Potential of Vibroacoustic Therapy in Persons with Cerebral Palsy: An Advanced Narrative Review

Abstract

Vibroacoustic therapy (VAT) is a treatment method that uses sinusoidal low-frequency sound and music. The purpose of this narrative review is to describe the effects of VAT on motor function in people with spastic cerebral palsy (CP) according to study design as well as providing information about the age of the participants, measurement tools, and sound frequencies that were used. The systematic search strategy based on the first two steps of a standard evidence-based approach were used: (1) formulation of a search question and (2) structured documented search including assessment of the relevance of abstracts and full texts to the search question and inclusion criteria. Out of 823 results of the search in 13 scholarly databases and 2 grey literature sources, 7 papers were relevant. Most of the relevant studies in children and adults presented significant improvement of motor function. According to the study design, only five experimental studies and two randomized controlled trial (RCT) studies were available. In the discussion, findings of this review are compared to other related methods that use mechanical vibrations without music. The authors recommend continuing to research the effects of VAT on motor function and spasticity in adolescents and young adults with spastic CP.

Full text

International Journal of
Environmental Research
and Public Health
Review
Potential of Vibroacoustic Therapy in Persons with
Cerebral Palsy: An Advanced Narrative Review
JiˇríKantor 1, * , Lucia Kantorová1, Jana Mareˇcková2, Danping Peng 3and Zdenˇek Vilímek 1
1Institute of Special Education Studies, Faculty of Education, Palacky University Olomouc, Žižkovo nám. 5,
77900 Olomouc, Czech Republic; lucia.kantorova@bahai.sk (L.K.); z.vilimek@gmail.com (Z.V.)
2Department of Anthropology and Health Education, Faculty of Education, Palacky University Olomouc,
Žižkovo nám. 5, 77900 Olomouc, Czech Republic; jana.mareckova@upol.cz
3
Institute of Education and Social Studies, Faculty of Education, Palacky University Olomouc, Žižkovo n
á
m.
5, 77900 Olomouc, Czech Republic; pengdanping2013@gmail.com
*Correspondence: jiri.kantor@upol.cz
Received: 15 September 2019; Accepted: 14 October 2019; Published: 16 October 2019


Abstract:
Vibroacoustic therapy (VAT) is a treatment method that uses sinusoidal low-frequency
sound and music. The purpose of this narrative review is to describe the effects of VAT on motor
function in people with spastic cerebral palsy (CP) according to study design as well as providing
information about the age of the participants, measurement tools, and sound frequencies that were
used. The systematic search strategy based on the first two steps of a standard evidence-based
approach were used: (1) formulation of a search question and (2) structured documented search
including assessment of the relevance of abstracts and full texts to the search question and inclusion
criteria. Out of 823 results of the search in 13 scholarly databases and 2 grey literature sources,
7 papers were relevant. Most of the relevant studies in children and adults presented significant
improvement of motor function. According to the study design, only five experimental studies
and two randomized controlled trial (RCT) studies were available. In the discussion, findings of
this review are compared to other related methods that use mechanical vibrations without music.
The authors recommend continuing to research the effects of VAT on motor function and spasticity in
adolescents and young adults with spastic CP.
Keywords:
children; adults; cerebral palsy; vibroacoustic therapy; spasticity; motor; movement; spasticity
1. Introduction
Cerebral palsy (CP) is a complex functional disability, which, in medical literature, is defined
as “a group of permanent disorders of the development of movement and posture, causing activity
limitation, that are attributed to non-progressive disturbances that occurred in the developing fetal or
infant brain. The motor disorders of cerebral palsy are often accompanied by disturbances of sensation,
perception, cognition, communication, and behavior, by epilepsy, and by secondary musculoskeletal
problems” [
1
] (p. 572). CP is one of the most common childhood disabilities [
2
], with prevalence rates
between 2–3.5 per 1000 live births reported [3].
Spasticity is the most prevalent form of CP, with increased muscle tone and typical spastic
symptoms ranging from mild neurological deficits to severe impairment. Spasticity is composed of
neural and secondary non-neural components, including muscle structure or connective tissues [
4
].
It affects over an estimated 12 million people worldwide, and about 80% of people with CP have varying
degrees of spasticity [
5
]. Spasticity is linked with limited range of motion, which is a measurement
of movement around a joint. Other symptoms are stiffness or tightness of the muscles, muscle and
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Int. J. Environ. Res. Public Health 2019,16, 3940 2 of 15
joint deformities, muscle fatigue, inhibition of longitudinal muscle growth, and so on [
6
]. The level of
severity is categorized by the Gross Motor Function Classification System (GMFCS), with values of I–V.
As for the development of motor functions, age is an adverse factor for a high percentage of people
with CP. According to Rosenbaum et al. [
7
], children in all severity levels achieve most of their potential
function early; by age seven, function generally begins to level off. Tendencies of motor function
to decline in adulthood have been mentioned by other studies as well [
8
]. Possible explanations
proposed for motor decline are increased body size; decreased activity; changes in spinal alignment [
9
],
muscle flexibility, strength, and endurance; and increased spasticity, arthritis, falls and fractures,
and pain or fatigue [
10
]. Ritzman, Stark, and Krause [
4
] (p. 1620) state the following in relation
to therapeutic possibilities and age: “In the last few decades, scientific debate in the field of
neurorehabilitation has consistently concluded that training regimes commonly achieve higher
efficiency in children compared to adolescent patient groups.”
The treatment methods of spastic CP include physiotherapy [
11
], surgery, and drug administration,
such as botulinum toxin A [
12
]. There is also a growing scientific evidence of the effects of vibration
therapy—a non-invasive and safe training modality that uses mechanical oscillations. Growing research
on vibration therapy and CP population nowadays includes a range of randomized controlled trial
(RCT) studies as well as systematic reviews [4,13,14].
So far, the discussions about different possible theories about therapeutic mechanisms of vibration
therapy and CP are still ongoing. Basically, vibrations influence neuromuscular structures in the body [
4
],
with somatosensory perception playing a key role. The theory of neuromodulation explains the therapeutic
effect via stimulation of alpha-motor neurons; however, vibrations also stimulate mechanoreceptors and
induce neuroplasticity via somatosensory/motor pathways and (concerning whole body vibrations, WBV)
increase neural drive to the muscles with resulting increase in muscle mass and strength [
15
]. Vibration
determinants refer to the frequency (number of complete cycles per second, 5–200 Hz), amplitude (vertical
displacement 0.5–10 mm), and type of vibration therapy (VT; sinusoidal vertical and side-alternating) [
4
].
The vibration can be provided as focal vibration to a specific muscle/tendon or as whole-body vibration.
Low-frequency stimulation can be derived from mechanical vibrations (e.g., through an oscillating
platform or membrane) as well as from sound vibrations. To conclude briefly, there is more than one
strategy of vibrations application for therapeutic purposes.
Vibroacoustic therapy (VAT) is a relatively new method in the area of vibration therapy, as its
foundations were laid in the 2nd half of the 20th century. It uses low-frequency sound (under 100 Hz)
in the audible range to produce mechanical vibrations, which differs from methods using only
infrasonic frequencies (under 20 Hz) that are not audible to the human ear [
16
]. In VAT, low-frequency
vibrations are derived from technologically modified sound waves (not from mechanical vibrations).
Another distinctive characteristic of VAT is using low-frequency vibrations together with music
listening (comparing, for example, WBV that are typically applied while standing on an oscillating
platform that displaces the individual and alters the gravitational forces of the body) [17].
The roots of VAT are connected to a Nordic neurologist and pedagogue, Skille, and his experiments
using deep vibrations in people with multiple disabilities. He defined VAT as “using sinusoidal
low-frequency sound in 30–120 Hz range complemented by music for therapeutic purposes” [
18
] (p. 36).
In the 1990s, the physioacoustic method based on scanning the body with sinusoidal sound between
27–113 Hz and specially selected music listening was developed by Lehikoinen [
19
]. Other examples
of vibroacoustic devices include Eakin’s multiple designs of Somatron Corporation first released in
1985 (Tampa, Florida, USA), the music vibration table (MVT) designed by Chesky in the late 1980s
(there is no indication that MVT is in manufacture) [
20
], the HealBED first released in 1990–1991
(HealBED, Haapsalu, Estonia) [
21
], Multivib products (that use a mattress or a cushion with embedded
vibration speakers, Multivib as, Trondheim, Norway) [
22
], Vibrobed developed in 2018 by Vil
í
mek
and Švarc (Vibroacoustic Brothers, Olomouc, Czech Republic) [
23
], the Relaxation Lounge V1 and
V2 of Nex Neuro Vibro-Acoustic Therapy [
24
], Sonobed
™
from Heritage Medical Associates, P.C.,

