Wolff's law, developed by the German anatomist and surgeonJulius Wolff (1836–1902) in the 19th century, states that bone in a healthy animal will adapt to the loads under which it is placed.^[1] If loading on a particular bone increases, the bone will remodel itself over time to become stronger to resist that sort of loading.^[2][3] The internal architecture of thetrabeculae undergoes adaptive changes, followed by secondary changes to the external cortical portion of the bone,^[4] perhaps becoming thicker as a result. The inverse is true as well: if the loading on a bone decreases, the bone will become less dense and weaker due to the lack of the stimulus required for continuedremodeling.^[5] This reduction in bone density (osteopenia) is known asstress shielding and can occur as a result of a hip replacement (or other prosthesis).^{[citation needed]} The normal stress on a bone is shielded from that bone by being placed on a prosthetic implant.

The remodeling of bone in response to loading is achieved viamechanotransduction, a process through which forces or other mechanical signals are converted to biochemical signals in cellular signaling.^[6] Mechanotransduction leading to bone remodeling involves the steps of mechanocoupling, biochemical coupling, signal transmission, and cell response.^[7] The specific effects on bone structure depend on the duration, magnitude, and rate of loading, and it has been found that only cyclic loading can induce bone formation.^[7] When loaded, fluid flows away from areas of high compressive loading in the bone matrix.^[8] Osteocytes are the most abundant cells in bone and are also the most sensitive to such fluid flow caused by mechanical loading.^[6] Upon sensing a load, osteocytes regulate bone remodeling by signaling to other cells with signaling molecules or direct contact.^[9] Additionally, osteoprogenitor cells, which may differentiate into osteoblasts or osteoclasts, are also mechanosensors and will differentiate depending on the loading condition.^[9]

Computational models suggest that mechanical feedback loops can stably regulate bone remodeling by reorienting trabeculae in the direction of the mechanical loads.^[10]

• In relation to soft tissue,Davis' law explains how soft tissue remodels itself according to imposed demands.
• Refinement of Wolff's Law:Utah-Paradigm of Bone physiology (Mechanostat Theorem) byHarold Frost.^[11]

• Theracquet-holding arm bones oftennis players become stronger than those of the other arm. Their bodies have strengthened the bones in their racquet-holding arm, since it is routinely placed under higher than normal stresses. The most critical loads on a tennis player's arms occur during the serve. There are four main phases of a tennis serve, and the highest loads occur during external shoulder rotation and ball impact. The combination of high load and arm rotation results in a twisted bone density profile.^[12]
• Weightlifters often display increases inbone density in response to their training.^[13]
• Astronauts often suffer from the reverse: being in a microgravity environment, they tend to lose bone density.^[14]
• The deforming effects oftorticollis on craniofacial development in children.^[15]

• Functional matrix hypothesis
• Iron Shirt, Wushu/Kungfu bone conditioning
• Osteogenic loading

• Das Gesetz der Transformation der Knochen - 1892. Reprint: Pro Business, Berlin 2010,ISBN 978-3-86805-648-8.
• Wolff, J. (Apr 2010)."The Classic: On the Inner Architecture of Bones and its Importance for Bone Growth".Clin Orthop Relat Res.468 (4):1056–1065.doi:10.1007/s11999-010-1239-2.PMC 2835576.PMID 20162387.

• Julius Wolff Institut, Charité - Universitätsmedizin Berlin, main research areas are the regeneration and biomechanics of the musculoskeletal system and the improvement of joint replacement.