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Fig. 7. The effect of sarcomere length and tendon morphology on active and passive
force production in the anterior division of the adductor mandibula of the
ratfish. Sarcomere length is estimated from predicted muscle strains during
jaw opening (see Fig. 5) and a
resting length of 2.0 µm. In the untwisted condition (A,B), passive tension
increases more rapidly in the anterior face than in the posterior face as the
jaw is opened (A). This results in the two portions of the muscle beginning
their active tension generation at disparate points on their active curves (B)
and having heterogeneous force production capabilities, lowering the whole
muscle force output at prey contact. In contrast, the faces of the muscle in
the twisted condition (C,D) occupy similar portions on both their active (D)
and passive (C) tension curves, allowing more optimal active tension
generation and a wider gape without the detrimental effects of high passive
tension forces.