Publications by authors named "Stephen Sprigle"

86 Publications

Validating a wheelchair in-seat activity tracker.

Assist Technol 2021 Apr 6:1-11. Epub 2021 Apr 6.

Rehabilitation Engineering and Applied Research Lab, Georgia Institute of Technology, Atlanta, Georgia, USA.

Wheelchair users often experience prolonged periods of stationary sitting. Such periods are accompanied with increased loading of the ischial tuberosities. This can lead to the development of pressure ulcers which can cause complications such as sepsis. Periodic pressure offloading is recommended to reduce the onset of pressure ulcers. Experts recommend the periodic execution of different movements to provide the needed pressure offloading. Wheelchair users, however, might not remember to perform these recommended movements in terms of both quality and quantity. A system that can detect such movements could provide valuable feedback to both wheelchair users as well as clinicians. The objective of this study was to present and validate the WiSAT - a system for characterizing in-seat activity for wheelchair users. WiSAT is designed to detect two kinds of movements - weight shifts and in-seat movements. Weight shifts are movements that offload pressure on ischial tuberosities by 30% as compared to upright sitting and are maintained for 15 seconds. In-seat movements are shorter transient movements that involve either a change in the center of pressure on the sitting buttocks or a transient reduction in total load by 30%. This study validates the use of WiSAT in manual wheelchairs. WiSAT has a sensor mat which was inserted beneath a wheelchair cushion. Readings from these sensors were used by WiSAT algorithms to predict weight shifts and in-seat movements. These weight shifts and in-seat movements were validated against a high-resolution interface pressure mat in a dataset that resembles real-world usage. The proposed system achieved weight shift precision and recall scores of 81% and 80%, respectively, while in-seat movement scores were predicted with a mean absolute error of 22%. Results showed that WiSAT provides sufficient accuracy in characterizing in-seat activity in terms of weight shifts and in-seat movement.
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http://dx.doi.org/10.1080/10400435.2021.1893237DOI Listing
April 2021

Friction characteristics of preventative wound dressings under clinically-relevant conditions.

Wound Repair Regen 2021 03 31;29(2):280-283. Epub 2020 Dec 31.

Tribology and Surface Engineering Lab, GW Woodruff School of Mechanical Engineering, Georgia Institute of Technology, Atlanta, Georgia, USA.

Wound dressings can be used prophylactically or during actual treatment. Preventative dressings have become a standard of care to prevent pressure ulcers in patients while in bed. While the mechanism of the preventative benefit has not been completely explained, the friction between the dressing and linen is hypothesized as being a key performance factor. The objective of this project was to quantify the static and kinetic coefficients of friction (COF) of various brands of prophylactic dressings under the stresses experienced in situ, while the dressings are in contact with bed linen materials. The COF of six commercial dressings were calculated using tribometer measurements. The ranges of static COF were 0.333-0.542 and kinetic COF were 0.333-0.513. Four dressings exhibited COF that were consistent with skin-linen values reported in the literature and all dressing COF appear to be lower than the COF of moist skin against linen.
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http://dx.doi.org/10.1111/wrr.12880DOI Listing
March 2021

Assessment of wheeled mobility devices provided to a commercially insured population in 2017.

Assist Technol 2020 Oct 13:1-8. Epub 2020 Oct 13.

Health Economics and Analytics Lab, Georgia Institute of Technology, Atlanta, Georgia.

In the United States, wheeled mobility devices (WMD) are classified as durable medical equipment (DME). Consistent with the definition of DME, wheeled mobility devices are typically covered by health insurance when deemed medically necessary. Despite the number of persons using wheelchairs, little knowledge is available about the types of wheelchairs provided, user's specific diagnoses and the costs associated with WMD provision. The objective of this analysis was to define the number and types of wheelchairs and associated seating and mobility (S&M) accessories provided in the calendar year 2017. The analysis focused on user demographics, categories of WMDs and associated S&M equipment as well as cost accounting according to the type of insurance and contributions by beneficiaries. Analysis of over 81,000 wheelchair acquisitions found that manual wheelchairs accounted for nearly 90% with standard manual wheelchairs accounting for 86% of all wheelchairs provided. Wheelchair recipients tended to be older with the majority being female. Based upon ICD-10 diagnostic categories over 50% of captured ICD-10 codes came from three classifications, musculoskeletal (M), circulatory (I) and a general category of not otherwise classified disorders (R). Costs associated with seating and mobility equipment were fairly large, exceeding $79 million over a single calendar year.
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http://dx.doi.org/10.1080/10400435.2020.1812765DOI Listing
October 2020

Does the setting matter? Observing wheelchair transfers across different environmental conditions.

Assist Technol 2020 Oct 13:1-8. Epub 2020 Oct 13.

Rehabilitation Engineering and Applied Research, Georgia Institute of Technology, Atlanta, Georgia, USA.

The setting in which wheelchair transfers are performed can affect the difficulty and the risks associated with completion. This article presents results from an observational study involving 13 wheelchair users performing independent transfers across four settings. The aim is to understand how the environment affects how different types of independent transfers are performed. Descriptive analysis was performed alongside an objective assessment using the Transfer Assessment Instrument (TAI). The perceived difficulty reported after each transfer was also collected. Two participants exhibited radically different transferring techniques in different scenarios. Additionally, the transferring scenario was found to significantly affect the perceived difficulty of sitting transfers (toilet 2.17 ±.88; bed 1.47 ±.65, =.001; car 1.63 ±.82, =.012) and standing transfers (car 3.5 ±.71; bed 1 ± 0, =.03; toilet 1 ± 0, =.03), and the TAI score attributed to sitting pivot with use of a transfer board (couch 4.3 ±.88; bed 6.93 ± 1.29, =.022; car 7.13 ± 1.32, =.018). Overall, environmental constraints can lead to major technique changes and, more often, to different positioning of hands and feet which could impact the transfer's biomechanics.
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http://dx.doi.org/10.1080/10400435.2020.1818328DOI Listing
October 2020

Modeling manual wheelchair propulsion cost during straight and curvilinear trajectories.

PLoS One 2020 18;15(6):e0234742. Epub 2020 Jun 18.

Rehabilitation Engineering and Applied Research Laboratory, Georgia Institute of Technology, Atlanta, Georgia, United States of America.

