Topics in Stroke Rehabilitation
ISSN: 1074-9357 (Print) 1945-5119 (Online) Journal homepage: http://www.tandfonline.com/loi/ytsr20
Effects of whole body vibration training on people with chronic stroke: a systematic review and metaanalysis Jun Lu, Guangxu Xu & Yuchen Wang To cite this article: Jun Lu, Guangxu Xu & Yuchen Wang (2015) Effects of whole body vibration training on people with chronic stroke: a systematic review and meta-analysis, Topics in Stroke Rehabilitation, 22:3, 161-168 To link to this article: http://dx.doi.org/10.1179/1074935714Z.0000000005
Published online: 24 Feb 2015.
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Effects of whole body vibration training on people with chronic stroke: a systematic review and meta-analysis Jun Lu, Guangxu Xu, Yuchen Wang
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Department of Rehabilitation, First Affiliated Hospital of Nanjing Medical University, Nanjing 210029, China Background: The effects of whole body vibration (WBV) on chronic stroke (CS) patients have been investigated by some previous studies. However, controversy still exists. Objective: The objective of this meta-analysis was to review existing studies that assess the effects of WBV training on CS patients. Methods: We searched Medline, Web of Science, EMBASE, and the Cochrane Library for papers published between January 2000 and January 2014.The meta-analyses were performed using Review Manage Version 5.2.Weighted mean difference (WMD) or standard mean difference (SMD) and its 95% confidence intervals (CI) were used as summary statistics. Funnel plot was used to assess the publication bias. Results: Seven studies with 298 CS patients (159 patients underwent WBV training in experimental group and 139 patients underwent nothing or the same exercise without vibration or with a ‘‘placebo’’ vibrating platform in control group) were included. No significant difference was found in muscle strength (isometric knee extension strength: SMD5{0.15, 95% CI, {0.43 to 0.13, P50.30; isometric knee flexion strength: WMD5{0.05, 95% CI, {0.13 to 0.03, P50.22), balance (berg balance scale, WMD5{0.23, 95% CI, {1.54 to 1.09; P50.74) and gait performance (6-min walk test, WMD5{50.40, 95% CI, {118.14 to 17.34; P50.14) between groups. No indication of publication bias was found in the funnel plot. Conclusions: WBV training had no beneficial effects in muscle strength, balance and gait performance of CS patients. Keywords: Whole body vibration, Training, Chronic stroke, Systematic review, Meta-analysis
Introduction Stroke is an important cerebrovascular disease which can cause chronic disability and death.1 Among all stroke patients, more than 62% of new strokes, 69.8% of prevalent strokes, 45.5% of deaths from stroke, and 71.7% of disability-adjusted life years lost because of stroke were in people younger than 75 years old, and these incidences still continue to rise in the coming years.2,3 Muscle weakness is the most prominent impairment after stroke.4 Stroke survivors have two sequelae: acute stroke and chronic stroke (CS).2,5 Among them, CS is associated with substantial motor disability.6 It has been reported that muscle weakness, spasticity, and chronic disuse significantly contributed to demineralization and geometric changes in the radius Correspondence to: Guangxu Xu, Department of Rehabilitation, the First Affiliated Hospital of Nanjing Medical, University, No. 300 Guangzhou Road, Nanjing 210029, China. Email: [email protected] ß W. S. Maney & Son Ltd 2015
DOI 10.1179/1074935714Z.0000000005
following CS.7 Paretic muscle strength and the ability to load the paretic limb are important factors underlying the ability to rise from a chair in individuals with CS.8 Therefore, it is necessary to find an appropriate approach for improving the muscle strength of CS patients. It has been reported that muscle activation could be induced by whole body vibration (WBV) via stimulation of the muscle spindle system.9,10 Moreover, WBV has been a novel rehabilitation training widely used in clinical application and research.11 Ahlborg et al.12 reported that WBV could increase muscle strength, without negative effect on spasticity, in adults with cerebral palsy. Roelants et al.13 showed that knee-extension strength and speed of movement could be improved after WBV training in older women. Simultaneously, the effects of WBV on CS patients have also been investigated in some published studies.14–17 However, the Topics in Stroke Rehabilitation
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controversy still exists. Tankisheva et al.17 found that WBV might potentially be a safe and feasible way in increasing knee muscle strength in adults with CS.17 However, WBV did not induce additional effects on knee muscle strength among CS patients in the study of Pang et al.16 Therefore, we conducted this study to determine whether reliable evidence exists for the potential effects of WBV training on CS patients by systematic review and meta-analysis.
Materials and Methods Literature search strategy
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Literature search was performed by two investigators (Wentong Zhang and Lin Li) on databases such as MEDLINE, PubMed, Web of Science, EMBASE and the Cochrane Library from January 2000 to January 2014, using the terms of ‘‘stroke’’ AND ‘‘whole body vibration’’ AND ‘‘chronic stroke’’ OR ‘‘stroke’’ AND ‘‘training’’ OR ‘‘stroke’’ AND ‘‘whole body vibration’’ AND ‘‘training.’’ Meanwhile, the reference lists of retrieved articles were also manually searched for additional studies. Furthermore, reviews, reports and unpublished articles were not considered in this study.