Int. J. Environ. Res. Public Health 2019,16, 3940 3 of 15
Nashville, Tennessee, developed in 1993, and the Vibroacoustic Therapy System VTS1000 of Sound
Oasis Company (Marblehead, Massachusetts, USA) [
25
] or Subpac (Subpac Inc, Toronto, Canada) [
26
].
Based on the type of low-sinusoidal stimulation, selective low-frequency (SLF) and full-frequency
music (FFM) may be differentiated [
27
]. SLF uses specific low frequencies for vibroacoustic stimulation,
such as Skille’s equipment, whereas FFM uses “a single sound source and plays music using a wide
range of frequencies” (such as quantified mechanical vibration design of Chesky
´
s music vibration
table) [
27
] (p. 112). As for the selective low-frequency stimulation, an important issue is connected to
the selection of suitable frequencies [
28
]. Although Skille [
29
] formulated a set of seven frequencies,
this set is based merely on practical experiences, and there is a lack of theoretical support. One of the
exceptions is the theory of thalamic frequency of 40 Hz [30].
VAT is traditionally indicated for use in spastic CP and other brain problems, as it helps to enhance
physiotherapeutic intervention and improves motor and brain functions [
31
] (e.g., through circuit
connectivity through oscillatory coherence). VAT is also beneficial for its effects on quality of life,
well-being, and stress management [
28
]. Concerning spinal cord and brain injuries, VAT can lead
to changes in the levels of spasticity, pain, physical discomfort, general health condition, fatigue,
and anxiety [
32
]. Although it is possible to find other information on the effects of VAT in normalisation
of muscle tone in people with spastic CP [
18
,
31
], systematically led reviews on research about its effects
(comparing some other approaches in vibration therapy) are lacking. However, such evidence would
be of benefit to the scientific background of VAT since current science and practice is increasingly
applying the evidence-based healthcare (EBHC) concept: “evidence-based medicine requires skills
of literature retrieval, critical appraisal, and information synthesis. It also requires judgment of the
applicability of evidence to the patient at hand and systematic approaches to make decisions when
direct evidence is not available“ [
33
]. The most robust evidence for practice is, according to this concept,
found in the results of secondary research represented by systematic reviews using a meta-analysis or
meta-aggregation. The hierarchy of primary research evidence starts with randomized controlled trials
and ends with expert opinion (see Figure 1). The authors of this paper have, therefore, focused on
the use of these elements of the EBHC concept to identify, classify, and describe the design of existing
studies on the effects of VAT on motor functions in people with CP.
Int. J. Environ. Res. Public Health 2019, 16, x 3 of 14
Vibroacoustic Therapy System VTS1000 of Sound Oasis Company (Marblehead, Massachusetts,
USA) [25] or Subpac (Subpac Inc, Toronto, Canada) [26].
Based on the type of low-sinusoidal stimulation, selective low-frequency (SLF) and
full-frequency music (FFM) may be differentiated [27]. SLF uses specific low frequencies for
vibroacoustic stimulation, such as Skille´s equipment, whereas FFM uses “a single sound source and
plays music using a wide range of frequencies” (such as quantified mechanical vibration design of
Chesky´s music vibration table) [27] (p. 112). As for the selective low-frequency stimulation, an
important issue is connected to the selection of suitable frequencies [28]. Although Skille [29]
formulated a set of seven frequencies, this set is based merely on practical experiences, and there is a
lack of theoretical support. One of the exceptions is the theory of thalamic frequency of 40 Hz [30].
VAT is traditionally indicated for use in spastic CP and other brain problems, as it helps to
enhance physiotherapeutic intervention and improves motor and brain functions [31] (e.g., through
circuit connectivity through oscillatory coherence). VAT is also beneficial for its effects on quality of
life, well-being, and stress management [28]. Concerning spinal cord and brain injuries, VAT can
lead to changes in the levels of spasticity, pain, physical discomfort, general health condition,
fatigue, and anxiety [32]. Although it is possible to find other information on the effects of VAT in
normalisation of muscle tone in people with spastic CP [18,31], systematically led reviews on
research about its effects (comparing some other approaches in vibration therapy) are lacking.
However, such evidence would be of benefit to the scientific background of VAT since current
science and practice is increasingly applying the evidence-based healthcare (EBHC) concept:
“evidence-based medicine requires skills of literature retrieval, critical appraisal, and information
synthesis. It also requires judgment of the applicability of evidence to the patient at hand and
systematic approaches to make decisions when direct evidence is not available“ [33]. The most
robust evidence for practice is, according to this concept, found in the results of secondary research
represented by systematic reviews using a meta-analysis or meta-aggregation. The hierarchy of
primary research evidence starts with randomized controlled trials and ends with expert opinion
(see Figure 1). The authors of this paper have, therefore, focused on the use of these elements of the
EBHC concept to identify, classify, and describe the design of existing studies on the effects of VAT
on motor functions in people with CP.
Figure 1. Levels of evidence in quantitative research [34].
Figure 1. Levels of evidence in quantitative research [34].