Minimizing the effort to propel a manual wheelchair is important to all users in order to optimize the efficiency of maneuvering throughout the day. Assessing the propulsion cost of wheelchairs as a mechanical system is a key aspect of understanding the influences of wheelchair design and configuration. The objective of this study was to model the relationships between inertial and energy-loss parameters to the mechanical propulsion cost across different wheelchair configurations during straight and curvilinear trajectories. Inertial parameters of an occupied wheelchair and energy loss parameters of drive wheels and casters were entered into regression models representing three different maneuvers. A wheelchair-propelling robot was used to measure propulsion cost. General linear models showed strong relationships (R2 > 0.84) between the system-level costs of propulsion and the selected predictor variables representing sources of energy loss and inertial influences. System energy loss parameters were significant predictors in all three maneuvers. Yaw inertia was also a significant predictor during zero-radius turns. The results indicate that simple energy loss measurements can predict system-level performance, and inertial influences are mostly overshadowed by the increased resistive losses caused by added mass, though weight distribution can mitigate some of this added cost.
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http://journals.plos.org/plosone/article?id=10.1371/journal.pone.0234742PLOS
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC7302523PMC
August 2020

Manual wheelchair propulsion cost across different components and configurations during straight and turning maneuvers.

J Rehabil Assist Technol Eng 2020 Jan-Dec;7:2055668320907819. Epub 2020 Apr 8.

Department of Bioengineering, University of Colorado Denver, Denver, CO, USA.

Aim: Maneuvering manual wheelchairs is defined by changes in momentum. The amount of effort required to maneuver a wheelchair is dependent on many factors, some of which reflect the design and configuration of the wheelchair.

Objective: The objective of this study was to measure the work required to propel a manual wheelchair configured with three weight distributions, three drive wheels and four casters.

Methods: A novel wheelchair-propelling robot was used as the test platform to measure work while traversing two surfaces using three different maneuvers which were defined to highlight different kinetic energies and energy loss mechanisms.

Results: Overall, propulsion cost decreased with an increase in load on the drive wheels. Pneumatic drive wheels exhibited lower propulsion costs compared to a solid tire. Two casters, a 4″ dia × 1.5″ and a 5″ dia × 1″, exhibited better overall performance compared to 5″ dia × 1.5″ solid and 6″ dia × 1″ pneumatic casters.

Discussion: The results indicate that drive wheel load and types of drive wheels and casters impact propulsion cost and their influences differ across maneuvers and surfaces. The approach is well suited to assess equivalency in components and configurations. Assessment of performance equivalency would empower clinicians and users with important knowledge when selecting components.
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http://dx.doi.org/10.1177/2055668320907819DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC7144678PMC
April 2020

Pressure Ulcer Risk Factors in Persons with Mobility-Related Disabilities.

Adv Skin Wound Care 2020 Mar;33(3):146-154

Stephen Sprigle, PhD, PT, is Professor, Rehabilitation Engineering and Applied Research Lab, Georgia Institute of Technology, in Atlanta, Georgia. Douglas McNair, MD, PhD, is Senior Advisor, Global Health - Analytics Innovation, Bill and Melinda Gates Foundation, in Seattle, Washington. Sharon Sonenblum, PhD, is Principal Research Engineer, Rehabilitation Engineering and Applied Research Lab, Georgia Institute of Technology, in Atlanta, Georgia. The authors have disclosed no financial relationships related to this article. Submitted August 30, 2019; accepted in revised form October 1, 2019.

Objective: To assess pressure ulcer (PU) risk in persons with mobility impairments using a large data set to identify demographic, laboratory, hemodynamic, and pharmacologic risk factors.

Methods: The cohort of interest was persons with disabilities who have mobility impairments and are diagnostically at risk of PUs. To define this cohort, diagnoses that qualify patients for skin protection wheelchair cushions were used. Data were obtained from the Cerner Health Facts data warehouse. Two cohorts were defined: persons with and without a history of PUs. Analysis included descriptive statistics and multivariate logistic regression modeling. Variables retained in the model were identified using LASSO, gradient boosting, and Bayesian model averaging.

Main Results: The resulting cohorts included more than 87,000 persons with a history of PUs and more than 1.1 million persons who did not have a PU. The data revealed seven disability groups with the greatest prevalence of PUs: those with Alzheimer disease, cerebral palsy, hemiplegia, multiple sclerosis, paraplegia/quadriplegia, Parkinson disease, and spina bifida. Ulcers in the pelvic region accounted for 82% of PUs. Persons with disabilities who were male or black had a greater prevalence of PUs. Physiologic risk factors included the presence of kidney or renal disease, decreased serum albumin, and increased serum C-reactive protein.

Conclusions: The results indicate that, although persons with disabilities can exhibit a wide functional range, they remain at risk of PUs and should be evaluated for proper preventive measures, including support surfaces and wheelchair cushions.
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http://dx.doi.org/10.1097/01.ASW.0000653152.36482.7dDOI Listing
March 2020

Seated buttocks anatomy and its impact on biomechanical risk.

J Tissue Viability 2020 May 23;29(2):69-75. Epub 2020 Jan 23.

Lecturer in Diagnostic Radiography, Room 17J10, School of Health Sciences Ulster University, Shore Road, Jordanstown, Newtownabbey, Antrim, Ireland. Electronic address:

Aim: The objective of this study was to describe the amount, types, and shapes of tissue present in the buttocks during sitting (i.e., seated buttocks soft tissue anatomy), and the impact of seated buttocks soft tissue anatomy on biomechanical risk.

Materials And Methods: The buttocks of 35 people, including 29 full-time wheelchair users with and without a history of pelvic pressure ulcers were scanned sitting upright on 3" of flat HR45 foam in a FONAR Upright MRI. Multi-planar scans were analyzed to calculate bulk tissue thickness, tissue composition, gluteus maximus coverage at the ischium, the contour of the skin, and pelvic tilt.

