Cardiovascular Responses to Exercise
This is one of my favorite systems of study and research in human physiology. Just take some time to think about the challenges we have as humans for heart function, and the needed regulation for the effective distribution of pumped blood to and from the tissues of the body. Then add exercise stress to that scenario, along with thermal stress, dehydration, demands from cellular oxygen need and waste removal, and so the list goes on. The heart must respond to exercise stress with near immediacy, resulting in increased heart rate and ejection from the heart (stroke volume and ejection fraction). This must be coordinated by vascular regulation so that some tissues are prevented to have increased flow during exercise, while allowing as much of the central cardiac output to be delivered to the now working muscle. Just the heart rate increase alone is amazing. The heart could increase from 40 beats/min to close to 200 beats/min in a relatively young and healthy individual; a five-fold increase. This means that the time for blood to fill the heart goes down appreciably, as does the time the heart can contract to eject blood. Yet, as heart rate increases during exercise, the heart responds by also pumping more blood per beat. Thus, more blood received and ejected in less time, with no signs of failure or inadequacy in the healthy heart. Truly amazing. You will learn that such responses require both blood hormonal and neural regulation to control this rapid and effective response to exercise stress. However, you will also learn that difficulty in measuring heart function during exercise has caused numerous errors in our understanding of central cardiovascular determinants of exercise performance. As such, the function and regulation of the cardiovascular system remains a worthy field of research inquiry.
Recommended sequence of topics:
Heart rate responses to exercise
Using heart rate to quantify relative exercise intensity
Stroke volume responses to exercise
Cardiac output responses to exercise
Integrated cardiovascular responses to exercise