Proprioceptive Based Training for stroke recovery. Proposal of new treatment modality for rehabilitation of upper limb in neurological diseases

The impairment of motor function represents one of the major causes of disability after stroke. More than 69 % of cerebrovascular lesions provokes impairment of motor function to the upper limb, moreover about 56 % of subjects experience severe hemiparesis even after 5 years from stroke [1, 2]. The functional impairment of the upper limb can impact negatively on quality of life and limit the autonomy in many activities of daily living (ADL). The recovery process occur through neural mechanisms mediating spontaneous cortical reorganization, but evidence indicates that intensive stimulation is essential to improve motor recovery either [3–7]. Several studies, both in animals and humans, have shown different reorganization of the central nervous system (CNS), at molecular as well as synaptic connectivity levels, dependent on the type of behavioral interactions with the external environment [4, 7]. The possibility to estimate as early as possible the outcomes achievable due to rehabilitation is one of the most meaningful clinical point to address, with the aim to promote the best recovery after stroke. This information is important for prognosis and personalization of rehabilitation programs for every individual patient [8, 9]. Several modalities for upper limb motor rehabilitation after stroke were proposed recently, among that the bilateral training has received outstanding attention. The bilateral training is a method based on the execution of repetitive tasks with both (affected and non–affected) upper extremities, with the aim of regaining a better motor function. This approach is based on the rationale that bilateral movements allow to optimize the activation/inhibition balance between the two hemispheres. The bilateral motor training emphasizes the importance of bilateral approach, intended as the involvement of both limbs in daily life practice (e.g. dressing, bathing, feeding, driving, cooking). Several studies on healthy subjects showed that when a motor task is performed the dominant arm has the goal to reach the target, whereas the non-dominant arm play a role in stabilizing adjacent musculoskeletal districts [10]. Evidence from studies with transcranial magnetic stimulation (TMS) in stroke survivors showed that both hemispheres induce a reduction of intra-cortical inhibition, when bilateral movements were performed. On the contrary, if only one arm was activated the increased inhibition was observed in the ipsilateral hemisphere [10, 11]. However, it is not clear whether the modifications in cortical excitability are attributable to the non-use of the affected limb or to compensatory overuse of the healthy limb [12]. These findings raise the hypothesis that the reduction of excitability of the healthy hemisphere can help to improve motor function of the paretic limb after stroke.

The conventional neuromotor rehabilitation for upper limbs early after stroke in case of complete plegia, consists mainly of passive mobilization or electrical stimulation, since most of the current available therapies require that residual voluntary activation of muscles or partial movements are present [13, 14]. Most of the studies on bilateral arm training focused their attention on the functional improvement of the affected limb and in most of them the motor training is provided by robotic devices, performing passive movement of affected arm and active movement of non-affected limb [15, 16]. The current findings did not report a meaningful advantage on functional outcomes for the affected limb treated with bilateral training [17]. However, clinical studies with functional magnetic resonance imaging (fMRI) seemed to confirm the importance of bilateral exercises to improve motor learning [5]. Therefore, to understand exhaustively which recovery mechanisms occur after stroke it is fundamental that new therapeutic modalities are tested in clinical settings. The proprioceptive based training (PBT) aims to stimulate the emergence of voluntary contraction and is based on motor learning principles, such as the repetition of tasks with concurrent use of feedbacks. The proposed concept is based on the concurrent repetitions of movements performed with the non-affected limb and with the affected one, passively mobilized by physiotherapist in charge of guaranteeing the optimal kinematic execution. Executing the intention to move in the affected limb, supported by physiotherapist, aims to re-educate the proprioceptive sensitivity coherently to each movement phase. Proprioception is the capacity of CNS to determine where all of body parts are positioned at any given time. Proprioceptors located in soft tissues can sense changes and pass afferent information to the brain. Hypothetically PBT can reinforce proprioception through simple movement executed in one plane where any compensatory movements (e.g. shoulder rotation) are abolished. Furthermore, the treatment modality requires recognition of position of both limbs which can act on affected arm proprioception. The common application of bilateral arm training (BAT), is based only on passive movements supported by robotic devices and the potential active movement of affected limb is not permitted. Therefore the difference between PBT and BAT is that the movement in the unaffected limb is performed synchronously with patient’s efferent motor command to both limbs, as assisted by physiotherapist on affected side. Thus, the treatment requires generation of voluntary activation from patient, as reference for both limbs, moreover physiotherapist is asked to adapt passive mobilization of affected limb simultaneously with voluntary active movements of unaffected one. The recognition of position of both limbs, therefore, is always requested. The advantage of the proposed approach relies on the possibility to be applied since the early acute phase after stroke, when several therapeutic modalities (e.g. Constraint-Induced Movement Therapy) cannot be provided because of the absence of residual voluntary muscular activation. Moreover, according to Whitall et al. the involvement of unaffected limb in bilateral training represents a fundamental component for training, based on the rationale of the interlimb coupling theory, where stimuli from two limbs concur to create a “neurofunctional” unit [18].

The purpose of this pre-post pilot study was to evaluate the feasibility of PBT for fast recovery of voluntary muscle contraction, after stroke. The end-point of the proposed treatment modality was based on mean force increase of at least 20 % of all the muscles considered for the PBT treatment.