The impact of shoulder abduction loading on EMG-based intention detection of hand opening and closing after stroke

Abstract

Many stroke patients are subject to limited hand functions in the paretic arm due to a significant loss of Corticospinal Tract (CST) fibers. A possible solution for this problem is to classify surface Electromyography (EMG) signals generated by hand movements and uses that to implement Functional Electrical Stimulation (FES). However, EMG usually presents an abnormal muscle coactivation pattern shown as increased coupling between muscles within and/or across joints after stroke. The resulting Abnormal Muscle Synergies (AMS) could make the classification more difficult in individuals with stroke, especially when attempting to use the hand together with other joints in the paretic arm. Therefore, this study is aimed at identifying the impact of AMS following stroke on EMG pattern recognition between two hand movements. In an effort to achieve this goal, 7 chronic hemiparetic chronic stroke subjects were recruited and asked to perform hand opening and closing movements at their paretic arm while being either fully supported by a virtual table or loaded with 25% of subject’s maximum shoulder abduction force. During the execution of motor tasks EMG signals from the wrist flexors and extensors were simultaneously acquired. Our results showed that increased synergy-induced activity at elbow flexors, induced by increasing shoulder abduction loading, deteriorated the performance of EMG pattern recognition for hand opening for those with a weak grasp strength and EMG activity. However, no such impact on hand closing has yet been observed possibly because finger/wrist flexion is facilitated by the shoulder abduction-induced flexion synergy.

Reducing the Impact of Shoulder Abduction Loading on the Classification of Hand Opening and Grasping in Individuals with Poststroke Flexion Synergy

“…Decoding EMG signals for neural machine interface is a great challenge in the individuals with chronic hemiparetic stroke due to prevalent motor deficits, such as flexion synergy (Lan et al, 2011 ; Yao et al, 2015 ). Many studies made great efforts acquiring better quality of EMGs or features to improve the overall classification accuracy.…”

“…It has been shown that after a stroke synergy-induced EMG signals from the impaired hand can reach to a significant level with increased shoulder abduction (SABD) loading, even when a study participant was instructed to relax the hand (Miller and Dewald, 2012 ). These synergy-induced EMGs do not represent the intention of hand movements and thus are detrimental to the accurate classification of volitional hand movements (Lan et al, 2011 ). For example, when the impaired arm was fully supported, i.e., no effect of flexion synergy, the classification of hand movements can reach an overall accuracy of 96% with high-density myoelectric recordings (Zhang and Zhou, 2012 ), or 95% with bipolar surface EMG recordings (Lan et al, 2011 ), but when lifting the paretic arm, the overall accuracy drops by 10 to 16% using EMG signals (Lan et al, 2011 ) or using EEG signals (Yao et al, 2015 ).…”

Stroke survivors talk while doing: Development of a therapeutic framework for continued rehabilitation of hand function post stroke

“…31–34 Increased abduction of the shoulder is associated with an increase in involuntary elbow, wrist, and finger flexor synergy. 35,36 Preliminary studies from our lab found that facilitating scapular mobilization and external rotation can decrease spasticity in the entire upper arm and increase the available range in shoulder external rotation, and elbow, wrist and finger extension. 37 Thus strengthening the muscles that restore scapulo-humeral rhythm may avoid abnormal arm movement patterns and facilitate learning of desirable movements.…”

Are Movement Disorders and Sensorimotor Injuries Pathologic Synergies? When Normal Multi-Joint Movement Synergies Become Pathologic

“…As the lesions become larger and cause neural damage beyond these areas, the overall picture of loss of fractionated finger movements is similar (Raghavan et al, 2006 ). Even in people who are severely affected poststroke, one can see abnormal synergistic control, as indicated by coactivation and more stereotypic movement patterns across the entire arm (Lan et al, 2011 ; Miller and Dewald, 2012 ). The degree of pathological synergy (i.e., loss of fractionated movement) is consistently correlated with the loss of functional upper limb ability, regardless of the specific subpopulation studied and/or the methods for quantifying synergistic movements and function (Bourbonnais et al, 1989 ; Lang and Schieber, 2003 , 2004 ; Raghavan et al, 2006 ; Lang and Beebe, 2007 ; Beebe and Lang, 2008 ; Miller and Dewald, 2012 ; Ohn et al, 2013 ).…”