Poorly Understood Aspects of Striated Muscle Contraction
Force-velocity (load-velocity) relationship of frog muscle fiber. (a) Force-velocity relationship for shortening (positive velocity). Inset: assumed velocity dependence of attachment rate () for certain model predictions in (a) and (b). (b) Force-velocity relationship for loads (forces) close to isometric (normalized force: 1.0) and for eccentric contractions (negative velocities). Inset: extended region for eccentric contraction. Purple symbols in (a) and (b): experimental data from  (circles),  (triangles), and  (squares). Green lines: model  with same attachment rate that would fit rise of tension in isometric contraction. Black lines: model  with attachment rate accounting well for the maximum power-output during shortening. Orange lines: model  with velocity dependent attachment rate for shortening (inset in (a)) and lengthening. In the latter case, the attachment rate constant increased from a maximum value of 67 s−1 in isometric contraction (inset (a)) to 335 s−1 at lengthening velocities ≥ 600 nm hs−1 s−1. Figures from Biophysical Journal  reprinted with permission from Elsevier/The Biophysical Society.
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