Research Report
Sensory-Specific Balance Training in
Older Adults: Effect on Proprioceptive
Reintegration and Cognitive Demands
Kelly P Westlake, Elsie G Culham
KP Westlake, PT, PhD, MSc, is
Post-Doctoral Fellow, Rehabilitation Research and Development
Center, VA Palo Alto HCC, 3801
Miranda Ave, Palo Alto, CA 94304
(USA). Address all correspondence
to Dr Westlake at: westlake@rrd.
stanford.edu.
EG Culham, PT, PhD, is Professor
and Director, School of Rehabilitation Therapy, Queen’s University,
Kingston, Ontario, Canada.
[Westlake KP, Culham EG.
Sensory-specific balance training
in older adults: effect on proprioceptive reintegration and cognitive
demands.
Phys
Ther.
2007;87:1274 –1283.]
© 2007 American Physical Therapy
Association
Background and Purpose
Age-related changes in the ability to adjust to alterations in sensory information
contribute to impaired postural stability. The purpose of this randomized controlled
trial was to investigate the effect of sensory-specific balance training on proprioceptive reintegration.
Subjects
The subjects of this study were 36 older participants who were healthy.
Methods
Participants were randomly assigned to a balance exercise group (n⫽17) or a falls
prevention education group (n⫽19). The primary outcome measure was the centerof-pressure (COP) velocity change score. This score represented the difference
between COP velocity over 45 seconds of quiet standing and each of six 5-second
intervals following proprioceptive perturbation through vibration with or without a
secondary cognitive task. Clinical outcome measures included the Fullerton Advanced Balance (FAB) Scale and the Activities-specific Balance Confidence (ABC)
Scale. Assessments were conducted at baseline, postintervention, and at an 8-week
follow-up.
Results
Following the exercise intervention, there was less destabilization within the first 5
seconds following vibration with or without a secondary task than there was at
baseline or in the falls prevention education group. These training effects were not
maintained at the 8-week follow-up. Postintervention improvements also were seen
on the FAB Scale and were maintained at follow-up. No changes in ABC Scale scores
were identified in the balance exercise group, but ABC Scale scores indicated
reduced balance confidence in the falls prevention education group postintervention.
Discussion and Conclusion
The results of this study support short-term enhanced postural responses to proprioceptive reintegration following a sensory-specific balance exercise program.
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October 2007
Balance Training in Older Adults
P
ostural control depends on the
ability to extract peripheral sensory inputs, integrate this information within the central nervous
system (CNS), and coordinate and
execute an appropriate motor response. Proprioception is an essential component of this sequence of
events, providing orientation information about passive and active
movements and positions of the
joints as well as the force resulting
from muscular contractions. Agerelated changes in the ability to assess the contribution of proprioceptive inputs relative to those of other
sensory inputs become evident under conditions in which the proprioceptive inputs are distorted or distorted and then suddenly restored.1
Whereas young adults who are
healthy are able to restore balance
quickly by taking advantage of sensory redundancy and centrally reweighing available information,2– 4
older adults do not as readily interpret misleading cues or recognize
and reintegrate accurate proprioceptive information and therefore can
experience postural instability.3,5
These effects are particularly evident
when attentional resources are
divided.3,6 – 8
Given that the sensory inputs related
to various environmental conditions
are constantly changing,9 the ability
to adjust instantly to a change in sensory information is central to the reduction of fall risk in older adults.10
To date, there have been no reports
of training interventions designed to
enhance the ability of older adults to
use proprioceptive information in
balance control. The successful identification of training effects necessarily involves a randomized controlled
trial with an exercise intervention
designed to induce specific changes
in the recognition and effective use
of sensory information. Findings that
sensory-specific balance exercises,
such as training on unsteady support
surfaces with transitions between
October 2007
sensory environments, result in increased postural stability compared
with the effects of nonspecific activity interventions, such as running or
strength training, lend support to
this theory.11–13
One method used to evaluate the
contribution of proprioceptive inputs to postural control and the integrity of the integrative mechanisms
within the CNS is to measure
changes in postural sway during or
following vibration applied over the
muscle belly or tendon.14 This technique directly targets the primary
muscle afferents contributing to proprioception and may effectively reflect a perturbation of this system.
