Modification of heart rate variability induced by focal muscle vibration in patients with severe acquired brain injury.

BACKGROUND/PURPOSE: Heart rate variability (HRV) is a biomarker of autonomic nervous system (ANS) reaction in persons with severe acquired brain injury (sABI) who undergo a rehabilitation treatment, such as focal muscle vibration (FMV).This study aims to evaluate if and how FMV can modulate HRV and to compare potential differences in FMV modulation in HRV between patients with sABI and healthy controls. METHODS: Ten patients with sABI and seven healthy controls have been recruited. Each individual underwent the same stimulation protocol (four consecutive trains of vibration of 5 minutes each with a 1-minute pause). HRV was analyzed through the ratio of frequency domain heart-rate variability (LF/HF). RESULTS: In the control group, after performing FMV, a significant LF/HF difference was observed in the in the second vibration session compared to the POST phase. Patients with SABI treated on the affected side showed a statistically significant LF/HF difference in the PRE compared to the first vibration session. CONCLUSION: These preliminary results suggest that FMV may modify the cardiac ANS activity in patients with sABI.

Unilateral vibration stimulation decreases F-wave persistence and F/M amplitude ratio in contralateral homonymous muscle corresponding to the stimulated muscle during stimulation.

[Purpose] This study aimed to examine the effects of unilateral vibratory stimulation on contralateral homonymous muscle. [Participants and Methods] The study included 14 participants without a history of any disease. Participants were tested under three separate conditions: vibratory stimulation, pressure stimulation, and rest. F-waves were measured at two time points for 15 seconds in the rest position under each of the testing conditions. [Results] The F/M amplitude ratio analysis showed interactions between the vibratory stimulation‒pressure stimulation and vibratory stimulation‒rest conditions. The F-wave persistence analysis demonstrated interactions between the vibratory and pressure stimulation conditions. Vibratory stimulation significantly decreased the F/M amplitude ratio and F-wave persistence at two time points, before and during the stimulation. [Conclusion] The vibratory stimulation used in this study could suppress the contralateral homonymous muscle tone.

Effects of lower limb segmental muscle vibration on primary motor cortex short-latency intracortical inhibition and spinal excitability in healthy humans.

We examined the effects of lower limb segmental muscle vibration (SMV) on intracortical and spinal excitability in 13 healthy participants (mean age: 34.9 ± 7.8 years, 12 males, 1 female). SMV at 30 Hz was applied to the hamstrings, gastrocnemius, and soleus muscles for 5 min. Paired-pulse transcranial magnetic stimulation protocols were used to investigate motor-evoked potential (MEP)  amplitude, short-interval intracortical inhibition (SICI) and short-interval intracortical facilitation (SICF) from the abductor hallucis muscle (AbdH). These assessments were compared to the results of a control experiment (i.e., non-vibration) in the same participants. F-waves were evaluated from the AbdH on the right (vibration side) and left (non-vibration side) sides, and we calculated the ratio of the F-wave amplitude to the M-response amplitude (F/M ratio). These assessments were obtained before, immediately after, and 10, 20, and 30 min after SMV. For SICI, there was no change immediately after SMV, but there was a decrease over time (before vs. 30 min after, p = 0.021; immediately after vs. 30 min after, p = 0.015). There were no changes in test MEP amplitude, SICF, or the F/M ratio. SMV causes a gradual decrease in SICI over time perhaps owing to long-term potentiation. The present results may have implications for the treatment of spasticity.

The reflex mechanism underlying the neuromuscular effects of whole-body vibration: Is it the tonic vibration reflex?

