Clinical observational gait analysis to evaluate improvement of balance during gait with...

4 Physiother. Res. Int. 17 (2012) 4–11 © 2011 John Wiley & Sons, Ltd.

RESEARCH ARTICLE

Clinical Observational Gait Analysis to Evaluate Improvement of Balance during Gait with Vibrotactile BiofeedbackMaurice Janssen1,7,8,*, Rianne Pas2, Jos Aarts3, Yvonne Janssen-Potten4, Hans Vles5,8, Christine Nabuurs2, Rob van Lummel6, Robert Stokroos7,8 & Herman Kingma1,2,4,7,8

1Department of Biomedical Engineering, University Hospital Maastricht, Maastricht, the Netherlands2Faculty of Biomedical Engineering, Eindhoven University of Technology, Eindhoven, the Netherlands3Instrument Development Engineering & Evaluation, University Maastricht, Maastricht, the Netherlands4Movement Laboratory, University Hospital Maastricht, Maastricht, the Netherlands5Department of Neuropediatrics, University Hospital Maastricht, Maastricht, the Netherlands6McRoberts Sensor Technology, the Hague, the Netherlands7Division of Balance Disorders, University Hospital Maastricht, Maastricht, the Netherlands8Research Institute Brain & Behaviour, University Maastricht, Maastricht, the Netherlands

Abstract

Background and Purpose. This study explores the effect of vibrotactile biofeedback on gait in 20 patients with

bilateral vestibular arefl exia using observational gait analysis to score individual balance. Methods. A tilt sensor

mounted on the head or trunk is used to detect head or body tilt and activates, via a microprocessor, 12 equally

distributed vibrators placed around the waist. Two positions of the tilt sensor were evaluated besides no biofeedback

in three different gait velocity tasks (slow/fast tandem gait, normal gait on foam) resulting in nine different random-

ized conditions. Biofeedback activated versus inactivated was compared. Twenty patients (10 males, 10 females, age

39–77 years) with a bilateral vestibular arefl exia or severe bilateral vestibular hyporefl exia, severe balance problems

and frequent falls participated in this study. Results. Signifi cant improvements in balance during gait were shown

in our patients using biofeedback and sensor on the trunk. Only two patients showed a signifi cant individual gait

improvement with the biofeedback system, but in the majority of our patients, it increased confi dence and a feeling

of balance. Conclusion. This study indicates the feasibility of vibrotactile biofeedback for vestibular rehabilitation

and to improve balance during gait. Copyright © 2011 John Wiley & Sons, Ltd.

Received 12 March 2010; Revised 19 October 2010; Accepted 30 October 2010

Keywords

biofeedback; observational gait analysis; postural balance; posture; rehabilitation; vestibulopathic gait

*Correspondence

Maurice Janssen, Department of Biomedical Engineering, University Hospital Maastricht, P.O. Box 5800, Provisorium 3.T1.026, 6202 AZ

Maastricht, the Netherlands.

Email: [email protected]

Published online 5 January 2011 in Wiley Online Library (wileyonlinelibrary.com) DOI: 10.1002/pri.504

Physiother. Res. Int. 17 (2012) 4–11 © 2011 John Wiley & Sons, Ltd. 5

M. Janssen et al. Balance Improvement with Vibrotactile Biofeedback

Introduction

The vestibular labyrinths play a key role in posture and

balance, retinal image stabilization and spatial orienta-

tion that are all affected in case of substantial vestibular

defi cits and lead to a major handicap (oscillopsia, pos-

tural imbalance) in patients with a bilateral vestibular

arefl exia. A potent aid for these patients might be an

artifi cial labyrinth to restore the feedback of linear and

angular accelerations of the head or body to the brain.

