From “sliding” to “winding” filaments theory: A narrative review of mechanisms behind skeletal muscle contraction

The physiological mechanisms behind muscle contraction are a main concept in sport medicine and rehabilitation. The sarcomere is the functional unit of skeletal muscle and several proteins definite its complex structure. The most common theory to explain muscle contraction was proposed in the last 50's and has become widely popular and accepted: the "sliding filaments" theory. Even if this hypothesis was able to justify some form of muscle contraction, other processes are not fully described by it. Eccentric contraction and some phenomena, like the "force enhancement during stretch" concept described in the 2002, are not explicable according to the sliding filament theory. Therefore, several hypotheses have been suggested over the years, such as the "popping sarcomeres" theory and the "winding filament" theory. Some other proteins, like titin, have gained a main role in the physiology of the sarcomere and should be relevant to explain mechanisms of eccentric contraction, where the sarcomere generates highest level of tension while it is lengthening. The aim of this review is to summarize the physiological theories of muscle contraction and to define concepts applicable in sport medicine and in rehabilitation areas.