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Published in final edited form as:
Gait Posture. 2009 November ; 30(4): 436–440. doi:10.1016/j.gaitpost.2009.06.016.

Whole-body vibration improves walking function in individuals
with spinal cord injury: a pilot study
Lanitia L. Ness, PhD1,3 and Edelle C. Field-Fote, PhD, PT1,2
1The Miami Project to Cure Paralysis, University of Miami Miller School of Medicine, Miami, FL, USA
2Department of Physical Therapy, University of Miami Miller School of Medicine, Miami, FL, USA
3Department of Biomedical Engineering, University of Miami, Coral Gables, FL, USA

Abstract
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Injury to the central nervous system often results in impairments that negatively affect walking
function. Prior evidence suggests that vibration may improve walking function. The purpose of thisstudy was to determine whether repeated use of whole-body vibration (WBV) is associated withimprovements in walking function in individuals with spinal cord injury (SCI). Subjects were 17
individuals with chronic (≥ 1 year), motor-incomplete SCI. Subjects were tested before and afterparticipation in a 12-session (3 days/week- for 4 weeks) intervention of WBV. We assessed change
in walking function via 3D motion capture, with walking speed as the primary outcome measure.
We also assessed the influence of the WBV intervention on secondary gait characteristics, including
cadence, step length, and hip angle-to-knee angle intralimb coordination. Walking speed increased
by a mean of 0.062 ± 0.011 m/s, a change that was statistically significant (p<0.001). The WBVintervention was also associated with statistically significant increases in cadence, and both thestronger and weaker legs exhibited increased step length and improved consistency of intralimb
coordination. Changes in cadence and step length of the stronger leg were strongly correlated withimprovements in walking speed. The improvement in walking speed observed with the WBVintervention was comparable to that reported in the literature in association with locomotor training.
This magnitude of change has been identified as being clinically meaningful, even in non-clinicalpopulations. These findings suggest WBV may be useful to improve walking function with effects
that may persist for some time following the intervention.

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Keywords
Gait; locomotor; afferent input; human movement system© 2009 Elsevier B.V. All rights reserved.
Corresponding author: Edelle Field-Fote, PhD, PT; The Miami Project to Cure Paralysis, University of Miami Miller School of Medicine;1095 NW 14 Terr (R-48); Miami, FL 33136, USA. edee@miami.edu Tel: (305) 243-7119, Fax (305) 243-3913.
Conflict of Interest
There is no conflict of interest with any of the authors.
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Loss of walking function is a common consequence of spinal cord injury (SCI), and for these
individuals, regaining walking function is a high priority.1 Individuals with SCI, and otherpopulations with disorders of the central nervous system, often have various impairments thatnegatively impact walking function. For example, muscle weakness and sensory impairment
result in reduced levels of muscle activation and decreased walking speed.2 Spasticity may
result in altered muscle timing and co-contraction associated with spastic gait patterns.2, 3
Decreased walking function results from any one, or a combination, of these deficits.2,4
In non-disabled (ND) individuals, vibration to the muscle body or tendon increases walking
speed, depending on the combination of vibration placement and direction of progression.5 In
individuals with Parkinson’s disease, vibration applied through the soles of the feet during
walking increases walking distance, speed, stride length, and improves stride variability.6
Vibration may also excite spinal circuitry (i.e., locomotor pattern generators) involved in the
production of locomotor output.7

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Whole-body vibration (WBV) is increasingly being used in elderly individuals8, 9 and inclinical populations.10-14 In individuals with SCI, our studies offer preliminary evidence thata 12-session intervention of WBV decreases spasticity of the quadriceps muscles.15 The useof WBV has also been associated with changes in walking function.8, 10-12 Elderly individuals
who received a 2-month WBV intervention in combination with balance, muscle strengthening,
and walking exercises demonstrated increased walking speed and step length compared toindividuals who did the same exercise program without WBV.8 In individuals with Parkinson’s
disease, a 3-week intervention of WBV is associated with improvements in walking speed.11
In adults with spastic diplegia due to cerebral palsy, an 8-week intervention of WBV is
associated with improvements in muscle strength and reductions in spasticity of the knee
extensor muscles, but the distance walked in 6 minutes was unchanged.10 In individuals withSCI who were unable to stand without long-leg braces, a case series published in an abstract
attributed the use of WBV with the progression of function from standing to walking.12
Evidence of the effects of WBV on walking function is limited in individuals with SCI.

