Student Projects in Accelerometric Motion Analysis

Investigator: Eric E. Sabelman, PhD

The VA Rehabilitation R&D Center wishes to expand the merit review-supported Reliability and Validity of Accelerometric Gait and Balance Diagnosis (E601) to include a variety of support and testing activities. This PAIRE-supported project provides funds for students to work on these projects.

Human Body Motion Analysis for Fall Prevention - Normal Subject Testing

To establish baselines to which to compare abnormal balance, we are testing as many as 240 normal subjects aged 60 to 90 years. The student(s) work with a team of engineers and therapists to recruit, schedule and test gait and balance of each subject during 2 or 3 sessions a weak apart. Testing consists of recording acceleration, joint angle, forces and/or video images of subjects performing standing, reaching and walking tasks; students will operate some of the recording instruments, measure subjects' dimensions and record other data.

During 1998, three student assistants with interest and experience in working with older subjects, and ability to meticulously record experimental data helped with testing at the VA Rehabilitation R&D Center and also at senior centers and other sites between San Jose and San Francisco

Controlled Falls in the Laboratory - Lateral falls onto the Hip

Research Plan - A private physician, Dr. Marshall J. Keyes of Los Angeles, has patented a designfor an active protection device to prevent injury from falls onto the hip. This device incorporates an air bag in a belt, to be inflated during a fall before the wearer's hip contacts the floor. Our knowledge of postural instability and the motion patterns preceding falls could substantially contribute to design of the fall-detection component of the HIPD and to the real-time software necessary to unambiguously detect onset of a fall and trigger inflation of the airbag within the HIPD. Dr. Keyes' company, Maven Technologies, is underwriting a small study through PAIRE to acquire accelerometric data during laboratory-induced falls. The data will be used to evaluate algorithms for real-time motion analysis; it is necessary that such fall-detection programs be nearly-infallible, triggering the HIPD on all falls likely to cause hip injury, while excluding false alarms due to any other abrupt body motions.

Results / Status - Students have made two versions of a platform for causing falls by tilting and/or sliding while a subject stands on it. The floor onto which the subject falls is padded, and the subject wears wrist braces and a climbing harness attached to a rope to prevent actually impating the hip. Five subjects were tested in falling laterally, at 45 degrees and backward; the latter two configurations are to acquire data on falls which might cause false alarm triggering of a protective device.

Dynamic Test Fixture for Accelerometers

Need - To date, we have had no means for testing the frequency response of the complete accelerometry system. The frequency spectrum of body motion contains clues to different types of balance deficits.

Research Plan - Students have been asked to develop a test fixture for the acceleration sensors that can be used to characterize their frequency responses. The ideal fixture would be able to apply selectable accelerations ranging from -10 to +10 G's at selectable frequencies ranging from 0 to 100 Hz. The most critical ranges are -2 to +2 G's and 0 to 20 Hz..

Results / Status - The initial student-designed test fixture used 4-foot diameter constant-speed rotors coupled to a slider producing linear sinusoidal motion; it could not be operated safely at any but the lowest speed. A new design with a 6 inch rotor driven at varying speed by a stepper motor is being worked on. (No students elected to work on this project during summer of 1998.)

Data Analysis

Need - Extraction of clinically relevant information from the 12-channel acceleration data stream is difficult. One approach is to codify the qualitative criteria used by clinicians to obtain judgements of postural steadiness, and apply these criteria to acceleration data.

Research Plan - Students are asked to help adapt and/or develop software to yield head and torso velocity vectors in real-time, to track rotational centers of the head and trunk for identificaiton of line-of-sight direction, to distinguish between inertial acceleration and tilt relative to gravity, to identify distinct motion patterns, and to group able-bodied (as well as balance-impaired) subjects according to their idiosyncratic movement strategies, using pattern recognition and frequency-domain analytical methods.

Results / Status - A team of students in a Stanford course on signal processing (EE280) explored pattern recognition algorithms, resulting in a new method of encoding repetitive activities based on unique sequences of positive and negative acceleration peaks, and a technique for identifying the transition between motion patterns (e.g.: standing and walking) based on frequency content.

Hardware Assembly and Troubleshooting

The VA Rehabilitation R&D Center has a part-time opening for a student or recent AA or BSEE graduate with electrical engineering skills. We need assistance in assembling, testing, and troubleshooting accelerometric motion sensors and wearable motion analysis systems used in an ongoing project investigating diagnosis and therapy of balance and mobility disorders in the elderly.

The applicant should be able to hand-solder components onto flexible and rigid circuit boards, calibrate sensor gain and offset, and isolate and repair faults in analog circuits. He/she should also be familiar with fundamentals of analog-digital conversion and C-based data processing software. Opportunity exists to become involved in next-generation all-digital system design incorporating field-programmable DSP and fuzzy logic devices.

Analysis of Assisted Gait and Balance

This student project is reported in related PAIRE-supported project, Design/development of Walking Aids, which has now been terminated and combined with the present project.

Special Purpose Accelerometry Systems

Students have assisted in the preparation of plans for an accelerometry system to simultaneously measure head and eye motion for research on vestibular disorders (with David Tomko and Geoff Bush of NASA-Ames Research Center).

Funding Source: PAIRE