Inclusion and exclusion criteria The included studies should meet the following criteria: (i) studies were randomized controlled trials (RCTs); (ii) participants aged from 18 to 75 years old were diagnosed with CS based on the criteria of world health organization; (iii) patients were randomly assigned to either the experimental group (patients underwent exercise training with WBV) or control group (patients underwent nothing or the same exercise without vibration or with a ‘‘placebo’’ vibrating platform); (iv) studies evaluated the muscle strength through test for isometric knee extension or flexion muscle strength, balance through berg balance scale (BBS) or tinetti balance scale, or gait performance through timed up and go test (TUG) or walk test. Studies were excluded if (i) the training was local muscle vibration, (ii) the participants were acute stroke patients, (iii) studies were duplicated publications, (iv) the full text could not be obtained or (v) the language of included studies was not English.
Quality assessment and data extraction Two researchers independently extracted data and assessed the quality of included RCTs. Extracted 162
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data included general information of the studies (the first author’s name, year of publication), characteristics of participants (gender, age, duration of disease, paralyzed side and stroke type), study design (frequency and amplitude of WBV, time per series, number of series per session, number of sessions and control) and outcomes. For the quality assessment, the Cochrane Collaboration’s Tool was used to assess the risk of bias following the instructions given in the Cochrane Handbook for Systematic Reviews.18 The following items were used to evaluate the bias of each included study: random sequence generation (selection bias), allocation concealment (selection bias), blinding of participants and personnel (performance bias), blinding of outcome assessment (detection bias), incomplete outcome data (attrition bias), selective reporting (reporting bias) and other bias. Judgments were categorized as ‘‘low risk of bias’’ (z), ‘‘high risk of bias’’ ({), or ‘‘unclear risk of bias’’ (?).
Statistical analysis The meta-analyses were performed using Review Manage Version 5.2 (Cochrane Library, Oxford, UK). The heterogeneity among included studies was measured using I 2 statistic and chi-square test. A significant heterogeneity was confirmed with Pv0.10 and I 2w50%, then random-effects model was used to pool the data. Otherwise, fixed-effects model was applied. Weighted mean difference (WMD) or standard mean difference (SMD) and its 95% confidence intervals (CI) were used as summary statistics to evaluate the effects of WBV on CS patients. Descriptive analysis was used when data could not be pooled. Funnel plot was used to assess the publication bias.
Results Literature search The process of literature search and study selection is shown in Fig. 1. In the initial search, 261 literatures were identified through searching databases and no additional studies were found from manually searching. After removing duplications, a total of 213 articles were remained. Then 172 obviously irrelevant literatures were excluded by scanning the titles and abstracts. Among the remaining 41 reports, 34 articles (including 16 reviews, 5 non-RCTs, 10 studies in which local muscle vibration was used, and 3 studies in which participants were acute stroke patients) were excluded according to the inclusion and exclusion criteria. As a result, seven studies14–17,19–21 were included in this study. Among them, data from three studies14,16,20 were available to do statistical
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Figure 1 Literature search and study selection.
analysis. The other four studies were used for review in this study.
Characteristics of included studies The included studies were all recent reports with publication year from 2012 to 2014. The characteristics of participants in each study are shown in Table 1. The patients were from China,14,16,19 Sweden,20 Belgium,17 Brazil,21 and Spain,15 respectively. A total of 298 CS patients including 159 patients underwent
exercise training with WBV and 139 patients underwent nothing or the same exercises without vibration or with a ‘‘placebo’’ vibrating platform) were considered in this study. There were 185 ischemic stroke patients and 113 hemorrhage patients. The average duration of disease ranged from 30.4 months to 7.71 years. The characteristics of methods and outcomes are shown in Table 2. There are differences in the WBV protocols among the included studies. The frequencies of WBV in the studies of
Table 1 Characteristics of participants
Study
Region
Brogardh et al. (2012)20
Sweden Experimental Control Belgium Experimental Control China Experimental Control Brazil Experimental Control China Experimental Control Spain Experimental Control China Experimental Control
Tankisheva et al. (2013)17 Pang et al. (2013)16 Silva et al. (2014)21 Chan et al. (2012)19 Marin et al. (2013)15 Lau et al. (2012)14
Group
N
Gender (M/F) Age (years)
16 15 7 8 41 41 28 10 15 15 11 9 41 41
13/3 12/3 4/3 6/2 26/15 32/9 19/9 8/2 10/5 11/4 6/5 5/4 26/15 32/9
Duration of disease
Side (L/R) Type(I/H)
61.3+ 8.5 37.4+ 31.8 m 9/7 33.1+ 29.2 m 7/8 63.9+ 5.8 57.4+ 13 7.71+ 8.6 y 4/3 5.28+ 3.6 y 4/4 65.3+ 3.7 57.3+ 11.3 4.6+ 3.5 y 20/21 5.3+ 4.2 y 14/27 57.4+ 11.1 60.75+ 11.8 40.85+ 68.76 m 17/11 39.6+ 63.55 m 7/3 58.1+ 8.14 56.07+ 11.04 30.4+ 25.8 m 12/3 54.93+ 7.45 38.87+ 38.22 m 7/8 62.3+ 10.6 4.3+ 2 y 5/6 4.3+ 3 y 5/4 64.4+ 7.6 57.3+ 11.3 4.6+ 3.5 y 20/21 5.3+ 4.2 y 14/27 57.4+ 11.1
14/2 13/2 6/1 5/3 20/21 21/20 25/3 8/2 10/5 5/10 10/1 7/2 20/21 21/20
Note: WBV, whole body vibration; M, male; F, female; L, left; R, right; I, ischemic stroke; H, hemorrhage.