Several researchers are currently engaged with the

development of such a device. Some of them try to

improve performance in posture and balance in humans

using (non-implantable) sensory substitution — gal-

vanic vestibular stimulation (Orlov et al., 2008), audi-

tory feedback (Hegeman et al., 2005), visual feedback

(Hirvonen et al., 1997), electrotactile stimulation of the

tongue (Tyler et al., 2003) or vibrotactile feedback to

the trunk (Kentala et al., 2003). Others try to restore

image stabilization by implanting electrodes to restore

the input to the brain in animals (Lewis et al., 2002) or

in humans (Wall et al., 2007). See Janssen et al. (2010)

for a recent overview.

Vibrotactile feedback through the trunk is a very

intuitive approach and has been used as support orien-

tation for blind people (Ram and Sharf, 1998), in indus-

trial telemanipulators (Dennerlein et al., 1997) and in

virtual environments (Okamura et al., 1998). Therefore,

an ambulatory vibrotactile biofeedback (AVBF) system

to reduce body sway and increase postural stability for

patients with vestibular dysfunction was developed

(Janssen et al., 2010), based on the approach used by

Wall et al. (2001). In a placebo-controlled study, we

previously showed the AVBF system to be effective

during quiet stance in 40% of our patients with bilateral

vestibular loss (Janssen et al., 2010).

In this study, we focus on the use of the AVBF system

to increase postural stability during gait in patients with

severe bilateral vestibular losses. To our knowledge, only

two studies on the effect of biofeedback on gait have

been published (Hegeman et al., 2005; Dozza et al.,

2007). Hegeman et al. (2005) measured trunk sway

during different gait tasks using two angular velocity

transducers, while Dozza et al. (2007) measured motion

kinematics using a motion analysis system. We assess

gait performance, of patients with divers pathologies

(including spasticity and severe vestibular hypore-

fl exia), in our clinical movement laboratory with a

Sybar system (Harlaar et al., 2000) to register and inter-

pret gait and to evaluate treatment based on observa-

tion. In this paper, a description of the AVBF system

will be given, along with an evaluation of the effect

of the AVBF system on gait using observational gait

analysis.

Materials and methods

AVBF system

The AVBF system, schematically shown in Figure 1,

consists of four major components:

1. a DynaPort MiniMod (McRoberts, 5.5 mG [1 mG

≈ cm s–2] or 0.30° resolution at a sample fre-

quency of 50 Hz) drift-free sensor, small and light

weight (64 × 62 × 13 mm, 55 gram), containing

three orthogonal linear (piezo)capacitive acceler-

ometers, which can be mounted on the patient’s

head or high on the trunk;

2. an elastic belt with 12 equally distributed actuators

(ZUB.NO32.VIB, eccentric vibra-motors like

applied in Nokia 3210 at 300 Hz and an amplitude

of 0.5 mm; Jones and Sarter, 2008) around the

waist, mounted with a Velcro fastener;

3. an ATMEGA128 (Atmel) processor to translate

sensor output into activation of correct actuators

with a delay of <1 ms;

4. a LiPo battery pack (11.1 V, 3,270 mAh) to supply

power to all components, thus making the AVBF

system an ambulatory, comfortable and simple

system;

Figure 1 Schematic overview of the AVBF system. The processor

and battery pack can be detached from the upper belt and, for

example, fastened on the trousers, having the upper belt only

containing the sensor. AVBF = ambulatory vibrotactile

biofeedback

Balance Improvement with Vibrotactile Biofeedback M. Janssen et al.


The battery pack and processor unit dimensions are 12

× 7 × 3 cm, weighing 330 gram and 240 gram, respec-

tively. The battery can power the processor, actuators

and sensor for 72 hours continuously and can be

recharged within 8 hours, making sure that patients can

use the AVBF system for several days and recharge it

overnight even without the explicit need of a spare

battery.