Int. J. Environ. Res. Public Health 2019,16, 3940 4 of 15
2. Materials and Methods
The purpose of this review is to identify relevant published information (from research studies in
scientific databases and grey literature sources) on the effects of VAT on motor function in people with
spastic CP according to the study design. Additional aims include the identification of:
•the age of the included people with CP;
•
what measurement tools have been implemented in research on effects of VAT on motor function
of people with spastic CP; and
•
what low-frequency or types of low-sinusoidal stimulations have been used in research on the
effects of VAT on motor function of people with spastic CP.
To meet the objective, a search question (SQ) was formulated using the problem–intervention–
comparison–outcome (P–I–(C–not applicable)–O) components with additional synonymous and related
terms (Table 1): What is the research evidence on the therapeutic effects of vibroacoustic therapy (I) on
motor function (O) in people with spastic cerebral palsy (P)?
Table 1. Synonymous and related terms for the P–I–O components.
Primary search terms
P Spastic cerebral palsy
I Vibroacoustic therapy
C NA
O Motor function
Primary search terms +synonyms +related terms
P“cerebral palsy“ OR “spastic paralysis“ OR quadriparesis OR diparesis OR
hemiparesis
I
“vibroacoustic therapy“ OR “vibroacoustic music“ OR “vibroacoustic sound“ OR
“somatosensory music therapy“ OR physioacoustic OR “physio acoustic sound”
OR somatron OR “low-frequency sound stimulation” OR “vibrotactile
stimulation” OR “music vibration table”
C NA
O “motor function” OR “range of motion“ OR “movement AND spasticity”
P—problem; I—intervention; C—comparison; O—outcome; NA—not applicable.
A standard search strategy was applied as recommended by evidence-based healthcare
methodology [
12
]. The primary search terms, as an input to the development of the search strategy,
were P, cerebral palsy; I, vibroacoustic therapy; C, not applicable; and O, motor function. To increase
the search sensitivity, synonyms and related terms were added to the primary search terms using the
Boolean operator “OR” (Table 1). Roget
´
s 21st Century Thesaurus was used to formulate synonyms
and similar terms. To increase the search specificity of partial results for the P–I–O, components were
connected using the Boolean operator “AND” (Table 1). The following strategy was used: title/abstract;
search period not limited (to increase search sensitivity); no language restrictions. The search was
carried out in May 2019, and the Cochrane Library, Joanna Briggs Institute Library (JBI), and Prospero
databases were added in September 2019.
The following databases were searched:
•PubMed,
•MEDLINE complete,
•Bibliographia Medica ˇ
Cechoslovaca (the Medvik interface),
•EBSCO host,
•EBSCO discovery,

