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Effectiveness of Focal Muscle Vibration in Neuromotor Hypofunction
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This entry is adapted from the peer-reviewed paper 10.3390/jfmk8030103

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.

muscle vibration proprioception muscle spindle proprioceptive training

1. Introduction

Neuromotor hypofunction refers to a condition in which an individual has difficulty or limitations controlling and coordinating a movement and can affect various aspects of motor skills, from fine motor skills (such as writing, eating, buttoning a shirt) to gross motor skills (such as lifting weights, walking or running). The functional impairment consists of ‘negative symptoms’, such as asthenia, weakness, poor motor coordination and fatigue. These functional deficits can be induced by various neuromuscular diseases and by musculoskeletal trauma during daily, sporting and professional activities. For the latter, several individual characteristics are possible risk factors, such as age, poor fitness level, comorbidities, etc. Often, motor function may be restored after a long period of rehabilitation by providing impairment-specific intervention protocols. It should be noted that the motor and functional level obtained at the end of a rehabilitation period may not be sufficient to ensure full motor recovery. This is particularly true in sports, where full recovery of coordination and conditioning skills can be achieved with an additional conditioning period. An obvious limitation of exercise-based rehabilitation protocols is imposed by the individual’s functional residual, as well as expected individual compliance.
Optimisation of rehabilitation [1][2] is an area of study that always offers new topics, as research is constantly looking for protocols that reduce duration, avoid relapse and ensure full recovery of motor functions. A new direction of research suggests the possibility of acting on motor control in addition to or as an alternative to traditional exercise [3].
Reviews report evidence that sustained activation of the proprioceptive system can induce immediate improvements in motor abilities in healthy subjects [4][5][6]. Indeed, literature data show that improvements in muscle strength, motor task readiness, muscle power and movement fluidity and coordination can be achieved with proprioceptive stimulation, suggesting that this intervention be included in traditional rehabilitation programmes to improve subsequent functional motor deficits. These possibilities find important support in the consideration that motor movements and performance are largely based on proprioceptive input, upon which motor planning and execution are built and controlled [3]. On the other hand, proprioception deficits lead to profound alterations in motor execution, altering the control of postural reflexes, muscle tone and motor behaviour [7], as well as the spatial and temporal aspects of movement [8][9]. Although motor execution is supported by different sensory modalities (auditory, visual and tactile systems are involved), the proprioceptive system is considered the main source of information to plan and perform elementary and complex motor tasks. Improved proprioceptive processing could improve the accuracy of motor execution, as well as motor efficiency (i.e., muscle strength, fatigue), the latter being profoundly influenced by coordination. Therefore, an improvement of proprioceptive input could be a reasonable approach to improve or restore motor function. Furthermore, training the proprioceptive system does not require loading the skeletal system, avoiding one of the most relevant obstacles and allowing rehabilitation procedures to be anticipated, possibly preventing possible relapses.

