Neural adaptations in quadriceps muscle after 4 weeks of local vibration training in young versus older subjects

Local vibration induces changes in spinal and corticospinal excitability in vibrated and antagonist muscles

Local vibration (LV) applied over the muscle tendon constitutes a powerful stimulus to activate the muscle spindle primary (Ia) afferents that project to the spinal level and are conveyed to the cortical level. This study aimed to identify the neuromuscular changes induced by a 30-min LV-inducing illusions of hand extension on the vibrated flexor carpi radialis (FCR) and the antagonist extensor carpi radialis (ECR) muscles. We studied the change of the maximal voluntary isometric contraction (MVIC, experiment 1) for carpal flexion and extension, motor-evoked potentials (MEPs, experiment 2), cervicomedullary motor-evoked potentials (CMEPs, experiment 2), and Hoffmann's reflex (H-reflex, experiment 3) for both muscles at rest. Measurements were performed before (PRE) and at 0, 30, and 60 min after LV protocol. A lasting decrease in strength was only observed for the vibrated muscle. The reduction in CMEPs observed for both muscles seems to support a decrease in alpha motoneurons excitability. In contrast, a slight decrease in MEPs responses was observed only for the vibrated muscle. The MEP/CMEP ratio increase suggested greater cortical excitability after LV for both muscles. In addition, the H-reflex largely decreased for the vibrated and the antagonist muscles. The decrease in the H/CMEP ratio for the vibrated muscle supported both pre- and postsynaptic causes of the decrease in the H-reflex. Finally, LV-inducing illusions of movement reduced alpha motoneurons excitability for both muscles with a concomitant increase in cortical excitability.NEW & NOTEWORTHY Spinal disturbances confound the interpretation of excitability changes in motor areas and compromise the conclusions reached by previous studies using only a corticospinal marker for both vibrated and antagonist muscles. The time course recovery suggests that the H-reflex perturbations for the vibrated muscle do not only depend on changes in alpha motoneurons excitability. Local vibration induces neuromuscular changes in both vibrated and antagonist muscles at the spinal and cortical levels.

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.

Shoulder vibratory exercises improves shoulder external rotation muscle strength and shoulder function: Randomized comparison trial

BACKGROUND

Based on electromyography measurements, shoulder vibratory exercises efficiently stimulate shoulder muscles activity. Yet very few studies have supported that shoulder vibratory exercises increased shoulder muscles strength and function, and the noninferiority compared with conventional elastic resistance exercises remains unknown.

OBJECTIVE

This study investigated the effect of vibratory exercises versus conventional elastic resistance exercises with elastic bands on shoulder external rotation muscles strength and functional performance in young adults.

METHODS

26 young adults (7 males and 19 females, with age 23.89 ± 3.02) were recruited and randomly allocated to shoulder vibratory exercises with FLEXI-BAR (FLEXI-BAR group) or conventional resistance exercises with elastic band (TheraBand group) for 3 times/week, 4 weeks totally. Shoulder external rotator muscles strength test and Underkofler softball distance throw test (USDTT) were performed before and after the training period.

RESULTS

After 4 weeks training, shoulder external rotator muscles strength increased 22.25 ± 15.06 N (P= 0.004, effect size = 1.48) within FLEXI-BAR group and 22.81 ± 14.94 N (P= 0.007, effect size = 1.53) within TheraBand group. There were no statistically significant differences between groups in the three muscle strength tests (P> 0.65). Regarding shoulder function, FLEXI-BAR exercises increased the throw distance 0.81 ± 0.92 meters in USDTT (P= 0.041, effect size = 0.88) while TheraBand exercise did not (P= 0.284), yet there was no statistically significant between group effects (P= 0.608).

CONCLUSIONS

These findings suggest that shoulder vibratory exercises can improve shoulder muscles strength in young adults and can be a useful alternative to the conventional elastic resistance exercises to improve the shoulder muscles strength and function. This provides therapists with more options in terms of choosing training equipment for rehabilitation programs.

Acute effects of quadriceps muscle versus tendon prolonged local vibration on force production capacities and central nervous system excitability

PURPOSE

The present study aimed to directly compare the effects of 30 min muscle (VIB_muscle) vs. tendon (VIB_tendon) local vibration (LV) to the quadriceps on maximal voluntary isometric contraction (MVIC) and rate of torque development (RTD) as well as on central nervous system excitability (i.e. motoneuron and cortical excitability).

