1. H-reflex Methods and Significance Chetan Phadke, P.T., Ph.D. Post-doctoral Fellow, Mentor: Carolynn Patten Neural Control Movement Lab VA, BRRC

2. Monosynaptic reflex pathway

3. H-reflex Paul Hoffmann first described it in 1910 Electrical analog of stretch reflex By-passes muscle spindle and Gamma Direct sensory fiber (Ia) electrical stimulation

4. Muscle Spindle Muscle Ia α M-wave H-reflex Stimulus Artifact The H-reflex Courtesy: University of Louisville (Dept. of Neurosurgery) and Frazier Rehab.

5. Window into Spinal Cord Enables study of spinal excitability Excitability is regulated by inhibition from supraspinal and sensory flow The level of inhibition on the H-reflex determines the amplitude Easily evoked in most muscles Soleus widely studied Palmieri (2004), Zehr (2001)

6. Functional Significance Greater in Sitting than Standing Greater in stance phase than swing Pedaling modulation similar to walking Arm swing and arm cycling alter soleus H- reflex Walking on a narrow beam Gymnasts Capaday (1987), Trimble (2001), Phadke (2007), Boorman (1992), Zehr (2001), Llewellyn (1990),

7. Phase dependent H–reflex modulation

8. Non-injured SCI 5V 31.25 ms H-reflex post-SCI

9. Functional Correlation Greater amplitude post-SCI and slower ground walking speed Single LT and bicycling session: Smaller reflexes in walking and semi-reclined and increased ground walking speed Long-term LT resulted in smaller reflexes in walking and faster ground walking speed Trimble (2001), Phadke (2009), Behrman (2008 - unpublished)