2. Effects of RMV Stimulation on Motor Function

The twenty-two selected studies and their main points are summarised in Table 1. Subjects with poor motor function showed significant improvements in muscle strength after RMV stimulation [10][11][12][13][14][15][16][17][18][19][20][21][22][23][24][25][26][27] and in power [22][23][28][29][30]. Other less common outcomes expressing an improvement in function are improved joint mobility [31], positive electrophysiological changes in the spinal cord [13], reduced pain caused by insufficient joint stabilisation [17][20][22] and rate of strength development [27]. The after-effects were evident and statistically significant immediately after the end of the treatment. This finding, as well as the long persistence (up to 1 year after treatment), agrees with studies on healthy individuals previously reviewed [4][5][6].
Table 1. Main characteristics of the selected studies included in the review. NR: not reported. The outcome values at the end of the follow-up are reported (* p < 0.01; ** p < 0.001).
Table
Study Origin of the Deficit Sbjts FV Frequency & Amplitude Single Application Duration & Repetition Muscle Body Part Treated/Muscle Contraction Tests 1st Test and Last Test Maximal After-Effect
Brunetti et al., 2006 [10] ACL reconstruction 30 100 Hz; 0.2–0.5 mm 10 min; 3 times a day during 3 consecutive days Quadriceps/Yes Stability (cop area, velocity); extensor muscle peak torque 24 h; 270 days Reduction sway (closed eyes) -40% *; extensor peak force difference vibrated/not vibrated +25% *
Filippi et al., 2009 [28] Ageing 60 100 Hz; 0.2–0.5 mm 11 min; 3 times a day during 3 consecutive days Quadriceps/Yes Stability (cop area, velocity); vertical jump height; muscle power 24 h; 90 days Power ≈ +50% *; height ≈ +90% *; sway Area ≈ –35% *
Pietrangelo et al. 2009 [11] Ageing 9 300 Hz; N.R. 15 min; 1–3 times a week for 12 weeks Quadriceps/No MVC Immediately after treatment ending; 16 weeks MVC ≈ +51% *
Bakhtiary et al., 2011 [31] Limited hamstring extendibility 30 50 Hz; N.R. 20–60 sec; 3 times a day, 3 times a week for 8 weeks Hamstring/no Passive knee extension Immediately after treatment ending Knee extension +46% *
Celletti et al., 2011 [12] Joint hypermobility syndrome 15 100 Hz; 0.2–0.5 mm 10 min; 3 times a day for 3 consecutive days Quadriceps/Yes Berg balance scale 10 and 40 days Berg balance +27% *
Zaho et al., 2011 [13] Immobilisation 30 100 Hz; 0,3 mm 1 min; 48 times a day for 2 weeks Soleus/No V-wave/M-wave Immediately after treatment ending Soleus V/M did not change in treated individuals. Untreated showed—30.78% **
Brunetti et al., 2012 [29] Volleyball players 18 100 Hz; 0.2–0.5 mm 10 min; 3 times a day for 3 consecutive days Quadriceps/Yes Explosive and reactive leg power 24 h; 240 days Treated group explosive leg power +26% **, reactive power +13% **; control group explosive leg power +11% *, reactive power +7.8% *
Tankisheva et al., 2015 [16] Ageing 50 30–45 Hz; N.R. 30–60 sec; 4–8 times a day for 26 weeks Quadriceps, Gluteus maximum and medium/No MVC Immediately after treatment ending Quadriceps MVC +13.84% *
Rabini et al., 2015 [18] Osteoarthritis 50 100 Hz; 0.2–0.5 mm 10 min; 3 times a day for 3 consecutive days Quadriceps/Yes WOMAC, SPPB. POMA 3 and 6 months WOMAC −30% **; SPPB +45% **; POMA +31% **
Celletti et al., 2015 [14] Ageing 350 100 Hz; 0.2–0.5 mm 10 min; 3 times a day for 3 consecutive days Quadriceps/Yes POMA test 1; 6 months 59% of the tested individuals reached the full POMA score **
Brunetti et al., 2015 [30] Ageing 60 100 Hz; 0.2–0.5 mm 10 min; 3 times a day for 3 consecutive days Quadriceps/Yes Stability (cop area, velocity); vertical jump height; muscle power 1; 12 months Sway −35% **; Vertical Jump + 40% **; Power + 40% **
Ribot-Ciscar et al., 2015 [17] facio-scapulo-humeral muscular dystrophy 9 80 Hz; 0.5 mm 50 min; A total of 7 sessions, 1 every 4 days Biceps brachialis; triceps brachialis; pectoralis major/No Pain analogue visual scale; voluntarily shoulder abduction and flexion maximum amplitudes; MVC Immediately after treatment ending Pain analog visual scale, no significant changes; voluntarily shoulder abduction and flexion +20% *; MVC +41% *
Paoloni et al., 2015 [15] Foot drop 44 120 Hz; 0,001 mm 30 min; 3 times a week, for 12 weeks Tibialis anterior, peroneus longus/N.R. Gait analysis 1 month Improvements in ankle dorsiflexion,
Pazzaglia et al., 2016 [19] Charcot-Marie-Tooth 1A disease 14 100 Hz; 0.2–0.5 mm 10 min; 3 times a day for 3 consecutive days Quadriceps/Yes Berg Balance scale; Dynamic gait index; 6-min walking test; Muscular strength of lower limbs; Body balance; SF-36; 1 week; 1 month Berg Balance scale +8% *; Dynamic gait index +15% *; =6-min walking test; =Muscular strength of lower limbs; ↑Body balance (Sway path * and velocity *); =SF-36;
Saggini et al., 2017 [21] Ageing 30 300 Hz; N.R. 15 min; 2 times a week, for 6 months Trapezius, triceps brachii, latissimus dorsi, rectus abdominis, gluteus maximus, rectus femoris, biceps femoris, and tibialis anterior/N.R. Hand grip; knee extensores isokinetic strength; POMA test; ECOS-16 questionaire Immediately after treatment ending Grip +11% *; Isokinetic strength of the knee extensor +6% *; Poma Test + 5% *; Ecos-16 −17% *