Muscle vibration evokes a sensation
of movement in a direction that normally would cause elongation of the
vibrated muscle. Accordingly, vibration of antagonistic muscle groups
results in immediate disruption of
the proprioceptive system.3 Postural
responses to such a perturbation
then can be assessed in a quiet standing position by recording center-ofpressure (COP) outcomes on a force
platform.3,15 This position effectively
reduces confounding variables, such
as muscle activation, torque generation, and biomechanical changes,
that are present during more dynamic tasks. Such variables inevitably would become a source of accurate proprioceptive information that
could override the controlled effect
of proprioceptive perturbation at the
ankle joints. Because the present
study represents one of the earliest
reports on the ability to train sensory
integration immediately following vibration perturbation, the quiet standing protocol was considered advantageous as a means to isolate changes
in this ability.
Thus, the primary hypothesis of the
present study was that older adults,
having completed a sensory-specific
exercise program, would demonVolume 87
strate reduced postural destabilization and earlier restabilization immediately following the termination of
proprioceptive perturbation through
vibration in comparison with preexercise outcomes or with the outcomes in a falls prevention education group. These effects were
postulated to improve during a concomitant cognitive task. The secondary hypothesis was that the enhanced postural stability would be
reflected in superior scores on a balance performance scale and a
balance confidence questionnaire.
Method
Study Participants and
Study Design
Participants were volunteers over 65
years of age who were healthy and
recruited through advertisements
and flyers in the community. Exclusion criteria were pre-existing major
lower-extremity pathology (eg,
chronic ankle instability or severe
osteoarthritis), neurological disorders or balance difficulties (eg, vertigo, poor vision, dizziness, stroke,
or epilepsy) that would prevent
standing for the duration of the testing procedures without the aid of an
assistive device, and health conditions (eg, heart disease, uncontrolled
hypertension, chronic obstructive
pulmonary disease, or osteoporosis)
that would preclude participation in
a balance exercise program.
A brief clinical examination was used
to screen for symptoms of peripheral
neuropathy, which are considered a
risk factor for falls.16 This examination identified the presence, diminution, or absence of sensation to light
touch on the dorsal and plantar aspects of the foot, the Achilles tendon
reflex, and position sensation of the
big toe. Subjects demonstrating the
absence or diminution of one or
more of these characteristics were
excluded from participation. Physician approval was required before
the subjects were allowed to particNumber 10
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Balance Training in Older Adults
together position. Progressions to
these tasks included simultaneous
alterations of visual and vestibular
inputs. To alter visual cues, participants were instructed to close their
eyes, to engage vision with a reading
or tracking secondary task, or to perform balance tasks with a distracting
background, such as a checked pattern or moving people. To modify
vestibular cues, participants were instructed to tilt their head backward
or to quickly move their head side to
side and up and down.
Figure 1.
Experimental setup of the vibrators at the Achilles and tibialis anterior tendons. Participants stood as steadily as possible with arms alongside the body, heels positioned
according to height, and forefeet splayed to a comfortable stance.
ipate in the exercise program. All
subjects gave written informed consent prior to data collection.
In this single-blind, randomized controlled trial, participants were assigned to an exercise group or a falls
prevention education group. Both
groups were assessed at baseline
and within 1 week postintervention.
Follow-up testing was done for the
exercise group only at 8 weeks
postintervention.
Of the 64 older adults who responded to study advertisements, 44
met study criteria and were randomized into the exercise or education
group. Eight participants dropped
out of the study for reasons such as
time commitment issues, lack of
transportation, language barrier, and
disinterest. By the end of the 8-week
interventions, 17 and 19 participants
remained in the exercise and education programs, respectively. The
mean numbers of all visits attended
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Volume 87
by participants in the exercise group
and the education group were 21.5
(89.9%) and 5.4 (66.3%), respectively. The 36 participants who completed the exercise (n⫽17) and
education (n⫽19) interventions returned for postintervention testing.
By the 8-week follow-up, conducted
only with the exercise group, 15 participants returned for testing.
