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Which of the following has been shown to interfere with cross-bridge "cycling" during exercise?

a. a decrease in Na+
b. an accumulation of H+
c. a decrease in Pi (inorganic phosphate)
d. an accumulation of ATP

1 Answer

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Final answer:

An accumulation of H+ interferes with cross-bridge cycling during exercise by altering pH and inhibiting ATP synthesis, critical for the detachment and attachment cycle of myosin and actin for muscle contraction and relaxation.

Step-by-step explanation:

The student's question relates to what interferes with cross-bridge cycling during exercise. The correct answer is that an accumulation of H+ (protons) can interfere with this process. During exercise, the increased production of lactic acid leads to a rise in hydrogen ion concentration (H+) within the muscle cells.

This accumulation of protons can affect muscle contraction and relaxation by altering the pH and inhibiting enzymes critical for ATP production, impairing the ATP re-synthesis needed for the detachment of myosin from actin.

During the cross-bridge cycle, ATP must bind to the myosin head for the cross-bridge (actin-myosin binding) to detach. This is necessary for muscle relaxation and for the myosin heads to return to their 'cocked' position. If ATP binding is compromised, the cross-bridges cannot properly cycle through attachment and detachment, disrupting muscle contraction and relaxation.

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