Running Specific Prostheses (RSPs) enable running for athletes with lower limb amputations. The RSP design is inspired by human ankle behaviour while running, aiming to replicate its dynamic properties. RSPs are produced using carbon fiber composites that exhibit elastic properties, allowing them to store and return energy. Unlike biological legs, RSPs cannot generate net positive mechanical power. Furthermore, current RSP designs limit ground reaction forces (GRFs) while running. In addition, current RSP designs lack stiffness adaptation to running speed, which is required to optimize running speed. Running speed is a crucial performance indicator, influenced by step length, step frequency, and ground reaction forces (GRFs). This study explores the design of an innovative RSP running blade with improved push-off and load-dependent stiffness, focusing on how it can affect running gait, speed, and user satisfaction for lower limb amputees. This research aims to provide insights into the performance of the RSP. Mechanical compression tests were performed to characterize prototype stiffness. In addition, insights into user satisfaction and running biomechanics were obtained through qualitative feedback and quantitative gait analysis from amputee participants.