In Ca²⁺-activated skinned fibres, addition of orthophosphate (Pi) suppresses the force and, in a lesser extent, the ATPase rate of isometric contraction and these effects have been recently explained by a kinetic model where force-generating myosin motors can detach from actin at an early stage of the ATPase cycle, with Pi still bound to its catalytic site, and then rapidly release the hydrolysis products and bind another ATP (Linari et al. Proc Royal Soc B 277:19, 2010). Orthovanadate (Vi), a phosphate analog, suppresses isometric tension (T₀) (Dantzig and Goldman, J Gen Physiol 86:305, 1985) and, to a greater extent than Pi, ATPase rate (Wilson et al, Biophys J 68:216, 1995). We reinvestigate the effects of Vi on the transient and steady state mechanical characteristics of the isometric contraction in skinned fibres from rabbit psoas (pCa, 4.5, 12°C). Addition of 0.1 mM Vi (i) reduces T₀ to 0.44±0.02 (mean±SEM) with an apparent second order rate constant of 0.9±0.1 *10³M^-1s^-1 and cross-bridge stiffness (e₀) in proportion to T₀, (ii) does not affect either the rate of force development following the end of unloaded shortening k_TR, or the Pi-dependence of T₀. When these results are fed to the reaction scheme proposed by Linari et al. (2010) indicate that the pathways related to force inhibition by Vi and Pi are different and that only with Pi in the catalytic site the attached myosin motor can take the short ATP splitting path. (Supported by Ministero della Salute, Italy).