A mesoscopic approach is followed for mathematical modelling of the sp
ecific deformation properties of tendon. The approach starts from our
general concept of modelling mechanical behaviour of heterogeneous med
ia and assumes that the structure of tendon is optimized in such a way
that it enables its adjacent muscle to work with a constant performan
ce in the course of increasing loading (acting like a gearbox in a car
). The model based on this assumption gives results that are in a very
good accordance with observed properties of tendons. Clinical experie
nce reveals that if this function of tendon is violated pathological c
hanges appear in the respective muscle.