A patient wearing the AVBF system can set a refer-

ence vector at any desired moment, simply by pressing

a button on the processor unit. Setting this reference

vector is necessary for the AVBF system to know its

sensor orientation. Subsequently, the processor calcu-

lates the vector difference between the reference vector

and the current sensor orientation. This difference is

the patient’s tilt angle (size/angle and direction) and is

translated into the activation of specifi c actuators; see

Figure 2, in order to code the amount of body tilt (tilt

angle) and the direction of body tilt (tilt direction). One

actuator is activated in the direction of a patient’s body

tilt if it exceeds a tilt magnitude of 1° (no. 1 in Figure 2

if the patient tilts forward). If the tilt angle increases in

the same direction and exceeds 2.5°, the two adjacent

actuators (no. 2 and 12 in Figure 2) are activated, and

the fi rst actuator (no. 1) is deactivated. If the tilt angle

increases and exceeds 4°; two adjacent and the middle

actuators (nos. 3, 1 and 11 in Figure 2) and the previous

actuators (nos. 2 and 12) are deactivated. Thus, the

actuator that is activated between 1° and 2.5° of tilt

indicates the tilt direction, whereas the number of actu-

ators (the intensity of tactile stimulation [one, two or

three actuators]) indicates the tilt angle. In this way, the

AVBF system can code body tilt in any direction. When

the patient correctly responds to these actuators, they

will be deactivated when the tilt angle drops below 1°

in any direction. However, if for example the patient

responds by tilting backwards and more than 1° to the

right, an actuator on the right side will be activated.

The number of activated actuators is based on the

sensor resolution and chosen to avoid sensory adapta-

tion because of continuous vibrotactile stimulation.

The activation scheme is based on our observations and

knowledge that the limit of stability in healthy subjects

is about 6° (Nashner et al., 1989) and that the typical

sway angle in healthy subjects is about 0.5° (Horlings

et al., 2008).

Patients

Twenty patients participated in this study (10 males, 10

females, age 39–77 years) to assess the effect of the

AVBF system on postural stability during gait. All

patients had severe balance problems with frequent falls

(more than fi ve times per year) and showed no responses

to caloric irrigations (30°C and 44°C) and reduced or

zero gains (≤0.2) at sinusoidal stimulation of the hori-

zontal and vertical canals on rotatory chair testing

(0.1 Hz, Vmax = 60° sec−1), pointing to a bilateral vestibu-

lar arefl exia or severe bilateral vestibular hyporefl exia.

Procedure

Each patient had 5 minutes to familiarize with the

AVBF system. Thereafter, each patient practiced with

the AVBF system for 15 minutes to learn how to use the

system and to experience the relation between trunk or

head movement and actuators. They were instructed to

improve their balance using the vibrotactile biofeed-

back information, during stance and gait, both on a

fi rm surface, with eyes open and closed.

After practicing, gait was assessed with eyes open in

challenging situations (Janssen et al., 2010) in all

patients, and performance was scored using three stan-

dardized gait velocity tasks in our clinical movement

laboratory with a 9-m-long and 1-m-wide horizontal

track using the Sybar video system:

1. slow tandem gait (one step every 2 seconds; as

described by Dozza et al., 2007);

2. fast tandem gait (more than two steps per second);

3. normal gait on 2-cm foam.

Figure 2 Activation scheme of the actuator belt worn around the

waist. The different marked actuators are activated at different tilt

angles, relative to the reference vector, when the patient moves

in the marked piece of the pie. In this case, actuator no. 1 is

activated at tilt angles >1° and <2.5°, as well as >4°



Gait was recorded in the frontal (front and back) and

sagittal plane using the Sybar video system (Harlaar

et al., 2000). An example video capture of a patient is

shown in Figure 3. All gait tasks were performed under

three different conditions:

• noAVBF; without biofeedback;

• AVBFtrunk: with biofeedback on the waist and sensor

on the trunk;

• AVBFhead: with biofeedback on the waist and sensor

on the head,

resulting in nine different tasks. Both the gait tasks and

biofeedback conditions were randomized. Gait assess-

ment took on average 40 minutes per patient.