Celletti et al., 2017 [20] postmastectomy recovery 14 100 Hz; 0.2–0.5 mm 10 min; 3 times a day for 3 consecutive days Pectoralis minor and the biceps brachi/Yes DASH; questionnaire, Body Image Scale, McGill pain questionnaire, Constant Scale, and Short Form 36 questionnaire. Immediately after treatment ending DASH scale −28% *; Constant scale +14% *; theMcGill pain questionnaire −23% *; ↑Short Form 36 questionnaire (=physical mental score)
Benedetti et al., 2017 [22] Ageing 30 150 Hz; N.R. 20 min; Once a day through five consecutive days, for 2 consecutive weeks Rectus femoris, vastus medialis, and vastus lateralis WOMAC; VAS; STAIR CLIMBING; TUG 48 h WOMAC −20% **; VAS −49% **; STAIR CLIMBING −13% **; TUG −11% **
Souron et al., 2018 [23] Ageing 17 100 Hz; 1 mm 1 h; 3 times a week, for 4 weeks Rectus femoris/No MVC, Vertical jump performance Immediately after treatment ending MVC ≈ +11% *; Maximal jump heights SJ ≈ +15.2% *, CMJ ≈ +6.5% *
Iodice et al., 2019 [25] Athletes’ effects of eccentric exercise 30 120 Hz; 1,2 mm 15 min; once Vastus intermedius, rectus femoris, vastus lateralis, vastus medialis, gluteus maximus, biceps femoris, adductor longus and magnus isokinetic evaluation, stabilometric test, perceived soreness evaluation 48 h MVC ≈ +13% **
Attanasio et al., 2020 [24] Ageing 30 100 Hz; 0.2–0.5 mm 10 min; 3 times a day for 3 consecutive days Quadriceps/Yes Body balance, POMA test, TUG test 1 week Sway ≈ −27% *; POMA test ≈ +20% **; TUG: rotation speed ≈ +8% **; duration ≈−19% *, standing up ≈ −13% **
Rippetoe et al., 2020 [26] Diabetic Peripheral Neuropathy 23 120 Hz; 1.2 mm 10 min; 3 times a week, for 4 weeks Tibialis anterior, quadriceps, and gastrocnemius/No Gait Analysis Immediately after treatment ending ↑Gait speed *, ↑cadence *, ↑stride time *, ↑left and right stance time *, ↑duration of double limb support *, ↑left and right knee flexor moments*
Coulandre et al., 2021 [27] ACL reconstruction 30 100 Hz; 1 mm 1 h; only once Quadriceps/No MVC Rof force development Immediately after treatment ending Force decrease in vibrated subject −50% then unvibrated participants
As shown in Table 1, however, in several studies, the improvements have shown their positive effectiveness in tests involving many more muscles than the one treated and in multi-joint tasks. Functional scales [12][14][15][17][18][19][20][21][22][23][24] and digital analysis [10][19][24][26][27][28][29][30] showed complex after-effects. In several cases, the results were able to improve common everyday activities [12][14][18][20][21][22] beyond expectations. Special attention could be paid to the results highlighted in a study [32], not mentioned in the table, showing that stimulatory training applied to the muscles of the floor of the mouth aimed at reducing drooling in children with cerebral palsy. In this case, the significant reduction in drooling was attributed, albeit with indirect evidence, to an improvement in swallowing, a highly coordinated motor task. Finally, one study specifically tested the effectiveness of the proprioceptive stimulation protocol on the training of volleyball players after the seasonal rest break [29]. Their explosive and reactive leg power was assessed at the beginning of the seasonal training and up to 240 days later. Although the athletes followed the same training, the stimulated group showed a much greater improvement than the control group. Interestingly, only 24 h after the end of treatment, the treated athletes showed significant and greater results than their colleagues 240 days later. This finding, discussed later, suggests a prominent role of proprioceptive drive in determining motor efficacy.
In the different studies, improvements persisted until the end of follow-up (up to 12 months after RMV application) without showing a decline. Maintenance was also found in the absence of regular exercise training [11][13][14][16][19][21][23][24][28][30], although the role of associated training seems relevant [28]. Similar long-lasting persistence has been shown in a group of studies [33], not mentioned in Table 1 as they relate to perceptual functions on the recovery of neglect. After a brief and repeated vibratory stimulation applied to the neck muscle related to the perceptual deficit, relief was significant and persistent during the follow-up period (1.5 years) without decay. Another aspect is the diversity of the origin of the deficit in the studies reviewed: there are orthopaedic [10][12][18][27][31], neurological [15][17][20] and post-surgical [10][20][27] conditions, metabolic dysfunctions [26], immobilisation [13] in athletes after prolonged training break or intense physical activities [26][30] and the main cause in Table 1, as well as in society, ageing [11][14][16][21][22][23][24][27][30].
Although the RMV protocols are applied to show a variety of parameters, it is evident (see Table 1) that certain features are dominant. Of the 22 selected studies, 18 report a stimulation frequency between 80–150 Hz. However, 11 [10][12][13][14][18][19][20][24][28][29][30] applied the same protocol (100 Hz, 0.2–0.5 mm, 10 min, 3 applications/day, repeated for 3 consecutive days). On the other hand, only two studies [16][31] applied frequencies lower than this range, and only in two cases [11][21] was the frequency of the FV (Focal Vibration) well above (300 Hz) in the most common range. The positive and lasting after-effects (range 1–12 months), with no signs of decay at the end of the follow-up period, elicited by the shorter but more concentrated protocol, confirm the previous meta-analysis [6].

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