The 'stiffness' concept originates from Hooke's law which states that the force required to deform an object is related to a spring constant and the distance that object is deformed. Research into stiffness in the human body is undergoing unprecedented popularity; possibly because stiffness has been associated with sporting performance and some lower limb injuries. However, some inconsistencies surrounding stiffness measurement exists bringing into question the integrity of some research related to stiffness. The aim of this study was to review literature which describes how vertical, leg and knee stiffness has been measured in adult populations while running, jumping or hopping.
Serpell, B., Ball, N., Scarvell, J., & Smith, P. (2012). A review of models of vertical, leg, and knee stiffness in adults for running, jumping or hopping tasks. Journal of Sports Sciences, 30(13), 1347-1363. https://doi.org/10.1080/02640414.2012.710755