Features and Physiology of Spinal Stretch Reflex Pathways in People with Chronic Spinal Cord Injury

In spastic individuals with chronic spinal cord injury (SCI), the stretch reflex gain and reflex stiffness are high at rest and do not decrease with muscle activation. The soleus H-reflex is also large during voluntary muscle contraction, and the soleus stretch and H-reflexes are abnormally modulated during walking. Hyperexcitable stretch reflexes are most problematic in mid-late swing through early stance as they can trigger clonus and negatively affect locomotion. These observations of stretch reflex behaviors in SCI do not appear to match what has been found in hemiparetic stroke or cerebral palsy. Different from pharmacologically or surgically disabling a reflex pathway, changing a reflex behavior through neurobehavioral training such as locomotor training and reflex operant conditioning could provide new means to enhance motor function recovery in people with SCI.