Experiences Using the Mobile Usability Lab to Investigate Medical Device Biomechanical Barriers

RESNA 28th Annual Conference - Atlanta, Georgia

Melissa R. Lemke, BS, Jack M. Winters, PhD


Inaccessible medical instrumentation often denies people with disabilities the right to receive or provide adequate healthcare services. The Mobile Usability Lab (MU-Lab) has been developed to perform systematic accessibility and usability analyses of patients and providers using medical devices. In this study, audio, video and survey data are collected for patients using medical devices, with an emphasis on performing biomechanical tasks. Weight scales, dental chairs, hospital beds, an examination table, dental monitor and x-ray are evaluated while being used by people with diverse abilities. In-field data-collection with the MU-Lab was convenient and dependable, while the data collected is usable for identifying task-based biomechanical barriers for individuals with disabilities using medical devices.


Medical devices; accessibility; usability; biomechanics


Approximately nineteen percent of people over the age of five living in the United States have some type of disability or lasting condition, and most of these individuals require healthcare services (1). People with disabilities are often denied adequate healthcare because of architectural barriers, inaccessible medical equipment and communication barriers between healthcare providers and consumers (2). The MU-Lab was created by the Rehabilitation Engineering Research Center on Accessible Medical Instrumentation (RERC-AMI) to perform accessibility and usability analyses of medical devices. The system is used to investigate physical barriers to healthcare access by integrating audio, video and questionnaire data collection. The MU-Lab is designed to permit detailed time-sequence analyses of patients and providers using medical devices, aimed at investigating overall barriers to use (3).


Subject Recruitment

Subjects with disabilities are recruited to participate in this study through several methods, including working with local agencies (i.e., IndependenceFirst, Badger Association of the Blind and Visually Impaired, Inc. and United Cerebral Palsy Association of Southeastern Wisconsin) and creating a flyer for distribution to potential subjects. Subjects are contacted initially via telephone, and a pre-screening interview is administered through the MU-Lab Protocol Manager (PM). The pre-screening questionnaire is used to determine the subject’s demographic information (e.g., gender, age, race), impairments or health problems that cause difficulties (e.g., vision, hearing, arthritis), tasks that cause difficulties (e.g., reaching, pushing buttons, balance), assistive devices used (e.g., cane, walker, wheelchair) and opinions about any experiences, difficulties or discomforts with each medical device under investigation. A total of 12 subjects with diverse abilities and task difficulties (e.g., due to cerebral palsy, multiple sclerosis, muscular dystrophy, spinal cord injury) are selected to participate in this study.

MU-Lab Data Collection

The medical devices investigated in this study were selected primarily based on results from the RERC-AMI national consumer survey, although clinical availability and biomechanical task requirements were also considered. Survey results identified examination tables, x-ray equipment, weight scales and examination chairs as moderately difficult to impossible to use for at least 50% of the respondents (4).

Each subject participates in three sessions of roughly ninety minutes each, at different facilities on the Marquette University campus (i.e., biomedical engineering, nursing, dentistry). During each of the sessions the subject uses three different devices, which results in the evaluation of nine common medical devices. Table 1 provides a more detailed description of the medical devices evaluated and tasks attempted by the subjects in this study.

Table 1: Description of Medical Devices Evaluated and Tasks Attempted
Device Class Device Make Tasks Attempted
Examination table Generic physician's examination table (with stirrups) Get onto table
Sit on table
Lie supine on table
Lie prone on table
If female, use stirrups
Get off table
Weight scale Detecto-Medic 350lb. Beam Scale Get onto scale
Measure weight
Seca Combo Medical 800lb. Scale, Model 684 Obtain weight readout
Get off scale
Power Adjustable Hospital Bed (head and foot sections) Simmons Multi-Matic, Model HM-792M Get into bed
Adjust bed to eat
Invacare Home Care Bed, Model 5410IVC Adjust side safety rails
Get out of bed
Dental monitor NEC 15-inch TFT screen, Model 1550M Sit in dental chair
Obtain audio information
Obtain video information
Dental chair A-dec Cascade/Radius, Model 1040 Get into dental chair
Sit in dental chair
A-dec model Lie back in dental chair
Get out of dental chair
Portable x-ray Trophy, Model 77347 Sit in dental chair
Obtain simulated x-ray(s)

Subjects are read a short scenario (e.g., you need to determine your weight) and then they attempt to perform routine tasks with each medical device (e.g., get onto scale, get off of scale). After the first trial, the researcher or subject notes any concerns or clarifies a task that was not adequately performed, and then another similar trial is carried out. Finally, the subject is given a keywords list and asked to comment on any design barriers, good or bad device features, positioning challenges, awkward movements, times of high force exertion, and device features that make them feel vulnerable to injury.