Int. J. Environ. Res. Public Health 2019,16, 3940 5 of 15
•ERIC,
•Wiley Online Library,
•EBM Reviews,
•ProQuest,
•Scopus,
•CINAHL Plus (with Full Text),
•Cochrane Library,
•JBI
•Prospero,
•MedNar, and
•Google Scholar.
Grey literature resources from web search engines MedNar and Google Scholar were included
based on the Joanna Briggs Institute (JBI) standard recommendations to increase the thoroughness of
search results [
34
]. When searching in the e-sources, the specifics of their search engines were taken
into consideration (Table 2). Moreover, the search strategy included an additional manual search of
references of relevant studies, which diminished the risk of overlooking relevant studies or not finding
them due to inadequate indexing.
Table 2. Search results.
Database Results for P
(n)
Results for I
(n)
Results for O
(n)
Search Results
(n)
PubMed 31,713 333 265,208 1
Medline 25,671 292 310,806 1
BM ˇ
C (Medvik) 196 1 1572 0
EBSCO discovery 112,674 1547 2,905,734 8
ERIC 2980 255,974 1,673,393 0
Wiley Online Library 9980 0 2,300,473 0
EBM Reviews 4962 39 37,242 1
ProQuest 99,370 652 2,756,038 4
Scopus 59,723 2407 2,649,382 2
CINAHL Plus 8998 40 60,427 0
Cochrane Library 77 45 99 0
JBI 38 484 2 1
Prospero 598 0 92 0
MedNar * 1388 313 2385 344
Google Scholar * cca 550,000 cca 8990 cca 5,560,000 461
* Results for primary keywords, not the synonyms.
Inclusion criteria: only primary research studies relevant to the search question (i.e., the P–I–O
components) were included in the narrative review. Only studies that involved participants with
spasticity symptoms were included. The minimum JBI level of evidence 4d was used for quantitative
evidence (Figure 1). By the term vibroacoustic therapy we mean the sound-induced, low-frequency
vibrations (not mechanical vibrations) mixed with music listening [8].
Exclusion criteria: 1. application of similar therapeutic methods without technologically modified
low-sinusoidal sound (e.g., monochords, acoustic vibration beds, or methods using mechanical
vibrations); 2. application of low-frequency sound in multimodal therapeutic settings (where it is

Int. J. Environ. Res. Public Health 2019,16, 3940 6 of 15
not possible to evaluate the effect of sinusoidal sound separately from other stimuli); 3. all types of
reviews, preconference abstracts, bachelor and diploma theses; and 4. research with participants with
extrapyramidal syndromes and central hypotony and no spasticity.
The selection and analysis of studies was based on removing duplicates and assessing the relevance
of abstracts to the search question and its components represented by P–I–O and the inclusion criteria.
For relevant abstracts, full texts of articles were retrieved and once again carefully assessed for relevance to
the search question. Full texts of the relevant studies were sorted and divided into categories based on the
type of study design. Categories according to the JBI levels of evidence in quantitative research (Figure 1)
were used for the analysis of advanced search results. In case that full texts of papers included information
on the methodological design, the evidence level by JBI was determined based on that information. In
case the design of the study was not mentioned in the full text, the authors determined it based on an
analysis of the research methodology and other information provided in the study.
3. Results
For the search question, 823 resources were identified (18 abstracts in scholarly databases and 805
in grey literature sources). After assessment of their relevance to the inclusion and exclusion criteria
(see the Methods section), 7 of them were classified as relevant. Five of them were full texts of studies
indexed in scholarly databases, and the remaining 2 (dissertations) were included in the grey literature.
The search process is shown in Figure 2.
Int. J. Environ. Res. Public Health 2019, 16, x 6 of 14
Figure 2. Flow diagram of the literature search (searches in databases with zero results are not listed
in the flow diagram).
3. Results
For the search question, 823 resources were identified (18 abstracts in scholarly databases and
805 in grey literature sources). After assessment of their relevance to the inclusion and exclusion
criteria (see the Methods section), 7 of them were classified as relevant. Five of them were full texts
of studies indexed in scholarly databases, and the remaining 2 (dissertations) were included in the
grey literature. The search process is shown in Figure 2.
Since the dissertation “The effects of vibroacoustic therapy on clinical and non-clinical
populations“ [18] presented a series of 5 studies, the relevance of each was assessed separately.
Chapters 4 and 5 were found relevant [35,36]. These chapters were also published in “Music
vibration and health” [37]. The dissertation ”The effect of 40 Hz sound wave vibration on spasticity
and motor functions in children with cerebral palsy“ of Katušic [38] was evaluated as a duplication
as it contained the research published in the RCT study of Katusic, Alimovic, and Mejaski-Bosnjak
[39]. There were also 2 papers in Chinese language [40,41] that were translated into English and
included in the relevant search results.
The analysis of the methodological design of relevant studies (see below) showed that
secondary research studies (systematic reviews) were completely lacking; however, 2 contributions
with RCT design [39,42] and 5 contributions with experimental study design [35,36,40,41,43] were
available. The following sections present in detail available information on the methodological
design of 7 studies, the effects of VAT on movement and spasticity, instruments used for measuring,
ages of participants, and frequencies used in the research. Since age is an important factor
influencing motor functions in persons with CP [10], the studies were divided, for the purposes of
this paper, into two sections of those concerning children with CP (4 studies summarised in Tables
3–6) and those exploring the adult population with CP (3 studies summarised in Tables 7–9).
Figure 2.
Flow diagram of the literature search (searches in databases with zero results are not listed in
the flow diagram).

