Soft-Tissue Pathomechanics - Fundamentals and Assessment Tools for Occupational Ergonomics - page 345

FIGURE 15.3 The role of Ca 2þ in activating the cross-bridges. (Copyright Brooks

Cole —Thomson Learning, 2001.)

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the area over which thin and thick filaments overlap is reduced, and thus there is a decrease in the
number of cross-bridges that can be formed resulting in a reduction in force (Figure 15.5). Thus,
maximal force is generated when sarcomeres are at a length that produces the optimal overlap
between thin and thick fibers.

FIGURE 15.4 Muscle twitch, twitch summation, and tetanus. (a) If a muscle fiber is restimulated after complete
relaxation, the second response is the same as the initial response. (b) If the muscle fiber is restimulated before
complete relaxation takes place, the second twitch is added to the first twitch. (c) If the muscle fiber is stimulated
rapidly such that it does not have the opportunity to relax, a maximal contraction or tetanus occurs. (Copyright
Brooks Cole — Thomson Learning, 2001.)

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