METHODS

Before (PRE) and immediately after (POST) LV applied to the quadriceps muscle or its tendon, we investigated MVIC and RTD (STUDY #1; n = 20) or vastus lateralis (VL), vastus medialis (VM) and rectus femoris (RF) electromyography responses to thoracic electrical stimulation (TMEPs; motoneuron excitability) and transcranial magnetic stimulation (MEPs; corticospinal excitability) (STUDY #2; n = 17). MEP/TMEP ratios were further calculated to quantify changes in cortical excitability.

RESULTS

MVIC decreased at POST (P = 0.017) without any difference between VIB_tendon and VIB_muscle, while RTD decreased for VIB_tendon (P = 0.013) but not VIB_muscle. TMEP amplitudes were significantly decreased for all muscles (P = 0.014, P < 0.001 and P = 0.004 for VL, VM and RF, respectively) for both LV sites. While no changes were observed for MEP amplitude, MEP/TMEP ratios increased at POST for VM and RF muscles (P = 0.009 and P = 0.013, respectively) for both VIB_tendon and VIB_muscle.

CONCLUSION

The present results suggest that prolonged muscle and tendon LV are similarly effective in modulating central nervous system excitability and decreasing maximal force. Yet, altered explosive performance after tendon but not muscle LV suggests greater neural alterations when tendons are vibrated.

Impact of Local Vibration Training on Neuromuscular Activity, Muscle Cell, and Muscle Strength: A Review

This paper presents a review of studies on the effects of local vibration training (LVT) on muscle strength along with the associated changes in neuromuscular and cell dynamic responses. Application of local/direct vibration can significantly change the structural properties of muscle cell and can improve muscle strength. The improvement is largely dependent on vibration parameters such as amplitude and frequency. The results of 20 clinical studies reveal that electromyography (EMG) and maximal voluntary contraction (MVC) vary depending on vibration frequency, and studies using frequencies of 28-30 Hz reported greater increases in muscle activity in terms of EMG (rms) value and MVC data than the studies using higher frequencies. A greater muscle activity can be related to the recruitment of large motor units due to the application of local vibration. A greater increase in EMG (rms) values for biceps and triceps during extension than flexion under LVT suggests that types of muscles and their functions play an important role. Although a number of clinical trials and animal studies have demonstrated positive effects of vibration on muscle, an optimum training protocol has not been established. An attempt is made in this study to investigate the optimal LVT conditions on different muscles through review and analysis of published results in the literature pertaining to the changes in the neuromuscular activity. Directions for future research are discussed with regard to identifying optimal conditions for LVT and better understanding of the mechanisms associated with effects of vibration on muscles.

The Focal Mechanical Vibration for Balance Improvement in Elderly - A Systematic Review

Background

Aging has been associated with the progressive depletion of lean mass, reductions in muscle strength and the coordination of the lower extremities, accompanied by decreased gait assurance and balance control. Also, less balance control favors falling which is the leading cause of injury among the elderly. The aim of this systematic review is to identify and evaluate existing evidence regarding the use of focused vibration (FV) to improve balance and reduce the risk of falling during the rehabilitation of elderly populations.

Methods

The PICO question is what are the effects of focal/segmental/local vibration training on the assessment of balance and the risk of falls among the elderly population? A thorough literature review was conducted between May 1, 2009, and June 30, 2019, for studies in English, randomized clinical trials, including crossover and prospective design studies with assessing balance and the risk of falls in elderly populations (age > 60 years).

Results

Eight articles (N = 8) satisfied the inclusion criteria and were considered, of which 6 are RTC, one cross-sectional study and one clinical study, for a total of 635 participants. A total of 6 different vibration devices were used, each of which was associated with different FV frequency and amplitude characteristics and different treatment protocols.

Conclusion

In conclusion, FV can be effective in decreasing the risk of falls and improving the assessment of balance, but more evidence is necessary considering the limits of the studies; however, it does look an important promise during rehabilitative treatment.

Local vibration training improves the recovery of quadriceps strength in early rehabilitation after anterior cruciate ligament reconstruction: A feasibility randomised controlled trial

BACKGROUND

After anterior cruciate ligament reconstruction (ACLR), quadriceps strength must be maximised as early as possible.

OBJECTIVES

We tested whether local vibration training (LVT) during the early post-ACLR period (i.e., ∼10 weeks) could improve strength recovery.