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The purpose of this study was to determine whether repeated use of WBV is associated withimprovements in walking function, as defined by changes in walking speed, in individuals withchronic, motor-incomplete SCI. In individuals with SCI, increased walking speed is a standard
benchmark for improvement in walking function.16-18 In addition, we assessed changes insecondary gait parameters including step length, cadence, and consistency of hip angle-to-knee
angle intralimb coordination. Our prior studies of interventions to improve walking function
in individuals with SCI have focused on locomotor training16,19 or nutrient supplementation.
20 While there is preliminary evidence in that WBV may improve walking function in elderly
individuals9 and individuals with Parkinson’s disease,11 there are no published studies related
to the influence of WBV on walking function in individuals with SCI, many of whom have alimited ability to maintain standing. Based on the prior evidence, we hypothesized that the 12session intervention of WBV would be associated with improvements in walking speed andthe secondary gait parameters. In this consideration-of-concept study,21 our goal was todetermine whether there was value in pursuing this line of study, and whether it was feasible
to use WBV in individuals with SCI relative to subject tolerance and incidence of adverse
events.

Subjects
Seventeen subjects (3 women, 14 men; age 28-65) with SCI enrolled in the study. All subjects
underwent clinical examination prior to testing. Subject inclusion criteria was motor

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incomplete, chronic (≥ 1 year duration) SCI, and ability to rise from sitting to standing withno more than moderate assistance from one person, and ability to stand (using upper extremity
support) for at least 1 minute. American Spinal Injury Association (ASIA) motor and sensory
scores,22 and ASIA Impairment Scale (AIS) classification22 were evaluated by a physicaltherapist who was not otherwise involved in the study. All individuals had asymmetrical lower
extremity motor scores that were used to identify the weaker and stronger extremity. Subject
height was recorded for the purpose of normalizing gait parameters. Information about daily
use of medications and assistive devices for mobility was also recorded.
Demographic data for the subjects is given in Table 1. All subjects gave written and verbal
informed consent to participate in a protocol approved by the Human Subjects Research Officeat the institution. All subjects were instructed to maintain their regular exercise and medication
habits until completion of the study.

WBV Intervention

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Subjects received an intervention consisting of WBV (Power Plate; Northbrook, IL) 3 days
per week for 4 weeks. Each session included four 45-second bouts with one minute of seatedrest without vibration between bouts according to previously published protocols (Figure 1).
13, 14 During each WBV bout, subjects stood on the vibration platform with knees flexed
approximately 30 degrees from anatomical neutral. Vibration was delivered at 50 Hz with avertical displacement of 2-4 mm (depending on subject weight).

Testing Procedure
The effects of the 12-session WBV intervention on walking function were quantified bycomparing the kinematic data acquired prior to the intervention (initial test) to that collected
within seven days of the last WBV session (final test). One subject returned an additional timeat 5-weeks post WBV for a follow-up test session to allow assessment of persistence ofintervention effects. An array of twenty-one reflective markers were placed bilaterally at thelateral malleoli, 5th ray metatarsal-phalangeal joints, heels, lateral knee joints, greater
trochanters, anterior superior iliac spines, shoulders, elbows, and wrists as well as at C7, T10,
and the sacrum. Kinematic data was collected using an 8-camera 3D motion capture system(Peak Motus® Software, Peak Performance, Centennial, CO). Recording of kinematic data
was performed in a calibrated space with data captured at 60 Hz.

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For each walking test session, subjects walked 5 times across a 10-meter walkway at theirpreferred walking speed; subjects were allowed to rest between walking tests. During eachwalking test, subjects were given 30 seconds to complete the 10-meter walk, and all outcome
measures were extracted from data captured within the central 6 meters of the walkway.
Subjects used assistive devices as required during testing. Fourteen subjects used a rollingwalker, one subject did not have the necessary hand function to grip the handles of a standard
rolling walker and performed the test using a rolling walker with bilateral forearm platform
supports, and two subjects did not require assistive devices. If a subject required an assistive
device, the same device was used both for the initial and final test sessions.

