trainer instrumentation system

J Biomechunics Vol. 12. pp. 543 -549, 0 Pergamon Press Ltd. 1979. Printed

1X21-9290/79/0701-0543

SO2.00,0

in Great Britain.

A GAIT ANALYZER/TRAINER INSTRUMENTATION SYSTEM*t R. H. GABEL,R. C. JOHNSTONand R. D. CROWNINSHIELD Biomechanics Laboratory, Orthopaedic Surgery Department, University of Iowa, Iowa City, Iowa, U.S.A. Abstract - A device is described which permits the collection of numerous temporal and distance factors of gait. The device, which utilizes a microprocessor and instrumented walkway, was designed to make practical the routine clinical evaluation of the gait parameters. The self-contained clinical device, which can be made portable, does not require the attachment of any apparatus to the patient.

INTRODUCI’ION

The temporal and distance factors of gait have frequently been used to describe and evaluate the ambulatory function of patients afflicted by a variety of musculoskeletal diseases (Crowninshield et al., 1978 ; Gove et al., 1975 ; Murray et al., 1975 ; Murray et al., 1964; Murray et al., 1969). Factors which have been considered important include cycle time, step and stride lengths, velocity, stance times, single limb sup port times and double limb support times. This report describes a gait analysis instrumentation system which has been developed to permit efficient routine measurement of these quantities in a clinical setting and to provide audible biofeedback for training a patient to walk symmetrically. The system employs a microprocessor and an instrumented walkway to produce all measurements in a manner that does notrequire the patient to wear, or to be connected to, any apparatus. The operator interacts with the microprocessor through a series of switches on an instrument panel. By the systematic monitoring of its own real-time clock and sensors mounted on the walkway surface, the microprocessors can detect and chronologically record the position of each foot as the patient moves along the instrumented length of the walkway. Subjects may walk on the walkway from either direction. For any given trial (walk), thirteen gait parameters (Table 1) are computed for one gait cycle from the position/time data stored in microprocessor memory. These results are immediately printed on a miniature printer. At the

* Received 14 November 1978. t This work was supported in part by Grant AM 14486 of the National Institutes of Health and gifts from the Hearst Family Foundation and the Dows Family. $ Tape Switch Corp. of America, 100 Schmitt Blvd., Farmingdale, NY 11735, U.S.A. $ IM 6100, Intersil Corp., 10900 North Tantau Ave., Cupertino, California, U.S.A.

option of the operator, the thirteen parameters can be retained in memory and used later in the computation and printing of a set of averages for several trials. A training mode is available which provides audible feedback to the subject for training symmetrical step lengths. The pitch of the audible tone is related to the step length, shorter steps having a lower frequency. The subject can learn, over several trials, to produce a gait pattern with minimal deviation of pitch in the audible tone from step to step.

METHOD The walkway consists of an array of flat linear pressure sensitive switchest (Fig. 1) which, when positioned parallel to each other, form a horizontal surface of transversely active sensing elements. The use of switches in multiples of 16 (i.e. 160, 240) are convenient owing to the 16 channel multiplexers which have been utilized (see Figs. 2 and 3). The position of a switch along the walkway is then the product of the switch number (numbered consecutively from one end of the walkway) and the interswitch interval. By addressing and monitoring each switch with a microprocessor,5 the closing of any switch during gait can be sensed. Prior to an experimental session, the subject’s height and foot length are entered into the microprocessor through thumbwheel switches. The microprocessor executes from ROM a gait analyzer program which sequentially addresses and monitors the state of closure of each switch along the walkway (Fig. 2). The switch numbers of those switches found to have changed state (i.e. closed, then opened) and the time of that state change are stored in RAM (scratchpad). The addressing of switches occurs through one gait cycle, from first heel strike to third heel strike. At the completion of the gait cycle, the operator must indicate which foot, right or or left, was first present on the walkway. The thirteen gait parameters are then calculated by the microprocessor. A limitation of the system is that each step length must exceed the subject’s foot

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R. H. GABEL,R. C. JOHNSTONand R. D. CROWNWSHIELD

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Table 1. Calculated temporal and distance factors of gait.

Units

Gait parameter

Step length - right Step length ratio - right Step length - left Step length ratio - left Stride length

cm Body height (‘A) cm Body height (%) cm

Stride length ratio Velocity Gait cycle time Stance time - right Stance time - left Single limb support time - left Single limb support time - right Double limb support time

Body height (%) cm/xx Et Gait Gait Gait Gait

cycle cycle cycle cycle cycle

time time time time time

(%) (%) (“4) (%) (“/,)

length. If the number of consecutive switches closed is in excess of the subject’s foot length, an error message is presented. Upon operator command, the thirteen computed gait parameters are displayed on the digital panel and printed on paper tape. The computed parameters are saved in RAM and are later available for the calculation of the average for any number of gait cycles. An unsuccessful gait cycle may be rejected and not included in the average. The microprocessor can also execute from ROM a gait trainer program. Individual step lengths recorded on the walkway are represented by voltages through a digital-analog converter (Fig. 4). The step lengths are then represented by frequency dependent tones through a voltage controlled oscillator. The range of the oscillator is 200-800 Hz representing step lengths of O-l m. As a subject walks on the walkways, asymmetries in step length produce pitch variations in the tone. This provides audible feedback for the patient learning to walk symmetrically.

