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【单选题】
Why is the latent period longer during an isotonic twitch of a skeletal muscle fiber than it is during an isometric twitch?A.
Excitation-contraction coupling is slower during an isotonic twitch.
B.
Action potentials propagate more slowly when the fiber is shortening, so extra time is required to activate the entire fiber.
C.
In addition to the time for excitation-contraction coupling, it takes extra time for enough cross-bridges to attach to make the tension in the muscle fiber greater than the load.
D.
Fatigue sets in much more quickly during isotonic contractions, and when muscles are fatigued the crossbridges move much more slowly.
E.
The latent period is longer because isotonic twitches only occur in slow (Type I) muscle fibers.
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