Int. J. Environ. Res. Public Health 2019,16, 3940 7 of 15
Since the dissertation “The effects of vibroacoustic therapy on clinical and non-clinical
populations“ [
18
] presented a series of 5 studies, the relevance of each was assessed separately. Chapters 4
and 5 were found relevant [
35
,
36
]. These chapters were also published in “Music vibration and health” [
37
].
The dissertation ”The effect of 40 Hz sound wave vibration on spasticity and motor functions in children
with cerebral palsy“ of Katušic [
38
] was evaluated as a duplication as it contained the research published
in the RCT study of Katusic, Alimovic, and Mejaski-Bosnjak [
39
]. There were also 2 papers in Chinese
language [40,41] that were translated into English and included in the relevant search results.
The analysis of the methodological design of relevant studies (see below) showed that secondary
research studies (systematic reviews) were completely lacking; however, 2 contributions with RCT
design [
39
,
42
] and 5 contributions with experimental study design [
35
,
36
,
40
,
41
,
43
] were available.
The following sections present in detail available information on the methodological design of 7 studies,
the effects of VAT on movement and spasticity, instruments used for measuring, ages of participants,
and frequencies used in the research. Since age is an important factor influencing motor functions in
persons with CP [
10
], the studies were divided, for the purposes of this paper, into two sections of
those concerning children with CP (4 studies summarised in Tables 3–6) and those exploring the adult
population with CP (3 studies summarised in Tables 7–9).
Table 3. Studies on children with CP—Katusic, Alimovic, and Mejaski-Bosnjak [39].
Research Design Randomized Controlled Trial, Single-Blinded
JBI level of evidence 1c
Objective(s) stated in
the study
To determine the effects of VAT on spasticity and motor function in children with
CP (age 4–6) undergoing physiotherapy compared to physiotherapy alone
Sample
89 children (age 4–6) with spastic CP from a daycare center for rehabilitation were
randomized into conventional therapy or conventional +VAT.
Randomization Stratified according to GMFCS level
Intervention
Experimental group: VAT (on top of conventional therapy) twice a week for 12
weeks (40 Hz with sinusoidal amplitude variations −6.8 s between peaks).
Control group: physiotherapy 3 times a week for 40 min.
Measurements
Pre- and post-12-week period MMAS spasticity, GMFM-88 by blinded evaluators.
Statistical methods: non-parametric Wilcoxon matched pairs test and
Mann–Whitney U test.
Results
The 12-week-change MMAS total score showed that spasticity level decreased
more in the VAT group (p<0.001). GMFM-88 significantly improved more in the
VAT group (p<0.001).
Abbreviations used: JBI—Joanne Briggs Institute, CP—cerebral palsy, VAT—vibroacoustic therapy, GMFM-88—Gross
Motor Function Measure, GMFCS—Gross Motor Function Classification System, and MMAS—Modifed Modified
Ashworth Scale.

Int. J. Environ. Res. Public Health 2019,16, 3940 8 of 15
Table 4. Studies on children with CP—Liu, Zhang, and Zhao [40].
Research Design Quasi-Experimental Prospective Study
JBI level of evidence 2c
Objective(s) stated in
the study
To determine the effects of VAT on muscle tension and range of motion in
children with spastic CP (age 1–6) compared with physiotherapy and placebo.
Sample
90 children (age 1–6) from Nanhai Affiliated Maternity and Children’s Hospital of
Guangzhou University of Traditional Chinese Medicine allocated equally into
three groups: conventional therapy, placebo, and VAT. The study does not specify
how participants were allocated into groups. There was no significant difference
between the groups for gender, age, and for some of the muscle tone and range of
motion measurements (p>0.05).
Intervention
Conventional therapy group—physical therapy, massage, and Chinese herb bath
(once a day for 20 d). Experimental group—conventional therapy +VAT (60 Hz
with Jiao music). Control group—conventional therapy +Jiao music.
Interventions for both groups: 30 min a day for 20 d.
Measurements
An average of 3 measurements of muscle tone and range of motion (before,
midway, and after treatment) were used, muscle tone assessed by MMAS, and
statistical methods used included matching ttest and variance.
Results
There was no statistically significant difference for the conventional group after 20
d of treatment. Listening (placebo) group had a decrease in muscle tone (p<0.05).
In the VAT group, the range of motion of hips, knees, and ankles improved, and
muscle tone decreased (p<0.05).
89 children (age 4–6) with spastic CP from a daycare center for rehabilitation were
randomized into conventional therapy or conventional +VAT.
Abbreviations used: JBI—Joanne Briggs Institute, CP—cerebral palsy, VAT—vibroacoustic therapy, and
MMAS—Modifed Modified Ashworth Scale.
Table 5. Studies on children with CP—Katusic and Mejaski-Bosnjak [43].
Research Design Pretest–Post-Test Quasiexperimental Study
JBI level of evidence 2d
Objective(s) stated in
the study
To determine the effects of VAT on spasticity and motor function in children with
spastic CP (age 3–4)
Sample 13 children (age 3–4) from a daycare center for rehabilitation.
Intervention VAT once a week for 12 weeks, 20 min (40 Hz sine wave with sinusoidal
amplitude variation, 6.8 s between peaks).
Measurements Pre- and post-12 week treatment GMFM-88, GMFCS standardised assessments,
non-parametric Wilcoxon matched pairs test and Pearson c 2-test.
Results
Significant improvement in motor function. There was a significant improvement
in total GMFM score (z=3.17, p=0.00), as well as on dimension A (lying and
rolling, z=3.05, p=0.00) and dimension B (sitting, z=2.80, p=0.00). There was a
significant difference between GMFCS levels of children before and after
intervention (df =6, p=0.00).
Abbreviations used: JBI—Joanne Briggs Institute, CP—cerebral palsy, VAT—vibroacoustic therapy, GMFM-88—Gross
Motor Function Measure, and GMFCS—Gross Motor Function Classification System.

