Passive and active mechanical tests at different scales of the skeletal muscle: a literature review

International audienceHuman skeletal muscle is a complex tissue with a strict and ordered hierarchy (muscle, fiber, myofibril) similar to rodent animal used to study the mechanical properties of healthy and pathological muscles (e.g. mdx mouse to mimic Duchenne disease). Collagen envelopes, actin and titin are the structures implicated in the passive mechanical properties. The active mechanical properties are related to the formation of actin-myosin cross bridges. This article presents the most commonly used mechanical tests to measure in vitro, at different scales, the passive (incremental stepwise extension test, stretch-release test, compressive test, fatigue-recovery test, eccentric contraction test) and active (force-frequency test, tetanus and twitch contraction tests) behaviors of rodent muscles. The next section of this literature review covers the need for in vivo protocols to be as close as possible to physiological conditions, allowing to keep the animal alive and to perform longitudinal mechanical studies, with the presentation of imaging methods (MRI and ultrasound-based elastography) in living rodents. Then the main factors (protocol heterogeneity, aging, etc.) influencing the mechanical properties are presented