Tendon vibration during submaximal isometric strength and postural tasks

Vibration-induced postural reactions: a scoping review on parameters and populations studied

Objective

Mechanical vibration is an effective way for externally activating Ia primary endings of the muscle spindles and skin mechanoreceptors. Despite its popularity in proprioception and postural control studies, there is still no review covering the wide variety of vibration parameters or locations used in studies. The main purpose of this scoping review was thus to give an overview of general vibration parameters and to identify, if available, the rationale for justifying methodological choices concerning vibration parameters.

Methods

Three databases (Pubmed, CINHAL, and SPORTDiscus) were searched from inception to July 2022. Included articles were to focus on the study of muscle spindles and skin mechanoreceptors vibration in humans and assess postural control. Following inclusion, data regarding demographic information, populations, vibration parameters and rationale were extracted and summarized.

Results

One hundred forty-seven articles were included, mostly targeting lower extremities (n = 137) and adults (n = 126). The parameters used varied widely but were most often around 80 Hz, at an amplitude of 1 mm for 10-20 s. Regarding rationales, nearly 50% of the studies did not include any, whereas those including one mainly cited the same two studies, without elaborating specifically on the parameter's choice.

Conclusion

This scoping review provided a comprehensive description of the population recruited and parameters used for vibration protocols in current studies with humans. Despite many studies, there remain important gaps of knowledge that needs to be filled, especially for vibration amplitude and duration parameters in various populations.

Influence of Proprioceptive Inputs and Force Feedback Modality on Force Reproduction Performance

The sense of force can be assessed using a force reproduction task (FRT), which consists of matching a target force with visual feedback (TARGET phase) and reproducing it without visual feedback (REPRODUCTION phase). We investigated the relevance of muscle proprioception during the TARGET phase (EXP1) and the influence of the sensory source used for the force feedback (EXP2). Accordingly, EXP1 compared the force reproduction error (RE) between trials with (LV) and without (NoLV) local tendon vibration applied on the first dorsal interosseous during the TARGET phase, while EXP2 compared RE between trials performed with visual (VISIO) or auditory (AUDIO) feedback. The FRT was performed with the index finger at 5% and 20% of the maximal force (MVC). RE was greater with LV compared with NoLV at 5% (p = 0.004) but not 20% MVC (p = 0.65). The involvement of muscle proprioception in RFT was further supported by the increase in RE with LV frequency (supplementary experiment). RE was greater for VISIO than AUDIO at 5% (p < 0.001) but not 20% MVC (p = 0.054). This study evidences the relevance of proprioceptive inputs during the target PHASE and the influence of the force feedback modality on RE, and thereby on the assessment of the sense of force.

Acute effects of muscle vibration on elbow joint position sense in healthy young men: A randomized trial

BACKGROUND

The study aimed to investigate and compare the acute effects of 2 local vibration frequencies (63 Hz vs 42 Hz frequencies) applied to the biceps brachii muscles on the elbow joint position sense (JPS) in healthy young men.

METHODS

A 3-arm parallel-group design with randomization of participants was used. Forty-five healthy young men aged 19 to 30 years were randomly assigned to 3 groups: to receive 63 Hz (n = 15) in experimental group 1 (EG1) or 42 Hz (n = 15) in experimental group 2 (EG2) or sham vibration in the control group (n = 15). Participants in the EG1 and EG2 received 5 bouts of 1-minute vibration exposure to the biceps brachii muscle, with a 1-minute rest between the bouts. In control group, sham vibration was applied with the same duration and interval as in EG1 and EG2. The active elbow joint position error was selected as an outcome measure to assess elbow JPS. The target angle and the angle reproduced were measured using a Universal Goniometer. The difference between the target and the reproduced angles was calculated to determine active elbow joint position error. Measurements were made before the vibration application and right after it.

RESULTS

No statistically significant difference was observed in the JPS of the elbow joint over time in any group (P = .625). No statistically significant differences were observed between the 33 groups in the JPS of the elbow (P = .075).

CONCLUSION

There was no acute effect of vibration of the biceps brachii muscle at 63 and 42 Hz on active elbow JPS in healthy adults.

