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Case Study: Aerobic Capacity
Noah Mayeda
Liberty University
EXSC 510: Advanced Exercise Physiology
Dr. Kilian
September 11, 2022
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During exercise, blood flow is to skeletal muscles is increased. This is done by lessening
blood flow to other tissues and organs. This redirection of blood flow is to support muscular
work. The term, “autoregulation”, describes the most important method of how blood flow is
controlled during exercise. Muscles and tissues can adjust their own blood flow to meet the
metabolic needs. During rest, arterioles in muscle have a high vascular resistance due to
increased vasoconstriction. Exercise creates a demand for increased blood flow in proportion to
the metabolic demand. This increase is a result of decreased vascular resistance and by recruiting
more capillaries in muscles. Exercise results in opening all the capillaries in contracting muscle,
compared to while at rest only 50% to 80% are open (Powers, 231). The intensity and number of
motor units recruited during exercise define the metabolic needs of the muscle, which then
determine the amount of vasodilation. The metabolic needs are the demand for oxygen and
nutrients. This autoregulation of blood flow is crucial to exercise performance.
Autoregulation is controlled by several locally formed vasodilators. These include nitric
oxide, prostaglandins, ATP, adenosine, and endothelium-derived hyperpolarization factors
(Powers, 231). These factors increase blood flow by relaxing smooth muscles in arterioles. Nitric
oxide and prostaglandins are strong vasodilators. ATP and adenosine are vasodilators and
increase muscle blood flow. Endothelium derived hyperpolarization factors relax smooth
muscles and dilate arterioles. All of these work together to cause vasodilation and increase blood
flow to working muscles. As said previously, increased vasodilation reduces vascular resistance,
thus increasing blood flow.
Another way blood is redirected to contracting muscles is by increasing resistance in the
flow of blood towards organs and inactive tissues. So, while contracting muscles decrease
resistance, vascular resistance increases towards organs and tissues. This results from increased
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sympathetic output to organs and tissues. It is controlled by the cardiovascular control center.
Blood flow to organs and unused tissues can decrease 20% to 30% that of resting values.
Apart from increased blood flow, cardiovascular training can also boost performance.
Cardiovascular training will increase the athlete’s aerobic capacity which increases the ability to
perform work for an extended period of time. Aerobic capacity, also known as VO2 max, is the
amount of oxygen the body can transport and use oxygen. An athlete can physiologically
improve their aerobic capacity through endurance training. By using a large muscle mass for at
least 20 minutes, 3 times per week, at an intensity of at least 50% of their VO2 max, their aerobic
capacity can increase. Using a large muscle mass would include running, cycling, or rowing.
Another way to increase aerobic capacity is interval training. Which would be bouts of near
maximal effort for 30 to 120 seconds. This increase in aerobic capacity grows due to stroke
volume and arteriovenous oxygen difference. Stroke volume is the amount of blood the heart can
pump with each stroke. The arteriovenous oxygen difference is the amount of oxygen absorbed
from the blood into the tissues. Since maximum heart rate cannot increase, “increases in
maximum cardiac output must come from increases in stroke volume” (Powers, 319). This
means that once the heart reaches its maximum beats per minute, the only way for it to pump
more blood is by increasing the stroke volume. The arteriovenous oxygen difference is not
affected by heart rate, but by the demand of oxygen by the muscle. This ability to extract oxygen
from the blood results from an increase in capillary density and mitochondrial volume. The
increase in capillary density adjusts for the increase in blood flow and decreases the distance
oxygen must travel into the mitochondria. The increase in capillaries also slows the rate of blood
flow and allows for more time for oxygen to be absorbed.
-Noah Mayeda
