Can muscle fibers be stable on the descending limbs of their sarcomere length-tension relations?

The authors of a paper published in this journal (Allinger et al. (1996) J. Biomechanics 29, 627-633) have concluded, based on a theoretical analysis, that muscle fibers may be stable even if some of their constituent sarcomeres have lengths falling on the descending limbs of their static length-tension relations. This note reconsiders the question of fiber stability and concludes that fibers are unstable if at least one of their sarcomeres is on the descending limb. A positive 'short-range' sarcomere stiffness has no effect on fiber stability, and a positive 'effective stiffness' of the whole fiber does not imply sarcomere stability.