Data analysis

Blinded as to the vibrotactile feedback condition,

balance during gait was specifi cally scored indepen-

dently by three expert observers (Y.J., H.V. and H.K.)

based on the video recordings. Per standardized gait

velocity task, the observers identifi ed the condition with

best and worst balance during gait, upon which the

three conditions were ranked on a three-point scale

(2 = best, 1 = medium, 0 = worst; Scholtes et al., 2007).

This resulted in an individual maximum score for one

of the biofeedback conditions of 6 for each gait velocity

task and a score of 18 for the three gait tasks combined.

Wilcoxon’s signed ranked test was used to determine

the effect of the AVBF system activated (AVBFtrunk and

AVBFhead) versus the AVBF system deactivated (noAVBF)

for each gait velocity task and for the three gait tasks

combined.

As Bayesian analysis allows for a direct patient-spe-

cifi c statement regarding the probability that a treat-

ment was benefi cial (Adamina et al., 2009), classical

Bayesian probability statistics was used to determine a

patient specifi c effect of the AVBF system, which was

signifi cant for a total score >16 or <2. The level of sig-

nifi cance in all tests applied was p < 0.05.

Interobserver reliability was assessed by using intra-

class correlation coeffi cients, validated for use with

multiple raters and calculated in a two-way random

model based on absolute agreement, as described by

Brunnekreef et al. (2005).

After having tested a patient, the patient was asked

in open question to comment on the functionality of

the AVBF system and its effect on balance.

Results

The individual total gait scores are shown in Table 1.

The inter-observer reliability of gait performance

scoring was 0.68 (95% confi dence interval: 0.50–0.81),

which was substantial. Patients’ balance was signifi -

cantly better in the AVBFtrunk condition than the noAVBF

condition both during normal gait (p = 0.04) and fast

tandem gait (p = 0.03). AVBFhead and noAVBF were not

signifi cantly different in these gait tasks. During slow

tandem gait, no signifi cant differences could be shown.

Over the total score, patients’ balance during gait was

signifi cantly better in both the AVBFtrunk (p = 0.01) and

AVBFhead (p = 0.03) condition than the noAVBF condi-

tion. Using Bayesian statistics to determine a patient-

specifi c effect of the AVBF system, two patients (9 and

10) demonstrated signifi cant individual improvements

of balance during gait with the AVBF system activated

as both performed worst without the AVBF system.

No gender or age relations are apparent as shown in

Table 1.

Sixteen patients (80%) commented that they felt

more confi dent regarding their postural stability using

the AVBF system, and 14 of them were very interested

to acquire a system. Balance improvement, increased

confi dence, independence, feeling more safe and the

ability to perform multiple tasks in stance or during

walking (e.g. talking and looking around) were reported.

No incidents occurred during the whole procedure.

Figure 3 An example video capture of a patient wearing the

AVBF system and the sensor on the trunk, with the sagittal camera

at the left and the frontal camera at the right. AVBF = ambulatory

vibrotactile biofeedback



Tab

le 1

. In

divi

dual

gai

t pe

rfor

man

ce s

core

s pe

r pa

tient

, so

rted

by

the

tota

l gai

t pe

rfor

man

ce s

core

with

out

biof

eedb

ack.

For

eac

h pa

tient

, to

tal g

ait

perf

orm

ance

(th

e th

ree

gait

task

s co

mbi

ned)

an

d pe

rfor

man

ce p

er g

ait

velo

city

tas

k is

sho

wn

Pati

ent

Age

Gen

der

Tota

l gai

t pe

rfor

man

ce s

core

sSl

ow t

ande

m g

ait

Fast

tan

dem

gai

tN

orm

al g

ait

on f

oam

noA

VB

FAV

BF t

run

kAV

BF h

ead

noA

VB

FAV

BF t

run

kAV

BF h

ead

noA

VB

FAV

BF t

run

kAV

BF h

ead

noA

VB

FAV

BF t

run

kAV

BF h

ead

956

F0

189

06

30

63

06

3

1054

F1

1610

16

20

45

06

3

352

M2

1213

04

52

43

04

5

1258

F2

1213

03

62

52

04

5

1556

M2

11.5

13.5

23

40

36

05.