Results: Bulk tissue thickness varied from 5.6 to 32.1 mm, was composed mostly of adipose tissue, and was greatest in the able-bodied cohort. Skin contours varied significantly across status group, with wheelchair users with a history of pressure ulcers having tissue with a peaked contour with a radius of curvature of 65.9 mm that wrapped more closely to the ischium (thickness at the apex = 8.2 mm) as compared to wheelchair users with no pressure ulcer history (radius of curvature = 91.5 mm and apex thickness = 14.5 mm). Finally, the majority of participants presented with little to no gluteus coverage over their ischial tuberosity, regardless of status group.

Conclusions: This study provides quantitative evidence that Biomechanical Risk, or the intrinsic characteristic of an individual's soft tissues to deform in response to extrinsic applied forces, is greater in individuals at greater risk for pressure ulcers.
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http://dx.doi.org/10.1016/j.jtv.2020.01.004DOI Listing
May 2020

Measurement of rolling resistance and scrub torque of manual wheelchair drive wheels and casters.

Assist Technol 2019 Dec 31:1-13. Epub 2019 Dec 31.

Rehabilitation Engineering and Applied Research Lab, Georgia Institute of Technology, Atlanta, Georgia, USA.

The effort needed to maneuver a manual wheelchair is a function of the occupied wheelchair's inertia and energy loss. The primary source of energy loss is due to the resistance of the drive wheels and casters on the ground. Specifically, manual wheelchairs have two major sources of frictional energy loss: rolling resistance and scrub torque. The objective of this study was to develop and validate component-level test methods to evaluate the energy loss properties of drive wheels and casters on different surfaces and with different applied loads. Rolling resistance is measured using a weighted coast-down cart and scrub torque is calculated by measuring the force required to rotate a plate that is loaded onto the tire's surface. Each test method was iterated and then applied to a cohort of drive wheels and casters. Both test methods demonstrated acceptable repeatability and the ability to distinguish energy loss parameters between common wheelchair components. The results show that caster and drive wheel energy losses can vary significantly across surfaces and with increased load on the casters. However, the findings also illuminate complex relationships between rolling resistance and scrub torque performance that embody a tradeoff in performance as applied to mobility during everyday life.
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http://dx.doi.org/10.1080/10400435.2019.1697907DOI Listing
December 2019

Everyday use of power adjustable seat height (PASH) systems.

Assist Technol 2019 Aug 22:1-9. Epub 2019 Aug 22.

Rehabilitation Engineering and Applied Research Laboratory, College of Design and The George W. Woodruff School of Mechanical Engineering, Georgia Institute of Technology , Atlanta , Georgia , USA.

The objective of this study was to measure how, why, and where the power adjustable seat height (PASH) system of Quantum's iLevel® wheelchairs were used. We instrumented iLevel® power wheelchairs for 24 adults to measure wheelchair occupancy, seat height, in-seat activity level, and bouts of mobility. Participants elevated their wheelchair 3.9 (4.4) (mean (SD)) times per day, including 1.0 (1.6) times per day past 9". Twenty-nine percent of elevation events were transient, lasting < 1 min, while 42% of elevate events lasted >5 minutes. Sixty-seven percent of participants transferred while elevated at least once, typically from heights <5" or >9", and 14 people changed their seat height between the transfer to and from the wheelchair. Twenty-three of 24 participants wheeled while elevated. Finally, in-seat activity level was greater while elevated. For many participants, the PASH system provided a functional benefit on a daily basis. Individuals elevated 4 times per day for activities including transfers, reach, gaze, or mobility. However, 14 participants did not elevate on at least 1 day. Further study is needed to identify the characteristics of people who will benefit most from a PASH system as well as to document the value associated with PASH system use.
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http://dx.doi.org/10.1080/10400435.2019.1634659DOI Listing
August 2019

Visualizing Tissue Strain Under the Sacrum and Coccyx in Different Supine Postures: A Case Series.

Adv Skin Wound Care 2019 Jun;32(6):264-271

At the Rehabilitation Engineering and Applied Research Lab, Georgia Institute of Technology, in Atlanta, Georgia, Stephen Sprigle, PhD, PT, is a Professor; and Sharon Sonenblum, PhD, is a Senior Research Scientist. Acknowledgments: The authors thank Dr John Greenhalgh and FONAR Corporation for their expertise in collecting the MRI scans and use of the scanner. Internal funding was used to support this study. The authors have disclosed no other financial relationships related to this article. Submitted August 31, 2018; accepted in revised form November 26, 2018.

Objective: To visually assess and report the influence of supine positioning and sacrum and coccyx anatomy on tissue deformation.

Methods: A convenience sample of three participants was scanned using MRI. All participants were scanned in a supine position with a rig oriented in a flat or horizontal position and with the torso portion of the rig elevated to 30° to simulate head-of-bed elevation. Representative images were identified to visualize and depict (1) the differences in tissue thickness and deformation in response to changes in supine positioning (0° and 30°), (2) the relative displacement of the skeleton relative to the skin during 30° incline, and (3) differences in sacrococcygeal morphology.

Results: The tissue thickness under the sacrum stayed the same or increased when torsos were elevated. Skeletons were displaced relative to the skin when the rig was elevated regardless of the pelvis location. Further, in the elevated position, coccyges flexed when pelvises were placed on the elevated segment but did not flex when pelvises were placed on the horizontal segment.

Conclusions: This case series is useful in defining new areas of research that can (1) identify the deformation induced by normal and frictional forces resulting from different positions of the bed chassis, (2) assess the impact of positioning the pelvis on elevated versus horizontal segments of the bed chassis, and (3) define the association between sacral and coccyx morphology and pressure ulcer occurrence in hospitalized patients.
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http://dx.doi.org/10.1097/01.ASW.0000554445.59743.44DOI Listing
June 2019

The influence of operator and wheelchair factors on wheelchair propulsion effort.

Disabil Rehabil Assist Technol 2020 04 27;15(3):328-335. Epub 2019 Feb 27.

School of Industrial Design, Georgia Institute of Technology, Atlanta, GA, USA.

