Older adults show higher increases in lower-limb muscle activity during whole-body vibration exercise

Effect of whole-body vibration on neuromuscular activation and explosive power of lower limb: A systematic review and meta-analysis

OBJECTIVE

The review aimed to investigate the effects of whole-body vibration (WBV) on neuromuscular activation and explosive power.

METHODS

Keywords related to whole-body vibration, neuromuscular activation and explosive power were used to search four databases (PubMed, Web of Science, Google Scholar and EBSCO-MEDLINE) for relevant studies published between January 2000 and August 2021. The methodology of the Preferred Reporting Items for Systematic Reviews and Meta-Analyses was used. The eligibility criteria for the meta-analysis were based on PICOST principles. Methodological assessment used the Cochrane scale. Heterogeneity and publication bias were assessed by I2 index and funnel plots, respectively. The WBV training cycle is a random effect model. Publication bias was also assessed based on funnel plots. This study was registered in PROSPERO (CRD42021279439).

RESULTS

A total of 156 participants data in 18 studies met the criteria and were included in the meta-analysis for quantitative synthesis. Results of the meta-analysis showed significant improvements in lower limb neuromuscular activation immediately after WBV compared with the baseline (SMD = 0.51; 95% CI: 0.26, 0.76; p<0.001), and no significant heterogeneity was observed (I2 = 38%, p = 0.07). In addition, the highest increase in lower limb explosive power was observed (SMD = 0.32; 95% CI: 0.11, 0.52; p = 0.002), and no significant heterogeneity (I2 = 0%, p = 0.80) was noted.

CONCLUSIONS

WBV training could improve neuromuscular activation and explosive power of the lower limb. However, due to different vibration conditions, further research should be conducted to determine standardized protocols targeting performance improvement in athletes and healthy personnel experienced in training.

A Study on the Classification Effect of sEMG Signals in Different Vibration Environments Based on the LDA Algorithm

Myoelectric prosthesis has become an important aid to disabled people. Although it can help people to recover to a nearly normal life, whether they can adapt to severe working conditions is a subject that is yet to be studied. Generally speaking, the working environment is dominated by vibration. This paper takes the gripping action as its research object, and focuses on the identification of grasping intentions under different vibration frequencies in different working conditions. In this way, the possibility of the disabled people who wear myoelectric prosthesis to work in various vibration environment is studied. In this paper, an experimental test platform capable of simulating 0–50 Hz vibration was established, and the Surface Electromyography (sEMG) signals of the human arm in the open and grasping states were obtained through the MP160 physiological record analysis system. Considering the reliability of human intention recognition and the rapidity of algorithm processing, six different time-domain features and the Linear Discriminant Analysis (LDA) classifier were selected as the sEMG signal feature extraction and recognition algorithms in this paper. When two kinds of features, Zero Crossing (ZC) and Root Mean Square (RMS), were used as input, the accuracy of LDA algorithm can reach 96.9%. When three features, RMS, Minimum Value (MIN), and Variance (VAR), were used as inputs, the accuracy of the LDA algorithm can reach 98.0%. When the six features were used as inputs, the accuracy of the LDA algorithm reached 98.4%. In the analysis of different vibration frequencies, it was found that when the vibration frequency reached 20 Hz, the average accuracy of the LDA algorithm in recognizing actions was low, while at 0 Hz, 40 Hz and 50 Hz, the average accuracy was relatively high. This is of great significance in guiding disabled people to work in a vibration environment in the future.

Biodynamic Responses to Whole-Body Vibration Training: A Systematic Review

In recent years, whole-body vibration (WBV) training has received an increasing interest in the sports and medical fields. However, there has been inconsistency among several studies regarding the effect of WBV training on the human body, which is partly due to the lack of the existence of guidelines for using WBV training machines. To understand the effect of WBV training on the human body and build the needed regulations, it is essential first to understand the biodynamic responses to vibration which represent how vibration is transmitted to and through the human body. The purpose of this study is to systematically review previous studies that measured biodynamic responses when using WBV training machines to highlight inconsistencies in their results and provide possible reasons for them. An extensive literature search was performed on the SCOPUS database to obtain relevant studies. One hundred and fifty-six potentially relevant studies were obtained but after further screening, 23 papers from 2007 to 2020 met inclusion criteria and were included in the study. The papers were analysed with respect to acceleration, transmissibility, interface force, and apparent mass during different vibration settings, body posture, age, and sex. Results and conflicts among studies were highlighted and possible explanations for the inconsistency were provided.