Int. J. Environ. Res. Public Health 2019,16, 3940 9 of 15
Table 6. Studies on children with CP—Liu et al. [41].
Research Design Pretest–Post-Test Quasiexperimental Study
JBI level of evidence
2d
Objective(s) stated
in the study
To determine effects of VAT on muscle tension and range of motion in children with
spastic CP (age 2–8)
Sample
36 children (2–8 years) with spastic cerebral palsy in outpatient and hospitalized care
at children´s rehabilitation hospital clinic.
Intervention Application of vibroacoustic therapy (16–150 Hz) with Jiao music 30 min each time.
No mention of length of therapy.
Measurements
Measuring range of motion, muscle tension: MMAS. Statistical methods used: ttest.
Results After VAT, the adductor angle, popliteal fossa angle, food dorsiflexion angle, and
muscle tone improved (p<0.05).
Abbreviations used: JBI—Joanne Briggs Institute, CP—cerebral palsy, VAT—vibroacoustic therapy, and
MMAS—Modifed Modified Ashworth Scale.
Table 7. Studies on adults with CP—Kvam [42].
Research Design Double-Blind Randomized Controlled Trial
JBI level of
evidence 1c
Objective(s) stated
in the study
To determine effects of VAT in adults with CP (age 27–48) on gross and fine
movements compared to placebo
Sample From 1 sheltered workshop of 14 workers, 12 had CP and were included.
Randomization
Stratified randomization of sample size 12: 6 pairs were created based on similarities
in age, level of communication, physical functioning, and level of independence. One
member of each pair was randomly selected for the experimental group.
Intervention Experimental group: application of VAT (40–80 Hz) twice weekly for 9 weeks.
Control group: application of music only, no vibrations, twice weekly for 9 weeks.
Measurements
Videotapes of gross and fine movements and drawing/writing tests (Swedish test by
Bille) blind evaluation by 4 assessors, AND post-trial interviews. Statistical methods
used: non-parametric one-tailed Wilcoxon signed rank test for matched pairs,
inter-rater reliability of the test was 90% and of the drawing test 92%.
Results
All experimental participants showed greater improvement after treatment in motor
test, and most participants were also better in drawing tests than those in the control
group. In the area of hand–eye coordination, there was a statistically significant
improvement (p=0.034), and improvement in fine movements was quite significant
(p=0.069). In the final interviews with participants, the experimental group was
more positive as to the effect of the treatment (p=0.054) and more certain of their
desire to continue (statistically significant, p=0.034). No participant results were
worse after the treatment.
Abbreviations used: JBI—Joanne Briggs Institute, CP—cerebral palsy, and VAT—vibroacoustic therapy.

Int. J. Environ. Res. Public Health 2019,16, 3940 10 of 15
Table 8. Studies on adults with CP—Wigram, chapter 4 [35].
Research Design Pretest–Post-Test Quasiexperimental Study (Included Subjects Studied with a
Single Blind Evaluation)
JBI level of evidence 2d
Objective(s) stated in the
study
To determine effects of VAT on range of motion in adults (age 28–77) with CP and
high muscle tone compared with placebo (only music)
Sample 10 residents of a large mental hospital took part in the trials (28–77 years), with
severe disorder with spastic cerebral palsy, with high muscle tone.
Intervention All 10 subjects received 6 sessions of 30 min VAT (44 Hz) as well as 6 only music
(no vibrations) sessions, randomly ordered, 2 times a week over 6 weeks.
Measurements
Blind evaluation of spinal mobility and limb flexion and extension using tape
measures of range of movement before and after each session. Statistics:
Wilcoxon matched pairs signed rank test.
Results VAT treatment showed significantly improved range of movement than placebo
(no vibrations), p=0.0051.
Abbreviations used: JBI—Joanne Briggs Institute, CP—cerebral palsy, and VAT—vibroacoustic therapy.
Table 9. Studies on adults with CP—Wigram, chapter 5 [36].
Research Design Pretest–Post-Test Quasiexperimental Study
JBI level of evidence 2d
Objective(s) stated in
the study
To determine effects of VAT on range of motion in adults (age 24–68) with high
muscle tone compared to placebo
Sample
10 participants were randomly chosen from a group of 27 residents of a large
mental hospital (24–68 years) all with high muscle tone who were included in a
different part of the same study.
Intervention Three 30 min VAT sessions using 44 Hz and three music (placebo) sessions in
each of the 10 participants administered blindly.
Measurements Range of motion, extension of arms and legs in centimeters measured before
and after each treatment, statistics: Wilcoxon matched pairs signed rank test.
Results All 10 participants had improved motor function after VAT compared with a
placebo (only music) with a significant difference p=0.0051.
Abbreviations used: JBI—Joanne Briggs Institute, CP—cerebral palsy, and VAT—vibroacoustic therapy.
3.1. Results of Relevant Studies Applying VAT in Children with CP
The 4 studies (Tables 3–6) applying VAT in children with CP (age 1–8), including one RCT study [
39
],
all stated a statistically significant improvement in children’s range of motion (motor function).
The 3 other studies used a pretest–post-test quasiexperimental design [
40
,
41
,
43
]. Moreover, two of the
studies also focused on investigating spasticity and found that VAT significantly reduced muscle tone in
CP [
39
,
40
]. One study found statistically significant differences in the classification (GMFCS, see below)
levels of children before and after intervention [39].
One study implemented a new instrument (developed for this study) for measuring range of
motion [
41
]. The remaining 3 studies on children with CP used standardized methods: Gross Motor
Function Measurement (GMFM) for measuring range of motion, Modified Modified Ashworth Scale
(MMAS) for measuring muscle tone, and Gross Motor Function Classification System (GMFCS) to
classify children with CP according to their motor function.
Furthermore, the studies have experimented with applying various frequencies of sinusoidal sound.
In two studies [
39
,
43
], a frequency 40 Hz was used as recommended by Skille [
11
]. The team of Liu [
40
]
decided to use a frequency 60 Hz, and another study by Liu [41] stated using 16–150 Hz frequencies.