The goal of this study was to evaluate the relative influence of operator and wheelchair factors on propulsion effort during over-ground wheelchair manoeuvres. This observational study included 23 full-time manual wheelchair users and 13 able-bodied subjects. The operator factors included shoulder position, aerobic capacity and propulsion strength. The wheelchair factors included system mass, weight distribution, and frictional loss in straight and turning trajectories. The performance of over-ground manoeuvres was defined as the propulsion effort measured by VO as operators propelled along a modified figure-8 course on tile and carpet surfaces. According to our regression model, shoulder position was the only significant contributor within operator factors, whereas weight distribution was the only significant contributor within wheelchair factors in influencing propulsion efforts. When combining operator and mechanical factors in the regression model, weight distribution became the only significant contributor to influence propulsion effort. Weight distribution and shoulder position had a significant influence on propulsion effort. These variables are related to the operator's relationship to the drive wheels. However, system mass and muscle strength had the least influence on wheelchair manoeuvres. Our finding can help clinicians to improve wheelchair configurations and manufacturers to improve wheelchair design by understanding the importance of shoulder position and weight distribution.Implication for rehabilitationStudying wheelchair manoeuvers by considering both wheelchair and operator factors might provide a unique insight to address the complex interactions among wheelchair designs and users.Propulsion effort decreases as percentage weight is increased on the drive wheels and the shoulder becomes more aligned with the axle position, which highlights the need to optimize wheelchair axle position.Wheelchair configuration, as represented by weight distribution, had a more significant influence on everyday manoeuvre than wheelchair mass does.It is essential for wheelchair users to choose a wheelchair that can match their daily needs and anthropometric measurements for saving propulsion efforts.
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http://dx.doi.org/10.1080/17483107.2019.1578425DOI Listing
April 2020

Pressure redistributing in-seat movement activities by persons with spinal cord injury over multiple epochs.

PLoS One 2019 13;14(2):e0210978. Epub 2019 Feb 13.

H. Milton Stewart School of Industrial & Systems Engineering, Georgia Institute of Technology, Atlanta, Georgia, United States of America.

Pressure ulcers, by definition, are caused by external forces on the tissues, often in the regions of bony prominences. Wheelchair users are at risk to develop sitting-acquired pressure ulcers, which occur in the regions of the ischial tuberosities, sacrum/coccyx or greater trochanters. As a means to prevent pressure ulcers, instruction on performing pressure reliefs or weight shifts are a part of the rehabilitation process. The objective of this study was to monitor the weight shift activity of full-time wheelchair users with acute spinal cord injury over multiple epochs of time in order to determine consistency or routine within and across epochs. A second objective was to evaluate the accuracy of self-reported pressure relief frequency within each measurement epoch. A wheelchair in-seat activity monitor was used to measure weight shifts and other in-seat movement. The data was classified into multiple in-seat activity metrics using machine learning. Seventeen full-time wheelchair users with spinal cord injury were measured within multiple epochs, each lasting more than 1 week. Across all in-seat activity metrics, no consistent pattern of activity changes emerged. None of the in-seat activity metric changed in any one direction across a majority of subjects. Subjects tended to over-estimate their frequency of performing pressure reliefs. Self-reported pressure relief behaviors are not reliable, and therefore, cannot be used to evaluate preventative behaviors either clinically or within research. This study had the capability of fully investigating in-seat movements of wheelchair users. The results indicated that in-seat movement does not reflect a routine, either in pressure reliefs, weight shifts or other functional in-seat movements. This study has illustrated the complexity of assigning causation of pressure ulcer occurrence to seated behaviors of wheelchair users and identifies the need for improved clinical techniques designed to develop routine behaviors to prevent pressure ulcers.
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http://journals.plos.org/plosone/article?id=10.1371/journal.pone.0210978PLOS
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC6373897PMC
October 2019

Use of a Low-Cost, Chest-Mounted Accelerometer to Evaluate Transfer Skills of Wheelchair Users During Everyday Activities: Observational Study.

JMIR Rehabil Assist Technol 2018 Dec 20;5(2):e11748. Epub 2018 Dec 20.

Rehabilitation Engineering and Applied Research Laboratory, Georgia Institute of Technology, Atlanta, GA, United States.

Background: Transfers are an important skill for many wheelchair users (WU). However, they have also been related to the risk of falling or developing upper limb injuries. Transfer abilities are usually evaluated in clinical settings or biomechanics laboratories, and these methods of assessment are poorly suited to evaluation in real and unconstrained world settings where transfers take place.

Objective: The objective of this paper is to test the feasibility of a system based on a wearable low-cost sensor to monitor transfer skills in real-world settings.

Methods: We collected data from 9 WU wearing triaxial accelerometer on their chest while performing transfers to and from car seats and home furniture. We then extracted significant features from accelerometer data based on biomechanical considerations and previous relevant literature and used machine learning algorithms to evaluate the performance of wheelchair transfers and detect their occurrence from a continuous time series of data.

Results: Results show a good predictive accuracy of support vector machine classifiers when determining the use of head-hip relationship (75.9%) and smoothness of landing (79.6%) when the starting and ending of the transfer are known. Automatic transfer detection reaches performances that are similar to state of the art in this context (multinomial logistic regression accuracy 87.8%). However, we achieve these results using only a single sensor and collecting data in a more ecological manner.

Conclusions: The use of a single chest-placed accelerometer shows good predictive accuracy for algorithms applied independently to both transfer evaluation and monitoring. This points to the opportunity for designing ubiquitous-technology based personalized skill development interventions for WU. However, monitoring transfers still require the use of external inputs or extra sensors to identify the start and end of the transfer, which is needed to perform an accurate evaluation.
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http://dx.doi.org/10.2196/11748DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC6320409PMC
December 2018

Developing a process for assessing equivalency of wheelchair cushion pressure redistribution performance.

Assist Technol 2020 19;32(2):92-99. Epub 2018 Sep 19.

Rehabilitation Engineering and Applied Research Lab, Georgia Institute of Technology, Atlanta, Georgia, USA.

For wheelchair users who are at risk for developing pressure ulcers, cushion prescription seeks to address tissue integrity. Because many designs of wheelchair cushions exist, a need exists to estimate their performance in supporting the body. The objective of this research was to develop an approach to assess the equivalency of cushions with respect to their pressure redistribution performance.Two instrumented compliant buttock models, differing in form, were used in the evaluation. Stress and strain parameters were used to characterize load-bearing performance. A cohort of 8 wheelchair cushions was compared to a standard reference material, HR45 foam. Each cushion was measured using both models under two loading conditions.The use of compliant buttock models that are capable of measuring both stress and strain parameters offer greater capability in measuring load-bearing performance compared to previously described methods. The proposed approach was able to evaluate cushion performance and use a logic-based approach to define whether or not a cushion was equivalent to the HR45 material. Additional study is needed to further validate the approach and to define the thresholds and criteria used to define cushion equivalency.
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http://dx.doi.org/10.1080/10400435.2018.1493709DOI Listing
January 2021

Measuring the impact of cushion design on buttocks tissue deformation: An MRI approach.