Data analysis and statistics
Statistical Analysis Software 9.1.3 (Cary, NC) was used for all statistical analyses. All data
were checked and met the parametric assumptions of homogeneity (Levene’s test for equalityof variances) and normality (Kolmogorov-Smirnov Z test). Significance was set at α=0.05.
Walking speed (SPEED; meters/second; m/s) was calculated from the distance traversed in the
direction of forward progression as measured from the sacral marker. A one-tailed, paired ttest was used to compare the mean speed of the five walking trials from the initial and final
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test sessions. A convenience sample of one participant (selected because he lived locally)
returned for a follow-up walking test session 5-weeks after the last session of WBV. Walking
speed for this subject was compared to both the initial and final tests to assess persistence ofchange in speed associated with the WBV intervention.
Gait parameters were calculated from the kinematic measures. Data were filtered using a
Butterworth filter with a 6 Hz cutoff. Bilateral step lengths were extracted from the coordinatesof the heel in the direction of progression. Step lengths (m) were determined by the distance
between two consecutive contralateral heel strikes, and normalized to subject height. A onetailed, paired t-test was used to compare the mean initial and final test values of the strong leg
step length (SSL) and weak leg step length (WSL). Cadence (CAD; steps/minute) was
calculated by dividing the total number of steps by the time need to complete the steps. A onetailed, paired t-test was used to compare the mean CAD of the initial and final tests. The valuesof SSL, WSL and CAD are directly derived from a single reflective marker and may therefore
be expected to be interrelated, therefore a Bonferroni correction was used to adjust the alphalevel for 4 pair-wise (SPEED, CAD, SLL, WSL) comparisons resulting in a corrected valueof α=0.0083.

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Intralimb coordination was defined as the ability to produce a consistent relationship of hipangle-to-knee-angle coupling over multiple step cycles.19, 23 The hip angle was defined by thetrunk and thigh segments. The knee angle was defined by the thigh and shank segments. Vector
coding was used to quantify intralimb coordination wherein the angular component of thecoefficient of correspondence (ACC) represents the degree of consistency of the hip angle-toknee angle relationship over multiple cycles.19, 23 It has been suggested that ACC values offer
insights into the organization of control mechanisms (i.e., locomotor central pattern generators)
underlying coordination of innate, cyclic behaviors.19, 23 In individuals with SCI, changes in
the ACC value correlate well with changes in walking speed associated with locomotor
training.19 ACC was calculated for both the strong ACC (SACC) and weak ACC (WACC)
legs. An increase in ACC value from initial to final was interpreted as increased consistencyof intralimb coordination. A one-tailed, paired t-test was used to compare the mean SACC and
WACC values from the initial and final tests.
To determine which gait parameters were most closely associated with changes in walking
speed, Pearson correlations where used to identify the relationship between SPEED and theparameters of CAD, SSL, WSL, SACC, and WACC. Pearson r values were interpreted asfollows: 0.00-0.25 was considered little or no relationship, 0.25-0.50 was considered a fairrelationship, 0.50-0.75 was considered a moderate relationship, and 0.75-1.0 was considered
to be a good to excellent relationship.24

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The pooled standard deviation and Cohen’s d was used to calculate the effect size of the change
in SPEED associated with use of the WBV intervention.

Results
The group mean walking speed (SPEED) increased by 0.062 ± 0.011 (mean ± standard error)m/s (from 0.259 ± 0.248 m/s in the initial test to 0.321 ± 0.260 m/s in the final test), an increasethat was statistically significant (p<0.001) but considered a small effect size (d=0.249).
Subject 16, who returned for a follow-up test 5-weeks after the last WBV session, had an initial
SPEED of 0.128 m/s, a final SPEED of 0.215 m/s and a 5-week follow-up SPEED of 0.241
m/s. SPEED values of all subjects, group mean, and Subject 16 are illustrated in Figure 2.
The 12-session intervention of WBV was also associated with a statistically significant increase
in CAD (from 33 ± 5 step/min [initial] to 36 ± 5 steps/min [final]; p=0.002). SSL significantly
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increased (from 0.194 ± 0.090 m [initial] to 0.23 ± 0.063 m [final], p=0.006) and WSL
significantly increased (from 0.180 ± .082 m [initial] to 0.212 ± 0.075 m [final], p=0.003). The
relationship between change in SPEED to changes in, CAD, SSL, and WSL are illustrated in
Figure 3.
There was a statistically significant change in SACC (from 0.68 ± 0.22 [initial] to 0.77 ± 0.12
[final], p=0.018) and in WACC (from 0.67 ± 0.22 [initial] to 0.74 ± 0.14 in [final], p=0.026).
The relationship between change in SPEED to changes in SACC and WACC is illustrated in
Figure 4.
Changes in SPEED had a significant, moderate, direct correlation with CAD (r=0.528,
p=0.029), and a non-significant, fair, direct relationship with SSL (r=0.344, p=0.176). Changes
in SPEED had a non-significant, weak, direct correlation with WSL (r=0.154, p=0.554), SACC
(r=0.018, p=0.946), and WACC (r=0.204, p=0.433).

