Biomechanical analysis is vital for understanding human movements and provides important information in the fields of sports and healthcare. Although traditional technologies like optical motion capture systems and force platforms can provide high-precision biomechanical data, their applications are subject to limited capture areas, reliance on lab environments and high costs. To address these limitations, various versatile technologies are being developed, including capacitive, piezoresistive, triboelectric, and piezoelectric sensors. Among these, triboelectric nanogenerators (TENGs) are a rapidly evolving technology which has become a leading candidate for future wearable biomechanical sensing applications. TENGs are low-cost, easy to fabricate, and lightweight, with excellent output performances. More recently, advanced wearable TENGs have been developed for biomechanical sensing using flexible polymer films in 2D and 3D forms as well as using textiles in fibre, yarn and fabric forms facilitating excellent electrical, mechanical and wearable performance, fast response times and stable operation. These applications include joint angle monitoring, pressure sensing and motion or activity detection. Despite their outstanding progress, TENGs still face challenges related to continuous sensing, conformality, high impedance, low current, static discharge and system-level integration, which need to be addressed to make this a viable technology for future biomechanical sensing applications. Research into new material and device structures, advanced integration technologies, the use of artificial intelligence and improved biomechanical test protocols are envisioned to address some of these challenges. This paper comprehensively reviews the recent developments in TENGs for biomechanical sensing, along with their comparison with existing technologies, limitations, integration challenges and prospects.