TYPICALRESULTS

A study of gait parameters was conducted, involving normal subjects, degenerative joint disease patients and patients with total hip replacements. The data was collected outside the laboratory environment at a physician’s office, with the device being operated by secretarial personnel. The data is presented primarily as a demonstration of the usefulness of this gait analysis instrumentation. Data was collected from the group of normal and abnormal subjects in a hallway without instruction as to how or at what velocity each subject was to walk. The data from six walking cycles was averaged for each subject. One hundred and forty normal subjects, 20 in each of 7 decades of age, perform a total of 840 gait cycles. Similarly, evaluations were made on 40 preoperative total hip replacement candidates and 50 patients with total hips, l-7yr post surgery. Representative of the gait parameters measured by the device, subject walking velocity, cadence, stride length and single support times, are correlated with subject age and presented in Figs. 5-8. The velocity of gait (Fig. 5) was calculated as the distance between the first and third heel strike (stride length, Fig. 7) divided by the elapsed cycle time. A single support time is calculated for each extremity. In normaf subjects, the single support times of each extremity are quite similar; however, in abnormal subjects, the times may be considerably different. The single support times of Fig. 8 are, in the case of the normal subjects, the right extremity, and in the abnormal subjects, the side involved with disease or surgical treatment. DISCUSSION The

widespread application of quantitative evaluation of a patient’s disability, response to physical

Fig. l(b). Gait analyzer/trainer walkway 3.6 m long with 240 sensing elements.

Fig. l(a). Gait analyzer/trainer

walkway

545

3.6 m long with 240 sensing

elements

547

A gait analyzer/trainer instrumentation system

1 I I I

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I

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-J Fig. 2. Block diagram of the microprocessor controlled gait analyzer/trainer.

therapy, and progress after surgical treatment requires easily operated and accurate evaluation tools. Initial use of this device has demonstrated its usefulness in measuring gait parameters in a clinical environment. The demands on operator training, patient and operator time, and manual operator tasks are minimized.

A dependence of gait parameters on subject age is demonstrated in Figs. 5-8. The “free walking velocity” (Fig. 5) of both the normal and abnormal subjects decreases with age. This free walking velocity is perhaps a useful index of gait performance; however, it is not a precisely defined parameter. A considerable

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Fig. 3. Walkway switch scanning system.

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R. H. GABEL,R. C. JOHNSTONand R. D. CROWMNSHIELD

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Fig. 4. Audio feedback system for gait training operation.

Free Walking

Velocity

Stride

Vs. Age

0.51

Decade

I 3rd

4th

6th

5ih

7th

0th

9ih

Fig. 5. Free walking velocity of normal subjects, preoperative and l-7yr post-operative total hip patients. Brackets at each age decade represent plus and minus one standard deviation.

impact on an individual’s free walking velocity can be demonstrated. Since many other gait parameters are velocity dependent (Crowninshield et al., 1978), a consistent environment of data collection is important. The cadence ofgait (Fig. 6) is shown to be environmental

Fig. 7. Stride length, normalized to body height, of normal, pre-operative and post-operative total hip patients.

nearly constant for the normal subjects of different ages. Since walking velocity decreases with age while walking cadence remains constant, the stride length (Fig. 7) must decrease with age. The preoperative hip patients are shown to walk with generally lower velocity, lower cadence, shorter stride lengths and shorter single support times than normal subjects. The postoperative total hip patients are shown to walk in a manner similar to normal subjects of comparable age.

Single Cadence

Support

Vs. Age I

5th

6th

7th

0th

Length Vs. Age

0th

Decade

Fig. 6. Cadence of gait of normal, pre-operative and postoperative total hip patients.

Normal

7

r

Time

Vs. Age

1year+Post-OP

Decade

Fig. 8. Single support time, as a portion of cycle time, of one limb of normal subjects and the involved or surgically treated limb of abnormal subjects.

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A gait analyzer/trainer instrumentation system In another study of total hip patients (Murray et al., 19X), similar gait parameters were found to corroborate subjective evaluations of patient performance and provided objective measures of preoperative and postoperative performance. Accurate knowledge of these gait parameters can provide a valuable index of patient disability and recovery from a number of diseases affecting locomotion.

REFERENCES

Crowninshieki, R. D.,Brand, R. A. and Johnston, R. C. (1978) The effect ofvelocity on the kinematics and kinetics of gait. Clin. Orthop. Rel. Res. 132, 140-144. Gore, D. R., Murray, P. M., Sepic, S. B. and Gardner, G. M. (1975) Walking patterns of man with unilateral surgical hip fusion. J. Bone Jt Surg. (A) 57, 759-765. Murray, M. P., Brewer, B. J., Gore, D. R. and Zuege, R. C. (1975) Kinesiology after McKee-Farrar total hip replacement. J. Bone Jt Surg. (A) 57, 337-342. Murray, M. P., Drought, A. B. and Kory, R. C. (1964) Walking patterns of normal men. J. Bone Jr Surg. (A) 46, 335-360. Murray, M. P., Kory, R. C. and Clarkson, B. H. (1969) Walking patterns of healthy old men. JI. Gmnt. 24, 169-178.