Sensory-specific balance classes
were held 3 times per week, for 1
hour each session, over an 8-week
period. The exercise protocol followed the FallProof Program,17
which emphasizes static and dynamic balance exercises with transitions between different sensory conditions. Activities were designed to
optimize and force use of the somatosensory system. Tasks included
standing or walking on various support surfaces, such as a rocker board,
foam, or narrow beam, and standing
in a tandem position, a semitandem
position, on one leg, or in a feet-
Number 10
Measurement of Central
Integration and Attentional
Capacity
The mean COP velocity for the total
COP path length was measured on a
force platform* as an estimate of the
frequency of postural corrections.
Of the COP stability parameters,
COP velocity generally is considered
to be most useful in identifying agerelated changes and fall risk.18 –20
The mean velocity also demonstrated the highest sensitivity to the
effects of vibration on posturographic measurements21 and had the
smallest reproducibility error (intraindividual standardized coefficient of
variation of 14) over a 1-week
period.20
Data were sampled at 200 Hz and
smoothed with a fourth-order
double-pass Butterworth filter with a
cutoff frequency of 10 Hz. Proprioceptive input was perturbed by use
of 4 vibrators oscillating at 80 Hz, 1
mm in amplitude,2,22 and secured at
both ankles with 3-cm-wide elastic
bands (Fig. 1).
The COP velocity was measured for
each of the 45-second postural conditions shown in Table 1, completed
as one set in a random order, followed by 3 minutes of seated rest.
* Biodex Medical Systems Inc, 20 Ramsay Rd,
Shirley, NY 11967.
October 2007
Balance Training in Older Adults
Three sets were performed, and the
average of 3 trials was recorded for
each condition. Conditions 3 and 4
included 5 seconds of stable standing followed by 10 seconds of vibration activation3,21 and then 30 seconds of deactivation. The initial 5
seconds was used so that participants could become acclimated to
standing on the force platform prior
to the onset of vibration. The third,
30-second interval was used because
previous work had indicated that 10
seconds was insufficient for complete recovery of postural stability in
the absence of vision in either a
young or an older population.3 The
COP velocity was analyzed over
5-second intervals from the moment
the vibration was turned off, at 15.05
to 20 seconds (time 1), 20.05 to 25
seconds (time 2), 25.05 to 30 seconds (time 3), 30.05 to 35 seconds
(time 4), 35.05 to 40 seconds (time
5), and 40.05 to 45 seconds (time 6).
For the secondary task in conditions
2 and 4, participants counted backward by 3 from a random 3-digit
number as quickly and accurately as
possible throughout the 45-second
trials.7
Clinical Measures
The Fullerton Advanced Balance
(FAB) Scale was used to measure
functional limitations associated
with 10 high-level balance tasks incorporating tests that challenge sensory integration.23 The FAB Scale
included modified clinical tests for
sensory integration in balance: walking with head turns, Functional
Reach Test, 360-degree turn, tandem
walking, one-leg stance, 2-foot jump,
step up and over, and reactive postural control. Scores ranged from 0
(unable) to 4, with a maximum score
of 40. Psychometric testing of this
scale indicated good convergent validity compared with the Berg Balance Scale (␳⫽.75) and demonstrated high test-retest (␳⫽.96),
intrarater (␳⫽.97–1.00), and interrater (␳⫽.94 –.97) reliability.23 The
October 2007
Table 1.
Postural Conditions Used to Evaluate Proprioceptive Reintegration With or Without a
Secondary Task
a
Testing
Conditiona
Description
1
Quiet standing, eyes closed
2
Quiet standing, eyes closed, secondary task
3
Quiet standing, eyes closed, vibration
4
Quiet standing, eyes closed, vibration, secondary task
The duration of each condition was 45 seconds.
responsiveness of the FAB Scale following an exercise intervention had
not yet been established.
