Quantification of gaps in the EMG interference pattern in chronic hemiparesis

Area of Science:

• Neuroscience
• Rehabilitation Medicine
• Biomedical Engineering

Background:

• Chronic hemiparesis, often resulting from stroke (cerebrovascular accident - CVA), leads to motor impairments.
• The electromyography (EMG) interference pattern (IP) during maximal voluntary contraction is a key indicator of motor unit recruitment and control.
• Previous observations suggested impersistence in the EMG IP of paretic muscles, but lacked quantitative data.

Purpose of the Study:

• To quantitatively measure the impersistence in the EMG interference pattern (IP) during maximal effort in patients with chronic hemiparesis.
• To compare EMG activity in paretic versus non-paretic forearm muscles and healthy controls.
• To establish quantitative metrics for assessing muscle impairment and recovery.

Main Methods:

• Recorded EMG from flexor carpi radialis (FCR) and extensor carpi radialis longus (ECR) muscles using monopolar needles.
• Included 19 patients with unilateral CVA-induced hemiparesis and 10 healthy controls.
• Subjects performed maximal voluntary isometric wrist flexion or extension.

Main Results:

• Paretic forearm muscles showed significantly more gaps (lapses) in the EMG IP and fewer total seconds of EMG activity compared to non-paretic or control muscles.
• The number of gaps was similar between paretic FCR and ECR muscles.
• Reduced active time in the paretic ECR muscle indicated proportionally more gaps per second of EMG activity, suggesting greater impairment in wrist extensors.

Conclusions:

• Developed quantitative measures for EMG IP lapses and sustained EMG activity during contractions.
• These measures can differentiate the severity of impairment between paretic wrist flexor and extensor muscles.
• The findings provide the first quantitative confirmation of impersistent motor unit recruitment in hemiparesis, valuable for tracking recovery.