We considered various stability issues related to biomechanical models of the spine, taking as our point of departure the scalar quantities proposed in Howarth et al. (2004). We discussed their significance and applicability by considering some mechanical toy models. In particular, we analysed the relevance of the behaviour of some of these measurements, namely, the determinant of the Hessian matrix and other quantities containing information of a similar spectral nature, and the role they may play in this type of studies. We showed that although in some cases these markers contain information about the load acting on the subject, this information may also be masked and not be detectable from these indexes. These models also allowed us to see how a system with these characteristics may become highly sensitive even to small load changes, and prompted us to put forward the hypothesis that trying to preserve stability at all costs might, under some circumstances, be an actual cause for system damage.