Practical usage of piezoelectric nanogenerators (PENGs) under heavy loading environments for high power generation, such as smart shoes, has been limited due to the low mechanical endurance of many piezoelectric materials. Durability and performance under harsh environments are a stumbling block for the practical application of PENGs. Synthesis of piezoelectrically enhanced nanofibers electrospun from nanocomposite of barium titanate nanoparticles (BT NPs) dispersed in poly(vinylidene fluoride-trifluoroethylene) (P(VDF-TrFE)) enables successful fabrication of a robust, efficient, flexible and lead-free PENG. A nanofiber PENG (nf-PENG) fabricated by embedding nanocomposite nanofibers in an elastomer film is demonstrated for biomechanical energy harvesting and storage during walking. When placed inside of a shoe, a nf-PENG loaded with 15wt% BT NPs can generate an output of 25V at a walking frequency of 0.6Hz with high mechanical durability under very high loads (600N). This can charge a 4.7µF capacitor after approximately 72 steps. The stored charge can operate a strain sensor without any external power supply. The high performance of the nf-PENG is mainly attributed to the self-poled nanocomposite nanofibers. Additionally, embedding the nanofibers into an elastomer provided high durability by protecting the nanofibers from mechanical damage. Furthermore, the devices small form factor, flexibility, and transparency make this nf-PENG suitable for applications in wearable electronics, where aesthetics and comfort are also desired (in addition to performance). This work demonstrates the possibility of highly durable, efficient, and self-powered wearable sensing systems that can work under extreme environments.