In vivo estimation of the short-range stiffness of cross-bridges from joint rotation

Short range stiffness elastic limit depends on joint velocity

“…Model parameters for lever inertia, stiffness and damping (I l , k l , b l ) were taken from (van Eesbeek et al, 2010) and kept constant throughout all optimizations. Joint damping, b j , appeared to have a negligible effect on the predicted torque, T l , and was therefore fixed at a small value (10 À 5 Nm s/rad) to provide for numerical stability.…”

“…Essential aspects of the used method for estimation of short range stiffness (SRS) are provided but for a full description of the method the reader is referred to a previous study (van Eesbeek et al, 2010). the rotation imposed by the motor resulted only in flexion/extension rotation of the wrist joint ( Fig.…”

“…For comparison of the results to previous findings on single muscles and fibers, the elastic limit was expressed as relative muscle strain. For this purpose, we used the relationship provided (van Eesbeek et al, 2010): 0.066 rad wrist rotation corresponding to 17 74 nm stretch per half sarcomere for the wrist flexor muscles. Using L 0 ¼2.8 mm as the sarcomere length at neutral wrist angle (Friden and Lieber, 2002), 0.066 rad wrist rotation results in a mean strain of 34/2800 ¼1.2%L 0 .…”

“…Past studies on the in vivo human joint that focused on SRS were limited to passive conditions and slow movements to avoid additional torque changes from stretch reflexes (Axelson and Hagbarth, 2001;Lakie et al, 1984;Loram et al, 2007). Using an identification procedure we were able to estimate SRS and its concomitant elastic limit in vivo at different levels of muscle activation and fast rotations (van Eesbeek et al, 2010).…”

Parameter estimation of the Huxley cross-bridge muscle model in humans

“…In addition, the Hill-model fails to describe the stiffness and damping properties correctly under several conditions [2,3], most notably, fast eccentric contractions [4]. Moreover, the Hill model does not account for shortrange stiffness (SRS), the property of muscle tissue undergoing eccentric contraction exhibiting an initial high level of stiffness followed by a marked drop in stiffness when subjected to further elongation [5,6]. It is thought that SRS provide joint stabilization before reflexive or conscious control is possible.…”