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Wed, May 5

Speaker: Cliff Klein, PhD (Postdoctoral Candidate)

Title: Relative contributions of activation impairment and muscle atrophy to dorsiflexor weakness in chronic stroke survivors

Abstract: Maximal voluntary strength is often less in the paretic (contralesional) than the nonparetic limb of chronic stroke survivors. This weakness may be severe enough to increase fatigue and compromise function. Studies suggest that the slow gait of stroke subjects is partially explained by weakness. Lesion-induced impairment in muscle activation, excessive antagonist coactivation, and spasticity may be determinants of post-stroke weakness. However, changes in skeletal muscle (motor unit) physiology secondary to the lesion and disuse may also contribute. For example, weakness may arise from muscle atrophy or a drop in specific tension (force/unit area). Despite the importance of strength for normal function, the contributions of neural impairment and muscle atrophy to post-stroke weakness have not been evaluated concurrently in the same individuals. The large intersubject variability of weakness may reflect differing amounts of activation impairment and atrophy, and so rehabilitation would need to be adjusted accordingly.

My recent research has focused on the examination of central and peripheral determinants of weakness and fatigue in the ankle dorsiflexor and plantar flexor muscles of chronic stroke survivors. For today’s talk, I will present some of the findings pertaining to the dorsiflexors. Torque, voluntary activation (twitch interpolation), and  electromyographic (EMG) amplitude, during submaximal and  maximal voluntary dorsiflexor contractions were recorded bilaterally in seven stroke survivors (40-63 y, 24-51 months post-stroke). Maximal 50 Hz stimulation was applied to determine the dorsiflexor torque generating capacity. The dorsiflexor volume was determined with magnetic resonance imaging (MRI). Specific torque was equal to the 50 Hz torque/volume ratio. The results suggest that dorsiflexor weakness in mobile chronic stroke survivors reflects activation impairment.

Host: Dr. Zev Rymer