Final answer:
During a stress test, the patient exercises on a bicycle or treadmill to stress the heart and increase the demand for oxygen in the heart muscle cells.
Step-by-step explanation:
During a stress test, the patient exercises on a bicycle or treadmill because these actions stress the heart and require more oxygen for the heart muscle cells. Oxygen is necessary for aerobic respiration, which is the process that generates energy for the cells. When the heart is stressed, it needs to pump more oxygenated blood to keep up with the increased demand, and the exercise helps to assess the overall cardiovascular function.
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