OBJECTIVES: Whole-body vibration (WBV) is applied to the sole of the foot, whereas local mechanical vibration (LMV) is applied directly to the muscle or tendon. The time required for the mechanical stimulus to reach the muscle belly is longer for WBV. Therefore, the WBV-induced muscular reflex (WBV-IMR) latency may be longer than the tonic vibration reflex (TVR) latency. The aim of this study was to determine whether the difference between WBV-IMR and TVR latencies is due to the distance between the vibration application point and the target muscle. METHODS: Eight volunteers participated in this study. The soleus reflex response was recorded during WBV, LMVs, and tendon tap. LMVs were applied to the Achilles tendon and sole of the foot. The latencies were calculated using the cumulative averaging technique. RESULTS: The latency (33.4±2.8 ms) of the soleus reflex induced by the local foot vibration was similar to the soleus TVR latency (30.9±3.2 ms) and T-reflex (32.0±2.4 ms) but significantly shorter than the latency of the soleus WBV-IMR (42.3±3.4 ms) (F(3,21)=27.46, p=0.0001, partial η2=0.797). CONCLUSIONS: The present study points out that the neuronal circuitries of TVR and WBV-IMR are different.

The effect of local muscle vibration on clinical and biomechanical parameters in people with knee osteoarthritis: A systematic review.

Background: To identify and synthesize available published studies on the effect of local muscle vibration (LMV) on pain, stiffness, and function in individuals with knee OA. Methods: Five databases were searched to find relevant papers on April 29, 2020, including, PubMed, Scopus, EMBASE (Ovid), Science Citation Index, and COCHRANE Central Register for Controlled Trials (CENTRAL). Randomized controlled trials (RCTs) and nonrandomized-controlled-trials (non-RCTs), such as interrupted time series and prospective cohort studies were included. Two independent reviewers screened articles and assessed inclusion through predefined criteria. Participants' characteristics, study design, intervention characteristics, outcomes, and main results were collected independently by 2 reviewers. The risk of bias assessment of included studies was conducted using Cochrane risk of bias tools for RCTs and non-RCTs. Results: Six studies were included: 3 RCTs and 3 non-RCTs. The risk of bias in included studies was generally moderate to high. Improvement of pain, stiffness, and function following the application of LMV were reported in all studies. Conclusion: This review revealed the promising effect of LMV on pain, stiffness, function, and knee range of motion (ROM) improvements for individuals with knee Osteoarthritis (OA). However, further well-designed studies are required to have a convincing conclusion on the effect of LMV in individuals with knee OA.

Promoting post-stroke recovery through focal or whole body vibration: criticisms and prospects from a narrative review.

OBJECTIVE: Several focal muscle vibration (fMV) and whole body vibration (WBV) protocols have been designed to promote brain reorganization processes in patients with stroke. However, whether fMV and WBV should be considered helpful tools to promote post-stroke recovery remains still largely unclear. METHODS: We here achieve a comprehensive review of the application of fMV and WBV to promote brain reorganization processes in patients with stroke. By first discussing the putative physiological basis of fMV and WBV and then examining previous observations achieved in recent randomized controlled trials (RCT) in patients with stroke, we critically discuss possible strength and limitations of the currently available data. RESULTS: We provide the first systematic assessment of fMV studies demonstrating some improvement in upper and lower limb functions, in patients with chronic stroke. We also confirm and expand previous considerations about the rather limited rationale for the application of current WBV protocols in patients with chronic stroke. CONCLUSION: Based on available information, we propose new recommendations for optimal stimulation parameters and strategies for recruitment of specific stroke populations that would more likely benefit from future fMV or WBV application, in terms of speed and amount of post-stroke functional recovery.

The effects of vibration-induced altered stretch reflex sensitivity on maximal motor unit firing properties.

It is well known that muscle spindles have a monosynaptic, excitatory connection with α-motoneurons. However, the influence of muscle spindles on human motor unit behavior during maximal efforts remains untested. It has also been shown that muscle spindle function, as assessed by peripheral reflexes, can be systematically manipulated with muscle vibration. Therefore, the purpose of this study was to analyze the effects of brief and prolonged vibration on maximal motor unit firing properties. A crossover design was used, in which each of the 24 participants performed one to three maximal knee extensions under three separate conditions: 1) control, 2) brief vibration that was applied during the contraction, and 3) after prolonged vibration that was applied for ~20 min before the contraction. Multichannel EMG was recorded from the vastus lateralis during each contraction and was decomposed into its constituent motor unit action potential trains. Surprisingly, an approximate 9% reduction in maximal voluntary strength was observed not only after prolonged vibration but also during brief vibration. In addition, both vibration conditions had a large, significant effect on firing rates (a decrease in the rates) and a small to moderate, nonsignificant effect on recruitment thresholds (a small increase in the thresholds). Therefore, vibration had a detrimental influence on both maximal voluntary strength and motor unit firing properties, which we propose is due to altered function of the stretch reflex pathway. NEW & NOTEWORTHY We used vibration to alter muscle spindle function and examined the vibration's influence on maximal motor unit properties. We discovered that vibration had a detrimental influence on motor unit behavior and motor output by decreasing motor unit firing rates, increasing recruitment thresholds, which led to decreased maximal strength. We believe that understanding the role of muscle spindles during maximal contractions provides a deeper insight into motor control and sensorimotor integration.

