The disability brought about by post-stroke hemiparesis has negative consequences for the stroke survivor and the U.S. economy. There are evidence-based motor retraining programs that have been shown to promote movement recovery. If paresis in the affected upper extremity is too severe, however, individuals are not able to participate. The goal of the proposed project is to investigate the potential of an intervention that addresses the neural dysfunction underlying severe hemiparesis. The cross education effect is an established phenomenon in the exercise science literature that accounts for strength gains high-intensity, unilateral resistance training evokes in the contralateral, untrained limb. Though no definitive conclusions have been reached, the current consensus is that chronic interhemispheric and corticospinal adaptations underlie the strength gains observed in the untrained limb. These adaptations are the inverse of what is typically observed following hemiparetic stroke, inviting the possibility that high-intensity, unilateral resistance training ofthe non-paretic limb may drive the neural adaptations needed for movement restoration in the paretic limb. Using a prospective cohort, repeated-measures design, subjects will undergo 16 sessions of high-intensity, unilateral resistance training of the non-paretic wrist extensors. Sessions will take place at a frequency of four times per week over four weeks. The proposed project will take a multilevel approach to investigate changes in neural and behavioral function. The primary aim will test whether the intervention alters corticospinal excitability. It is hypothesized that there will be enhanced excitability of corticospinal projections to the paretic extensor digitorum communis. The secondary aim will examine whether the intervention elicits a hypothesized increase in active range of motion in the untrained, paretic wrist extensors. The third aim will evaluate whether the intervention leads to a hypothesized increase in functional capacity of the paretic upper extremity. The expected outcome of this project is an intervention that enhances paretic upper extremity movement production in persons with severe post-stroke hemiparesis. The ultimate goal is for this intervention to moderate paresis sufficiently for severely affected patients to participate in empirically-supported motor retraining programs. This project also will facilitate the experiences needed to achieve the training and career goals of Dr. Urbin.