Foundational Science: Part I

KEY TAKEAWAYS • Tendons function as multiscale load‑bearing tissues that support energy storage and release, power amplification, and force attenuation during movement. • These capabilities emerge from interactions across hierarchical levels. No single level of structure can explain tendon behavior on its own. • Several structural features shape tendon mechanics, including limited fascicle load sharing, long continuous fibrils with branching and weaving patterns, hydration‑dependent fibril behavior, and non‑collagenous matrix proteins that influence organization and viscoelasticity. • Advances in imaging and mechanical testing continue to reveal new layers of complexity and often raise as many questions as they answer. • This multiscale complexity forms the foundation for understanding how tendons adapt, fail, and respond to training or rehabilitation.