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All subjects tolerated the 12-sessions of WBV, were able to maintain the standing posture forthe 45-sec bouts of WBV, and reported no adverse effects. These results suggest that it isfeasible to use WBV as an intervention in future randomized, controlled studies that assessinterventions to improve walking function in individuals SCI. All subjects adhered to the study
protocol and completed the intervention; many of these individuals indicated they would liketo continue with these sessions and would be interested in participating in future studies
involving WBV.

Discussion

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Our results indicate that consistent use of WBV is associated with an increase in walking
function, as defined by walking speed, in individuals with SCI who have some ability tomaintain voluntary standing. While the lack of a control group, the inclusion of individuals
with varying degrees of walking ability, and the fact that it was not possible to blind subjects
to the intervention limits the conclusions that can be drawn from these findings, the fact remainsthat the observed changes in walking speed associated with WBV were equivalent to thosereported for studies of locomotor training.16 In individuals with SCI who participated in a 3month 5-day/week locomotor training intervention, walking speed changes of 0.023 m/s, 0.05
m/s, 0.05 m/s, and -0.005 m/s were associated with manually assisted treadmill training,
stimulation-assisted treadmill training, overground training, and robotic-assisted treadmill
training, respectively. It is possible that participation in a study made the subjects more
conscientious of their walking performance or that the pre-, post-test design increased
familiarity with the test, resulting in an improvement. However, we feel these explanations areunlikely, especially in light of comparisons to the locomotor training literature.16 In healthyelders, a change in walking speed of 0.05 m/s (with a similar effect size [d= 0.2]) has been
judged to be a clinically meaningful change.25 As illustrated in Figure 2, 10 out of 17 of thesubjects exceeded a change of 0.05 m/s after the 12-session intervention of WBV. Subject 13
was unable to take a single step in the initial test. After the 12-session intervention of WBV,
the subject was able to take 4 steps. It could be argued that this magnitude of change may beeven more meaningful in individuals with SCI than it is in healthy elders. Our findings are
consistent with improvements in walking function observed in elderly individuals8 and inindividuals with Parkinson’s disease who received a WBV intervention,11 and therefore
provide preliminary evidence that regular use of WBV may be a potent intervention forimproving walking function in individuals with SCI.
In the single subject who performed a follow-up test session 5 weeks after the WBVintervention, the effects on walking speed not only persisted, but increased 5 weeks after the
WBV intervention. These are similar to findings in individuals with Parkinson’s disease who

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had a persistent change in walking speed 4 weeks after receiving a 3-week WBV intervention.
11 The use of afferent input to induce positive plastic effects in the nervous system has received
considerable attention in the recent research literature.26-28 These plastic changes are mostmeaningful when they are associated with a lasting improvement in function.11, 26 Futurestudies should assess the persistence of effects of WBV through follow-up testing performedsome time after the final intervention.

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We observed improvements in cadence, step length of the strong and weak legs, andconsistency of hip angle-to-knee angle intralimb coordination after a 12-session interventionof WBV. Furthermore, changes in walking speed and cadence were moderately correlatedsuggesting the increase in walking speed associated with the WBV intervention is related to
an increase in the number of steps taken per minute. In addition to an increase in cadence,changes in walking speed also had a fair relationship with changes in the stronger step length,
suggesting that increased stronger leg step lengths may also contributed to the improvements
in walking speed. The improvements in walking speed and step length are consistent withincreases in stride length reported in individuals with Parkinson’s disease during vibration.6
However, this is contrary to evidence in ND individuals wherein no change in stride length
during walking was observed with vibration applied to tibialis anterior, triceps surae, biceps
femoris, rectus femoris, or quadriceps femoris.29 Changes in stride length may not be evident
in ND individuals because their strides are relatively longer compared to individuals with aneuropathology. For this reason, individuals with neuropathology may have a larger margin
for vibration-induced improvement of spatial walking characteristics compared to ND
individuals.
The degree of consistency of the hip-knee intralimb coordination of both legs improved, andthe improvement was comparable to those observed in a 3-month locomotor training wherein
the ACC values improved from 0.56 before to 0.65 after locomotor training.19 However, unlikethat prior study wherein the change in intralimb coordination was associated with the change
in walking speed, in the present study the change walking speed was only weakly correlatedwith the change intralimb coordination. Contrary to our findings, in ND individuals, bilateral
Achilles tendon vibration did not change walking speed or leg inter-segmentalcoordination30
Also in ND individuals, changes in intralimb ankle-knee coordination were not found withvibration applied to tibialis anterior, triceps surae, biceps femoris, rectus femoris, or quadriceps
femoris.29 Our findings and other evidence in individuals with SCI19 suggest that the consistentuse of afferent input improves the motor output of the control mechanisms that have been
impaired after a SCI.

