Term information
The Hill-type model consists of a contractile element (CE), and two non-linear (= the output is not directly proportional to its input) spring elements (= an elastic object used to store energy). One non-linear spring element is in series (SE), and the other one is in parallel (PE). The CE represents the actine and myosine cross-bridges, and it generates active force. It can shorten when it is activated and it is freely extensible when it is not activated. The SE represents the tendon and the intrinsic elasticity of the myofilaments and crossbridges. It allows a rapid change of the state of the muscle from inactive to active. It is also an energy storing mechanism. The PE represents the connective tissues (epimysium, perimysium, endomysium). It is responsible for the passive behaviour of the muscle when it is stretched, even when the CE is not activated. 4 source: http://en.wikipedia.org/wiki/Engineering_approach#The_Hill-type_model