Can local vibration alter the contribution of persistent inward currents to human motoneuron firing?

The response of spinal motoneurons to synaptic input greatly depends on the activation of persistent inward currents (PICs), which in turn are enhanced by the neuromodulators serotonin and noradrenaline. Local vibration (LV) induces excitatory Ia input onto motoneurons and may alter neuromodulatory inputs. Therefore, we investigated whether LV influences the contribution of PICs to motoneuron firing. This was assessed in voluntary contractions with concurrent, ongoing LV, as well as after a bout of prolonged LV. High-density surface electromyograms (HD-EMG) of the tibialis anterior were recorded with a 64-electrode matrix. Twenty males performed isometric, triangular, dorsiflexion contractions to 20% and 50% of maximal torque at baseline, during LV of the tibialis anterior muscle, and after 30-min of LV. HD-EMG signals were decomposed, and motor units tracked across time points to estimate PICs through a paired motor unit analysis, which quantifies motor unit recruitment-derecruitment hysteresis (ΔF). During ongoing LV, ΔF was lower for both 20% and 50% ramps. Although significant changes in ΔF were not observed after prolonged LV, a differential effect across the motoneuron pool was observed. This study demonstrates that PICs can be non-pharmacologically modulated by LV. Given that LV leads to reflexive motor unit activation, it is postulated that lower PIC contribution to motoneuron firing during ongoing LV results from decreased neuromodulatory inputs associated with lower descending corticospinal drive. A differential effect in motoneurons of different recruitment thresholds after prolonged LV is provocative, challenging the interpretation of previous observations and motivating future investigations. KEY POINTS: Neuromodulatory inputs from the brainstem influence motoneuron intrinsic excitability through activation of persistent inward currents (PICs). PICs make motoneurons more responsive to excitatory input. We demonstrate that vibration applied on the muscle modulates the contribution of PICs to motoneuron firing, as observed through analysis of the firing of single motor units. The effects of PICs on motoneuron firing were lower when vibration was concurrently applied during voluntary ramp contractions, likely due to lower levels of neuromodulation. Additionally, prolonged exposure to vibration led to differential effects of lower- vs. higher-threshold motor units on PICs, with lower-threshold motor units tending to present an increased and higher-threshold motor units a decreased contribution of PICs to motoneuron firing. These results demonstrate that muscle vibration has the potential to influence the effects of neuromodulation on motoneuron firing. The potential of using vibration as a non-pharmacological neuromodulatory intervention should be further investigated.

Electromyographic responses to unexpected Achilles tendon vibration-induced perturbations during standing in young and older people

This study aimed to investigate age-related differences in electromyographic (EMG) responses to unexpected Achilles tendon vibration (ATV) perturbations while standing blindfold. ATV with variable and random duration (12-15 s) and rest periods (20-24 s) was applied on 18 young and 16 older volunteers. The anterior/posterior center of pressure (CoP) and the soleus (SOL) and tibialis anterior (TA) EMG were analyzed for 1 s before and 8 s after the ATV onset and offset. ATV induced a posterior shift of CoP in both groups, with more pronounced shift in the older group. During ATV onset, the older group demonstrated less SOL and more TA EMG increase compared to the young group. During the first 0.5 s of ATV offset, SOL EMG was decreased in both age groups, while TA showed a burst of EMG activity that was greater in the older group. No difference in the latencies of EMG peaks or valleys was observed between the groups. It is concluded that ATV induces greater posterior CoP shift in older adults, and they adopt a recovery strategy, characterized by a decreased SOL activation and an increased TA activation. These differences are possibly attributed to the increased fear of falling, decreased limits of stability and reduced capacity of older people to reweight their sensory inflow when proprioception is distorted.