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Table 2 Characteristics of methods and outcomes
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Study
No. series per session (rest Time per Frequency Amplitude periods, series Posture (knee No. (Hz) (mm) seconds) (seconds) angle) sessions
Brogardh et al. (2012)20
25
3.75
4–12 (60)
40–60
Static (45uu, 60uu)
1 session/d, 2 d/wk, 6 wks
Tankisheva et al. (2013)17
35, 45
1.7 and 2.5
1
30–60
High squat (50 to 60uu), deep squat (90uu), widestance squat, one-legged squat
1 session/d, 3 d/wk, 6 wks
Pang et al. (2013)16
20–30
0.44–0.6
6
90–150
1 session/d, 3 d/wk, 8 wks
Silva et al. (2014)21
50
2
4 (60)
60
Side to side weight shift, semi-squat (30uu), forward and backward weight shift, forward lunge, standing on one leg, deep squat (90uu) Semi-squat (30uu), deep squat (90uu) unipodal landing
Chan et al. (2012)19
12
4
2 (60)
600
Marin et al. (2013)15
5–21
NR
4–7 (60)
30–60
Lau et al. (2012)14
20–30
044–0.6
1
90–150
1 session
Control
Outcomes
The same as experimental group but the amplitude is 0.2 mm
No significant differences between groups in body function and gait performance Not involved Muscle in any strength and training postural program control improved, no change in muscle spasticity Perform the Spasticity same reduced, no exercises on change in the same bone turnover, platform motor function without and muscle vibration strength
Keep the same position on the platform without vibration Keep the same position on the platform without vibration
No between group difference in EMG, 6 MWT, CT and TUG improved Semi-squat 1 session Ankle plantar flexion spasticity decreased, gait velocity, TUG and 10 MWT improved 17 Keep the No between Semi-squat sessions same group (30uu) position on difference in the platform BBS and without muscle vibration strength Side to side 24 Perform the No between weight shift, sessions/d, same group semi-squat 3 d/wk, 8 exercises on difference in (30uu), forward wks the same BBS, dynamic and backward platform postural weight shift, without control, 6 standing on vibration MWT, 10 one leg, deep MWT, muscle squat, forward strength had lunge fall-related self-efficacy
Note: BBS, Berg Balance Test; EMG, surface electromyography, 6 MWT, 6 minutes walking test; SCT, Stair–Climb Test; 10 MWT, 10 meters walking test; NR, not reported.
Chan et al.19 and Marin et al.15 were lower than 21 Hz, while they were between 20 and 30 Hz in the studies of Brogardh et al.,20 Pang et al.16 and Lau et al.14 Meanwhile, frequencies over than 30 Hz were 164
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applied in the studies of Tankisheva et al.17 and Silva et al.21 In addition, the WBV training in two studies14,16 used the same amplitude (0.44 to 0.6 mm), but they were obviously different among
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other studies. Furthermore, there were also differences in time per series (ranged from 30 to 600 s), numbers of series per session and numbers of sessions among these included studies.
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Quality assessment of included study The quality assessments for the included trails are shown in Fig. 2. All the included trails reported the method for randomization sequence generation and allocation concealment. Thus, the risk of selection bias was low for all the included studies. Meanwhile, all studies also had low risk of bias in the selection reporting and incomplete outcomes. However, high risk of performance bias existed in four included studies14,17,20,21 and high risk of bias in blinding of outcome assessment was found in one study.17 Notably, all the included studies had the high risk of other bias except the one reported by Marin et al.15
Muscle strength Four of these included studies analyzed the isometric knee extension strength.14,16,17,20 Among them, the frequency of WBV in the study of Tankisheva et al. (35 and 45 Hz)17 was higher than that in the other
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three studies (20 to 30 Hz).14,16,20 For avoiding the influence of different frequency on the results, we only reanalyzed the studies of Brogardh et al.,20 Lau et al.14 and Pang et al.16 by meta-analysis. The data of Tankisheva et al.17 were used for discussion by comparing with the results of this meta-analysis. In this analysis, no significant heterogeneity was found among the included studies, so fixed-effects model was used to pool the data (I 250%, P50.98). The overall estimate (SMD5{0.15, 95% CI: {0.43 to 0.13, P50.30) suggested that there was no significant difference in the isometric knee extension strength between experimental and control groups (Fig. 3A). Three trails investigated the isometric knee flexion strength with a total of 164 participants.14,16,17 Compared with the other studies (20 to 30 Hz), study of Tankisheva et al.17 with higher frequency (35 and 45 Hz) of WBV was just used for discussion. There was no evidence for the significant heterogeneity among the other two studies, so fixed-effects model was used for pooling data (I 250%, P50.35). The overall WMD was {0.05 (95% CI: {0.13 to 0.03; P50.22), indicating that no significant difference was found in the isometric knee flexion strength between experimental and control groups (Fig. 3B). However, Tankisheva et al.17 reported that WBV could significantly improve the isometric knee extension or flexion strength, which was inconsistent with the results of this meta-analysis.
Balance Three of these studies investigated the balance by BBS.14,15,20 The frequency of WBV in Marin et al (5 to 21 Hz)15 was lower than that in the other two studies (20 to 30 Hz),14,20 thus the study of Marin et al.15 was only used for discussion by comparing with the results of statistical analysis. No significant heterogeneity was found among the included studies, so fixedeffects model was used (I 250%, P50.95). The overall WMD of {0.23 (95% CI: {1.54 to 1.09; P50.74) demonstrated that there was no significant difference between experimental and control groups in balance which was examined by BBS (Fig. 3C). Moreover, the results of Marin et al.15 also indicated no significant differences in balance between groups.
Gait performance
Figure 2 Risk of bias for each included studies.