53.

5

148

M4

149

24

30

63

24

3

556

M4

1310

14

42

61

13

5

753

F5

139

23

43

60

04

5

1441

F6.

511

8.5

0.5

62.

53

33

33

3

1962

F7

146

25

20

63

53

1

1738

F7

119

42

33

33

06

3

1150

M8

136

06

36

12

26

1

440

M8

109

60

30

63

24

3

665

F8

712

21

60

36

63

0

1639

M9

108

42

31

53

43

2

248

M9

99

51

33

33

15

3

1858

M10

89

33

33

33

42

3

1377

M10

710

33

34

14

33

3

2046

F11

9.5

6.5

53

12

43

42.

52.

5

858

F16

29

51

35

13

60

3

Tota

l12

9.5

222

(0.0

1)18

8.5

(0.0

3)47

.5

66 (

>0.0

5)66

.5 (

>0.0

5)39

79

(0.

03)

62 (

>0.0

5)43

77

(0.

04)

60 (

>0.0

5)

Th

e gr

een

cel

ls i

ndi

cate

th

e si

gnifi

can

t pa

tien

t-sp

ecifi

c e

ffec

ts a

s de

term

ined

by

clas

sica

l B

ayes

ian

pro

babi

lity

stat

isti

cs, v

alu

es b

etw

een

bra

cket

s in

dica

te t

he

p-va

lues

as

dete

rmin

ed b

y W

ilcox

on’s

sig

ned

ran

ked

test

bet

wee

n t

he

AVB

F sy

stem

act

ivat

ed (

AVB

F tru

nk

and

AVB

F hea

d) v

ersu

s th

e AV

BF

syst

em d

eact

ivat

ed.

AVB

F tru

nk

= AV

BF

syst

em a

ctiv

ated

wit

h b

iofe

edba

ck o

n t

he

wai

st a

nd

sen

sor

on t

he

tru

nk;

AV

BF h

ead

= AV

BF

syst

em a

ctiv

ated

wit

h b

iofe

edba

ck o

n t

he

wai

st a

nd

sen

sor

on t

he

hea

d; n

oAV

BF

= th

e AV

BF

syst

em

deac

tiva

ted;

F =

fem

ale;

M =

mal

e.



During a follow-up consultation, some patients men-

tioned that the use of the AVBF system even had

improved their balance for several hours after the

system had been removed.

Discussion

Vibrotactile biofeedback system outcome

We used video recordings from the Sybar video system

and scores from three expert observers to determine

performance of balance during gait with and without

vibrotactile biofeedback in 20 patients with a bilateral

vestibular arefl exia. Both during normal gait and fast

tandem gait, the patients’ balance was signifi cantly

better with biofeedback of the AVBF system on the

waist and sensor on the trunk compared with no bio-

feedback. Additionally, using observational gait analysis

as a means to score gait performance, we were able to

identify signifi cant individual improvements of balance

during gait in two patients with the AVBF system

activated.

These improvements are in line with work of Dozza

and colleagues. They showed in patients with unilateral

vestibular loss that stability during slow tandem gait

improved using vibrotactile biofeedback (Dozza et al.,

2007). They also showed in their cross-over design that

stability improved with repetition of tandem gait trials,

thus indicating a learning effect of trial repetition, but

that performance was consistently better in the trials

with biofeedback than without biofeedback. In our

study, we controlled for a possible learning effect by

randomizing the biofeedback conditions and gait veloc-

ities; thus, the signifi cant improvements in our patients

can be attributed to effects of biofeedback. However, as

we did not perform a placebo-controlled study (Janssen

et al., 2010), the effects might also be because of the

patient’s belief (Yardley et al., 2001) or increased alert-

ness (Hegeman et al., 2005; Dozza et al., 2007; Basta

et al., 2008;).

