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Manella K.1, Roach K.2, Field-Fote E.3,4
1University of St. Augustine for Health Sciences, Doctor of Physical Therapy Program, Austin, United States, 2University of Miami, Department of Physical Therapy, Miami, United States, 3The Miami Project to Cure Paralysis, Miami, United States, 4Shepherd Center - Crawford Research Institute, Atlanta, United States
Background: In persons with spinal cord injury (SCI) walking function is impaired by reduced ability to produce voluntary muscle contraction and by hyperactive spinal reflex activity (hyperreflexia). Ankle clonus is common after SCI and is attributed to loss of supraspinally mediated inhibition of soleus stretch reflexes and maladaptive reorganization of spinal reflex pathways. The maladaptive reorganization underlying ankle clonus is associated with other abnormalities, such as coactivation and reciprocal facilitation of tibialis anterior (TA) and soleus (SOL), which contribute to impaired walking ability in individuals with motor-incomplete SCI. Operant conditioning can increase muscle activation and decrease stretch reflexes in individuals with SCI.
Purpose: We compared two operant conditioning-based interventions in individuals with ankle clonus and impaired walking ability due to SCI. Training included either voluntary TA activation (TA↑) to enhance supraspinal drive or SOL H-reflex suppression (SOL↓) to modulate reflex pathways at the spinal cord level.
Methods: Twelve persons, 16 - 75 yrs old, with stable motor-incomplete SCI (>1 yr), lesion level T12 or above, and ability to walk 6m with devices or assistance as needed participated in the study. Six participants were randomly assigned to either the TA↑ or SOL↓ intervention. We measured clonus duration, plantar flexor reflex threshold angle, timed toe tapping, dorsiflexion (DF) active range of motion, lower extremity motor scores (LEMS), walking foot clearance, speed and distance, SOL H-reflex amplitude modulation as an index of reciprocal inhibition, presynaptic inhibition, low-frequency depression, and SOL-to-TA clonus coactivation ratio.
Results: TA↑ decreased plantar flexor reflex threshold angle (-4.33°) and DF active range-of-motion angle (-4.32°) and increased LEMS of DF (+0.8 points), total LEMS of the training leg (+2.2 points), and nontraining leg (+0.8 points), and increased walking foot clearance (+4.8 mm) and distance (+12.09 m). SOL↓ decreased SOL-to-TA coactivation ratio (-0.21), increased nontraining leg LEMS (+1.8 points), walking speed (+0.02 m/s), and distance (+6.25 m).
Conclusion(s): In sum, we found increased voluntary control associated with TA↑ outcomes and decreased reflex excitability associated with SOL↓ outcomes.
Implications: Two operant conditioning training programs, one to increase voluntary DF motor control and the other to decrease PF stretch reflex excitability, were both associated with improved walking function in individuals with chronic motor-incomplete SCI. TA↑ decreased PF spasticity, increased ankle motor control and was associated with increased walking foot clearance and walking distance. SOL↓ was associated with decreased SOL/TA coactivation during clonus and increased walking distance. There were participants in both groups who met the criteria for clinically meaningful improvement in walking speed.
Funding acknowledgements: Internally funded by the University of Miami and The Miami Project to Cure Paralysis
Topic: Neurology: spinal cord injury
Ethics approval: This study complied with Declaration of Helsinki standards and was approved by the University of Miami Human Subjects Research Office.
All authors, affiliations and abstracts have been published as submitted.