J Tissue Viability 2018 Aug 9;27(3):162-172. Epub 2018 May 9.

School of Health Sciences, Ulster University, Shore Road, Jordanstown, Newtownabbey, County Antrim, BT38 0QB, Northern Ireland, United Kingdom. Electronic address:

Aim: To establish a research approach for describing how different wheelchair cushion designs impact buttocks tissue deformation during sitting.

Materials And Methods: The buttocks of 4 individuals with spinal cord injury and significant atrophy were scanned sitting in a FONAR Upright MRI. Scans were collected with the individuals' buttocks fully suspended without pelvic support, and seated on 3 different commercially available wheelchair cushions. Multi-planar scans were analyzed to provide 3D renderings and measurements of tissue thickness and shape.

Results: Bulk tissue thicknesses at the ischium, which rarely included muscle, were reduced by more than 60% on enveloping cushion designs studied (i.e., Roho HP and Matrx Vi), and more variably (23-60%) on an orthotic off-loading design (i.e., Java). Adipose was typically displaced posterior and superior from the unloaded condition, with more lateral displacement on the Roho HP and Matrx Vi and more medial displacement present on the Java. Large changes in angle at the sacro-coccygeal joint indicated significant loading on the region. Deformation at the greater trochanter was more consistent across surfaces. Greater interface pressures tended to be associated with greater deformation, but the relationship varied by individuals and was highly non-linear.

Conclusions: The buttocks in this study all deformed significantly, but at different locations and in different manners across all 3 surfaces. Attention needs to be paid to the regions of greatest deformation. A future metric of shape compliance should consider cushion performance at all high risk regions, and changes to the amount and shape of tissue in the regions of interest.
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http://dx.doi.org/10.1016/j.jtv.2018.04.001DOI Listing
August 2018

The Characterization of Plantar Skin Across Environmental Condition and Time.

Adv Skin Wound Care 2018 Mar;31(3):123-129

In Atlanta, Georgia, Deborah M. Wendland, PhD, DPT, PT, CPed, is Assistant Professor, Department of Physical Therapy, Mercer University, and Stephen H. Sprigle, PhD, PT, is Professor, Schools of Industrial Design and Mechanical Engineering, Georgia Institute of Technology.

Objective: In the presence of pathologic conditions such as diabetes or neuropathy and activity-related forces, the plantar surface of the foot is a common place for skin breakdown. With this risk, foundational knowledge of typical plantar skin behavior is needed. The purpose of this study was to characterize the plantar skin properties (tangential stiffness, normal compliance, and thickness) across environmental condition and time.

Design And Setting: Nonexperimental laboratory design.

Patients: Sixteen individuals participated (age range, 19-78 years; mean age, 48.5 ± 19.23 years; mean body mass index, 31.5 ± 7.61 kg/m).

Main Outcome Measures: Tangential stiffness, normal compliance, and thickness were assessed with the Tissue Interrogation Device (TID), Myotonometer, and ultrasound, respectively. Measurements were taken at 5 anatomic locations over 4 visits across a day (morning and afternoon), week, and month. Measurements were taken in standard (20° C to 24° C, 35%-50% relative humidity) and shoe conditions (32° C, 66% relative humidity).

Main Results: Tangential stiffness (P = .000), normal compliance (P = .000), and thickness (epidermis, P = .000; dermis, P = .044) all varied by location. No main effect differences were noted across visits or environment across devices. Reliability varied across visits.

Conclusions: All 3 skin properties were found to vary across location and people. Given skin property consistency over time and device reliability, it is reasonable to take and compare measurements within a week. Environmental conditions should be reported and controlled in research assessing plantar skin.
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http://dx.doi.org/10.1097/01.ASW.0000530067.37008.e8DOI Listing
March 2018

Buttock tissue response to loading in men with spinal cord injury.

PLoS One 2018 7;13(2):e0191868. Epub 2018 Feb 7.

George W. Woodruff School of Mechanical Engineering, Georgia Institute of Technology, Atlanta, Georgia, United States of America.

Objective/background: Despite the fact that most people with a spinal cord injury who use a wheelchair for mobility are considered at-risk for pressure ulcer (PrU) development, there still exists a spectrum of risk amongst this group. Efforts to differentiate risk level would benefit from clinical tools that can measure or predict the buttocks response to loading. Therefore, the goal of this study was to identify how tissue compliance and blood flow were impacted by clinically-measurable risk factors in young men with SCI.

Methods: Blood flow at the ischial tuberosity was measured using laser Doppler flowmetry while the seated buttock was unloaded, and loaded at lower (40-60 mmHg) and high (>200 mmHg) loads. Tissue compliance of the buttock was measured using the Myotonometer while subject were lifted in a Guldmann Net.

Results: Across 28 participants, blood flow was significantly reduced at high loads, while no consistent, significant changes were found at lower loads. At 40-60 mmHg, blood flow decreased in participants with a pressure ulcer history and lower BMI, but stayed the same or increased in most other participants. The buttock displaced an average of 9.3 mm (2.7 mm) at 4.2 N, which represented 82% (7%) of maximum displacement. BMI was related to the amount of buttock tissue displacement while smoking status explained some of the variation in the percent of max displacement.

Conclusion: Wide variability in tissue compliance and blood flow responses across a relatively homogeneous population indicate that differences in biomechanical risk may provide an explanation for the spectrum of PrU risk among persons with SCI.
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http://journals.plos.org/plosone/article?id=10.1371/journal.pone.0191868PLOS
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC5802854PMC
March 2018

Data-mining analysis of the provision of mobility devices in the United States with emphasis on complex rehab technology.

Assist Technol 2019 5;31(3):141-146. Epub 2018 Jan 5.

b Numotion , Mt. Pleasant , North Carolina , USA.

