Charlotte Yates yatescharlotte@uams.edu

Hyperreflexia, measured as a lack of low frequency-dependent depression of the H-reflex, is known to occur in both humans and animals after spinal cord injury (SCI).  Previous studies had shown that passive exercise for 3 months could be used to restore low frequency-dependent depression of the H-reflex after SCI.  This study was designed to determine the effects of various periods of time on the ability of passive exercise, in the form of Motorized Bicycle Exercise Training (MBET), to restore low frequency-dependent depression of the H-reflex.  Studies were carried out in the Spinal Cord Injury Mobilization Program of the Center for Translational Neuroscience, the research arm of the Jackson T. Stephens Spine & Neuroscience Institute.  Adult rats underwent complete spinal cord transection at the T10 level.  The hindlimbs were passively exercised in different groups of rats for 1 hr/day, 5 days/week for 15, 30, 45, 60 or 90 days, and low frequency-dependent depression of the H-reflex tested.  Statistically significant low frequency-dependent depression of the H-reflex was evident by 30 days of exercise, although numerical reductions were seen even at 15 days.  There was a linear decrease in low frequency-dependent depression of the H-reflex with duration of passive exercise.  Passive exercise can restore habituation of spinal reflexes in a time-dependent manner if used following complete spinal transection.