The Activities-specific Balance Confidence (ABC) Scale was used to assess
participants’ level of balance confidence in performing particular
tasks.24 Confidence in performing
each task was rated on a scale of 0
(no confidence) to 10. The ABC
Scale showed excellent internal consistency (Cronbach alpha⫽.96), testretest reliability (r⫽.92), and validity
for
community-dwelling
older
people.24,25
The Physical Activity Scale for the
Elderly (PASE) was used to determine group equivalences in activity
levels outside of the treatment intervention. Scores ranged from 0 to
greater than 400, depending on subjects’ reported activity intensities
and frequencies over 7 days. The
PASE showed good test-retest reliability (r⫽.75) and validity for older
subjects who were healthy.26,27
The concentric isokinetic strength of
the hip, knee, and ankle flexor and
extensor muscles of the dominant
leg was assessed by use of an isokinetic dynamometer (AMTI Multiaxis
Force Platforms, model OR 6-7)† set
at a velocity of 60°/s. These measurements were taken in consideration of
the potentially confounding influ†
Advanced Medical Technologies Inc, 176
Waltham St, Watertown, MA 02172.
Volume 87
ence of strength (force-generating
capacity) between and within
groups. Following one practice trial,
an average of the best 3 of 5 peak
torque values normalized to body
weight was recorded.
Data Analysis
The effects of the interventions on
the ability of older adults to regain
postural stability with or without a
secondary task were assessed by use
of a group ⫻ time interval ⫻ visit
(2 ⫻ 6 ⫻ 2) analysis of variance
(ANOVA) for repeated measures on
the last 2 factors. The dependent
variable was COP change scores, obtained by subtracting COP velocity
averaged over 3 trials for each time
interval of conditions 3 and 4 from
the average COP velocity in the three
45-second trials in conditions 1 and
2, respectively. The equivalences of
COP velocity across the six 5-second
intervals and over the entire 45second time interval during condition 1 were verified by use of data
from 10 randomly selected participants (F⫽0.37; df⫽6,54; P⫽.76).
Changes in strength and clinical measures were determined by use of a
group ⫻ visit (2 ⫻ 2) repeatedmeasures ANOVA for continuous
variables or a Friedman test for categorical variables.
The outcomes for the exercise group
at the 8-week follow-up were compared with the outcomes at baseline
and postintervention by use of a
Number 10
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Balance Training in Older Adults
COP Velocity Change (cm/s)
A
COP Velocity Change (cm/s)
B
4.0
3.5
3.0
2.5
2.0
1.5
1.0
0.5
0.0
-0.5
-1.0
4.0
3.5
3.0
2.5
2.0
1.5
1.0
0.5
0.0
-0.5
-1.0
Exercise Group
*
Education Group
*
1
2
3
4
Time Interval
5
6
Exercise Group
Education Group
*
*
1
2
3
4
Time Interval
5
6
Figure 2.
Change in center-of-pressure (COP) outcomes following vibration in exercise and
education groups postintervention (X⫾SD). (A) COP sway velocity change score following vibration perturbation. (B) COP sway velocity change score following vibration
perturbation and while performing a secondary task. *Significant difference between
groups (P⬍.044).
repeated-measures ANOVA or a
Friedman test with visit as the
within-subject factor. Significant interaction effects (P⬍.05) were analyzed with Bonferroni-adjusted post
hoc tests. Statistical procedures were
performed with SPSS, version 11.5.‡
‡
SPSS Inc, 233 S Wacker Dr, Chicago, IL
60606.
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Results
Proprioceptive Reintegration
Quiet standing with vibration
(condition 3). The first objective
of this study was to examine postural
recovery following vibratory perturbation without a secondary task. A
visit ⫻ time ⫻ group interaction was
identified
(F⫽3.82;
df⫽5,170;
P⫽.019). Group differences were
found only during time interval 1
(F⫽4.36; df⫽1,35; P⫽.044), with
Number 10
less destabilization occurring in the
exercise group (change score
[X⫾SD], 1.31⫾0.91 cm/s) than in
the education group (2.00⫾1.05
cm/s) postintervention (Fig. 2A).
Separate analysis of the exercise
group revealed a visit ⫻ time interaction (F⫽8.62; df⫽5,80; P⬍.001),
indicating training effects on both
the time to restabilize and the
amount of destabilization (Fig. 3A).
Change scores began to stabilize during time interval 4 at baseline and
during earlier time interval 3 postintervention. A reduction in the extent
of destabilization was indicated by a
significant decrease in change scores
from baseline to postintervention
during time interval 1 (2.23⫾1.18
versus 1.31⫾0.91 cm/s) (P⫽.002),
with a trend toward significance during time interval 2 (0.72⫾0.76 versus
0.43⫾0.52 cm/s) (P⫽.081). Analysis
of the education group revealed a
nonsignificant visit ⫻ time interaction (F⫽0.42; df⫽5,90; P⫽.70), indicating no change in the ability to
stabilize following vibration.
