Mapping of spastic muscle activity after stroke: difference between passive stretch and active contraction

Area of Science:

• Neuroscience
• Biomedical Engineering
• Rehabilitation Science

Background:

• Spasticity, a common motor disorder post-stroke, involves abnormal muscle overactivity.
• Understanding the spatial distribution of muscle activity is crucial for elucidating spasticity mechanisms.
• High-density surface electromyography (HD-sEMG) offers a detailed method for assessing muscle activation patterns.

Purpose of the Study:

• To investigate the spatial characteristics of biceps brachii muscle activity in spastic hemiparetic subjects during passive stretch and active contraction.
• To compare these characteristics with those of healthy subjects.
• To explore the relationship between muscle activation patterns and spasticity.

Main Methods:

• Recruited 14 spastic hemiparetic subjects and 10 healthy controls.
• Recorded biceps brachii (BB) muscle activity using HD-sEMG during passive stretch at various velocities and submaximal active contractions.
• Analyzed muscle activation intensity and spatial distribution using statistical methods like ANOVA and t-tests.

Main Results:

• Spastic subjects exhibited higher intensity and velocity-dependent heterogeneous activation during passive stretch compared to controls.
• Activation distribution was more lateral and proximal in spastic subjects during active contraction.
• Observed non-overlapping activation areas between passive stretch and active contraction in spastic subjects, with passive stretch showing more distal activation.

Conclusions:

• Altered BB muscle activity in spasticity may stem from impaired descending central control post-stroke.
• Complementary spatial distributions suggest opposite motor unit recruitment patterns during passive stretch versus active contraction.
• This HD-sEMG study provides neurophysiological evidence on the spatial relationship of muscle activity in spasticity, enhancing understanding of its mechanisms.