Three tails investigated the effect of WBV on gait performance by a 6-min walk test.14,20,21 Given that the frequency of WBV in the study of Silva et al. (50 Hz)21 was higher than that in the other two studies (20– 30 Hz),14,20 statistical analysis was only performed in the studies of Brogardh et al.20 and Lau et al.14 The result of Silva et al. was used for discussion through Topics in Stroke Rehabilitation
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Figure 3 Forest plots of meta-analysis. (A) Isometric knee extension strength. (B) Isometric knee flexion strength. (C) Berg balance scale. (D) 6-min walk test.
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comparing with the result of meta-analysis. No enough evidence was found for significant heterogeneity among studies (I 2557%, P50.13), so fixed-effects model was used. The overall WMD was {50.40 (95% CI: {118.14 to 17.34; P50.14), which indicated no significant difference in gait velocity between groups (Fig. 3D). However, Silva et al.21 provided evidence for significant improvement of gait performance by the 6-min walk and TUG test in the experimental group compared with that in control group. In addition, TUG test was also performed in other two studies.19,20 The results of the three studies all proved that WBV training could significantly improve the gait performance by TUG. Due to different frequencies of WBV among these studies,19–21 the statistical analysis was not conducted for the outcomes of TUG test. Thus, we analyzed the results of these studies through description and discussion in this study.
Publication bias No asymmetry indicated publication bias in this study. The funnel plot for the studies which reported balance by BBS is shown in Fig. 4. The representative points of studies of Lau et al. and Pang et al. were overlapped.
Discussion Chronic stroke is associated with substantial motor disability, which severely affected the health related quality of life.22 The objective of the present study was to assess the effects of WBV training on patients with CS. Following the meta-analyses, the results showed that there was no significantly difference between experimental and control groups in muscle strength, balance and gait performance, suggesting that WBV training could not significantly benefit the muscle strength, balance or gait performance of people with CS. The results in the study of Marin et al. (an increased frequency of 5 to 21 Hz) are consistent with the results of this meta-analysis (frequency ranged from 20 to
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30 Hz) in balance (BBS) and muscle strength (the maximal isometric voluntary contraction of the knee extensors). However, the study of Tankisheva et al.17 which used frequency of 35 and 45 Hz found that the isometric knee extension strength was significantly increased after 6 weeks of exercise training with WBV (frequency 35 and 45 Hz, amplitude 1.7 and 2.5 mm). Meanwhile, Silva et al. suggested that the gait performance (6MWT) of CS patients was improved by WBV (frequency 50 Hz, amplitude 2 mm), which was inconsistent with the result of this study. Thus, we speculated that the WBV training with higher frequency than 30 Hz might be more beneficial to the patients with CS than that with frequency less than 30 Hz. However, the study of Chan et al.19 demonstrated that a single session of WBV training (frequency 12 Hz, amplitude 4 mm) significantly improved the gait performance of CS patients by TUG test and 10-meter walk test. Although the frequency was lower in the study of Chan et al., the amplitude was larger than that in other studies, which may affect the effects of WBV on CS patients. In addition, it was reported that muscle activity and acceleration during WBV were varied with different frequencies and amplitudes.23 Therefore, frequency and amplitude may be the main factors for the effects of WBV on CS patients. It was reported that lower frequencies (from 25 to 35) of WBV were suitable for maximal activation of the lateral gastrocnemius, whereas higher frequencies (from 45 to 55 Hz) elicited the highest reflex responses in the vastus lateralis.24 Meanwhile, continuous muscle contraction could give rise to a widespread diffusion of the reflex responses, thereby affecting the muscle strength.25 Thus, the WBV may affect the muscle strength through increasing the reflex responses which was associated with frequency of vibration. Several limitations should be mentioned in the present study. First, due to lack of available data, only three out of seven included RCTs were used to do the metaanalysis, the others just used for review in this study. Second, high risk of other bias and bias in blinding method existed, which may affect the results of this study. Third, the study designs were different in the included studies, which may be the causes of other bias and can increase the instability of the results in this study. At last, the sensitivity analysis was not performed because of less included studies. Therefore, the reliable and stable of the results in this study need more high quality RCTs with larger sample size to verify.
Conclusion Figure 4 Funnel plot of studies examining balance by BBS.
In conclusion, WBV training showed no significant effects on improving muscle strength, balance and Topics in Stroke Rehabilitation
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gait performance of CS patients. Frequency and amplitude may be the major influence factors for the effects of WBV on patients with CS. Reflex responses of muscles on WBV with different frequencies should be considered in the further studies. In view of this, more studies considering the frequency, amplitude and response of body must be performed in future. Additionally, it is necessary to further investigate the effects of WBV on other outcomes, such as proprioception and activities of daily living.
Acknowledgements
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This review is part of the thesis of its first author, Jun Lu master degree candidate at Nanjing medical university, China. The authors would like to acknowledge the contribution of Professor Xu for his guidance in developing the review, Wentong Zhang and Lin Li for their support in the searching and obtaining the articles, and Xiaoying Zhou for her assistance and help in the editing process of the review. The authors also thank the staffs of the department of rehabilitation (First Affiliated Hospital of Nanjing Medical University) for their support to the first author. Contributors Jun Lu conceived the project. Jun Lu, Guangxu Xu and Yuchen Wang performed experiments and data analysis. Guangxu Xu wrote the manuscript. All authors read and approved the final manuscript. Funding None. Conflicts of Interest There are no conflicts of interest associated with this work. Ethics Approval Not applicable.
