Final answer:
Amanda's increased heart rate from exercise will boost her cardiac output and potentially her stroke volume. The heart works harder to pump more blood to deliver oxygen to the muscles, improving tissue perfusion. Exercise over time also strengthens the heart, increasing its size and efficiency.
Step-by-step explanation:
When Amanda exercises and her heart rate nearly doubles from a resting rate of 68 beats per minute, this will have significant effects on her cardiac output and stroke volume. As she exercises, her cardiac output, which is the amount of blood that her heart can pump out in a minute (heart rate x stroke volume), will increase. The normal increase for a healthy young adult is from about 5.0 liters per minute at rest up to a maximum of about 20 liters per minute during strenuous exercise.
In Amanda's case, the near doubling of her heart rate will increase her cardiac output to ensure that sufficient oxygen and nutrients are delivered to her working muscles. Increased cardiac output is typically associated with an increase in stroke volume, which is the amount of blood pumped by the left ventricle of the heart in one contraction.
As Amanda's heart is a muscle, consistent exercise will lead to an increase in the heart's size and mass, making it stronger and more efficient at pumping blood, which benefits both her stroke volume and overall cardiac output. Moreover, tissue perfusion, which is the flow of blood to tissues, will also increase during exercise, thereby improving the delivery of oxygen to Amanda's muscles.