Effects of tendon vibration and age on force reproduction task performed with wrist flexors

The sense of force is suggested to rely in part on proprioceptive inputs when assessed with a force reproduction task. The age-related alterations in proprioceptive system could, therefore, alter the sense of force. This study investigated the effects of tendon vibration on a force reproduction task performed with the wrist flexors in 18 young (20-40 year) and 18 older adults (60-90 year). Participants matched a target force (5% or 20% of their maximal force) with visual feedback of the force produced (target phase), and reproduced the target force without visual feedback (reproduction phase) after a 5-s rest period with or without vibration. The force reproduction error was expressed as the ratio between the force produced during the reproduction and the target phases. For the trials with vibration, the error was expressed as the ratio between the force produced during the reproduction phase performed with and without vibration. Tactile acuity was assessed with a two-point discrimination test. The error was greater at 5% than at 20% contraction intensity (p < 0.001), and in older [56.5 (32.2)%; mean (SD)] than in young adults [33.5 (13.6)%] at 5% (p = 0.002) but not 20% target (p = 0.46). Tendon vibration had a greater effect at 5% than 20% contraction intensity, and in older [41.7 (32.4)%, p < 0.001] than young adults [20.0 (16.1)%]. Tactile acuity was lesser in older than young adults (p < 0.001). The results support the contribution of proprioception in the sense of force, and highlight a decrease in performance with ageing restricted to low-force contractions.

The tightening parameters of the vibratory devices modify their disturbing postural effects

The purpose was to specify the impact of two different forces exerted by vibratory devices on the Achilles tendon on postural balance. The postural balance of 13 participants was evaluated on a force platform in two 40 s bipedal stance conditions with closed eyes. Tendon vibrations (80 Hz) were triggered 10 s after the beginning of the postural evaluation and applied during 20 s. Two levels of the force exerted by the vibrators were calibrated using load cells to control the tightening parameters of the vibrators: a strong tightening (ST) condition at 45 N and a light tightening (LT) condition at 5 N. The soleus electromyographic (EMG) activity and the spatio-temporal parameters of displacement of the centre of foot pressure (COP) were analysed. To analyse the effects of the introduction, the adaptation and the end of the stimulation, non-parametric tests were used. The results indicated that the soleus EMG activity increased only in the ST condition. However, during the vibration the anteroposterior COP position was significantly more in a backward position in the LT condition. At the end of the vibration, COP parameters increased more in the LT condition than the ST condition. This study demonstrated that the effects of the vibration depended on the force exerted by the devices on the tendons. The ST increased the vibration effects on EMG activity through greater stimulating effects compared to the LT. However, the ST could also increase the ankle joint stiffness and/or somaesthetic sensory information, which attenuated the COP backward shift.

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.

Effect of localised vibration on muscle strength in healthy adults: a systematic review

OBJECTIVE

To investigate the effects of local vibration on muscle strength in healthy adults.

DATA SOURCES

The electronic databases PubMed, CINAHL, Scopus and Web of Science were searched using a combination of the following keywords: vibration, vibration therapy, power, maximal voluntary contraction, performance, rate of force development and vibratory exercise. In addition, the Medical Subject Headings 'vibration', 'strength' and 'exercise' were used. The bibliographical search was limited to articles published in English.

STUDY SELECTION

Trials that evaluated the effect of localised vibration on muscle strength in healthy humans were included.

DATA EXTRACTION

Two independent evaluators verified the quality of the selected studies using the PEDro Scale and the Cochrane Collaboration's tool for assessing the risk of bias. Muscle strength was calculated for each intervention.

RESULTS

In total, 29 full-text studies were assessed for eligibility. Eighteen studies did not match the inclusion criteria, and were excluded. The 11 studies included in this review had an average PEDro score of 5.36/10. Most of the studies reported significant improvements in muscle strength after the application of local vibration. There was considerable variation in the vibration training parameters and target muscle location.

CONCLUSIONS

The use of local vibration on the target muscle can enhance muscle strength in healthy adults. Further well-designed controlled studies are required to confirm the effect of local vibration training on muscle strength.

Response to Tendon Vibration Questions the Underlying Rationale of Proprioceptive Training

CONTEXT

Proprioceptive training on compliant surfaces is used to rehabilitate and prevent ankle sprains. The ability to improve proprioceptive function via such training has been questioned. Achilles tendon vibration is used in motor-control research as a form of proprioceptive stimulus. Using measures of postural steadiness with nonlinear measures to elucidate control mechanisms, tendon vibration can be applied to investigate the underlying rationale of proprioceptive training.