Interventions for preventing falls in people post-stroke: A meta-analysis of randomized controlled trials

BACKGROUND

Falls are a serious challenge facing individuals post-stroke. In the past decades, various fall prevention interventions have been developed. It remains unknown if any of these interventions are effective in reducing falls in this population. Such a knowledge gap could impede the effort of preventing falls in people post-stroke.

RESEARCH QUESTIONS

1) Are there effective interventions to prevent falls among people in the post-acute and chronic stages of stroke? and 2) How do fall prevention interventions change three key fall risk factors in this population: balance, mobility, and lower limb strength?

METHODS

Eleven databases were searched for randomized controlled trials which included falls in people post-stroke as an outcome measure. Information on the participants, training protocol, and outcome measures were collected for each study. The primary outcome is the number of fallers and the explanatory variables included mean difference and standard deviation for fall risk factors. Studies were quality appraised using the Physiotherapy Evidence Database scale and the funnel plot.

RESULTS

Thirteen studies enrolling 1352 participants were identified. Effect size quantified by the odds ratio (OR) for falls and standardized mean difference (SMD) for fall risk factors were calculated. Overall no intervention appears to be significantly more effective in preventing falls than placebo training (OR = 0.88 with a range of [0.23 3.66]; 95 % confidence interval = [0.64 1.21], p = 0.44). All interventions showed little effect in improving the fall risk factors (SMD = -0.01 to 0.06 and p-value = 0.38-0.86), except one (the combined treadmill and overground walking) which significantly improved mobility.

SIGNIFICANCE

Currently no program is effective in reducing falls in people post-stroke. Future studies should measure falls as a primary outcome based on a consistent definition of falls and reliable approaches to collect falls data.

Power Absorbed by the Standing Human Body During Whole-Body Vibration Training

Absorbed power (AP) is a biodynamic response that is directly related to the magnitude and duration of vibration. No work has previously investigated the power absorbed by the standing human body during the exposure to vibration training conditions or otherwise. This article reports the power absorbed by the standing human body under whole-body vibration (WBV) training conditions. In this work, the force and acceleration used to calculate the apparent mass by Nawayseh and Hamdan (2019, "Apparent Mass of the Standing Human Body When Using a Whole-Body Vibration Training Machine: Effect of Knee Angle and Input Frequency," J. Biomech., 82, pp. 291-298) were reanalyzed to obtain the AP. The reported acceleration was integrated to obtain the velocity needed to calculate the AP. The effects of bending the knees (knee angles of 180 deg, 165 deg, 150 deg, and 135 deg) and vibration frequency (17-42 Hz) on the power absorbed by 12 standing subjects were investigated. Due to the different vibration magnitudes at different frequencies, the AP was normalized by dividing it by the power spectral density (PSD) of the input acceleration to obtain the normalized AP (NAP). The results showed a dependency of the data on the input frequency as well as the knee angle. A peak in the data was observed between 20 and 24 Hz. Below and above the peak, the AP and NAP tend to increase with more bending of the knees indicating an increase in the damping of the system. This may indicate the need for an optimal knee angle during WBV training to prevent possible injuries especially with prolonged exposure to vibration at high vibration intensities.

Modelling the apparent mass of the standing human body under whole-body vibration training conditions

Several studies have measured the vibration transmitted to and through the human body under vibration training conditions. However, no work has modelled the apparent mass of the human body under such conditions. In this work, a 2 degree-of-freedom model has been developed to predict the apparent mass of the standing human body under whole-body vibration training conditions. The parameters of the model were optimised using measured apparent mass of 12 subjects standing with different knee angle of 180°, 165°, 150° and 135°. Good agreement was found between the predicted and measured apparent mass with errors less than 3 kg in the median apparent mass magnitude and errors less than 6° in the apparent mass phase angle. The medians of the optimised parameters of the 12 individual apparent masses were close to the corresponding optimised parameters of the median apparent mass of the 12 subjects. Compared to standing with extended legs, bending the knees was found to affect mainly the parameters (i.e. stiffness and damping) of the model close to the source of vibration. Bending the knees decreased the mass of the model close to the source of vibration and increased the mass away from the source of vibration. Among the postures with bent knees, the change in the model parameters was generally not significant. The model can be used as a tool by manufacturers of whole-body vibration training machines to test the performance of the machines during the design stage and/or after production. This will decrease the number of experimentations with human subjects which guarantees consistency, repeatability, time-saving and safety.