METHODS

This was a multicentric, open, parallel-group, randomised controlled trial. Thirty individuals attending ACLR were randomised by use of a dedicated Web application to 2 groups: vibration (standardised rehabilitation plus LVT, n=16) or control (standardised rehabilitation alone, n=14). Experimenters, physiotherapists and participants were not blinded. Both groups received 24 sessions of standardised rehabilitation over ∼10 weeks. In addition, the vibration group received 1 hour of vibration applied to the relaxed quadriceps of the injured leg at the end of each rehabilitation session. The primary outcome - maximal isometric strength of both injured and non-injured legs (i.e., allowing for limb asymmetry measurement) - was evaluated before ACLR (PRE) and after the 10-week rehabilitation (POST).

RESULTS

Seven participants were lost to follow-up, so data for 23 participants were used in the complete-case analysis. For the injured leg, the mean (SD) decrease in maximal strength from PRE to POST was significantly lower for the vibration than control group (n=11, -16% [10] vs. n=12, -30% [11]; P=0.0045, Cohen's d effect size=1.33). Mean PRE-POST change in limb symmetry was lower for the vibration than control group (-19% [11] vs. -29% [13]) but not significantly (P=0.051, Cohen's d effect size=0.85).

CONCLUSION

LVT improved strength recovery after ACLR. This feasibility study suggests that LVT applied to relaxed muscles is a promising modality of vibration therapy that could be implemented early in ACLR.

TRIAL REGISTRATION

ClinicalTrials.gov: NCT02929004.

Is the Focal Muscle Vibration an Effective Motor Conditioning Intervention? A Systematic Review

Mechanical vibration, applied to single or few muscles, can be a selective stimulus for muscle spindles, able to modify neuromuscular management, inducing short and long-term effects, are now mainly employed in clinic studies. Several studies reported as treatments with focal vibratory (FVT) can influence neuromuscular parameters also in healthy people. However, the application modalities and the consequent effects are remarkably fragmented. This paper aims to review these studies and to characterize the FVT effectiveness on long-term conditional capacities in relation to FVT characteristics. A systematic search of studies published from 1985 to 2020 in English on healthcare databases was performed. Articles had to meet the following criteria: (1) treatment based on a locally applied vibration on muscle belly or tendon; (2) healthy adults involved; (3) outcomes time analysis enduring for more than 24 h. Twelve studies were found, all of them presented an excellent quality score of ≥75%. All selected papers reported positive changes, comparable with traditional long-lasting training effects. Muscle force and power were the most investigated parameters. The after-effects persisted for up to several months. Among the different FV administration modalities, the most effective seems to show a stimulus frequency of ≈100 Hz, repeated more times within three-five days on a voluntary contracted muscle.

Interactions between perceptions of fatigue, effort, and affect decrease knee extensor endurance performance following upper body motor activity, independent of changes in neuromuscular function

Prior exercise has previously been shown to impair subsequent endurance performance in non-activated muscles. Declines in the neuromuscular function and altered perceptual/affective responses offer possible mechanisms through which endurance performance may be limited in these remote muscle groups. We thus conducted two experiments to better understand these performance-limiting mechanisms. In the first experiment, we examined the effect of prior handgrip exercise on the behavioral, perceptual, and affective responses to a sustained, sub-maximal contraction of the knee extensors. In the second experiment, transcranial magnetic stimulation was used to assess the neuromuscular function of the knee extensors before and after the handgrip exercise. The results of the first experiment demonstrated prior handgrip exercise increased the perceptions of effort and reduced affective valence during the subsequent knee extensor endurance exercise. Both effort and affect were associated with endurance performance. Subjective ratings of fatigue were also increased by the preceding handgrip exercise but were not directly related to knee extensor endurance performance. However, perceptions of fatigue were correlated with heightened effort perception and reduced affect during the knee extensor contraction. In the second experiment, prior handgrip exercise did not significantly alter the neuromuscular function of the knee extensors. The findings of the present study indicate that motor performance in the lower limbs following demanding exercise in the upper body appears to be regulated by complex, cognitive-emotional interactions, which may emerge independent of altered neuromuscular function. Subjective fatigue states are implicated in the control of perceptual and affective processes responsible for the regulation of endurance performance.