Can muscle vibration be the future in the treatment of cerebral palsy-related drooling? A feasibility study.

Background: Drooling is an involuntary loss of saliva from the mouth, and it is a common problem for children with cerebral palsy (CP). The treatment may be pharmacological, surgical, or speech-related. Repeated Muscle Vibration (rMV) is a proprioceptive impulse that activates fibers Ia reaching the somatosensory and motor cortex. Aim: The aim of the study is to evaluate the effectiveness of rMV in the treatment of drooling in CP. Design, setting and population: This was a rater blinded prospective feasibility study, performed at the "Gli Angeli di Padre Pio" Foundation, Rehabilitation Centers (Foggia, Italy), involving twenty-two CP patients affected by drooling (aged 5-15, mean 9,28 ± 3,62). Children were evaluated at baseline (T0), 10 days (T1), 1 month (T2) and 3 months (T3) after the treatment. Methods: The degree and impact of drooling was assessed by using the Drooling Impact Scale (DIS), the Drooling Frequency and Severity Scale (DFSS), Visual Analogue Scale (VAS) and Drooling Quotient (DQ). An rMV stimulus under the chin symphysis was applied with a 30 min protocol for 3 consecutive days. Results: The statistical analysis shows that DIS, DFSS, VAS, DQ improved with significant differences in the multiple comparisons between T1 vs T2, T1 vs T3 and T1 vs T4 (p≤0.001). Conclusion This study demonstrates that rMV might be a safe and effective tool in reducing drooling in patients with CP. The vibrations can improve the swallowing mechanisms and favor the acquisition of the maturity of the oral motor control in children with CP.

Does focal mechanical stimulation of the lower limb muscles improve postural control and sit to stand movement in elderly?

BACKGROUNDS: Imbalance in elderly is a common problem strictly related to fall. AIMS: This study investigates the possibility that a new protocol based on the focal mechanical muscle vibration may improve balance and stability in elderly. METHODS: Pre-post non-randomized clinical trial has been used. Patients referring postural disequilibrium with negative vestibular bed-side examinations have been treated with focal muscle vibration applied to quadriceps muscles and evaluated before and immediately after therapy and after 1 week and after 1 month with postural stabilometric examination and with an inertial measurement units during the time up and go test. RESULTS: Stabilometric analysis showed statistically significant differences in both the area (p = 0.01) and sway (p < 0.01) of the center of pressure during the close eyes tests. Moreover, the global time of the time up and go test was reduced (p < 0.05) and the rotation velocity was increased (p < 0.01). CONCLUSIONS: The findings confirm the beneficial role of focal muscle vibration in elderly patients improve postural stability and mobility.

Short-term effect of neck muscle vibration on postural disturbances in stroke patients.

Balance disorders after stroke have a particularly detrimental influence on recovery of autonomy and walking. The present study is aimed at assessing the effect of proprioceptive stimulation by neck muscle vibration (NMV) on the balance of patients with right hemispheric lesion (RHL) and left hemispheric lesion (LHL). Thirty-one (31) patients (15 RHL and 16 LHL), mean age 61.5 years (±10.6), mean delay 3.1 (±1.6) months after one hemispheric stroke were included in this prospective study. The mean position in mediolateral and anteroposterior plane of the CoP (center of pressure) and the surface were evaluated using a force platform at rest and immediately after 10 min of vibration on the contralesional dorsal neck muscle. NMV decreases the lateral deviation balance induced by the stroke. Twenty patients (64.5 %) experienced a visual illusion of light spot moving toward the side opposite stimulus. These patients showed more improvement by vibration than those without visual illusion. There was an interaction between sensitivity and side of stroke on the effect of NMV. Proprioceptive stimulation by NMV reduces postural asymmetry after stroke. This short-term effect of the vibration is more effective in patients susceptible to visual illusion. This result was consistent with a central effect of NMV on the structures involved in the elaboration of perception of body in space.

