# Focal Muscle Vibration for Stroke Rehabilitation: A Review of Vibration Parameters and Protocols
## 1 Introduction  
Stroke is the second leading cause of death and one of the most common causes of adult-onset disability worldwide. According to a recent study, 26% of individuals with stroke have a disability in activities of daily living (ADL), and 50% have reduced mobility due to hemiparesis [1]. The post-stroke disruption of the sensory system plays an important role in motor dysfunction of the hemiparetic limb [2]. Loss of proprioception impairing corrections to movement errors and loss of tactile sensation are common consequences of stroke and affect control of limb motion [3]. Another major problem affecting nearly 20-30% of stroke survivors is gait disorders [4]. These disorders further increase therisk of falls and loss of balance, reducing patients' social participation. According to National Stroke Association's post-stroke recovery guidelines, only 10% of stroke survivors recover almost completely; 25% recover with minor impairments; 40% experience moderate to severe impairments requiring special care; 10% require care in a nursing home or other long-term care facility; and 15% die shortly after the stroke [5]. While numerous therapies have been developed over the last 10 years to treat acute ischemic stroke, the stark reality remains that 95% of these patients continue intervention in the chronic stage and go on to live with significant disability for many years. Because of the complexity of a stroke, various approaches to chronic stroke rehabilitation, such as facilitation technique [6; 7], functional electric stimulation (FES) [8; 9], transcutaneous electrical stimulation (TENS) [10; 11], electromyography (EMG) biofeedback [12], exercise [13; 14], physical and occupational therapy [15; 16], robotics [17; 18], and virtual reality [19; 20], have been studied to help functional recovery from hemipgesia due to brain damage. The limitations of the aforementioned intervention strategies are their sustainability due to one or more of these challenges: the requirement of trained and licensed professionals to administer the right dose to ensure safety; lack of precision and accuracy of intervention; lack of consensus among the findings; lack of sufficient evidence to establish the effectiveness of the intervention strategies; awareness of and access to existing intervention strategies; the cost of administration; and other similar disparities [21; 22; 23; 24]. One intervention strategy that has the potential for sustainable stroke rehabilitation is the use of mechanical vibration as a therapeutic intervention known as vibration therapy (VT) [25; 26; 27; 28; 29]. According to [PERSON] et al. (2014), VT as an intervention in rehabilitation can be dated back to 1969, when [PERSON] and [PERSON] observed tonic vibration reflex (TVR) in which the application of vibratory stimulus resulted in agonist muscle contraction and antagonist relaxation. [PERSON] and [PERSON] then used this observation as a basis to use vibration to decrease muscle spasticity in individuals with stroke [28; 29]. There are two types of VT: whole body vibration (WBV), in which mechanical vibrations are transmitted from the feet to the rest of the body using a vibrating platform, and focal muscle vibration (FMV), where mechanical vibrations are applied to a localized point in muscles, generally the muscle belly or the tendon on the affected/paretic side. The potential mechanism behind using vibration as an intervention in the treatment of motor disorders in patients is that vibration stimulates the primary muscle spindle endings, causing Ia afferent impulses to be conducted to alpha motor neurons and Ia inhibitory interneurons in the spinal cord. This afferent pathway produces involuntary contraction in the vibrated muscle (that is, a tonic vibration reflex, TVR) and inhibits the antagonist muscle [30; 31]. The effect of VT on the human body depends on the characteristics of the vibration applied, such as type of vibration (vertical, horizontal, or multidirectional), frequency, amplitude, and the protocol [27].