Use reasoning to lead to the answer of the following question:
This is an unavoidable physiological consequence of running. What is it?\nOptions:\n- breathlessness\n- increased heart rate\n- falling down\n- muscle bulk\n- calluses
 Reasoning process:
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Increased heart rate is caused while running. Increased heart rate is unavoidable. It is physiological consequence of running. Therefore, the final answer is increased heart rate.
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