The COP change scores for the exercise group were different postintervention (1.31⫾0.91 cm/s) and at
the 8-week follow-up (2.11⫾1.50
cm/s) during time interval 1
(P⫽.029), suggesting that postintervention improvements were not
maintained. No differences were
identified between baseline (2.29⫾
1.19 cm/s) and the 8-week follow-up
(P⫽1.00).
Quiet standing with vibration
and secondary task (condition 4).
The second objective of this study
was to examine postural stability following vibratory perturbation during
secondary task performance. One
outlier in the education group was
identified as having a mean change
score greater than 3 standard deviations above the group mean and was
excluded from subsequent analysis.
A visit ⫻ time ⫻ group interaction
October 2007
Balance Training in Older Adults
The inclusion of the 8-week
follow-up change scores for the exercise group revealed a visit ⫻ time
interaction (F⫽2.93; df⫽10,140;
P⫽.012), with higher change scores
at the 8-week follow-up (2.05⫾
1.47 cm/s) than postintervention
(1.14⫾0.61 cm/s) during time interval 1 (P⫽.023). These results further
support the fact that improvements
in the ability to stabilize after the
exercise intervention were not
maintained.
The response accuracy and speed of
performance of the secondary task
are shown in Table 2. No differences
were identified between groups, nor
was there a group ⫻ visit interaction.
October 2007
COP Velocity Change (cm/s)
Analysis of group differences for
each time interval across baseline
and postintervention visits indicated
a difference in the extent of destabilization during time interval 1
(F⫽4.90; df⫽1,34; P⫽.034) postintervention, with lower mean
change scores in the exercise group
(1.12⫾0.58 cm/s) than in the education group (1.71⫾0.85 cm/s)
(Fig. 2B). Separate analysis of the exercise group revealed a visit ⫻ time
interaction
(F⫽5.76;
df⫽5,80;
P⫽.001) (Fig. 3B). No improvements
in the time to stabilize were noted.
Further analysis of change scores between baseline and postintervention
as a function of each time interval
revealed a difference during time interval 1 (P⫽.002). This finding confirmed that there was less destabilization during the 5 seconds
immediately following vibration as a
result of the exercise intervention.
Analysis of the education group revealed a nonsignificant visit ⫻ time
interaction
(F⫽1.27;
df⫽5,85;
P⫽.30).
A
B
COP Velocity Change (cm/s)
was revealed (F⫽3.13; df⫽5,165;
P⫽.018).
4.0
3.5
3.0
2.5
2.0
1.5
1.0
0.5
0.0
-0.5
-1.0
4.0
3.5
3.0
2.5
2.0
1.5
1.0
0.5
0.0
-0.5
-1.0
*†
Baseline
Postintervention
†
†
†
*‡
‡
1
2
‡
3
4
Time Interval
5
6
Baseline
Postintervention
*†
†
†
*‡
1
‡
‡
2
3
4
Time Interval
5
6
Figure 3.
Change in center-of-pressure (COP) outcomes following vibration at baseline and
postintervention in exercise group (X⫾SD). (A) COP velocity change scores following
vibration perturbation. (B) COP velocity change scores following vibration perturbation
and while performing a secondary task. *Significant difference between baseline and
postintervention (P⬍.006). †Significant difference between baseline time intervals
(P⬍.025). ‡Significant difference between postintervention time intervals (P⬍.001).
Clinical Measures
Means and standard deviations for
clinical measures are shown in Table
3. In terms of the FAB Scale, the
Friedman test revealed differences
between visits in the exercise group
(␹2⫽16, P⬍.001). Post hoc analysis
revealed differences between baseline and postintervention total
scores (P⫽.001) and between baseline and 8-week follow-up total
scores (P⫽.001), suggesting that the
improvements in functional balance
Volume 87
postintervention and at follow-up
were maintained. Specific details regarding changes in the mean and
standard deviation of each FAB Scale
item are shown in Table 4. Post hoc
analysis revealed differences between baseline and postintervention
for items 6 (one-leg stance), 7 (standing on foam), and 9 (walking with
head turns) and differences between
baseline and the 8-week follow-up
for item 9 (Bonferroni-adjusted P
value of ⬍.025).