The MU-Lab is used to collect audio and video data whenever the subject is using a medical device. Video cameras are used to capture front, side and overhead or back views of each of the devices, and a boundary microphone is used to capture the sounds within the room. Following the audio and video-taped trials with each device, a post-activity questionnaire is administered through the PM to determine the subject’s opinions about their experiences with the previously used medical device (i.e., sensory usability, physical usability, error tolerance, safety and comfort, assistive technology accommodation). The post-activity questionnaire is based on the Principles of Universal Design (5), and its core questions are intended to be used for all medical devices. Customized device-specific questions can also be created, and 1-3 such questions were added for each of the devices evaluated in this study.

MU-Lab Task Analysis

Multimedia Video Task Analysis® (MVTA, NexGen Ergonomics) is the primary post-processing software package used to identify any biomechanical barriers that occur while the subject is attempting to use the medical device. A team developed the comprehensive biomechanical barrier records list for event marking in MVTA using an iterative process, and the final barriers include: orienting into position, transferring, auditory sensing (related to biomechanics), visual sensing (related to biomechanics), tactile sensing (related to biomechanics), positioning/postural support, reaching, manipulation, leg strength/weight bearing on lower extremities, gross balance/postural control, exertion, and safety. A time sequence analysis of each recorded trial is carried out to identify any biomechanical barriers (e.g. orienting, transferring, balance), physical interactions between the subject and medical device (e.g. active use of the headrest, tabletop, step, handrail) and assistive technology use with the device (e.g. wheelchair/scooter, transfer board, cane). The beginning and ending time is marked for each event in MVTA, and the timeline can simultaneously display multiple records and events.


Overall, data collection with the MU-Lab is convenient and dependable. The system is easily transported to locations outside of the RERC-AMI laboratory, and the set-up and break-down processes are feasible in approximately 15-60 minutes (depending on the number of cameras used and amount of fine-tuning required). Adequate supplies are contained within the MU-Lab suitcase, and the components are minimally obtrusive so more natural actions are recorded. Most subjects took approximately 15 minutes to use each device and 15 minutes to go through the comprehensive post-activity questionnaire.

Preliminary analyses indicate the presence of clear biomechanical barriers for subjects in this study, and task performance analyses reveal several device inadequacies (e.g., lack of balance aids or body support structures, presence of raised threshold edge that causes orienting difficulty, inadequate table height for transfer). Such barriers and device inadequacies caused several subjects difficulty in their attempts to use certain medical devices (e.g., dental chair, hospital bed, weight scale), while others found it impossible to use certain devices (e.g., exam table, weight scale).


Continued analysis of the collected data is needed to better understand the occurrences of biomechanical barriers, physical interactions between the subject and medical device, and the role of any assistive technologies used with each device. MVTA provides an effective means of documenting overall barriers to use, and the PM provides an effective means of collecting and documenting qualitative subject data. Correlation between the pre- and post-activity questionnaires and the MVTA analyses are still necessary to fully understand the nature of biomechanical accessibility and usability barriers.

The MU-Lab has been found to provide a convenient, dependable and useful means of collecting and analyzing accessibility and usability data, while the PM provides the researcher guidance with data collection and analysis. Insights from these biomechanical analyses are expected to be useful to other RERC-AMI projects, and are important in the ongoing process of improving medical device design for everyone, including individuals with disabilities.


This work is supported by the Rehabilitation Engineering Research Center on Accessible Medical Instrumentation, funded by the National Institute on Disability and Rehabilitation Research, U.S. Department of Education Grant #H133E020729. All opinions expressed are those of the authors.

We also thank Dr. Sarma Danturthi, Sean Campbell, Dr. Jill Winters, Dr. Michelle Robinson, Farheen Shaikh, Michael Baran, Danielle Richterkessing and Lora Mielcarek of Marquette University and Molly Follette Story, Dr. David Rempel and Alan Barr from the University of California, San Francisco.


  1. United States Census 2000, Economics and Statistics Administration
  2. Gibson, M.J., Freiman, M., Gregory, S., Kassner, E., Kochera, A., Mullen, F., et al. (2003). Beyond 50 2003: A report to the Nation on Independent Living and Disability, Washington, DC: AARP.
  3. Winters, J.M., Follette Story, M., Campbell, S., Lemke, M., Danturthi, S., Barr, A., and Rempel, D. (2004). Mobile Usability Lab: A Tool for Studying Medical Device Accessibility for Users with Diverse Abilities, RESNA 2004.
  4. Winters, J.M.W., Story, M.F., Barnekow, K., Premo, B., Kailes, J.I., Schwier, E., Rempel, D., Winters, J.M. (2004). Problems with medical instrumentation experienced by patients with disabilities. Proc. Human Factors and Ergonomics Society 48th Annual Meeting. September, 2004. New Orleans, LA.
  5. The Center for Universal Design (1997). The Principles of Universal Design. Raleigh, NC: North Carolina State University

Author Contact Information:

Melissa R. Lemke, BS
Marquette University
Department of Biomedical Engineering
PO Box 1881
Milwaukee, WI 53201-1881
(414) 288-6256
EMAIL: Melissa.Lemke@marquette.edu