The passive mechanical properties of whole muscle in active and nonactive s
tates are compared. The experimental results are presented as stress-strain
curves, which are analyzed in the framework of the current theoretical bac
kground [viz. the freely-jointed chain model (FJCM) and the worm-like chain
model (WLCM)] in a semi-quantitative fashion. This analysis shows that bot
h models can explain the mechanical behavior of whole muscle in non-active
state. In the active state, the presence of crossbridges alters the mechani
cal response, leading to a markedly different behavior, as expected. A disc
ussion of the mechanisms involved and the interpretation of the parameters
required for the fitting of the stress-strain curves is also presented.