Regulation of the magnitude and distribution of skeletal strain is achieved in limb bones both “internally” by alterations to bone morphology, and “externally” by coordination of muscle activity and modifications in the animal's behavior. Though not actually minimizing functional strain, these mechanisms conspire to produce a restricted strain environment, which allows an economical and optimized structure, and, in a variety of species over a wide range of activities, the architectural and behavioral modifications have resulted in remarkably similar peak functional strain magnitudes. This confined range of functional strains reflects a universal mechanism and objective of structural adaptation in bone.