Efficacy of Controlled Whole-Body Vibration Training on Improving Fall Risk Factors in Stroke Survivors: A Meta-analysis

Background. Controlled whole-body vibration (CWBV) training has been applied to people with stroke. However, it remains inconclusive if CWBV reduces fall risk in this population. Objective. To (1) assess the immediate and retention effects of CWBV training on fall risk factors in people at postacute and chronic stages of stroke and (2) examine if CWBV dosage is correlated with the effect size (ES) for 3 fall risk factors: body balance, functional mobility, and knee strength. Methods. Twelve randomized controlled trials were included. ES was calculated as the standardized mean difference, and meta-analyses were completed using a random-effects model. Results. CWBV training may lead to improved balance and mobility immediately after training (ES = 0.27, P = .03 for balance; ES = 0.34, P = .02 for mobility) but not at the 3-month follow-up test (ES = 0.02, P = .89 for balance; ES = 0.70, P = .11 for mobility). CWBV affects knee strength capacity with mild ES (ES = 0.08 and 0.11, respectively, for immediate and retention effect; P ≥ .68 for both). Metaregression indicated that the immediate ES is strongly correlated with training dosage for balance (r = 0.649; P = .029) and mobility (r = 0.785; P = .036). Conclusions. CWBV training may benefit balance and mobility immediately, but the training effect may not persist among people with stroke. Additionally, the CWBV dosage correlates with the ES for body balance and mobility. More high-quality studies are needed to determine the retention effects of CWBV training.

Effect of gender on the biodynamic responses to vibration induced by a whole-body vibration training machine

Whole-body vibration training machines are used by both male and female users. However, studies investigating the biodynamic responses to vibration during training have used either mixed-gender subjects or male subjects. No study has investigated the effect of gender on the biodynamic responses under vibration training conditions. The objective of this study is to investigate the effect of gender on the apparent mass and the vibration of the head of standing people during exposure to vibration. A total of 40 subjects (20 females and 20 males) were exposed to vertical vibration at six frequencies in the range 20-45 Hz and vibration acceleration in the range 10.8-20.9 m/s² (peak). The subjects stood on a force platform mounted on the vibrating plate of the machine adopting an upright standing posture with their knees unlocked and their arms straight along their bodies. The vertical acceleration and force at the interface between the vibrating plate and the feet were measured and used to calculate the apparent mass. The accelerations of the head in the x-, y- and z-directions were also measured and used to calculate the transmissibility to the head. The apparent mass of males was found higher than that of females. The transmissibility to the head in all directions was found higher in females than males. The differences in the biodynamic responses between males and females were attributed to the differences in body properties and structure of the two genders. The results of this study imply the need for gender-specific vibration training programmes.

Effects of Whole-Body Vibration on Lumbar-Abdominal Muscles Activation in Healthy Young Adults: A Pilot Study

BACKGROUND This study investigated how whole-body vibration (WBV), exercise, and their interactions influence core muscle activity in healthy young adults. MATERIAL AND METHODS Twenty-three healthy young adults (8 males and 15 females; age: 21.87±2.33 years) participated in the study. The activities of muscle multifidi (MM), rectus abdominis muscle (RM), erector spinae (ES), abdominis obliquus externus (AOE), and abdominis obliquus internus (AOI) were measured through surface electromyography (sEMG) while participants were performing 4 different exercise forms under 3 WBV conditions (condition 1: 5 Hz, 2 mm; condition 2: 10 Hz, 2 mm; and condition 3: 15 Hz, 2 mm) and a no-WBV condition in single experimental sessions. RESULTS The WBV frequency of 15 Hz is the best vibration stimulation for core muscles in all of the exercises (P<0.05). Single bridge is a better exercise for RM and AOE (P<0.05) compared with other exercises, and crunches is the best exercise for MM, AOI, and ES (P<0.05). Significant interaction effect was observed in different frequencies and exercises (P>0.05) except for AOI (F=0.990, P=0.378). CONCLUSIONS High vibration frequencies can lead to enhanced exercise benefits within an appropriate frequency range, and different exercises have diverse effects on various muscles. Single bridge and crunches are appropriate exercise forms for lumbar-abdominal muscles.