OBJECTIVE

To test whether the effect of vibration on young adults' postural control depended on the support surface.

DESIGN

Descriptive laboratory study.

SETTING

Research laboratory.

PATIENTS OR OTHER PARTICIPANTS

Thirty healthy adults and 10 adults with chronic ankle instability (CAI; age range = 18-40 years).

INTERVENTION(S)

With eyes open, participants stood in bilateral stance on a rigid plate (floor), memory foam, and a Both Sides Up (BOSU) ball covering a force platform. We applied bilateral Achilles tendon vibration for the middle 20 seconds in a series of 60-second trials and analyzed participants' responses from previbration to vibration (pre-vib) and from vibration to postvibration (vib-post).

MAIN OUTCOME MEASURE(S)

We calculated anterior-posterior excursion of the center of pressure and complexity index derived from the area under multiscale entropy curves.

RESULTS

The excursion response to vibration differed by surface, as indicated by a significant interaction of P < .001 for the healthy group at both time points and for the CAI group vib-post. Although both groups demonstrated increased excursion from pre-vib and from vib-post, a decrease was observed on the BOSU. The complexity response to vibration differed by surface for the healthy group (pre-vib, P < .001). The pattern for the CAI group was similar but not significant. Complexity changes vib-post were the same on all surfaces for both groups.

CONCLUSIONS

Participants reacted less to ankle vibration when standing on the BOSU as compared with the floor, suggesting that proprioceptive training may not be occurring. Different balance-training paradigms to target proprioception, including tendon vibration, should be explored.

Effects of Achilles tendon vibration, surface and visual conditions on lower leg electromyography in young adults with and without recurrent ankle sprains

Functional ankle instability is associated with decreased ankle muscle function. Compliant surfaces and eyes-closed training are commonly used for rehabilitation and prevention of ankle sprains. Brief Achilles tendon vibration is commonly used in the study of postural control. To test the level of activation of tibialis anterior (TIB) and fibularis longus (FIB), bilateral Achilles tendon vibration was applied for the middle 20 s in a series of 60-s trials, when 10 healthy young adults and 10 adults with history of repeated ankle sprains were standing bipedal: on floor, on memory foam, or on a Both Sides Up (BOSU) ball, with eyes open, and on floor and foam with eyes closed. Differences in Integrated surface electromyography (IEMG) of TIB and FIB were significant for both groups pre, during, and post vibration (Friedman Tests, p < 0.001 for all). In both groups, the highest IEMG for TIB was obtained during vibration when standing on foam with eyes closed, whereas the highest IEMG for FIB was obtained during vibration when standing on the BOSU. Bipedal stance on BOSU and brief Achilles tendon vibration may be a useful intervention when a session's goal is to facilitate lower leg muscles activation. Future research should explore training effects as well as the effect of FIB tendon vibration.

Visual and proprioceptive contributions to postural control of upright stance in unilateral vestibulopathy

Preserving upright stance requires central integration of the sensory systems and appropriate motor output from the neuromuscular system to keep the centre of pressure (COP) within the base of support. Unilateral peripheral vestibular disorder (UPVD) causes diminished stance stability. The aim of this study was to determine the limits of stability and to examine the contribution of multiple sensory systems to upright standing in UPVD patients and healthy subjects. We hypothesized that closure of the eyes and Achilles tendon vibration during upright stance will augment the postural sway in UPVD patients more than in healthy subjects. Seventeen UPVD patients and 17 healthy subjects performed six tasks on a force plate: forwards and backwards leaning, to determine limits of stability, and upright standing with and without Achilles tendon vibration, each with eyes open and closed (with blackout glasses). The COP displacement of the patients was significantly greater in the vibration tasks than the controls and came closer to the posterior base of support boundary than the controls in all tasks. Achilles tendon vibration led to a distinctly more backward sway in both subject groups. Five of the patients could not complete the eyes closed with vibration task. Due to the greater reduction in stance stability when the proprioceptive, compared with the visual, sensory system was disturbed, we suggest that proprioception may be more important for maintaining upright stance than vision. UPVD patients, in particular, showed more difficulty in controlling postural stability in the posterior direction with visual and proprioceptive sensory disturbance.