Int. J. Environ. Res. Public Health 2019,16, 3940 11 of 15
3.2. Results of Studies Applying VAT in Adults with CP
Three relevant studies (Tables 7–9) investigating the effects of VAT on motor function in adults
with CP (age 24–77) all showed a positive effect of VAT, one being RCT [
42
] and the other two a
pretest–post-test quasiexperimental design [
35
,
36
]. Although all participants showed improvement of
their motor functions in the study by Kvam [
42
] on 12 adults with CP, only hand–eye coordination
results were statistically significant. In this study, most participants were better in a drawing test,
and improvement in fine movements was quite significant. The group receiving VAT was more
sure of their desire to continue (with statistical significance) and more positive on the effect of the
treatment. The other two studies [
35
,
36
] on a total of 20 adults with CP showed a statistically significant
improvement of motor function in the VAT group when compared to the group receiving a placebo.
None of these studies explored effects on spasticity.
All three studies used nonstandardized measurement instruments. Kvam [
42
] used gross and fine
movement tests and drawing/writing tests (Swedish test by Bille). Studies by Wigram [
35
,
36
] measured
changes in range of motion in specifically given areas with a marker and a standard tape measure.
Wigram [
35
,
36
] used a sinusoidal sound of 44 Hz frequency, which was very close to the 40 Hz used
by Katusic mentioned above. The study by Kvam [
42
] stated using a range between 40–80 Hz frequency.
4. Discussion
This section is structured according to main and additional goals of this paper with the aim
to compare findings of this advanced review with findings of systematic reviews and RCT studies
from the broader area of vibration therapies (methods using mechanical vibrations), namely WBV.
These studies were found in Cochrane Library and PubMed databases.
There were two randomized controlled trials (RCTs): one in adults, one in children, and five
pretest–post-test quasiexperimental studies on VAT in people with CP. Out of the two RCT studies
found, one was a single-blind study [
39
], one double-blind [
42
], and there were no triple-blind studies
in this area. Systematic reviews focused on VAT and CP have not been realized so far, although some
related methods using mechanical vibrations have this level of evidence available, for example, in the
case of WBV [
13
,
43
] or vibration therapy generally [
4
]. According to the authors from our team, further
research in VAT is needed to achieve more robust scientific evidence in the future; specifically required
are RCT studies, which provide a higher level of evidence in quantitative research than experimental
studies [
33
]. The systematization of information concerning methodological designs of studies may
help in the future creation of systematic review protocols focused on exploring the effects of VAT on
motor functions of people with CP.
Published studies show that VAT may increase motor function in both children and adults with
CP. All seven studies presented an improvement of motor function in participants, six of them with
statistical significance [
35
,
36
,
39
–
41
,
43
]. Furthermore, three of these studies found that VAT reduced
spasticity in people with spastic CP [
39
–
41
]. These findings are consistent with findings of systematic
reviews on WBV [
13
,
44
], proving that low vibrations can improve movement and spasticity in people
with CP.
VAT studies focused on adult populations included participants aged 24–77 years old, and VAT
studies of child populations included participants aged 1–8 years old. Studies on adolescents and young
adults (ages 9–23) were, therefore, completely missing. This age category has, however, been explored
in studies dealing with WBV that brought positive results in, for example, a study done by Krause et
al. (ages 4–22) [
45
] or Tupimai (ages 6–18) [
46
]. It can, therefore, be assumed that it may be possible
to observe positive effects of VAT also in the age category of adolescents and young adults with CP,
although these results may not be as significant in terms of their healing potential as in the case of
children with CP. “Although VT (vibration therapy) demonstrably has a positive and age-independent
influence on neuromuscular, functional, and structural factors associated with the disease-related
deficits in patients with CP, we expect that VT will be particularly efficient in children, due to their