The objective of this study was to describe the provision of wheeled-mobility equipment from the perspective of a large equipment supplier in the United States. The records of clients who were prescribed a mobility device over a 6-month period were randomly sampled to product a dataset of 1,689 clients. Analysis was limited to descriptive statistics and measures of relationships. The majority of the clients were adults (72%) and female (58%) with 62% receiving a manual wheelchair. The majority of interventions (58%) included some contribution from the client or client's family. Overall, 86% of all prescribed wheelchairs were classified as complex rehab technology (CRT). About half (52%) of all interventions involved a therapist. Therapist involvement was 2.5 times more likely during CRT interventions compared to standard durable medical equipment (StdDME). The project provides a novel description of mobility-related equipment provision using a large retrospective dataset. The analysis demonstrates the utility of analyzing a large number of client interventions. The capabilities of such analyses have business, clinical, and policy implications. Combining the data available from suppliers with prospective collection of client-specific information, such as outcomes, would be a more powerful means to assess the provision of wheeled-mobility equipment.
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http://dx.doi.org/10.1080/10400435.2017.1402391DOI Listing
May 2020

How a diverse research ecosystem has generated new rehabilitation technologies: Review of NIDILRR's Rehabilitation Engineering Research Centers.

J Neuroeng Rehabil 2017 11 6;14(1):109. Epub 2017 Nov 6.

Georgia Institute of Technology, Atlanta, Georgia, USA.

Over 50 million United States citizens (1 in 6 people in the US) have a developmental, acquired, or degenerative disability. The average US citizen can expect to live 20% of his or her life with a disability. Rehabilitation technologies play a major role in improving the quality of life for people with a disability, yet widespread and highly challenging needs remain. Within the US, a major effort aimed at the creation and evaluation of rehabilitation technology has been the Rehabilitation Engineering Research Centers (RERCs) sponsored by the National Institute on Disability, Independent Living, and Rehabilitation Research. As envisioned at their conception by a panel of the National Academy of Science in 1970, these centers were intended to take a "total approach to rehabilitation", combining medicine, engineering, and related science, to improve the quality of life of individuals with a disability. Here, we review the scope, achievements, and ongoing projects of an unbiased sample of 19 currently active or recently terminated RERCs. Specifically, for each center, we briefly explain the needs it targets, summarize key historical advances, identify emerging innovations, and consider future directions. Our assessment from this review is that the RERC program indeed involves a multidisciplinary approach, with 36 professional fields involved, although 70% of research and development staff are in engineering fields, 23% in clinical fields, and only 7% in basic science fields; significantly, 11% of the professional staff have a disability related to their research. We observe that the RERC program has substantially diversified the scope of its work since the 1970's, addressing more types of disabilities using more technologies, and, in particular, often now focusing on information technologies. RERC work also now often views users as integrated into an interdependent society through technologies that both people with and without disabilities co-use (such as the internet, wireless communication, and architecture). In addition, RERC research has evolved to view users as able at improving outcomes through learning, exercise, and plasticity (rather than being static), which can be optimally timed. We provide examples of rehabilitation technology innovation produced by the RERCs that illustrate this increasingly diversifying scope and evolving perspective. We conclude by discussing growth opportunities and possible future directions of the RERC program.
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http://dx.doi.org/10.1186/s12984-017-0321-3DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC5674748PMC
November 2017

Everyday sitting behavior of full-time wheelchair users.

J Rehabil Res Dev 2016 ;53(5):585-598

George W. Woodruff School of Mechanical Engineering, Georgia Institute of Technology, Atlanta, GA.

The objective of this study was to describe the in-seat movement and weight-shifting behavior of full-time wheelchair users. We measured everyday sitting behavior for 192 d across 28 individuals who used manual wheelchairs as their primary mobility device. To obtain the measurements, we used eight thin force sensors placed under participants' wheelchair cushions. On a typical day, participants spent an average of 10.6 +/- 3.0 h in their wheelchair and transferred out of the wheelchair 8.4 +/- 4.3 times. Participants only performed pressure reliefs (90% off-loading of the entire buttocks for at least 15 s) 0.4 +/- 0.5 times per hour they were seated in the chair, but they performed weight shifts (WSs) (30%-90% off-loading of at least one side of the buttocks for 15 s) with a frequency of 2.4 +/- 2.2 times per hour. Despite the higher frequency of WSs, they were not performed in a routine manner. Half of the days studied included one segment of upright sitting lasting at least 2 h without a WS. Given these observations, we conclude that seating evaluations should emphasize positioning individuals in a way that facilitates reaching, leaning, and transferring in a safe manner, not only to improve function but also to affect buttocks loading.
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http://dx.doi.org/10.1682/JRRD.2015.07.0130DOI Listing
January 2018

Some people move it, move it… for pressure injury prevention.

J Spinal Cord Med 2018 01 14;41(1):106-110. Epub 2016 Nov 14.

a Rehabilitation Engineering and Applied Research Laboratory , Georgia Institute of Technology , Atlanta , GA , USA.

Objective: To describe differences in in-seat behavior observed between individuals with a spinal cord injury (SCI) with and without a history of recurrent pressure injuries.

Design: Cross-sectional cohort study.

Setting: General community.

Participants: Twenty-nine adults more than 2 years post SCI, who used a wheelchair as their primary mobility device and had the ability to independently perform weight shift maneuvers. Participants were grouped according to whether or not they had a history of recurrent pressure injuries (PrIs), with 12 subjects having had two or more pressure injuries in the pelvic area (PrI Group).

Interventions: Not applicable.

Main Outcome Measures: Daily time in wheelchair, number of transfers, and frequency of pressure reliefs (full unloading), weight shifts (30% load reduction), and in-seat movements (transient center of pressure movements or unloading).

Results: The median participant spent 10.3 hours in his wheelchair and performed 16 transfers to or from the wheelchair daily. Pressure reliefs were performed less than once every 3 hours in both groups. Weight shifts were performed significantly more often by the No PrI Group (median (interquartile range) 2.5 (1.0-3.6) per hour) than the PrI Group (1.0 (0.4-1.9), with P = 0.037 and effect size r = 0.39). In-seat movements were performed 46.5 (28.7-76.7) times per hour by the No PrI group and 39.6 (24.3-49.7) times per hour for the PrI group (P = 0.352, effect size r = 0.17).