Shaping motor cortex plasticity through proprioception.

Short-term upper limb disuse induces a hemispheric unbalance between the primary motor cortices (M1s). However, it is still unclear whether these changes are mainly attributable to the absence of voluntary movements or to the reduction of proprioceptive information. The goal of this work was to investigate the role of proprioception in modulating hemispheric balance during a short-term right arm immobilization. We evaluated the 2 M1s excitability and the interhemispheric inhibition (IHI) between M1s in 3 groups of healthy subjects. Two groups received during the immobilization a proprioceptive (P-VIB, 80 Hz) and tactile (T-VIB, 30 Hz) vibration to the right hand, respectively. Another group did not receive any conditioning sensory inputs (No-VIB). We found that in the No-VIB and in the T-VIB groups immobilization induced a decrease of left M1 excitability and IHI from left to right hemisphere and an increase of right M1 excitability and IHI from right to left hemisphere. Differently, only a partial decrease in left M1 excitability, no change in right M1 excitability and in IHI was observed in the P-VIB group. Our findings demonstrate that the maintenance of dynamic proprioceptive inputs in an immobilized arm through muscle vibration can prevent the hemispheric unbalance induced by short-term limb disuse.

Focal muscle vibration as a possible intervention to prevent falls in elderly women: a pragmatic randomized controlled trial.

BACKGROUNDS: Different and new approaches have been proposed to prevent the risk of falling of elderly people, particularly women. AIMS: This study investigates the possibility that a new protocol based on the focal mechanical muscle vibration may reduce the risk of falling of elderly women. METHODS: A pragmatic randomized controlled triple-blind trial with a 6-month follow-up after intervention randomized 350 women (mean age 73.4 years + 3.11), members of local senior citizen centers in Rome, into two groups: vibrated group (VG) and control group (CG). For VG participants a mechanical vibration (lasting 10 min) was focally applied on voluntary contracted quadriceps muscles, three times a day during three consecutive days. CG subjects received a placebo vibratory stimulation. Subjects were tested immediately before (T0) and 30 (T1) and 180 (T2) days after the intervention with the Performance-Oriented Mobility Assessment (POMA) test. All subjects were asked not to change their lifestyle during the study. CG underwent sham vibratory treatment. RESULTS: While CG did not show any statistically significant change of POMA at T1 and T2, VG revealed significant differences. At T2, ≈47% of the subjects who completed the study obtained the full score on the POMA test and ≈59% reached the full POMA score. CONCLUSIONS: The new protocol seems to be promising in reducing the risk of falling of elderly subjects.

Does proprioceptive system stimulation improve sit-to-walk performance in healthy young adults?

[Purpose] Sit-to-walk performance is linked to proper proprioceptive information processing. Therefore, it is believed that an increase of proprioceptive inflow (using muscle vibration) might improve sit-to-walk performance. However, before testing muscle vibration effects on a frail population, assessment of its effects on healthy young people is necessary. Thus, the aim of this study was to investigate the effects of muscle vibration on sit-to-walk performance in healthy young adults. [Subjects and Methods] Fifteen young adults performed the sit-to-walk task under three conditions: without vibration, with vibration applied before movement onset, and with vibration applied during the movement. Vibration was applied bilaterally for 30 s to the tibialis anterior, rectus femoris, and upper trapezius muscles bellies. The vibration parameters were as follows: 120 Hz and 1.2 mm. Kinematics and kinetic data were assessed using a 3D motion capture system and two force plates. The coordinates of reflective markers were used to define the center-of-mass velocities and displacements. In addition, the first step spatiotemporal variables were assessed. [Results] No vibration effect was observed on any dependent variables. [Conclusion] The results show that stimulation of the proprioceptive system with local muscle vibration does not improve sit-to-walk performance in healthy young adults.

