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Corticospinal and strength adaptations following unilateral strength training after stroke Ledwell, Noah Michael Huntington


Unilateral strength training of the less affected (LA) limb has been shown to improve strength bilaterally. This improved strength is referred to as cross-education in the literature. This intervention has the potential to be beneficial for individuals who cannot train both sides of the body due to post-stroke hemiparesis. To date only one group has researched cross-education in the upper limb in stroke, with varied results. The main purpose of our work was to determine if strength training of the LA forearm would change patterns of cortical excitability bilaterally after stroke, and additionally affect changes in strength and function bilaterally. Twenty-four participants with chronic (> 6 months) stroke-related hemiparesis engaged in three baseline sessions separated by 4-7 days. During these sessions individuals’ forearm strength, motor function, and motor impairment were tested, along with a TMS based assessment of corticospinal excitability and intracortical circuits. On a fourth visit participants completed their first training session using the LA arm, then were given the same wrist extension strength-training device to take home. Participants completed three 25-minute training sessions, weekly; one in the laboratory and the remaining two at home. After 5 weeks of training, participants returned to the laboratory for post-intervention retention tests. Cross-education increased strength in the LA wrist extensors (p = 0.026) and the untrained, more-affected (MA) wrist extensors (p = 0.05) in participants with chronic stroke, at the 1-week retention test. Further, LA arm strength remained increased at 5-week retention test (p = 0.023) despite there being no further training. There were strength improvements in the majority of participants in both their trained (17 of 24) and untrained (12 of 24) wrist extensors. There was a decrease in corticospinal inhibition in the LA hemisphere, and a release of interhemispheric inhibition (IHI) bilaterally. A significant increases in motor function and a decrease in motor impairment was seen, respectively. Results indicate that cross-education could be a valuable tool for increasing strength in chronic stroke. Cross-education training of the LA upper limb may allow individuals who do not have adequate function in their MA limb prior to training engage in rehabilitative interventions post-training.

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