Conclusion: Weight shifts that can be produced by functional activities and that partially unload the buttocks should be considered as an important addition to individuals' PrI prevention regimen.
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http://dx.doi.org/10.1080/10790268.2016.1245806DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC5810794PMC
January 2018

Wheelchair use in ultra-lightweight wheelchair users.

Disabil Rehabil Assist Technol 2017 05 19;12(4):396-401. Epub 2016 Jul 19.

a Rehabilitation Engineering and Applied Research Laboratory , Georgia Institute of Technology , Atlanta , GA , USA.

Purpose: The goal of this study was to describe how ultra-lightweight wheelchair users use their wheelchairs during everyday mobility.

Method: We instrumented a convenience sample of 69 ultra-lightweight wheelchair users with a seat switch to measure their occupancy, and an accelerometer on their wheel to measure distance wheeled, time spent wheeling and daily bouts of mobility.

Results: On the median day, subjects wheeled 83 bouts and 1.4 km over 45 min. A typical bout of mobility was 8.3 m in length, lasting 20 s and occurring at a speed of 0.44 m/s. Fast (>1 m/s) and long (>2 min) bouts represented less than 4% of bouts and were more common among younger participants and those who were employed or a student.

Conclusions: Highly functional manual wheelchair users present with a significant mobility disability, moving far less than their ambulating peers despite moving with similar mobility characteristics. The typical bout characteristics - short and slow bouts - are consistent with indoor mobility and transitions between functional activities. For wheelchair users, it highlights the importance of manoeuverability and the need for prescription and training to emphasize manoeuverability. Implications for Rehabilitation Measurement of wheelchair use, both how and how much, might provide unique insight to what equipment would be most appropriate for an individual. Participants who used an ultralight wheelchair presented with a significant mobility disability, wheeling only 1.7 km/day on average. Fast (>1 m/s) and long (>2 min) bouts are uncommon, representing less than 4% of bouts. Younger participants and those who were employed or a student were more likely to wheel one fast and long bout per day. Because wheelchair mobility was dominated by short, slow bouts, prescription and training need to emphasize maneuverability.
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http://dx.doi.org/10.1080/17483107.2016.1178819DOI Listing
May 2017

Inertial and frictional influences of instrumented wheelchair wheels.

J Rehabil Assist Technol Eng 2016 Jan-Dec;3:2055668316649892. Epub 2016 Jun 20.

Rehabilitation Engineering and Applied Research Lab, Georgia Institute of Technology, Atlanta, USA.

Background: Instrumented wheelchair wheels can be used to study the kinematics and kinetics of manual wheelchair propulsion. The objective of this study was to evaluate the impact of instrumented wheels on the inertial and frictional parameters of a wheelchair system.

Methods: This study compared mechanical parameters of an ultralightweight rigid frame wheelchair configured with pairs of SMARTwheels and spoke pneumatic wheels and loaded with an ISO 75 kg wheelchair dummy. Rectilinear and turning inertia of the occupied wheelchair and the rotational inertia of drive wheels were measured. A coast-down test measured frictional energy loss during straight and turning trajectories.

Findings: The addition of instrumented wheels increased occupied system mass by about 6% and turning inertia by about 16%. Frictional energy loss increased by over 40% in a straight trajectory and over 30% during turning.

Interpretation: Addition of instrumented increased the inertia and frictional energy loss of the wheelchair system. These relative effects will impact the wheelchair operator and increase the instantaneous propulsion torque during wheelchair maneuvers. The impacts will be less under conditions involving little or no change in velocity. Researchers should be encouraged to report changes in mass and weight distribution induced by addition of instrumented wheelchair wheels.
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http://dx.doi.org/10.1177/2055668316649892DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC6453031PMC
June 2016

Comparison of the inertial properties and forces required to initiate movement for three gait trainers.

Assist Technol 2016 ;28(3):137-43

c Sunny Hill Health Centre for Children , Vancouver , BC , Canada.

The purpose of this study was to evaluate the inertial properties and forces required to initiate movement on two different surfaces in a sample of three commonly prescribed gait trainers. Tests were conducted in a laboratory setting to compare the Prime Engineering KidWalk, Rifton Pacer, and Snug Seat Mustang with and without a weighted anthropometric test dummy configured to the weight and proportions of a 4-year-old child. The Pacer was the lightest and the KidWalk the heaviest while footprints of the three gait trainers were similar. Weight was borne fairly evenly on the four casters of the Pacer and Mustang while 85% of the weight was borne on the large wheels of the mid-wheel drive KidWalk. These differences in frame style, wheel, and caster style and overall mass impact inertial properties and forces required to initiate movement. Test results suggest that initiation forces on tile were equivalent for the Pacer and KidWalk while the Mustang had the highest initiation force. Initiation forces on carpet were lowest for the KidWalk and highest for the Mustang. This initial study of inertia and movement initiation forces may provide added information for clinicians to consider when selecting a gait trainer for their clients.
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http://dx.doi.org/10.1080/10400435.2015.1123780DOI Listing
January 2018

Evaluation of wheelchair resistive forces during straight and turning trajectories across different wheelchair configurations using free-wheeling coast-down test.

J Rehabil Res Dev 2015 ;52(7):763-74

The purpose of this study was to develop a simple approach to evaluate resistive frictional forces acting on manual wheelchairs (MWCs) during straight and turning maneuvers. Using a dummy-occupied MWC, decelerations were measured via axle-mounted encoders during a coast-down protocol that included straight trajectories and fixed-wheel turns. Eight coast-down trials were conducted to test repeatability and repeated on separate days to evaluate reliability. Without changing the inertia of the MWC system, three tire inflations were chosen to evaluate the sensitivity in discerning deceleration differences using effect sizes. The technique was also deployed to investigate the effect of different MWC masses and weight distributions on resistive forces. Results showed that the proposed coast-down technique had good repeatability and reliability in measuring decelerations and had good sensitivity in discerning differences in tire inflation, especially during turning. The results also indicated that increased loading on drive wheels reduced resistive losses in straight trajectories while increasing resistive losses during turning. During turning trajectories, the presence of tire scrub contributes significantly to the amount of resistive force. Overall, this new coast-down technique demonstrates satisfactory repeatability and sensitivity for detecting deceleration changes during straight and turning trajectories, indicating that it can be used to evaluate resistive loss of different MWC configurations and maneuvers.
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http://dx.doi.org/10.1682/JRRD.2014.10.0235DOI Listing
October 2016

Impact of Mass and Weight Distribution on Manual Wheelchair Propulsion Torque.

