man wearing glasses mounted with accelerometers

Reliability and Validity of Accelerometric Gait

Principal Investigators: Eric E. Sabelman, PhD and Carol H. Winograd, MD

Project Staff: Betty S. Troy, MS; Debbie E. Kenney, OTR; David L. Jaffe, MS; Ruth Yap, MS; and Beatrice B. Lee, MS

Objectives: The sense of balance declines with age due to combined vestibular, proprioceptive and visual losses, resulting in impaired mobility and increased risk of injurious falls. A wearable accelerometric instrument has been developed to record movements outside the laboratory, identify motion patterns that accompany loss of balance before a fall occurs, warn the individual of pre-fall behavior, and if necessary, signal that the wearer has fallen. Accelerometry is clinically useful as a diagnostic tool to quantify hitherto qualitative measures of balance, as a biofeedback device during therapy and as a fall-prevention aid - a balance orthosis for fall-prone elderly individuals.

Researchers, clinicians, and potential industrial partners familiar with accelerometry have noted the need for rigorously testing its reliability and validity before it can become a routine clinical tool. In this phase of the project, we will establish statistical reliability and validity by comparison of accelerometry with conventional laboratory gait and balance measures (force platform, goniometry and video imaging) using subjects having well-defined gender, age and mobility status.

Problem: Each year one third of the elderly living at home will fall, and nearly one in 40 will be hospitalized as a result. Balance problems and the fear of falling can limit mobility and make the difference between living at home or being in a nursing facility. As veterans age, they become increasingly at risk for injurious falls; hence, the need for a "balance orthosis" to help them maintain their independence.

Methodology: The accelerometric motion detection system consists of two small 3-axis sensors attached to both corners of eyeglass frames to measure head motion, and two sensors above each hip on a belt at the waist, along with a self-contained data acquisition package. An infrared remote control is used to command the wearable unit, so the wearer is unencumbered by cables. In a typical test, subjects perform tasks derived from qualitative balance assessment protocols, including: stand eyes open, then closed; ascend stairs, turn, then descend; rise from and sit in chair; normal walk 10 m; tandem (toe-to-heel) walk 3 m; walk over obstacles 1 m apart.

Among the factors that affect consistent interpretation of accelerometric data are: (1) mechanical and electronic stability, (2) installation and calibration (inter-rater reliability), (3) test-retest reliability, (4) accuracy vs. accepted techniques (concurrent validity), (5) presentation of results derived from accelerometric data in a form comparable to currently accepted measures. We will enroll and test on two or three occasions up to 240 able-bodied subjects in the spectrum between fit and deconditioned. Subjects will be grouped by gender and age decade (60s, 70s, 80s); all will have stable mobility status. Overall differences between initial and retest values and differences between accelerometric and conventional measures will be compared using appropriate statistics.

Progress: Progress: Data from subject populations comprising stroke, Parkinson's disease and hip arthroplasty patients, as well as able-bodied subjects induced to stumble in the laboratory, are being analyzed. Local collaborators have used the method for clnical diagnosis of veterans with peripheral neuropathy (Jonathan Katz, MD, VA Palo Alto Neurology Service), and non-local researchers have studied fatigue in walking by the elderly and standing balance in a variety of subjects, including children with cerebral palsy (Edith Naas, PhD PT, Univ of Nevada-Reno). Collaborations have been established for developing special-purpose devices for identifying and preventing lateral falls likely to result in hip fracture (with Neil Alexander, MD, Ann Arbor VAMC, Ann Arbor, MI), for measuring effects of training in Tai Chi Chuan on balance (with Wayne Phillips, PhD, now at Arizona State Univ; formerly Stanford Center for Research on Disease Prevention), and for combined head- and eye-tracking for vestibular research (with Geoff Bush, PhD, NASA-Ames Research Center).

Subject recruitment & characterization: Because few fit elderly subjects could be obtained from the hospital-based sources listed in the protocol, we have contacted senior centers and community recreation programs to solicit volunteers. We test a group of subjects one-after-another at such non-VA locations, but take only accelerometry and video data since the force plates and goniometers are not available. A total of 79 subjects have been tested at least twice. Test protocol - To reduce the number of subjects needed, we are simultaneously collecting hip, knee and ankle angle data using Penny & Giles goniometers strapped to the subjects' legs. We are not using the "EquiTest" device; otherwise the test protocol is as described in the proposal. Balance-impaired subjects are asked to perform a shortened series of tasks, as are subjects at test sites other than the Rehab R&D Center. On-site testing may be done elsewhere at Stanford Department of Functional Restoration facilities, the VA Medical Center (e.g.: bldgs 2 or 7), or in subjects' homes." We have added other Palo Alto VA divisions (San José, Livermore, Menlo Park) and senior and recreation centers as possible test sites. Although the full set of tasks takes only 30 minutes, due to set-up and removal of sensors, most subjects are in the test room for about 90 minutes.

Aspects of the analysis of subjects performing sit-to-stand have been presented in two papers at recent RESNA conferences. Other papers are in preparation.

Funding Source: VA RR&D Merit Review - Project E601-3RA

Specific Projects:

1. Upper Body Motion Analysis for Amelioration of Falls in the Elderly

Falling, especially in the elderly, can cause neurological and musculoskeletal injuries that results in mobility disability. The objective of this project is to develop a wearable device that can identify motions of the body associated with loss of balance and falling. The device can be also be used in the clinic to identify those persons most at risk for falling, and in the home to warn the user (e.g. an elderly person who has sustained a stroke) of conditions in which they may lose their balance. In this project, the instrument was used in the laboratory and the clinic to quantify standard qualitative balance assessment protocols, plus standardized tasks representative of activities of everyday living. In addition to normal old and young subjects, we have tested balance-impaired subjects such as Parkinson's, acute hip arthroplasty, and stroke patients, providing pilot data showing the ability to distinguish disability-specific motion patterns.

Project Staff: Carol Winograd, MD, Betty S. Troy, MS, Sandy Dunn Gabrielli, Ruth Yap, MS, Deborah E. Kenney, MS OTR, and Margaret Willits, MA

Funding Source: VA RR&D Merit Review

2. Reliability and Validity of Accelerometric Gait and Balance Diagnosis

In this phase, we will formally establish statistical reliability and validity of a wearable gait and balance analysis instrument by comparison of accelerometry with conventional laboratory gait and balance measures (force platform, goinometry, and video imaging) using subjects having well-defined gender, anthropometrics, age, and mobility status. This result will be a reference database for assessing clinically relevant features of impaired mobility.

3. Advanced Accelerometric Motion Analysis System

Technological progress since the first generation design permits the construction of a much more capable system; this is a necessity for entry of accelerometric methodology into routine clinical use. This design/development proposal will support building and testing second generation equipment, incorporating new sensors and wearable computers capable of real-time detection of movement abnormalities, develop software for extracting clinically useful information form its data, and enlist the support of a commercial partner in further development via a Cooperative Research and Development Agreement (CRADA).

4. Student Projects

Collaborators: The Rehabilitation R&D Center is making the accelerometric instrument available on loan to other researchers for testing of diverse subject populations. The collaboration arrangement calls for the VA to supply to participants equipment and supporting software on a no-cost loan basis; participants agree to share data, assist each other with interpretation, and credit the VA in publications.

Resources:

Related Publications:

Last updated September 20, 1998

Funding Source: VA RR&D Merit Review