Effect of muscle vibration on spatiotemporal gait parameters in patients with Parkinson's disease.

[Purpose] The purpose of this study was to investigate the effect of muscle vibration in the lower extremities in patients with Parkinson's disease (PD) during walking. [Subjects] Nine patients with PD participated in this study and were tested with and without vibration (vibration at 60 Hz). [Methods] Eight oscillators of vibration were attached to the muscle bellies (tibialis anterior, gastrocnemius, biceps femoris, and rectus femoris) on both sides of the lower extremities with adhesive tape in this study. Spatiotemporal gait parameters were measured using a motion analysis system. [Results] Stride length and walking speed with vibration were significantly increased compared with those without vibration in PD patients. [Conclusion] These results suggest that the application of vibration to lower extremity muscles in patients with PD may improve the parkinsonian gait pattern.

Focal muscle vibrations improve swallowing in persistent dysphagia after traumatic brain injury: A case report.

Dysphagia is a common complication following traumatic brain injury (TBI), and it is related to an increased risk of malnutrition, pneumonia, and poor prognosis. In this article, we present a case of TBI with persistent dysphagia treated with focal muscle vibration. A 100 Hz and 50 Hz vibratory stimuli were applied over the suprahyoid muscles and tongue (30 min twice a day; five days a week; for a total of four weeks) in addition to the conventional therapy to quickly recover swallowing and avoid the possibility of permanent deficits. In conclusion, this case highlights a novel therapeutic approach for persistent dysphagia in TBI, which should be considered in the management of dysphagia.

Immediate effects of local muscle vibration on static and dynamic balance control in individuals with chronic ankle instability.

OBJECTIVES: To investigate the immediate effects of local muscle vibration (LMV) on static and dynamic balance control in individuals with and without chronic ankle instability (CAI). DESIGN: Quasi-experimental study. SETTING: Research laboratory. PARTICIPANTS: Twenty-six individuals with CAI and 26 healthy controls. MAIN OUTCOME MEASURES: Center of pressure variables (mean total velocity and displacement in anteroposterior (AP) and mediolateral (ML) directions) during single-leg standing with eyes open and eyes closed and also reach distances in anterior (ANT), posteromedial (PM), and posterolateral (PL) directions of the modified star excursion balance test (MSEBT) were assessed before and after LMV. RESULTS: Statistical analyses showed a significant decrease in mean total velocity and displacement in AP direction from before to after LMV in eyes open condition for both individuals with CAI (p = 0.025, p = 0.041, respectively) and healthy controls (p = 0.001, p = 0.003, respectively). Similar results were observed in eyes closed condition for both individuals with CAI (p < 0.001, p < 0.001, respectively) and healthy controls (p = 0.040, p = 0.014, respectively). The results also showed increased reach distances in ANT (p < 0.001), PM (p < 0.001), and PL directions (p < 0.001) in all participants after LMV. CONCLUSION: Our results suggest that LMV may be a useful tool in rehabilitation of static and dynamic balance deficits in individuals with CAI.

Force-field perturbations and muscle vibration strengthen stability-related foot placement responses during steady-state gait in healthy adults.

Mediolateral gait stability can be maintained by coordinating our foot placement with respect to the center-of-mass (CoM) kinematic state. Neurological impairments can reduce the degree of foot placement control. For individuals with such impairments, interventions that could improve foot placement control could thus contribute to improved gait stability. In this study we aimed to better understand two potential interventions, by investigating their effect in neurologically intact individuals. The degree of foot placement control can be quantified based on a foot placement model, in which the CoM position and velocity during swing predict subsequent foot placement. Previously, perturbing foot placement with a force-field resulted in an enhanced degree of foot placement control as an after-effect. Moreover, timed muscle vibration enhanced the degree of foot placement control whilst the vibration was applied. Here, we replicated these two findings and further investigated whether Q1) timed muscle vibration leads to an after-effect and Q2) whether combining timed muscle vibration with force-field perturbations leads to a larger after-effect, as compared to force-field perturbations only. In addition, we evaluated several potential contributors to the degree of foot placement control, by considering foot placement errors, CoM variability and the CoM position gain (ßpos) of the foot placement model, next to the R2 measure as the degree of foot placement control. Timed muscle vibration led to a higher degree of foot placement control as an after-effect (Q1). However, combining timed muscle vibration and force-field perturbations did not lead to a larger after-effect, as compared to following force-field perturbations only (Q2). Furthermore, we showed that the improved degree of foot placement control following force-field perturbations and during/following muscle vibration, did not reflect diminished foot placement errors. Rather, participants demonstrated a stronger active response (higher ßpos) as well as higher CoM variability.