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ISSN: 1074-9357 (Print) 1945-5119 (Online) Journal homepage: http://www.tandfonline.com/loi/ytsr20
Effects of whole body vibration training on people with chronic stroke: a systematic review and metaanalysis Jun Lu, Guangxu Xu & Yuchen Wang To cite this article: Jun Lu, Guangxu Xu & Yuchen Wang (2015) Effects of whole body vibration training on people with chronic stroke: a systematic review and meta-analysis, Topics in Stroke Rehabilitation, 22:3, 161-168 To link to this article: http://dx.doi.org/10.1179/1074935714Z.0000000005
Published online: 24 Feb 2015.
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Effects of whole body vibration training on people with chronic stroke: a systematic review and meta-analysis Jun Lu, Guangxu Xu, Yuchen Wang
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Department of Rehabilitation, First Affiliated Hospital of Nanjing Medical University, Nanjing 210029, China Background: The effects of whole body vibration (WBV) on chronic stroke (CS) patients have been investigated by some previous studies. However, controversy still exists. Objective: The objective of this meta-analysis was to review existing studies that assess the effects of WBV training on CS patients. Methods: We searched Medline, Web of Science, EMBASE, and the Cochrane Library for papers published between January 2000 and January 2014.The meta-analyses were performed using Review Manage Version 5.2.Weighted mean difference (WMD) or standard mean difference (SMD) and its 95% confidence intervals (CI) were used as summary statistics. Funnel plot was used to assess the publication bias. Results: Seven studies with 298 CS patients (159 patients underwent WBV training in experimental group and 139 patients underwent nothing or the same exercise without vibration or with a ‘‘placebo’’ vibrating platform in control group) were included. No significant difference was found in muscle strength (isometric knee extension strength: SMD5{0.15, 95% CI, {0.43 to 0.13, P50.30; isometric knee flexion strength: WMD5{0.05, 95% CI, {0.13 to 0.03, P50.22), balance (berg balance scale, WMD5{0.23, 95% CI, {1.54 to 1.09; P50.74) and gait performance (6-min walk test, WMD5{50.40, 95% CI, {118.14 to 17.34; P50.14) between groups. No indication of publication bias was found in the funnel plot. Conclusions: WBV training had no beneficial effects in muscle strength, balance and gait performance of CS patients. Keywords: Whole body vibration, Training, Chronic stroke, Systematic review, Meta-analysis
Introduction Stroke is an important cerebrovascular disease which can cause chronic disability and death.1 Among all stroke patients, more than 62% of new strokes, 69.8% of prevalent strokes, 45.5% of deaths from stroke, and 71.7% of disability-adjusted life years lost because of stroke were in people younger than 75 years old, and these incidences still continue to rise in the coming years.2,3 Muscle weakness is the most prominent impairment after stroke.4 Stroke survivors have two sequelae: acute stroke and chronic stroke (CS).2,5 Among them, CS is associated with substantial motor disability.6 It has been reported that muscle weakness, spasticity, and chronic disuse significantly contributed to demineralization and geometric changes in the radius Correspondence to: Guangxu Xu, Department of Rehabilitation, the First Affiliated Hospital of Nanjing Medical, University, No. 300 Guangzhou Road, Nanjing 210029, China. Email: [email protected] ß W. S. Maney & Son Ltd 2015
DOI 10.1179/1074935714Z.0000000005
following CS.7 Paretic muscle strength and the ability to load the paretic limb are important factors underlying the ability to rise from a chair in individuals with CS.8 Therefore, it is necessary to find an appropriate approach for improving the muscle strength of CS patients. It has been reported that muscle activation could be induced by whole body vibration (WBV) via stimulation of the muscle spindle system.9,10 Moreover, WBV has been a novel rehabilitation training widely used in clinical application and research.11 Ahlborg et al.12 reported that WBV could increase muscle strength, without negative effect on spasticity, in adults with cerebral palsy. Roelants et al.13 showed that knee-extension strength and speed of movement could be improved after WBV training in older women. Simultaneously, the effects of WBV on CS patients have also been investigated in some published studies.14–17 However, the Topics in Stroke Rehabilitation
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controversy still exists. Tankisheva et al.17 found that WBV might potentially be a safe and feasible way in increasing knee muscle strength in adults with CS.17 However, WBV did not induce additional effects on knee muscle strength among CS patients in the study of Pang et al.16 Therefore, we conducted this study to determine whether reliable evidence exists for the potential effects of WBV training on CS patients by systematic review and meta-analysis.
Materials and Methods Literature search strategy
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Literature search was performed by two investigators (Wentong Zhang and Lin Li) on databases such as MEDLINE, PubMed, Web of Science, EMBASE and the Cochrane Library from January 2000 to January 2014, using the terms of ‘‘stroke’’ AND ‘‘whole body vibration’’ AND ‘‘chronic stroke’’ OR ‘‘stroke’’ AND ‘‘training’’ OR ‘‘stroke’’ AND ‘‘whole body vibration’’ AND ‘‘training.’’ Meanwhile, the reference lists of retrieved articles were also manually searched for additional studies. Furthermore, reviews, reports and unpublished articles were not considered in this study.
