Rheological Maxwell-type model is used to obtain a relation between energy input to a muscle and the work produced by it. The key role in the relation plays the muscle activity 1/? which describes how much energy is converted to work in unit volume element at unit time.
The activity is the muscle material value describing how much actin-myosin pairs are engaged in a given place to maintain the work production of the whole muscle system. The modelling of the system has been done and it is now possible to calculate the energy input in special muscle system activities by mechanical means.