The functional role of conscious sensation of movement.

This paper proposes a new framework for investigating neural signals sufficient for a conscious sensation of movement and their role in motor control. We focus on signals sufficient for proprioceptive awareness, particularly from muscle spindle activation and from primary motor cortex (M1). Our review of muscle vibration studies reveals that afferent signals alone can induce conscious sensations of movement. Similarly, studies employing peripheral nerve blocks suggest that efferent signals from M1 are sufficient for sensations of movement. On this basis, we show that competing theories of motor control assign different roles to sensation of movement. According to motor command theories, sensation of movement corresponds to an estimation of the current state based on afferent signals, efferent signals, and predictions. In contrast, within active inference architectures, sensations correspond to proprioceptive predictions driven by efferent signals from M1. The focus on sensation of movement provides a way to critically compare and evaluate the two theories. Our analysis offers new insights into the functional roles of movement sensations in motor control and consciousness.

Investigating the Effects of a Focal Muscle Vibration Protocol on Sensorimotor Integration in Healthy Subjects.

Background: The ability to perceive two tactile stimuli as asynchronous can be measured using the somatosensory temporal discrimination threshold (STDT). In healthy humans, the execution of a voluntary movement determines an increase in STDT values, while the integration of STDT and movement execution is abnormal in patients with basal ganglia disorders. Sensorimotor integration can be modulated using focal muscle vibration (fMV), a neurophysiological approach that selectively activates proprioceptive afferents from the vibrated muscle. Method: In this study, we investigated whether fMV was able to modulate STDT or STDT-movement integration in healthy subjects by measuring them before, during and after fMV applied over the first dorsalis interosseous, abductor pollicis brevis and flexor radialis carpi muscles. Results: The results showed that fMV modulated STDT-movement integration only when applied over the first dorsalis interosseous, namely, the muscle performing the motor task involved in STDT-movement integration. These changes occurred during and up to 10 min after fMV. Differently, fMV did not influence STDT at rest. We suggest that that fMV interferes with the STDT-movement task processing, possibly disrupting the physiological processing of sensory information. Conclusions: This study showed that FMV is able to modulate STDT-movement integration when applied over the muscle involved in the motor task. This result provides further information on the mechanisms underlying fMV, and has potential future implications in basal ganglia disorders characterized by altered sensorimotor integration.

Effectiveness of Focal Muscle Vibration in the Recovery of Neuromotor Hypofunction: A Systematic Review.

Adequate physical recovery after trauma, injury, disease, a long period of hypomobility, or simply ageing is a difficult goal because rehabilitation protocols are long-lasting and often cannot ensure complete motor recovery. Therefore, the optimisation of rehabilitation procedures is an important target to be achieved. The possibility of restoring motor functions by acting on proprioceptive signals by unspecific repetitive muscle vibration, focally applied on single muscles (RFV), instead of only training muscle function, is a new perspective, as suggested by the effects on the motor performance evidenced by healthy persons. The focal muscle vibration consists of micro-stretching-shortening sequences applied to individual muscles. By repeating such stimulation, an immediate and persistent increase in motility can be attained. This review aims to show whether this proprioceptive stimulation is useful for optimising the rehabilitative process in the presence of poor motor function. Papers reporting RFV effects have evidenced that the motor deficits can be counteracted by focal vibration leading to an early and quick complete recovery. The RFV efficacy has been observed in various clinical conditions. The motor improvements were immediate and obtained without loading the joints. The review suggests that these protocols can be considered a powerful new advantage to enhance traditional rehabilitation and achieve a more complete motor recovery.