Overground locomotor training modulates ankle flexor and extensor reflex activity in people with spinal cord injury.

Research Report
Population: Adult

Edelle C Field-Fote, PT, PhD, FAPTA, Director, Spinal Cord Injury Research, Shepherd Center – Crawford Research Institute Edee_Field-Fote@Shepherd.org

Kathleen Manella, PT, PhD, Assistant Professor, University of St. Augustine for Health Sciences – Texas kmanella@usa.edu

Keywords: Plasticity, Locomotor Training, Reflex Activity, Spinal Cord Injury

Increased reflex activity, commonly occurs following spinal cord injury (SCI), and may interfere with functional task performance, participation, and quality of life. In persons with SCI, locomotor training has been associated with improved reflex modulation. We aimed to investigate in persons with SCI the effects of four locomotor training protocols on six measures of spinal reflex activity: 1) flexor reflex response (FRR), and 2) soleus (SOL) H-reflex H/M ratio, 3) reciprocal inhibition (RI), 4) D1 inhibition, and 5) Low Frequency Depression (LFD), and 6) quadriceps pendulum test.
47 people (34 men, mean age 41.7 yr, median post injury time 46 months) with minimal walking function due to chronic (≥1 year) SCI participated. Eligibility criteria were injury above T12, ability to advance overground using an assistive device, and rise to standing with moderate assistance. People with orthopedic or cardiac conditions were excluded.
Participants were randomized to 1 of 4 locomotor training groups: 1) overground with peroneal nerve stimulation (OG) and 2) treadmill with peroneal nerve stimulation (TS), 3) with manual assistance (TM), or 4) with robotic assistance (LR). For all training protocols, partial (≤ 30%) body weight support was provided. Participants completed a mean of 49 ± 7 sessions (range 27 – 58) over 12 weeks. For FRR, noxious stimulation was applied to the plantar foot, tibialis anterior amplitude was recorded. For SOL H/M ratio, maximal SOL H-reflex and M-wave amplitudes were identified from recruitment curves. SOL H-reflex response to RI stimuli (2-ms ISI; 0.10 Hz) was recorded; D1 inhibition was recorded at 15ms and 20ms. For LFD, 10 SOL H-reflexes were evoked with paired-pulse stimuli (1-s ISI); the average 2nd-10th pulse amplitude was normalized to the 1st pulse amplitude. Quadriceps pendulum test angle of catch was recorded. Change in reflex measures was analyzed with Wilcoxon signed rank one-tailed tests.
OG training approached significance for decreased FRR (p = 0.06), and was associated with increased RI (p = 0.04) and decreased LFD (p = 0.03). TS training approached significance for increased RI (p = 0.06) and was associated with increased D1 inhibition (p = 0.02) and quadriceps angle of catch (p = 0.05). TM training was associated with increased quadriceps angle of catch (p = 0.01). LR training demonstrated no significant effects on reflex activity. Conclusion:
OG training was associated with improved modulation of FRR and RI. TS training was associated with improved modulation of RI and D1 inhibition.
Clinical Relevance:
OG training was associated with modulation of flexor and extensor reflex activity. Overground walking is distinguished from treadmill walking by its greater voluntary demand for step initiation and forward progression. During OG training, increased supraspinal drive likely activates inhibitory interneurons of spinal reflex pathways.

Field-Fote, Edelle C, PT, PhD, FAPTA; Manella, Kathleen J, PT, PhD. Overground locomotor training modulates ankle flexor and extensor reflex activity in people with spinal cord injury.. Poster Presentation. IV STEP Conference, American Physical Therapy Association, Columbus, OH, July 17, 2016. Online. https://u.osu.edu/ivstep/poster/abstracts/036_field-fote_manella/