Mechano-adaptation of bone: Are all strains equal?

Bone research has been re-directed in the 1990s by three revolutions: firstly the recognition that bones respond to changes in their mechanical environment in a dose-dependent way; secondly by the idea that these changes in bone size can be understood as self-adaptation to variant forces by a servo-control mechanism (mechanostat theory); and thirdly by the proposition that muscles ‘enslave’ bone’s mechan-adaptation. It has been an inherent assumption in most of these bone studies that bone deformations mostly result from bending and compression, and little to no attention was paid to torsional loading. Notably, axial strains dominate in axial loading, whilst torsional loading is associated with relatively large shear strains.