What do we currently know from in vivo bone strain measurements in humans?

Bone strains are the most important factors for osteogenic adaptive responses. During the past decades, scientists have been trying to describe the relationship between bone strain and bone osteogenic responses quantitatively. However, only a few studies have examined bone strains under physiological condition in humans, owing to technical difficulty and ethical restrictions. The present paper reviews previous work on in vivo bone strain measurements in humans, and the various methodologies adopted in these measurements are discussed. Several proposals are made for future work to improve our understanding of the human musculoskeletal system. Literature suggests that strains and strain patterns vary systematically in response to different locomotive activities, foot wear, and even different venues. The principal compressive, tension and engineering shear strain, compressive strain rate and shear strain rate in the tibia during running seem to be higher than those during walking. The high impact exercises, such as zig-zag hopping and basketball rebounding induced greater principal strains and strain rates in the tibia than normal activities. Also, evidence suggests an increase of tibia strain and strain rate after muscle fatigue, which strongly supports the opinion that muscle contractions play a role on the alteration of bone strain patterns.