The construction of the Nike Vaporfly 4% shoe has led to the widespread adoption of Advanced Footwear Technology (AFT) in running footwear design. Characterized by elements such as a compliant and resilient midsole material, a stiffening component within the midsole, and pronounced forefoot curvature, the technology is believed to enhance running performance. However, the contributions of the specific AFT features and the underlying biomechanical mechanisms remain unclear. Therefore, this thesis aimed to investigate the effects of selected AFT features, specifically the curved carbon fiber plate and PEBA midsole foam, on running performance and mechanics. In four individual studies, male recreational runners performed physiological and biomechanical running trials in an original version of the Nike Vaporfly 4% shoe, and two prototype (No Plate and EVA) versions of the same. The first study revealed that the curved carbon fiber plate and PEBA midsole foam significantly reduced the energy cost of running by 1.9% and 2.2%, respectively. However, these energetic improvements were not linked to changes in activation of two plantar flexor muscles. Subsequent studies investigated the teeter-totter effect and lower limb joint work as potential underlying mechanisms driving the energy cost improvements. The findings confirmed that the curved carbon fiber plate enhances propulsion and reduces energy cost. An investigation into lower limb joint work demonstrated that the curved plate decreases energy loss at the metatarsophalangeal (MTP) joint and redistributes positive work from the ankle to the MTP, contributing to more efficient running mechanics. The effects of midsole material varied among subjects, which may explain the large variations in performance improvements observed previously with the use of AFTs despite their overall effectiveness. This thesis enhances our understanding of how specific features of AFT optimize running performance and informs future innovations aimed at further improving running energetics.