Int. J. Environ. Res. Public Health 2019,16, 3940 12 of 15
advantage of neuroplasticity, and that VT may initiate long-term developmental effects that may persist
into adulthood” [4] (p. 1621).
As for the measurement tools, two studies on VAT [
39
,
43
] used GMFM-88 (Gross Motor Function
Measurement) to measure motor function and GMFCS (Gross Motor Function Classification System)
for classification according to motor function; three studies on VAT [
39
–
41
] used MMAS (Modified
Modified Ashworth Scale) to measure spasticity; one study on VAT [
42
] used Bille
´
s test of motor
function (FBH); two by one author used an original range of motion measurements [
35
,
36
]; and two
by one author [
40
,
41
] used measuring of range of motion of some body parts with a tape measure.
Only research studies in children used internationally recognized measurement tools. The benefit of
these standardized tools is their easy interpretation for researchers worldwide and the possibility of
enhancing the scientific robustness of such studies. Four studies used original measurement methods
that may be hard to exactly replicate, even with a thorough description, which is sometimes lacking.
Regarding frequencies of sinusoidal sound, two studies used a 40 Hz frequency [
39
,
43
]; two
studies used 44 Hz [
35
,
36
]; another one used 60 Hz [
40
]; one used a nonspecified range of 40–80 Hz [
42
];
and one stated a broad range of 16–150 Hz [
41
]. These findings correlate with Skille’s conclusions [
29
]
since he associates 40 and 60 Hz frequencies with the treatment of spasticity. Authors of this paper
have not found any studies aiming to determine the effects of various frequencies or of various types of
low-sinusoidal stimulation on movement or spasticity in people with CP. Also, findings from systematic
reviews from the area of vibration therapy are inconclusive in this issue. For example, Ritzmann,
Stark, and Krause [
4
] write: “Among the different intervention protocols, the analysis revealed no
apparent dosage-dependency of VT. The great variation in VT protocols makes it difficult to highlight
a clear favorite setting with efficiency beyond the others. Vibration has been applied at different levels:
5–50 Hz for WBV and reaching peak frequencies for focal vibration at 60–200 Hz” (p. 1620). There is a
possibility that different sound frequencies or different types of low-sinusoidal stimulation could have
different therapeutic outcomes; however, this must be explored in the future.
4.1. Recommendations for Future Research
Future researchers could, when designing research in this area, take the following into consideration.
•
There have been few RCTs, and, specifically, double-blind and triple-blind studies are
completely missing.
•Effects of VAT on adolescents and young adults with CP have not been explored yet.
•Using standardized measurement tools enables comparisons of results.
•It is advisable to include measuring spasticity (using MMAS).
•
There is little knowledge on the possibly of different therapeutic outcomes of various frequencies
or types of low-sinusoidal stimulation.
•
There are other topics not addressed sufficiently in this review that would be worthy of further
research (e.g., exploring the mechanisms of how VAT influences neuromuscular functions).
If future researchers could broaden primary research focused on the application of VAT in people with
spastic CP, it would then be possible to include such data (e.g., in a meta-analysis) in the creation of
systematic reviews and guidelines for the application of VAT. Modern approaches of evidence-based
practice (according to Cochrane or JBI methodology) lead experts towards using evidence from studies
with more robust levels of evidence that are listed higher in the hierarchy of studies. Based on this
assumption, it would be beneficial to create systematic reviews in order to prepare guidelines for VAT
practice in the future. We, therefore, recommend the expert community to continue realizing further
research focusing on the effects of VAT in people with CP, with priority on RCT study design.

Int. J. Environ. Res. Public Health 2019,16, 3940 13 of 15
4.2. Reflection of the Review
Some procedures of the standard evidence-based approach were used for this advanced narrative
review, namely the formulation of a search question; a structured, documented search; assessment
of the relevance of abstracts and full texts to the search question and inclusion criteria; searches in a
large number of relevant databases; inclusion of studies in different languages and their translations
(e.g., Chinese); and so on. Since this is not a systematic review, the studies were not assessed by two or
more independent evaluators, the methodological quality of contributions was not critically appraised,
and a meta-analysis of data was not included.
The scale of the researched issue had also been reflected. In this paper, only studies about VAT as
defined in the first section were searched. This means that we searched for studies based on sound-induced
vibrations (not mechanical vibrations) because academic literature differs methods in this area according
to the source and type of vibrations [
47
]. Furthermore, we searched for studies using low-frequency sound
in combination with music listening. This is another difference between VAT as defined by Skille [
8
] or
Lehikoinen [
19
] and typical practice of many therapists using methods based on mechanical vibrations
without music. The fact that music itself can significantly impact motion and spasticity [
48
] cannot
be ignored. Especially, modern VAT devices [
23
] that are based on an interaction of vibrations and
music bring a new aesthetic dimension for listening to music and, most importantly, a potentially new
combination of known mechanisms impacting somatic and mental (emotional) functions of the human
body. Therefore, only methods of vibroacoustics as described above were included in the search of this
review, which were then, in discussion, compared with other related methods.
5. Conclusions
The results show that VAT could potentially improve motor function in children and adults with
spastic CP. Although this conclusion has been confirmed by most of the found studies, primary studies
with highly robust evidence (RCT) are few, and evidence on the level of secondary research (SR) is
completely lacking. Partially, this deficit is possible to compensate by reflecting findings on VAT in
people with CP in the context of similar findings concerning related methods from the area of vibration
therapies (based on mechanical vibrations). The authors recommend continuing to research the effects
of VAT on motor function and spasticity in people with spastic CP (with priority of RCT study design),
to focus on adolescents and young adults, and to compare the effects of various frequencies and types
of low-sinusoidal sound stimulation. Furthermore, during future research in this area, standardized
methods of measurement already used in previous studies are preferred.
Note:
Although triple-blinded studies are recommended for clinical research [
24
], the design of double-blinded
studies seems sufficient for VAT research. There is a very low probability that a person offering intervention could
influence the result of the study.
Author Contributions:
Conceptualization, J.K., J.M. and Z.V.; methodology, J.M. and J.K.; software, L.K.;
validation, J.K., L.K., and J.M.; formal analysis, J.K., L.K. and D.P.; investigation, J.K., L.K. and D.P.; resources, J.K.
and L.K.; data curation, J.K., L.K. and J.M.; writing—original draft preparation, J.K., L.K. and Z.V.; writing—review
and editing, J.K., L.K. and J.M.; visualization, L.K.; supervision, J.M.; project administration, J.K.; funding
acquisition, J.K.”
Funding:
This research was funded by Faculty of Education, Palack
ý
University in Olomouc, IGA_2019_004—V
ý
zkum
muzikoterapie v oblasti rozvoje osob se speci
á
ln
í
mi potˇrebami (Research of music therapy in the development of
persons with special needs).
Conflicts of Interest: The authors declare no conflict of interest.
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