Dynamic joint stiffness: A critical review

Movement stability during gait can be studied at two levels: global or local. Global stability indicates the ability to maintain adequate sustainability of the body along the movement, while postural stability is the response to applied or volitional disturbances. Local stability, or joint stability, refers to the ability to maintain body segments in an adequate angular position along the execution of a movement. Stiffness of the joint components plays an important role in establishing the adequate support to internal and external forces to maintain the inter-segmental position or displacement in line with the task’s mechanical objective. This characteristic was previously defined as the resistance developed by muscles and other joint structures during inter-segmental displacement as a reaction to an external moment of force, and studied by different authors with different approaches. However, the developed studies used different terminologies to the same concept, such as dynamic joint stiffness, quasi-stiffness, or net quasi-stiffness. Moreover, the developed methodologies to determine and quantify the concept among the studies were also different. In this chapter, we intend to carry on a critical review of the different methods and approaches to determine the biomechanical output of the joint stiffness, which is designated as dynamic joint stiffness by the authors of this review.