Loading of the hip and knee joints during whole body vibration training

During whole body vibrations, the total contact force in knee and hip joints consists of a static component plus the vibration-induced dynamic component. In two different cohorts, these forces were measured with instrumented joint implants at different vibration frequencies and amplitudes. For three standing positions on two platforms, the dynamic forces were compared to the static forces, and the total forces were related to the peak forces during walking. A biomechanical model served for estimating muscle force increases from contact force increases. The median static forces were 122% to 168% (knee), resp. 93% to 141% (hip), of the body weight. The same accelerations produced higher dynamic forces for alternating than for parallel foot movements. The dynamic forces individually differed much between 5.3% to 27.5% of the static forces in the same positions. On the Powerplate, they were even close to zero in some subjects. The total forces were always below 79% of the forces during walking. The dynamic forces did not rise proportionally to platform accelerations. During stance (Galileo, 25 Hz, 2 mm), the damping of dynamic forces was only 8% between foot and knee but 54% between knee and hip. The estimated rises in muscle forces due to the vibrations were in the same ranges as the contact force increases. These rises were much smaller than the vibration-induced EMG increases, reported for the same platform accelerations. These small muscle force increases, along with the observation that the peak contact and muscle forces during vibrations remained far below those during walking, indicate that dynamic muscle force amplitudes cannot be the reason for positive effects of whole body vibrations on muscles, bone remodelling or arthritic joints. Positive effects of vibrations must be caused by factors other than raised forces amplitudes.

How whole-body vibration can help our COPD patients. Physiological changes at different vibration frequencies

Objective

Evaluate cardiac, metabolic, and ventilatory changes during a training session with whole-body vibration training (WBVT) with 3 different frequencies in patients with chronic obstructive pulmonary disease (COPD).

Methods

This was a prospective, interventional trial in outpatients with severe COPD. Participants performed 3 vertical WBVT sessions once a week using frequencies of 35, 25 Hz and no vibration in squatting position (isometric). Cardiac, metabolic, and ventilator parameters were monitored during the sessions using an ergospirometer. Changes in oxygen pulse response (VO₂/HR) at the different frequencies were the primary outcome of the study.

Results

Thirty-two male patients with a mean forced expiratory volume in 1 second of 39.7% completed the study. Compared to the reference of 35 Hz, VO₂/HR at no vibration was 10.7% lower (P=0.005); however, no statistically significant differences were observed on comparing the frequencies of 35 and 25 Hz. The median oxygen uptake (VO₂) at 25 Hz and no vibration was 9.43% and 13.9% lower, respectively, compared to that obtained at 35 Hz (both comparisons P<0.0001). The median expiratory volume without vibration was 9.43% lower than the VO₂ at the end of the assessment at 35 Hz vibration (P=0.002).

Conclusion

Vertical WBVT training sessions show greater cardiac, metabolic, and respiratory responses compared with the squat position. On comparing the 2 frequencies used, we observed that the frequency of 35 Hz provides higher cardiorespiratory adaptation.

The effect of whole-body vibration training on lean mass: A PRISMA-compliant meta-analysis

BACKGROUND

Whole-body vibration training (WBVT) confers a continuous vibration stimuli to the body. Although some reports have discussed the effects of whole-body vibration (WBV) on bone mineral density and muscle strength, study of WBV effects on lean mass have not been determined. The purpose of the present meta-analysis was to evaluate published, randomized controlled trials (RCTs) that investigated the effects of WBVT on lean mass.

METHODS

We identified only RCTs by searching databases, including Web of Science, PubMed, Scopus, Embase, and the Cochrane Library from inception to March 2017. Data extraction, quality assessment, and meta-analysis were performed.

RESULTS

Ten RCTs with 5 RCTs concentrating on older people, 3 on young adults, and 2 on children and adolescents were included. We additionally explored the effect of WBVT on postmenopausal women (6 trials from the 10 trials). Significant improvements in lean mass with WBVT were merely found in young adults (P = .02) but not in other populations compared to control group.

CONCLUSION

The effect of WBVT found in the present meta-analysis may be used in counteracting the loss of muscle mass in younger adults. Moreover, optimal WBVT protocols for greater muscle hypertrophy are expected to be investigated.