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Balance Training in Older Adults
Table 2.
Accuracy and Speed of Backward Counting by 3 During Condition 4a
Parameter
XⴞSD for the Following Group:
Baseline
a
Postintervention
8-wk
Follow-up
Exercise
Education
Exercise
Education
Exercise
Accuracy (no. of correct responses/total no. of
responses)
0.94⫾0.093
0.96⫾0.035
0.95⫾0.06
0.97⫾0.05
0.94⫾0.06
Speed (no. of responses/s)
0.41⫾0.13
0.44⫾0.16
0.47⫾0.16
0.47⫾0.15
0.43⫾0.19
Condition 4⫽quiet standing, eyes closed, vibration, secondary task.
group ⫻ visit interaction (P⫽.44)
were identified, thereby supporting
group equivalences at baseline and
postintervention.
Regarding the PASE scores, no differences were identified between
groups or visits at baseline or postintervention; significantly lower scores
were found in the exercise group at
the 8-week follow-up than postintervention (P⫽.003). Interestingly, a
Pearson correlation analysis between
PASE scores and time interval 1 for
conditions 3 and 4 revealed no relationships (r⫽⫺.16, P⫽.13, and r⫽
⫺.06, P⫽.57).
Discussion
The results of the present study appear to support the original hypothesis that the ability of older adults
to reintegrate proprioceptive inputs
is augmented following sensoryspecific training, and this effect is
not likely to be attributable to an
increase in lower-extremity strength
or activity level. Although a few studies reported training effects on postural stability when proprioceptive
input was reduced,28,29 an improved
ability of older adults to recognize
and use the restoration of accurate
proprioceptive information had not
previously been documented.
For the ABC Scale questionnaire, a
group ⫻ visit interaction was identified (F⫽4.27; df⫽1,34; P⫽.047),
with a lower balance confidence
score postintervention than at baseline only for the education group
(F⫽4.56; df⫽1,18; P⫽.047).
In terms of strength at the hip, knee,
and ankle, no main effect of group
(P⫽.66) or visit (P⫽.072) and no
Although it may be argued that enhanced signals arising at the level of
the proprioceptive receptors may
account for the postural improvements, we recently demonstrated
that this mechanism is not likely to
be the substrate for change.30 With
only 1 of 3 proprioceptive measures
indicating improvements with training in our previous work, it was difficult to ascribe a training effect at
the peripheral level. However, without sufficient physiological evidence
from receptor isolation techniques,
such as microneurography,14 the
possibility of an increase in the discharge of these receptors cannot be
discounted.
A more probable explanation for
these results is an increase during
the training intervention in the attention allocated to proprioceptive cues
(explicit learning), which eventually
Table 3.
Clinical Measures for Exercise and Education Groups at Baseline, Postintervention, and 8-Week Follow-up
Clinical Measurea
XⴞSD Score for the Following Group:
Baseline
Exercise
FAB Scale
PASE
ABC Scale
b,c
Postintervention
Education
Exercise
b
8-wk
Follow-up
Education
Exercise
35⫾5c
31⫾5
32⫾8
35⫾4
33⫾8
102.4⫾45.0
99.1⫾44.0
127.3⫾57.6d
101.6⫾51.4
84.8⫾9.3
87.5⫾10.7e
85.7⫾9.5
79.1⫾24.2e
79.5⫾24.9d
85.0⫾9.7
a
ABC⫽Activities-specific Balance Confidence, FAB⫽Fullerton Advanced Balance, PASE⫽Physical Activity Scale for the Elderly.
Significant difference between baseline and postintervention FAB Scale scores (P⬍.001).
Significant difference between baseline and 8-week follow-up FAB Scale scores (P⫽.02).
d
Significant difference between postintervention and 8-week follow-up PASE scores for exercise group (P⫽.003).
e
Significant difference between baseline and postintervention ABC Scale scores for education group (P⫽.047).
b
c
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Balance Training in Older Adults
Table 4.