Inclusion and exclusion criteria The included studies should meet the following criteria: (i) studies were randomized controlled trials (RCTs); (ii) participants aged from 18 to 75 years old were diagnosed with CS based on the criteria of world health organization; (iii) patients were randomly assigned to either the experimental group (patients underwent exercise training with WBV) or control group (patients underwent nothing or the same exercise without vibration or with a ‘‘placebo’’ vibrating platform); (iv) studies evaluated the muscle strength through test for isometric knee extension or flexion muscle strength, balance through berg balance scale (BBS) or tinetti balance scale, or gait performance through timed up and go test (TUG) or walk test. Studies were excluded if (i) the training was local muscle vibration, (ii) the participants were acute stroke patients, (iii) studies were duplicated publications, (iv) the full text could not be obtained or (v) the language of included studies was not English.
Quality assessment and data extraction Two researchers independently extracted data and assessed the quality of included RCTs. Extracted 162
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data included general information of the studies (the first author’s name, year of publication), characteristics of participants (gender, age, duration of disease, paralyzed side and stroke type), study design (frequency and amplitude of WBV, time per series, number of series per session, number of sessions and control) and outcomes. For the quality assessment, the Cochrane Collaboration’s Tool was used to assess the risk of bias following the instructions given in the Cochrane Handbook for Systematic Reviews.18 The following items were used to evaluate the bias of each included study: random sequence generation (selection bias), allocation concealment (selection bias), blinding of participants and personnel (performance bias), blinding of outcome assessment (detection bias), incomplete outcome data (attrition bias), selective reporting (reporting bias) and other bias. Judgments were categorized as ‘‘low risk of bias’’ (z), ‘‘high risk of bias’’ ({), or ‘‘unclear risk of bias’’ (?).
Statistical analysis The meta-analyses were performed using Review Manage Version 5.2 (Cochrane Library, Oxford, UK). The heterogeneity among included studies was measured using I 2 statistic and chi-square test. A significant heterogeneity was confirmed with Pv0.10 and I 2w50%, then random-effects model was used to pool the data. Otherwise, fixed-effects model was applied. Weighted mean difference (WMD) or standard mean difference (SMD) and its 95% confidence intervals (CI) were used as summary statistics to evaluate the effects of WBV on CS patients. Descriptive analysis was used when data could not be pooled. Funnel plot was used to assess the publication bias.
Results Literature search The process of literature search and study selection is shown in Fig. 1. In the initial search, 261 literatures were identified through searching databases and no additional studies were found from manually searching. After removing duplications, a total of 213 articles were remained. Then 172 obviously irrelevant literatures were excluded by scanning the titles and abstracts. Among the remaining 41 reports, 34 articles (including 16 reviews, 5 non-RCTs, 10 studies in which local muscle vibration was used, and 3 studies in which participants were acute stroke patients) were excluded according to the inclusion and exclusion criteria. As a result, seven studies14–17,19–21 were included in this study. Among them, data from three studies14,16,20 were available to do statistical
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Figure 1 Literature search and study selection.
analysis. The other four studies were used for review in this study.
Characteristics of included studies The included studies were all recent reports with publication year from 2012 to 2014. The characteristics of participants in each study are shown in Table 1. The patients were from China,14,16,19 Sweden,20 Belgium,17 Brazil,21 and Spain,15 respectively. A total of 298 CS patients including 159 patients underwent
exercise training with WBV and 139 patients underwent nothing or the same exercises without vibration or with a ‘‘placebo’’ vibrating platform) were considered in this study. There were 185 ischemic stroke patients and 113 hemorrhage patients. The average duration of disease ranged from 30.4 months to 7.71 years. The characteristics of methods and outcomes are shown in Table 2. There are differences in the WBV protocols among the included studies. The frequencies of WBV in the studies of
Table 1 Characteristics of participants
Study
Region
Brogardh et al. (2012)20
Sweden Experimental Control Belgium Experimental Control China Experimental Control Brazil Experimental Control China Experimental Control Spain Experimental Control China Experimental Control
Tankisheva et al. (2013)17 Pang et al. (2013)16 Silva et al. (2014)21 Chan et al. (2012)19 Marin et al. (2013)15 Lau et al. (2012)14
Group
N
Gender (M/F) Age (years)
16 15 7 8 41 41 28 10 15 15 11 9 41 41
13/3 12/3 4/3 6/2 26/15 32/9 19/9 8/2 10/5 11/4 6/5 5/4 26/15 32/9
Duration of disease
Side (L/R) Type(I/H)
61.3+ 8.5 37.4+ 31.8 m 9/7 33.1+ 29.2 m 7/8 63.9+ 5.8 57.4+ 13 7.71+ 8.6 y 4/3 5.28+ 3.6 y 4/4 65.3+ 3.7 57.3+ 11.3 4.6+ 3.5 y 20/21 5.3+ 4.2 y 14/27 57.4+ 11.1 60.75+ 11.8 40.85+ 68.76 m 17/11 39.6+ 63.55 m 7/3 58.1+ 8.14 56.07+ 11.04 30.4+ 25.8 m 12/3 54.93+ 7.45 38.87+ 38.22 m 7/8 62.3+ 10.6 4.3+ 2 y 5/6 4.3+ 3 y 5/4 64.4+ 7.6 57.3+ 11.3 4.6+ 3.5 y 20/21 5.3+ 4.2 y 14/27 57.4+ 11.1
14/2 13/2 6/1 5/3 20/21 21/20 25/3 8/2 10/5 5/10 10/1 7/2 20/21 21/20
Note: WBV, whole body vibration; M, male; F, female; L, left; R, right; I, ischemic stroke; H, hemorrhage.