Sensorimotor control during peripheral muscle vibration: an experimental study

OBJECTIVE

The aims of this study were to determine whether the application of vibration on a postural lower limb muscle altered the sensorimotor control of its joint as measured by isometric force production parameters and to compare present findings with previous work conducted on trunk muscle.

METHODS

Twenty healthy adults were asked to reproduce submaximal isometric plantar flexion under 3 different conditions: no vibration and vibration frequencies of 30 and 80 Hz on the soleus muscle. Time to peak torque, variable error, as well as constant error and absolute error in peak torque were calculated and compared across conditions.

RESULTS

Under vibration, participants were significantly less accurate in the force reproduction task, as they mainly undershot the target torque. Applying an 80-Hz vibration resulted in a significantly higher negative constant error than lower-frequency vibration (30 Hz) or no-vibration condition. Decreases in isometric force production accuracy under vibration influence were also observed in a previous study conducted on trunk muscle. However, no difference in constant error was found between 30- and 80-Hz vibration conditions.

CONCLUSION

The results suggest that acute soleus muscle vibration interferes with plantar flexion torque generation by distorting proprioceptive information, leading to decreases in accuracy of a force reproduction task. Similar results in an isometric trunk extension force reproduction task were found with vibration applied on erector spinae muscle. However, high-frequency vibration applied on soleus muscle elicited higher force reproduction errors than low-frequency stimulation.

Independent modulation of corticospinal and group I afferents pathways during upright standing

Balance control during upright standing is accompanied by an increased amplitude of motor-evoked potentials (MEP) induced by transcranial magnetic stimulation and a decreased amplitude of the Hoffmann (H) reflex in the soleus muscle. Nonetheless, whether these observations reflect reciprocal adjustments between corticospinal and group I afferents pathways during upright standing remains unknown. To further investigate this question, cathodal transcranial direct current stimulation (c-tDCS) applied over the motor cortex and vibration of Achilles tendons were used to modify the excitability of corticospinal and group I afferent pathways, respectively. MEPs and H reflexes were recorded in the soleus muscle during upright standing with or without bilateral Achilles tendon vibration, these recordings being performed before and after 20 min of c-tDCS (1.5 mA) or sham stimulation applied over the sensorimotor cortex. The results indicate that tendon vibration increased MEP amplitude (+28%) and decrease (-68%) the H-reflex amplitude (p<0.05). After c-tDCS, MEP amplitude was reduced by 13% and 26% without and with tendon vibration (p<0.05), respectively. In contrast, no significant change occurred in H-reflex amplitude after c-tDCS. Regardless of the conditions (c-tDCS and tendon vibration), no significant correlation was observed between changes in MEP and H-reflex amplitudes. The results failed to demonstrate close reciprocal changes in soleus MEP and H-reflex amplitudes during upright standing. These original findings suggest independent adjustments in corticospinal and group I afferents pathways during upright standing.

Reduced plantar sole sensitivity induces balance control modifications to compensate ankle tendon vibration and vision deprivation

The aim of this study was to investigate if sensory reweighting occurred to control balance when the sensitivity of the plantar sole is reduced using cooling. To address this question, visual information was manipulated and/or ankle proprioception was altered by Achilles tendon vibration. It was expected that Achilles tendon vibration and vision deprivation would induce greater center of pressure (CoP) excursions and/or increase of electromyographic (EMG) activity of the ankle muscles (triceps surea and tibialis anterior) with than without cooling of the plantar sole. To verify these hypotheses, the CoP and EMG activity of the ankle muscles were simultaneously recorded during quiet standing trials of 30s before and after feet cooling procedure. Results showed that plantar sole sensitivity alteration did not lead to larger CoP excursions even during Achilles tendon vibration in absence of vision. This could be explained by an increase in the EMG activity of the triceps surae after the cooling procedure without modification of tibialis anterior EMG activity. This study suggests that to compensate alteration in plantar sole sensitivity, the central nervous system increased the muscular activity of the triceps surae to limit CoP excursions.