Mechanical work as predictor of force enhancement and force depression

Authors: Kosterina, N.K., Westerblad, H, Eriksson, 
Document Type: Article
Pubstate: Published
Journal: Journal of Biomechanics
Volume: 42   1628-1634
Year: 2009


The steady-state force following active muscle shortening or stretch differs from maximum isometric force associated with the final length. This phenomenon proves that the isometric force production is not only dependent on current muscle length and length time derivative, but depends on preceding contraction history. Isolated extensor digitorum longus and soleus muscles from mice (NMRI strain) were used to investigate the force produced by a muscle, and some parameters hypothetically influencing this history-dependent force modification. The muscles were pre-stimulated at fixed length, then different stretch/shortening episodes were introduced, whereafter changes of active force were recorded while the muscles were held isometrically to approach a steady-state force before de-stimulation. The mechanical work during active stretch and shortening was evaluated by integrating the product of force and ramp velocity over the length-varying period. The results show a negative linear correlation between the force modification and the mechanical work produced on or by the muscle, continuous between shortening and stretch. A corresponding modification of the passive force component following each stimulation was also observed. The conclusion is that the isometric force reachable after stretch or shortening can be well described by an asymptotic force which is decided by the mechanical work.