H-reflex Methods and Significance Chetan Phadke P T

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

Monosynaptic reflex pathway

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

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

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)

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 Hreflex • Walking on a narrow beam • Gymnasts Capaday (1987), Trimble (2001), Phadke (2007), Boorman (1992), Zehr (2001), Llewellyn (1990),

Phase dependent H–reflex modulation

H-reflex post-SCI Non-injured 5 V 31. 25 ms SCI

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resulted in smaller reflexes in walking and faster ground walking speed Trimble (2001), Phadke (2009), Behrman (2008 - unpublished)