Effects of Preconditioning Local Vibrations on Subsequent Plantar Skin Blood Flow Response to Walking

Weight-bearing exercise such as walking may increase risk of foot ulcers in people with diabetes mellitus (DM) because of plantar ischemia due to repetitive, high plantar pressure. Applications of local vibrations on plantar tissues as a preconditioning intervention before walking may reduce plantar tissue ischemia during walking. The objective of this study was to explore whether preconditioning local vibrations reduce reactive hyperemia after walking. A double-blind, repeated-measures, and crossover design was tested in 10 healthy participants without DM. The protocol included 10-minute baseline, 10-minute local vibrations (100 Hz or sham), 10-minute walking, and 10-minute recovery periods. The order of local vibrations was randomly assigned. Skin blood flow (SBF) was measured over the first metatarsal head during baseline and recovery periods. SBF responses were characterized as peak SBF, total SBF, and recovery time of reactive hyperemia. SBF was expressed as a ratio of recovery to baseline SBF to quantify the changes. Peak SBF in the vibration protocol (6.98 ± 0.87) was significantly lower than the sham control (9.26 ± 1.34, P < .01). Total SBF in the vibration protocol ([33.32 ± 7.98] × 103) was significantly lower than the sham control ([48.09 ± 8.9] × 103, P < .05). The recovery time in the vibration protocol (166.08 ± 32.71 seconds) was not significantly different from the sham control (223.53 ± 38.85 seconds, P = .1). Local vibrations at 100 Hz could reduce walking-induced hyperemic response on the first metatarsal head. Our finding indicates that preconditioning local vibrations could be a potential preventive intervention for people at risk for foot ulcers.

Specific motor cortex hypoexcitability and hypoactivation in COPD patients with peripheral muscle weakness

Background

Peripheral muscle weakness can be caused by both peripheral muscle and neural alterations. Although peripheral alterations cannot totally explain peripheral muscle weakness in COPD, the existence of an activation deficit remains controversial. The heterogeneity of muscle weakness (between 32 and 57% of COPD patients) is generally not controlled in studies and could explain this discrepancy. This study aimed to specifically compare voluntary and stimulated activation levels in COPD patients with and without muscle weakness.

Methods

Twenty-two patients with quadriceps weakness (COPD_MW), 18 patients with preserved quadriceps strength (COPD_NoMW) and 20 controls were recruited. Voluntary activation was measured through peripheral nerve (VA_peripheral) and transcranial magnetic (VA_cortical) stimulation. Corticospinal and spinal excitability (MEP/Mmax and Hmax/Mmax) and corticospinal inhibition (silent period duration) were assessed during maximal voluntary quadriceps contractions.

Results

COPD_MW exhibited lower VA_cortical and lower MEP/Mmax compared with COPD_NoMW (p < 0.05). Hmax/Mmax was not significantly different between groups (p = 0.25). Silent period duration was longer in the two groups of COPD patients compared with controls (p < 0.01). Interestingly, there were no significant differences between all COPD patients taken together and controls regarding VA_cortical and MEP/Mmax.

Conclusions

COPD patients with muscle weakness have reduced voluntary activation without altered spinal excitability. Corticospinal inhibition is higher in COPD regardless of muscle weakness. Therefore, reduced cortical excitability and a voluntary activation deficit from the motor cortex are the most likely cortical mechanisms implicated in COPD muscle weakness. The mechanisms responsible for cortical impairment and possible therapeutic interventions need to be addressed.

Intermediate Muscle Length and Tendon Vibration Optimize Corticospinal Excitability During Knee Extensors Local Vibration

While local vibration (LV) has been recently proposed as a potential modality for neuromuscular conditioning, no practical recommendations to optimize its effects have been published. Because changes in corticospinal excitability may reflect at which degree the neuromuscular function is modulated during LV exposure, this study investigated the effects of muscle length and vibration site on LV-induced on motor evoked potentials (MEPs) changes. Twenty-one subjects participated in a single session in which MEPs were evoked on the relaxed knee extensors (KE) during three conditions, i.e., no vibration (CON), muscle (VIBMU), and tendon vibration (VIBTD). Three muscle lengths were tested for each condition, i.e., short/intermediate/long KE muscle length. Both VIBMU and VIBTD significantly increase MEPs compared to CON. Higher increases (P < 0.001) were found for VIBTD compared to VIBMU for vastus lateralis (mean increases of the three angles: +241% vs.+ 148%), vastus medialis (+273% vs. + 180%) and rectus femoris muscles (+191% vs. +141%). The increase in MEPs amplitude was higher (p < 0.001) at an intermediate (mean pooled increase for VIBTD and VIBMU: +265%, +290%, and +212% for VL, VM, and RF, respectively) compared to short (+136%, + 144%, and + 127%) or long (+ 184%, + 246% and + 160%) muscle lengths. These results suggest that LV should be applied to the tendon at an intermediate muscle length to optimize the acute effects of LV on the KE neuromuscular function.