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Table 2 Characteristics of methods and outcomes
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Study
No. series per session (rest Time per Frequency Amplitude periods, series Posture (knee No. (Hz) (mm) seconds) (seconds) angle) sessions
Brogardh et al. (2012)20
25
3.75
4–12 (60)
40–60
Static (45uu, 60uu)
1 session/d, 2 d/wk, 6 wks
Tankisheva et al. (2013)17
35, 45
1.7 and 2.5
1
30–60
High squat (50 to 60uu), deep squat (90uu), widestance squat, one-legged squat
1 session/d, 3 d/wk, 6 wks
Pang et al. (2013)16
20–30
0.44–0.6
6
90–150
1 session/d, 3 d/wk, 8 wks
Silva et al. (2014)21
50
2
4 (60)
60
Side to side weight shift, semi-squat (30uu), forward and backward weight shift, forward lunge, standing on one leg, deep squat (90uu) Semi-squat (30uu), deep squat (90uu) unipodal landing
Chan et al. (2012)19
12
4
2 (60)
600
Marin et al. (2013)15
5–21
NR
4–7 (60)
30–60
Lau et al. (2012)14
20–30
044–0.6
1
90–150
1 session
Control
Outcomes
The same as experimental group but the amplitude is 0.2 mm
No significant differences between groups in body function and gait performance Not involved Muscle in any strength and training postural program control improved, no change in muscle spasticity Perform the Spasticity same reduced, no exercises on change in the same bone turnover, platform motor function without and muscle vibration strength
Keep the same position on the platform without vibration Keep the same position on the platform without vibration
No between group difference in EMG, 6 MWT, CT and TUG improved Semi-squat 1 session Ankle plantar flexion spasticity decreased, gait velocity, TUG and 10 MWT improved 17 Keep the No between Semi-squat sessions same group (30uu) position on difference in the platform BBS and without muscle vibration strength Side to side 24 Perform the No between weight shift, sessions/d, same group semi-squat 3 d/wk, 8 exercises on difference in (30uu), forward wks the same BBS, dynamic and backward platform postural weight shift, without control, 6 standing on vibration MWT, 10 one leg, deep MWT, muscle squat, forward strength had lunge fall-related self-efficacy
Note: BBS, Berg Balance Test; EMG, surface electromyography, 6 MWT, 6 minutes walking test; SCT, Stair–Climb Test; 10 MWT, 10 meters walking test; NR, not reported.
Chan et al.19 and Marin et al.15 were lower than 21 Hz, while they were between 20 and 30 Hz in the studies of Brogardh et al.,20 Pang et al.16 and Lau et al.14 Meanwhile, frequencies over than 30 Hz were 164
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applied in the studies of Tankisheva et al.17 and Silva et al.21 In addition, the WBV training in two studies14,16 used the same amplitude (0.44 to 0.6 mm), but they were obviously different among
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other studies. Furthermore, there were also differences in time per series (ranged from 30 to 600 s), numbers of series per session and numbers of sessions among these included studies.
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Quality assessment of included study The quality assessments for the included trails are shown in Fig. 2. All the included trails reported the method for randomization sequence generation and allocation concealment. Thus, the risk of selection bias was low for all the included studies. Meanwhile, all studies also had low risk of bias in the selection reporting and incomplete outcomes. However, high risk of performance bias existed in four included studies14,17,20,21 and high risk of bias in blinding of outcome assessment was found in one study.17 Notably, all the included studies had the high risk of other bias except the one reported by Marin et al.15
Muscle strength Four of these included studies analyzed the isometric knee extension strength.14,16,17,20 Among them, the frequency of WBV in the study of Tankisheva et al. (35 and 45 Hz)17 was higher than that in the other
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three studies (20 to 30 Hz).14,16,20 For avoiding the influence of different frequency on the results, we only reanalyzed the studies of Brogardh et al.,20 Lau et al.14 and Pang et al.16 by meta-analysis. The data of Tankisheva et al.17 were used for discussion by comparing with the results of this meta-analysis. In this analysis, no significant heterogeneity was found among the included studies, so fixed-effects model was used to pool the data (I 250%, P50.98). The overall estimate (SMD5{0.15, 95% CI: {0.43 to 0.13, P50.30) suggested that there was no significant difference in the isometric knee extension strength between experimental and control groups (Fig. 3A). Three trails investigated the isometric knee flexion strength with a total of 164 participants.14,16,17 Compared with the other studies (20 to 30 Hz), study of Tankisheva et al.17 with higher frequency (35 and 45 Hz) of WBV was just used for discussion. There was no evidence for the significant heterogeneity among the other two studies, so fixed-effects model was used for pooling data (I 250%, P50.35). The overall WMD was {0.05 (95% CI: {0.13 to 0.03; P50.22), indicating that no significant difference was found in the isometric knee flexion strength between experimental and control groups (Fig. 3B). However, Tankisheva et al.17 reported that WBV could significantly improve the isometric knee extension or flexion strength, which was inconsistent with the results of this meta-analysis.
Balance Three of these studies investigated the balance by BBS.14,15,20 The frequency of WBV in Marin et al (5 to 21 Hz)15 was lower than that in the other two studies (20 to 30 Hz),14,20 thus the study of Marin et al.15 was only used for discussion by comparing with the results of statistical analysis. No significant heterogeneity was found among the included studies, so fixedeffects model was used (I 250%, P50.95). The overall WMD of {0.23 (95% CI: {1.54 to 1.09; P50.74) demonstrated that there was no significant difference between experimental and control groups in balance which was examined by BBS (Fig. 3C). Moreover, the results of Marin et al.15 also indicated no significant differences in balance between groups.
Gait performance
Figure 2 Risk of bias for each included studies.
