During a single twitch muscle contraction, there will be a single short-duration contraction of a motor unit in response to a single action potential. During a muscle action potential, the calcium is released from the sarcoplasmic reticulum and binds to troponin and myosin-binding sites on actin exposed results cross-bridge cycling with the use of ATP. The calcium is transferred from the cytosol to the sarcoplasmic reticulum by Calcium-ATPases for muscle relaxation.
If he Calcium-ATPases, the active pump which resort the calcium ion level in sarcoplasm is not present, the single muscle twitch will occur continuously until ATP runs out to continue the muscle contraction force.
Thus the answer is B) It will occur continuously until ATP runs out.
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