Final answer:
Cardiac output significantly increases during exercise, with contributions from both stroke volume and heart rate. In healthy adults, it can reach up to 10 to 15 L/min, or even higher in elite athletes. However, very high heart rates can lead to a plateau or decrease in cardiac output due to reduced ventricular filling time.
Step-by-step explanation:
In response to the question regarding cardiac output during exercise in healthy adult subjects, the correct description is that cardiac output increases considerably during exercise. During low workloads, both stroke volume (SV) and heart rate (HR) indeed contribute to increasing cardiac output. It is also true that cardiac output can significantly increase to 10 to 15 L/min at maximal exercise in non-athletes, but even more in elite athletes, potentially reaching over 30 L/min during peak performance. The statement that cardiac output increases linearly with increasing workload is generally correct up until a point. At very high heart rates, however, the increase in cardiac output may plateau or even decrease due to reduced ventricular filling time.
During physical activity, the stroke volume can increase from a resting volume of around 70 mL to approximately 130 mL, largely due to the strengthening of the heart's contractions. Concurrently, the heart rate can increase to around 150 beats per minute (bpm) or higher, facilitating a dramatic increase in cardiac output. These changes result in a significant increase in blood flow, which is necessary to meet the metabolic demands of exercising muscle tissues.
It is also crucial to note that exceeding the target heart rate range (approximately 120 to 160 bpm for a healthy young individual) could result in a decrease in cardiac output, as the quickly beating heart does not allow for adequate ventricular filling, which can lower stroke volume.