Reaching movements in stroke patients are characterized by decreased amplitudes at the shoulder and elbow joints compared to healthy subjects (1–6). The movement pattern of patients with stroke is highly related to their level of motor function impairment, which becomes modified due to the lack of inter-articular coordination (1). There is a decrease in the range of motion at the elbow joint with a tendency toward flexion, which avoids correct extension of the upper limb (UL), hampering the ability to perform appropriate reaching movements. Excessive shoulder abduction is also observed as a compensatory movement when there is a lack of appropriate shoulder flexion (7).
In the case of the trunk, greater trunk displacements have been observed in patients with stroke, forward displacements, and torsion movements, which are related to deficits in elbow extension, and shoulder flexion and adduction, as compensatory mechanisms that occur during reaching movements or other activity. Patients are able to develop new motor strategies to achieve their goal despite UL deficits (1–7). There is a greater involvement of the trunk and scapula during the execution of reaching movements due to the creation of new movement strategies to compensate for the deficiencies (8).
The scientific literature has shown that stroke patients need to create new movement strategies. This involves the development of pathological synergies to carry out the desired movements. An example of this is the excessive movements of the trunk and scapula to compensate the deficiencies resulting from the pathology (7). Proper activation of the interscapular muscles depends on the position of the trunk. Stroke patients, due to the deficits affecting their trunk and scapular movement patterns, are under unfavorable conditions for being able to perform appropriate and selective activation of these muscles, which has a negative impact on the movement of the UL (9–11).
Regarding the UL muscles involved in reaching movements, a deficit in muscle control and activation has been observed (5, 12, 13). The synergistic contraction of the shoulder flexor and extensor muscles during reach becomes deteriorated due to muscle weakness and; therefore, the resulting movement is deficient (14). Furthermore, spastic muscle patterns may also prevent the correct performance of UL movements (15–18).
Functional electrical stimulation (FES) is a form of treatment that seeks to activate the paretic muscles using short-duration electrical pulses applied via surface electrodes through the skin (19). The use of FES and neuroprostheses has spanned almost four decades (20, 21). The use of FES as a neuroprosthesis consists of self-treatment at home by means of a neuroprosthetic neuromuscular stimulation system. The objective of this modality is to assist the performance of an activity of daily living (ADL) (22). Recently, functional and clinical improvements have been reported with the therapeutic application of FES, in which stimulation was used to increase voluntary movement after stroke (22, 23). Therapeutic FES modalities have been used to recruit UL muscles, improving weakness, the dyscoordination of single and multiple joints movements, and spasticity (24).
Most studies employing therapeutic FES for paretic UL rehabilitation are based on stimulation of the shoulder, elbow, and wrist muscles without recruitment of the interscapular muscles (25–28). The importance of an appropriate and specific contraction of the interscapular musculature during UL movement is necessary to adapt the position of the scapulothoracic joint to the degree of movement of the glenohumeral joint. This musculature has a stabilizing function upon the entire glenohumeral complex, which is necessary for a correct reaching movement (29–31). In healthy subjects, the posture of the trunk has been shown to influence changes in scapular movement and interscapular muscle activity during UL elevation (29, 32). The motor control of shoulder movement influences the correct and proper activation and synchronization of these muscles (33).
In this study, we tested the ability of a FES system to assist the UL movement of stroke patients based on the stimulation of interscapular, shoulder, elbow, wrist, and finger muscles. To our knowledge, no empirical study to date directly addresses this question. The authors hypothesized that participants receiving FES to the UL and interscapular muscles would be able to perform the movement with less trunk anteroposterior tilt and major shoulder flexion and elbow extension. The aim of this feasibility study was to evaluate whether the application of FES to the UL and interscapular muscles of stroke patients with UL motor impairment would be able to modify their reaching patterns, measured using instrumental movement analysis systems.[…]