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.