In contrast to Dozza et al. (2007), we were not able

to show signifi cant improvements in balance during

slow tandem gait. This might be because of the task

(slow tandem gait) being too diffi cult for bilateral ves-

tibular arefl exia patients to show balance improvements

using vibrotactile biofeedback with limited practice

time. Additionally, Dozza et al. have shown a biofeed-

back effect in their patients with unilateral vestibular

loss using a gait task with eyes closed, whereas our

patients performed the gait tasks with eyes open. We

expect an increased gait performance with eyes closed

as well in our gait tasks, because patients will probably

use a biofeedback system more in such a challenging

situation. However, more training with the AVBF system

is then probably needed.

Hegeman et al. (2005) found only little improvement

in a group of patients with bilateral vestibular arefl exia

performing several gait tasks using auditory biofeed-

back, but their group may not have been a real at risk

group in contrast to our (frequent falls), because none

of their subjects had recently suffered a fall. Moreover,

our results are in line with work of others showing that

vestibular impaired patients are more stable using bio-

feedback in stance (Kentala et al., 2003; Tyler et al.,

2003; Danilov, 2004; Dozza et al., 2005b; Hegeman

et al., 2005; Danilov et al., 2006, 2007; Ernst et al., 2007;

Basta et al., 2008; Goebel et al., 2009).

Sensor location

Balance improvements during stance have been shown

using a sensor on the trunk (Kentala et al., 2003; Dozza

et al., 2004; Hegeman et al., 2005; Dozza et al., 2005a;

Dozza et al., 2005b; Dozza et al., 2007; Ernst et al., 2007;

Basta et al., 2008) as well as on the head (Wall et al.,

2001; Tyler et al., 2003; Danilov, 2004; Danilov et al.,

2006, 2007; Orlov et al., 2008; Goebel et al., 2009). We

know of only one study about optimal sensor location

in biofeedback (Janssen et al., 2010), which seems to be

the head, but which also showed that the placebo effect

of biofeedback might be substantial. The current study

appears to indicate that the trunk seems to be the

optimal location of the sensor, although not on an indi-

vidual basis. So the optimal sensor location in biofeed-

back is yet to be examined in future studies and might

even be individually determined.

Implications

Although signifi cant individual gait improvements

were only shown in a couple of our patients, vibrotactile

biofeedback increased confi dence, independence and a

feeling of balance and safety in the majority of our

patients, as was shown by Kentala et al. (2003) as well.

Some patients even mentioned that the use of the vibro-

tactile biofeedback system had improved their balance

for several hours after the device had been removed.

This indicates the feasibility of the AVBF system to

improve balance during gait, and that the brain is able



to include vibrotactile biofeedback in its predictive

behaviour to avoid falls.

Some critical remarks after evaluating our results

obtained so far and exploring the literature:

1. Improvement of balance by biofeedback is shown

in the minority of patients with balance problems

(Ernst et al., 2007; Janssen et al., 2010). The impact

of biofeedback might vary among patients, fi rst of

all because of differences in the severity of the ves-

tibular defi cit and its effect on balance during gait

and second because of the dependence on vestibu-

lar input for balance during gait compared with the

other senses.

2. Training to optimize use of biofeedback seems to

be essential (Danilov et al., 2006, 2007; Dozza et al.,

2007; Ernst et al., 2007; Basta et al., 2008).

3. Adaptation effects do occur and reduce the impact

of biofeedback in time during use (Ernst et al.,

2007) but also prolong the impact after use

(Danilov, 2004).

4. The placebo effect might be substantial (Dozza

et al., 2007; Janssen et al., 2010).

In future studies, it needs to be examined if patient

performance in daily life or quality of life indeed

increases using biofeedback. No doubt, it will be benefi -

cial for training, rehabilitation and sensory substitu-

tion; because biofeedback is a rewarding approach as it

gives a positive feeling if no feedback has been given

during a task and motivates a patient to be more active

and train challenging tasks.

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