We provide a comment to our paper “Comparative Sensitivity Analysis of Muscle Activation Dynamics,” Computational and Mathematical Methods in Medicine (2015), 16 pages, Article ID 585409, DOI 10.1155/2015/585409 [1], where we stated an erroneous form of Hatze’s activation dynamics that is not applicable to non-steady-state muscle processes. However, as we only considered steady-state situations, all results and consequences still hold true. The authors would like to apologize for any inconvenience caused.
In his consecutive work [2–4], Hatze introduced the dynamics of changes in activity (activation dynamics) for skeletal muscle fibers in response to neural stimulation as a multilevel process, with being the relative free calcium ion concentration and the length of the contractile element (CE). In [4, Eqns. , , and ], this process is summarized as follows:
In our main article [1, Eqn. ], we had reformulated the above equation system (1) as in an effort to eliminate the state variable in favor of . However, the specific formulation in (2) holds only true in the steady-state case . This is because the transformation [5, Eqns. –] was erroneously done by rather than properly taking the total derivativefor the total time derivative of .
In our framework only steady-state muscle conditions were investigated; that is, , such that the second term of the right hand side in (4) vanishes. Hence, the situation from (2) holds throughout the article. In non-steady-state isometric contractions, this second term seems to be of reversed sign to the first, but with a considerably smaller absolute value; compare [6].
Acknowledgments
The authors would like to thank Maria Hammer for drawing attention to their computational error.