Three tails investigated the effect of WBV on gait performance by a 6-min walk test.14,20,21 Given that the frequency of WBV in the study of Silva et al. (50 Hz)21 was higher than that in the other two studies (20– 30 Hz),14,20 statistical analysis was only performed in the studies of Brogardh et al.20 and Lau et al.14 The result of Silva et al. was used for discussion through Topics in Stroke Rehabilitation
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Figure 3 Forest plots of meta-analysis. (A) Isometric knee extension strength. (B) Isometric knee flexion strength. (C) Berg balance scale. (D) 6-min walk test.
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comparing with the result of meta-analysis. No enough evidence was found for significant heterogeneity among studies (I 2557%, P50.13), so fixed-effects model was used. The overall WMD was {50.40 (95% CI: {118.14 to 17.34; P50.14), which indicated no significant difference in gait velocity between groups (Fig. 3D). However, Silva et al.21 provided evidence for significant improvement of gait performance by the 6-min walk and TUG test in the experimental group compared with that in control group. In addition, TUG test was also performed in other two studies.19,20 The results of the three studies all proved that WBV training could significantly improve the gait performance by TUG. Due to different frequencies of WBV among these studies,19–21 the statistical analysis was not conducted for the outcomes of TUG test. Thus, we analyzed the results of these studies through description and discussion in this study.
Publication bias No asymmetry indicated publication bias in this study. The funnel plot for the studies which reported balance by BBS is shown in Fig. 4. The representative points of studies of Lau et al. and Pang et al. were overlapped.
Discussion Chronic stroke is associated with substantial motor disability, which severely affected the health related quality of life.22 The objective of the present study was to assess the effects of WBV training on patients with CS. Following the meta-analyses, the results showed that there was no significantly difference between experimental and control groups in muscle strength, balance and gait performance, suggesting that WBV training could not significantly benefit the muscle strength, balance or gait performance of people with CS. The results in the study of Marin et al. (an increased frequency of 5 to 21 Hz) are consistent with the results of this meta-analysis (frequency ranged from 20 to
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30 Hz) in balance (BBS) and muscle strength (the maximal isometric voluntary contraction of the knee extensors). However, the study of Tankisheva et al.17 which used frequency of 35 and 45 Hz found that the isometric knee extension strength was significantly increased after 6 weeks of exercise training with WBV (frequency 35 and 45 Hz, amplitude 1.7 and 2.5 mm). Meanwhile, Silva et al. suggested that the gait performance (6MWT) of CS patients was improved by WBV (frequency 50 Hz, amplitude 2 mm), which was inconsistent with the result of this study. Thus, we speculated that the WBV training with higher frequency than 30 Hz might be more beneficial to the patients with CS than that with frequency less than 30 Hz. However, the study of Chan et al.19 demonstrated that a single session of WBV training (frequency 12 Hz, amplitude 4 mm) significantly improved the gait performance of CS patients by TUG test and 10-meter walk test. Although the frequency was lower in the study of Chan et al., the amplitude was larger than that in other studies, which may affect the effects of WBV on CS patients. In addition, it was reported that muscle activity and acceleration during WBV were varied with different frequencies and amplitudes.23 Therefore, frequency and amplitude may be the main factors for the effects of WBV on CS patients. It was reported that lower frequencies (from 25 to 35) of WBV were suitable for maximal activation of the lateral gastrocnemius, whereas higher frequencies (from 45 to 55 Hz) elicited the highest reflex responses in the vastus lateralis.24 Meanwhile, continuous muscle contraction could give rise to a widespread diffusion of the reflex responses, thereby affecting the muscle strength.25 Thus, the WBV may affect the muscle strength through increasing the reflex responses which was associated with frequency of vibration. Several limitations should be mentioned in the present study. First, due to lack of available data, only three out of seven included RCTs were used to do the metaanalysis, the others just used for review in this study. Second, high risk of other bias and bias in blinding method existed, which may affect the results of this study. Third, the study designs were different in the included studies, which may be the causes of other bias and can increase the instability of the results in this study. At last, the sensitivity analysis was not performed because of less included studies. Therefore, the reliable and stable of the results in this study need more high quality RCTs with larger sample size to verify.
Conclusion Figure 4 Funnel plot of studies examining balance by BBS.
In conclusion, WBV training showed no significant effects on improving muscle strength, balance and Topics in Stroke Rehabilitation
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gait performance of CS patients. Frequency and amplitude may be the major influence factors for the effects of WBV on patients with CS. Reflex responses of muscles on WBV with different frequencies should be considered in the further studies. In view of this, more studies considering the frequency, amplitude and response of body must be performed in future. Additionally, it is necessary to further investigate the effects of WBV on other outcomes, such as proprioception and activities of daily living.
Acknowledgements
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This review is part of the thesis of its first author, Jun Lu master degree candidate at Nanjing medical university, China. The authors would like to acknowledge the contribution of Professor Xu for his guidance in developing the review, Wentong Zhang and Lin Li for their support in the searching and obtaining the articles, and Xiaoying Zhou for her assistance and help in the editing process of the review. The authors also thank the staffs of the department of rehabilitation (First Affiliated Hospital of Nanjing Medical University) for their support to the first author. Contributors Jun Lu conceived the project. Jun Lu, Guangxu Xu and Yuchen Wang performed experiments and data analysis. Guangxu Xu wrote the manuscript. All authors read and approved the final manuscript. Funding None. Conflicts of Interest There are no conflicts of interest associated with this work. Ethics Approval Not applicable.
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