Mean (⫾SD) and Friedman Mean Rank for Scores on the Fullerton Advanced Balance (FAB) Scale for the Exercise Group
FAB Scale Item
Baseline Group
XⴞSD
XⴞSD
Mean
Rank
Mean
Rank
1.9
4⫾0
2.0
4⫾0
2.0
.39
2. Forward reach
4⫾1
1.9
4⫾0
2.1
4⫾1
1.9
.26
3. 360° turn
3⫾1
1.8
3⫾1
1.9
4⫾1
2.3
.05
4. Step up and over
4⫾0
1.9
4⫾0
2.0
4⫾0
2.0
.37
5. Tandem walk
3⫾1
1.8
4⫾1
2.3
a
3⫾1
1.9
.14
a
6. One-leg stance
3⫾1
1.6
3⫾1
2.2
3⫾1
2.2
.02b
7. Stand on foam, eyes closed
3⫾1
1.7a
4⫾0
2.2a
4⫾0
2.0
.02b
8. 2-foot jump
3⫾1
1.8
3⫾1
2.1
3⫾1
2.1
.35
Total score
c
XⴞSD
P
4⫾0
10. Reactive postural control
b
8-Week Followup Group
1. Stand with feet together, eyes closed
9. Walk with head turns
a
Mean
Rank
Postintervention
Group
a,c
2⫾1
1.5
2⫾1
1.6
31⫾5
1.2a,c
3⫾1
a
2.3
3⫾1
c
2.2
.01b
3⫾1
2.2
3⫾1
2.2
.12
35⫾4
2.5a
35⫾5
2.3c
⬍.001b
Significant difference between baseline and postintervention scores (P⬍.025).
Significant difference between testing sessions (P⬍.05).
Significant difference between baseline and 8-week follow-up scores (P⬍.025).
led to a less attentionally demanding
recovery of postural stability (implicit learning).31 Improvements in
postural control in the exercise
group without evidence of reductions in the accuracy or speed of the
counting task support this theory. As
the accuracy of peripheral input declines with age, attentional resources
become more focused on the control
of posture.1 Thus, the introduction
of a sufficiently challenging secondary task or postural condition often
results in reduced task performance
or instability.6,32 Because the specific
instructions provided to participants
in the present study were to maintain focus on the secondary task, evidence that stability was increased
suggests an implicit learning effect.
Our previous finding that a velocity
discrimination test was the only proprioceptive outcome to improve
with exercise also suggests enhanced central mechanisms.30 This
test required subjects to identify the
faster of 2 presented velocities until
the smallest velocity difference was
October 2007
identified correctly. Thus, a greater
extent of cognitive resources was
necessary for this test than for other
proprioceptive measures, meaning
that the possibility of improved attention cannot be ruled out. Besides
the possible influence of attention in
recognizing and selecting proprioceptive information, it also has been
suggested that attention is involved
in sensory integration under conditions of sensory conflict.33
One surprising outcome was the decrease in COP velocity change scores
(ie, reduced destabilization) during
secondary task performance relative
to the results obtained in the nosecondary-task condition (Fig. 2). Although the difference was not significant, it was evident in both the
exercise and the education groups.
In contrast, previous studies6,33,34
demonstrated a destabilizing rather
than a stabilizing effect with the addition of a secondary task. These
conflicting results may be reconciled
by a recent study demonstrating that
Volume 87
postural stability improved or declined relative to baseline performance depending on the cognitive
demands of the secondary task.32
Perhaps the task of counting backward by 3, used in the present study,
did not represent a sufficiently challenging cognitive task to tax attentional resources effectively. Nevertheless, the finding that the extent of
destabilization was reduced postintervention with or without a secondary task suggests that either a shift in
attention or increased attentional capacity is possible. A follow-up training study involving a more cognitively demanding secondary task
under conditions of sensory conflict
may bring further clarity to this
discussion.
