Background: The residual hemiparesis after stroke results in a unilateral reduction in propulsive force during gait. Prior work has suggested the presence of a propulsive reserve in the paretic limb. Objective: The purpose of this study was to quantify the paretic propulsive reserve in individuals post-stroke and to determine the biomechanical mechanism underlying the generation of additional paretic propulsive limb force. Methods: Ten individuals with chronic hemiparesis post-stroke walked on a treadmill against an impeding force (ascending 0 to 10%BW, in 2.5%BW increments, followed by descending 10 to 0%BW, also in 2.5%BW increments) applied to the body’s center of mass. The resulting propulsive forces were measured bilaterally and compared between impeding force levels. We then assessed potential mechanisms (trailing limb angle and plantarflexion moment) underlying the changes in propulsion. Results: Overall, peak paretic propulsive force increased by 92% and the paretic propulsive impulse increased by 225%, resulting in a significant increase in the paretic limb’s contribution to propulsion. Participants continued to produce increased paretic propulsion upon removal of the impeding force. The trailing limb angle contributed significantly to the increase in paretic propulsion, whereas the plantarflexion moment did not. Conclusions: Participants exhibited a robust propulsive reserve on the paretic limb, suggesting that there is untapped potential that can be exploited through rehabilitation to improve gait recovery. The increase in propulsive symmetry indicates that a greater response was observed by the paretic limb rather than increased compensation by the non-paretic limb.