acceleration and 25.2±17.7% (p=.786) for peak force values. The timing of peak force and acceleration variables was less representative of the real-life data with larger mean differences. This pilot test has demonstrated that the altered mechanical test protocol can more closely replicate loading on the lower limb in walking. Further research should consider more variables related to the shock absorption properties of footwear. The results also demonstrate that testing of material properties of footbeds not only needs to be gait style specific (e.g. running versus walking), but also footwear style specific due to the differences in heel touch-down velocity in footwear styles. n n n nFigure 1 n nVertical heel velocity towards the floor in the human testing for the four footwear conditions. Triple-density sandal = SA, flip-flop = FF, shoe = SH and trainer = TR and Barefoot (BF). Error bars denote standard deviation across the 13 subjects tested. ...