Multijoint reflexes of the stroke arm: Neural coupling of the elbow and shoulder

• Published in: Muscle & nerve 2007-11, Vol.36 (5), p.694-703
• Main Authors: Sangani, Samir G., Starsky, Andrew J., Mcguire, John R., Schmit, Brian D.
• Format: Article
• Language: English
• Subjects: Adult; Arm; Biological and medical sciences; Elbow Joint - physiopathology; Electromyography - methods; Fundamental and applied biological sciences. Psychology; Humans; joint torque; Linear Models; Medical sciences; Motor control and motor pathways. Reflexes. Control centers of vegetative functions. Vestibular system and equilibration; neural coupling; Neurology; Reflex - physiology; Shoulder Joint - physiopathology; spasticity; stretch reflex; stroke; Stroke - pathology; Stroke - physiopathology; Torque; Vascular diseases and vascular malformations of the nervous system; Vertebrates: nervous system and sense organs
• ISSN: 0148-639X; 1097-4598
• DOI: 10.1002/mus.20852

The reflex torque responses of the elbow and shoulder to constant velocity angular extensions of the full comfortable range of the spastic elbow were measured in 16 people with unilateral stroke and 6 neurologically intact controls in order to identify the interjoint reflex coupling that occurs after stroke. The resulting responses showed a substantial reflex torque at the elbow and shoulder in subjects with stroke, with 12 of the 16 subjects producing adduction of the shoulder in response to passive extension of the elbow. The presence of simultaneous shoulder flexion torque with elbow flexion torque and with an identical waveform indicated an active role of biarticular elbow/shoulder flexors, such as the biceps. As the biceps muscle produces a shoulder abduction moment, shoulder adduction produced during elbow extension was thought to be associated with neural rather than biomechanical coupling. These results suggest that spasticity in people with stroke is more complex than its traditional perception as a hyperexcitable stretch reflex, and includes potent heteronymous reflex pathways. The reflex coupling observed between the shoulder and elbow should be considered in the diagnosis and clinical management of spasticity. The potential impact of this reflex on the coordination of volitional arm movements will be examined in future studies. Muscle Nerve, 2007