Several authors3,4,35 have proposed
that the explanation for impaired
postural responses in older adults
lies in age-related changes in central
integration mechanisms. During the
exercise intervention in the present
study, sensory inputs were manipulated by altering the support surface
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Physical Therapy f
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Balance Training in Older Adults
or by reducing the sensory redundancy of the visual and vestibular
systems; these manipulations forced
participants to effectively reweigh
remaining inputs within the CNS.17
The direct beneficial consequences
of these tasks were reflected in the
ability of the participants to regain
stability, likely by taking advantage
of the restored proprioceptive information and integrating it with vestibular inputs and other sensorimotor
cues. Evidence of similarly enhanced
central integration following sensory
training has been found in studies
demonstrating improved stability
during the manipulation of proprioceptive, vestibular, or visual systems
or all of these by use of the Sensory
Organization Test (SOT).28,36 Although the use of a sway reference
standing surface during the SOT is
considered to be a proprioceptive
perturbation, the muscle spindles
serving this system cannot be targeted as precisely as with vibration.
These studies also were limited because of the use of a cross-sectional
design including seasoned tai chi
practitioners36 and the use of the
SOT for both training and testing
procedures,28 which may have resulted in a learning effect.37
The functional significance of the results of the present research was evident because of improvements in
the FAB Scale scores in the exercise
group. These results, demonstrating
responsiveness to training, further
support the validity of FAB Scale
scores. Interestingly, the items demonstrating improvements across visits were items 6 (one-leg stance), 7
(standing on foam), and 9 (walking
with head turns), each of which
comprises an element of sensory integration. However, even though
subjects showed improvements in
and maintenance of FAB Scale scores
at the 8-week follow-up, the improvements did not translate to the
maintenance of enhanced postural
stability following vibratory pertur1282
f
Physical Therapy
Volume 87
bation. This lack of an effect suggests
that there are context-dependent differences following a targeted training intervention and thereby supports the need for ongoing sensory
training. In turn, compensatory sensory mechanisms may be selected
more efficiently under conditions of
sensory deprivation38 or restoration.
The decrease in balance confidence
in the education group postintervention may be explained by discussions
centered on effective means of
reducing fall risk. An increased
awareness of these topics may have
underscored the apprehension experienced during functional balance
tasks until changes could be implemented. Two recent studies examining the effectiveness of falls prevention education reported similar
findings, with almost half of the participants demonstrating increased
fear of falling39 and a 28% increase in
1 or more falls40 at follow-up.
Seasonal variations in PASE scores
may account for the reduction in
scores at the 8-week follow-up in the
exercise group.26 Follow-up testing
occurred during both the winter and
the summer months, when either
snow and ice or high heat and humidity may have forced participants
indoors. Arguably, the reduction in
activity level may explain the lack of
retention in the ability to reintegrate
proprioceptive information effectively. However, without a significant correlation between PASE
scores and COP velocity in the first 5
seconds following vibration, this theory is not substantiated.
Conclusion
The results of the present study suggested that sensory-specific exercise
had a training effect on proprioceptive reintegration. However, 2 limitations should be mentioned. The first
limitation is that 8-week follow-up
scores were not obtained for the education group. Therefore, although
Number 10
improvements in the FAB Scale
scores were maintained in the exercise group, it remains unclear
whether the control group also experienced changes over the 8-week
time period. The second limitation is
that the participants were older
adults who were healthy rather than
older adults with balance impairments, who may have benefited to a
greater extent. Future research may
include a group of older adults with
declining balance to assess the effect
of training on central sensory reintegration. Such an investigation also
may include a kinematic and kinetic
analysis of the effect of vibration on
dynamic stability tasks. A combination of findings from these studies
and those from the present study
may lead to more efficient balance
exercise interventions and, ultimately, to a reduction in fall risk in
older adults.
Both authors provided concept/idea/research design, writing, and data analysis. Dr
Westlake provided data collection, project
management, fund procurement, and subjects. Dr Culham provided facilities/equipment and consultation (including review of
manuscript before submission).
This study was approved by Queen’s University Health Science and Affiliated Teaching
Hospitals Research Ethics Board.
Data from this study were presented at the
International Congress of the World Confederation for Physical Therapy; June 2– 6, 2007;
Vancouver, British Columbia, Canada.
Dr Westlake was supported by a Canadian
Institutes of Health Research Fellowship.
This article was received September 7, 2006,
and was accepted May 8, 2007.
DOI: 10.2522/ptj.20060263
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