Combining adaptable supporting structure, large compliance, and intricate energy management, skeletal muscle is a natural system that exhibits numerous attractive characteristics. Recent mechanical modeling of muscle suggests some of the intriguing macroscale features are due to the assembly of nanoscale, metastable cross-bridge constituents. Inspired by the multifunctionality and versatility of muscle's architectural composition, this research investigates a new paradigm of modular structure-material development to achieve significant system adaptivity by utilizing building blocks possessing metastability . The proposed, assembled systems belong to the class of metastructures, a new concept for engineering adaptive structures from basic, functional units in ways such that the systems exhibit unprecedented characteristics resulting from a synergy of their elements. A modular and metastable building block is created to emulate the effective passive functionality of muscle's cross-bridge. Analytical and experimental results reveal that metastructures assembled from the metastable modules may supply unique changes in reaction force when the end displacement is prescribed, adapting not only the magnitude of force but also the direction, in addition to yielding a multitude of globally stable topologies. The investigations provide clear evidence that a metastructure may realize orders of magnitude change in stiffness for a constant system shape, and also enables the variation in required energy expense to globally deform the system. From these findings, the metastructural design framework represents a major leap forward in adaptive structures and material systems and has the potential to find broad future application.