Hill's model refers to either Hill's equation for tetanized muscle , or to the 3-element model.

Hill's equation

This is a popular state equation applicable to muscle that has been stimulated to show tetanus. It relates tension to velocity. It looks very much like the van der Waals equation, and it was derived by a famous thermodynamicist named Terrell Hill . Note that P stands for load or tension, while v stands for velocity. The equation thus has the units of energy dissipation, rather than energy, as in the above mentioned thermodynamic equation.

(v + b)(P + a) = b(P₀ + a).

3-Element Model