Important experimental factors for skeletal muscle modelling: Non-linear changes of muscle length force characteristics as a function of degree of activity

In muscle modelling submaximal force exertion is often modelled on the basis of simple scaling of maximal length force characteristics. In such a case it is implicitly assumed that two basic physiological properties of muscle, i.e. length force characteristics and activity of the muscle by recruitment and firing rate coding are factors which independently determine actual muscle force. In this review it is argued that, on the basis of intracellular properties of muscle fibres as well as architectural variables of muscle morphology, muscle length force characteristics are affected in such a drastic way that the assumption of independence of these variables is no longer tenable.