Implications for function
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These results provide preliminary support for the use of WBV as an intervention to improve
walking function in individuals with SCI, with changes that appear to be comparable to thoseachieved with some forms of locomotor training. With a 12-session intervention of WBV, wefound significant improvements in walking speed, cadence, step lengths, and intralimb
coordination over multiple steps. Furthermore, the effect of WBV on walking function may
continue to improve walking function even after the use of WBV has ended. However, thiswas assessed in a single subject and requires further investigation.

Acknowledgments
We gratefully acknowledge the technical contributions of Stephen Lindley and Saumtra Sinha Ray. This study was
supported by The Miami Project to Cure Paralysis and the NIH grant #HD667647.

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Figure 1.

Procedure for a single session of whole-body vibration (WBV). Each session of WBV consistedof 4 bouts of WBV at a frequency of 50 Hz and an intensity of 2-4 mm (depending on thesubject weight). Each vibration bout was separated by a period of one minute seated rest.

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Figure 2.

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All subjects change in walking speed (SPEED; mean ± standard error) associated with 12session whole-body vibration (WBV) intervention. Change in SPEED values for all subjects(thin lines) and group mean change (thick line). Group mean initial SPEED value (0.259 ±
0.248 m/s) and final SPEED value (0.321 ± 0.260 m/s) were significantly different (*). The yaxis has been broken from 0.6 m/s to 1 m/s because there were no SPEED values measured inthis range. One subject returned for a follow-up test 5-weeks (dashed line) after the last WBVsession, had an initial SPEED of 0.128 m/s, a final SPEED of 0.215 m/s and a 5-week followup SPEED of 0.241 m/s.

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Figure 3.

Group Mean Changes in walking speed (SPEED; m/s), change in walking cadence (CAD;
steps/min), and change in weak (WSL) and strong (SSL) step lengths (m) after a 12-session
whole-body vibration (WBV) intervention.
CAD, WSL and SSL significantly decreased (*) after the 12-session intervention of WBV.
Theses gait parameters contributed to the increase in SPEED. The y-axis values are dependent
on the reported measure and are denoted as group mean ± standard error bars. Note the breakin the y-axis from 0.5 to 30 to accommodate for values of cadence.

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Figure 4.

Group Mean Changes in walking speed (SPEED; m/s) and the change in strong (SACC) andweak (WACC) coefficients of correspondence (ACC) after a 12-session whole-body vibration(WBV) intervention. The y-axis values are dependent on the reported measure and are denoted
as group mean ± standard error bars. Note the break in the y-axis from 0.4 to 0.7 because novalues were reported in this range. SACC and WACC significantly decreased (*) after the 12session intervention of WBV.

NIH-PA Author Manuscript
Gait Posture. Author manuscript; available in PMC 2010 November 1.

NIH-PA Author Manuscript
Table 1

NIH-PA Author Manuscript

F

M

M

M

M

M

M

M

M

M

M

8

9

10

11

12

13

14

15

16

17

5

M

M

4

7

M

3

6

F

M

2

M

28

65

58

43

42

53

41

42

34

54

43

60

56

48

60

42

41

C4

C3

C6

T7

C4

T7

T6

C4

T4

T4

T8

T4

C5

C5

C6

C4

C5

39

36

31

42

23

34

23

24

29

36

26

34

38

33

17

23

25

Baclofen

None

None

None

Baclofen

None

None

Baclofen

None

None

None

None

Baclofen

None

Baclofen

Baclofen

Tizanidine

Wheelchair

Wheelchair

None

Wheelchair

Wheelchair

WalkerWheelchair

Wheelchair

Wheelchair

Wheelchair

Personal Transporter

Wheelchair

Wheelchair

Wheelchair

Wheelchair

Wheelchair

Wheelchair

Subject Gender Age Injury Level LEMS Scores Antispastic Agents Primary Daily Assistive Device

1

NIH-PA Author Manuscript

Demographics of participants; LEMS = lower extremity motor scores represent the sum of the motor scores for the 5 key muscles of bothlegs graded according to ASIA guidelines22 prior to the WBV intervention.
Ness and Field-Fote
Page 13

Gait Posture. Author manuscript; available in PMC 2010 November 1.