Assist Technol 2015 ;27(4):226-35; quiz 236-7

a Rehabilitation Engineering and Applied Research Laboratory , Georgia Institute of Technology , Atlanta , Georgia , USA.

Propulsion effort of manual wheelchairs, a major determinant of user mobility, is a function of human biomechanics and mechanical design. Human studies that investigate both variables simultaneously have resulted in largely inconsistent outcomes, motivating the implementation of a robotic propulsion system that characterizes the inherent mechanical performance of wheelchairs. This study investigates the impacts of mass and mass distribution on manual wheelchair propulsion by configuring an ultra-lightweight chair to two weights (12-kg and 17.6-kg) and two load distributions (70% and 55% on drive wheels). The propulsion torques of these four configurations were measured for a straight maneuver and a fixed-wheel turn, on both tile and carpet. Results indicated that increasing mass to 17.6-kg had the largest effect on straight acceleration, requiring 7.4% and 5.8% more torque on tile and carpet, respectively. Reducing the drive wheel load to 55% had the largest effect on steady-state straight motion and on both turning acceleration and steady-state turning; for tile and carpet, propulsion torque increased by 13.5% and 11.8%, 16.5% and 4.1%, 73% and 5.1%, respectively. These results demonstrate the robot's high sensitivity, and support the clinical importance of evaluating effects of wheelchair mass and axle position on propulsion effort across maneuvers and surfaces.
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http://dx.doi.org/10.1080/10400435.2015.1039149DOI Listing
April 2016

Measurement of Load Redistribution Properties of Wheelchair Cushions Using a Compliant Cushion Loading Indenter.

Assist Technol 2015 ;27(3):129-35

a REAR Lab, Georgia Institute of Technology , Atlanta , Georgia , USA.

The aim of this project was to develop and validate a compliant cushion loading indenter (CCLI) capable of evaluating wheelchair cushion performance by measuring internal pressures and deflection. The design of the CCLI consists of 3 subsystems: 1) an internal substructure with medial and lateral protuberances to mimic the load-bearing ischial tuberosities and trochanters, 2) an elastomeric shell to mimic soft tissue and 3) instrumentation to measure internal pressures at both protuberances and deflection of the elastomer at 7 locations. It is parametrically designed so can be scaled larger or smaller to represent different body sizes. To assess the repeatability and sensitivity of measurements, the model was loaded onto two wheelchair cushions, 3″ flat foam and Jay3, using two loads, 44kgf and 53kgf, representing the average upper body mass of 70kg and 83kg persons, respectively. The results showed a high precision of pressure and deflection measurement across two different cushions and loads. Under both loads, pressure measurements exhibited a standard error of < 1 mm and <3 mmHg. The standard deviations of deflection values were less than 2.5 mm (0.1 in.). The pressures and absolute deflection differed significantly across load and cushion type indicating sensitivity to change.
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http://dx.doi.org/10.1080/10400435.2014.986772DOI Listing
January 2018

3D anatomy and deformation of the seated buttocks.

J Tissue Viability 2015 May 2;24(2):51-61. Epub 2015 Apr 2.

Institute of Nursing and Health Research, School of Health Sciences, University of Ulster, Shore Road, Newtownabbey BT37 0QB, United Kingdom. Electronic address:

Aim: To describe the 3D anatomy and deformation of the buttocks during sitting.

Materials And Methods: The buttocks of 4 able-bodied individuals and 3 individuals with spinal cord injury were scanned sitting in a FONAR Upright MRI. T1-weighted Fast Spin Echo scans were collected with the individuals seated on a custom wheelchair cushion to unload the ischial tuberosities (ITs) and seated on a 3 inch foam cushion. Multi-planar scans were analyzed, and the muscle, bone and adipose tissue was manually segmented for 3D rendering and analysis of the quantity, geometry, and location of tissues.

Results: The gluteus maximus was positioned lateral and posterior to the IT, covering the inferior portion of the IT for only 2 able-bodied participants. Adipose thickness directly under the IT did not differ by diagnosis, nor did it have a consistent response to loading. However, the envelopment of the IT by the surrounding adipose tissue was much greater in two of the participants with spinal cord injuries. These two subjects also had the most curved skin surface as the tissue wrapped around the IT. Tissue strains around the ischium were most visible in the adipose and connective tissue. The gluteus maximus displaced and distorted upwards, posterior and lateral, away from the inferior IT.

Conclusions: Multi-planar imaging is necessary to investigate anatomy and deformation of the buttocks. 5 out of 7 participants did not sit directly on muscle. The tissue beneath their ITs was predominantly composed of fat and connective tissue, suggesting that these tissues might be most vulnerable to injury.
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http://dx.doi.org/10.1016/j.jtv.2015.03.003DOI Listing
May 2015

Design of a Robotic System to Measure Propulsion Work of Over-Ground Wheelchair Maneuvers.

IEEE Trans Neural Syst Rehabil Eng 2015 Nov 20;23(6):983-91. Epub 2014 Nov 20.

A wheelchair-propelling robot has been developed to measure the efficiency of manual wheelchairs. The use of a robot has certain advantages compared to the use of human operators with respect to repeatability of measurements and the ability to compare many more wheelchair configurations than possible with human operators. Its design and implementation required significant engineering and validation of hardware and control systems. The robot can propel a wheelchair according to pre-programmed accelerations and velocities and measures the forces required to achieve these maneuvers. Wheel velocities were within 0.1 m/s of programmed values and coefficients of variation . Torque measurements were also repeatable with . By determining the propulsion torque required to propel the wheelchair through a series of canonical maneuvers, task-dependent input work for various wheelchairs and configurations can be compared. This metric would serve to quantify the combined inertial and frictional resistance of the mechanical system.
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http://dx.doi.org/10.1109/TNSRE.2014.2371339DOI Listing
November 2015
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