Fig. 3

Linearized stiffness matrix at SBP, elderly and middle-aged group. Results from linearization at SBP. Normalized linear model stiffness matrix (A) and ratio between the change and the original values (B) for males (left) and females (right) at SBP in the elderly and middle-aged group. Panel A reveals the impact of stiffness alone on stress, while panel B include stretch and thus show the combined effect of stiffness and stretch on stress. There were no differences between sexes. \({nS}_{\theta \theta }\) had a higher value compared to \({nS}_{\theta z}\), \({nS}_{z\theta }\) and \({nS}_{zz}\), which, on the other hand, were of the same magnitude. In males, \({R}_{\theta z}\) had a lower value compared to \({R}_{\theta \theta }\), \({R}_{z\theta }\) and \({R}_{zz}\) which, in turn, were of the same magnitude. In females, \({R}_{\theta z}\) was lower compared to \({R}_{\theta \theta }\), and appeared to be lower compared to \({R}_{z\theta }\) and \({R}_{zz}\) which, in turn were of the same magnitude. Error bars ± 1 SD.