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Math Awareness Month 1999

Effects of Exercise on the Cardiovascular System

Effect on Heart Rate:

heart at rest

heart working hard

Exercise uses up a lot of energy, which the cells derive from oxidizing glucose. Both glucose and oxygen have to be delivered by the blood. This means that the heart has to work harder to pump more blood through the body. This means it has to beat faster in order to achieve a higher throughput, as described by this equation:

Heart rate for a human being at rest is about 70 beats/min. During vigorous exercise, heart rate can increase dramatically (the rule of thumb given for maximal heart rate is 220 minus your age). This will result in an increase in blood flow.

a) Blood flow will double
b) Blood flow will triple
c) Blood flow will halve
d) Blood flow will remain the same

Effect on Circulatory System:

The circulatory system responds to an increased need for blood by adjusting the width of the blood vessels, primarily the arterioles and venules. The dependence of vessel resistance on the radius of the tube is described by Poiseuille's law and is described in detail in the exhibit, "Poiseuille's Law: Resistance and Radius ."

From the formula given there, we see that blood flow depends very sensitively on the width of the blood vessels, so that changing the radius slightly has a large impact on the flow of blood.

The circulatory system exploits this property rather nicely, by constricting blood flow the organs that need less oxygen during exercise and widening the arterioles to the organs which need more. For instance, the brain may use up to 30% of total blood flow while you're doing your homework, but when you're at the gym less than 10% of total blood flow goes through it. On the other hand, muscles use less than 10% of blood flow when at rest, but can take up to 50% of it when they're working. This regulation is an essential mechanism for delivering oxygen and glucose to the tissues that need it most.

M & B Exhibits | intro | pg 2 | pg 3 | pg 4 | pg 5 | pg 6 | pg 7 | pg 8