Various explanations of the size principle

The size principle consists in the activation of motoneurons of a muscle pool in ascending order of their sizes when that pool of motoneurons receives a common, increasing input. This technical report is a survey of possible explanations of the size principle for recruitment of motor units. As a pre-study for further works, we collected existing explanations, suggested some new ones and collected them. According to the constitution of our own group, the report is divided into 2 parts: a collection from a physiological point of view and a collection from a more theoretical point of view. 2 Part II: The view of theoreticians 6 2.1 Explanations emerging from an optimization task or what recruitment by size is good