Autoregulation
Blood is the substance that carries the chemicals necessary to bring life and
energy throughout the body. If blood does not circulate, then the tissues and such will die
off. Fully functioning circulation is necessary to bring the proper amount of nutrients and
blood to each individual system of the body. The body has such a mechanism that
provides the way in which for this to happen depending of the needs of the different parts
of the body. This process is called autoregulation.
Autoregulation is defined as mechanism by which an organ regulates blood flow
to match metabolic rate (Powers 2018). It delivers blood where needed by tissues and
muscles and redistributes blood where it is not essential at that moment. For instance, at
rest, the body will not provide the muscles with a lot of blood flow because the muscles
aren’t needing the attention of those at that particular time. However, during exercise, the
body will turn its attention to those muscles that are in need and will provide almost all of
the blood in the body to focus its attention on where it’s needed most, which in the case
during exercise, would be the muscles. This very system that is able to automatically
regulate, hence the name, and operate on its own to provide blood flow to where the body
needs most is called autoregulation and it has three aspects to it. The way in which
autoregulation operates is vasodilation, vasoconstriction, and capillary recruitment.
Vasodilation is the dilating, or widening, of the blood vessels. The widening of the
blood vessels is necessary to allow more blood flow throughout the body. The body does
this during exercise and is regulated by the “metabolic needs of the muscle,” which is
oxygen and nutrients. As the intensity of the exercise increases and the recruitment of the
motor units are recruited, determines the amount of the blood flow sent to the muscles by
the process of autoregulation. The process of vasodilation takes place with “local changes
such as increased production of nitric oxide, prostaglandins, ATP, adenosine, and
endothelium. Each of the factors are independently shown to smooth muscle relaxation in
the arterioles.” As vasodilation is taking place for the muscles, vasoconstriction is
occurring in the organs. Around 84% of the blood flow of the body will be circulating to
the muscles during exercise, which implies that the other 16% is covering the rest of the
body.
Vasoconstricting is the constricting, or narrowing, of the blood vessels. The
body’s purpose of narrowing the blood vessels to restrict the amount of blood flow to a
certain area by increasing the vascular resistance. One example of the body performing
vasoconstricting is at rest, the body will shorten the blood flow to the muscles, dropping
it from 84% to around only 20% of the blood in the body. At this time, the body through
autoregulation is more concerned with the circulation of blood to the organs and not the
muscles, since the muscles are not being used.
The last aspect of autoregulation is capillary recruitment. Capillaries are tiny
blood vessels used to “facilitate exchange of fluid, nutrients, electrolytes, hormones and
other substances between the blood and the interstitial fluid in the various tissues of the
body.” Capillary blood flow travels heart to lung to heart to artery to arterioles to
capillaries to muscles to venules to veins and back to the heart. During exercise and when
vasodilation is occurring, the capillaries will dilate as well, from a sphincter that allows
the increase or decrease in diameter of the capillaries to allow blood flow to the muscles.
Nearly, if not all, of the capillaries will be opened to allow blood flow into the muscles.
These capillaries will also go through constriction when the muscles are not needed the
extra supply of blood. The use of the capillaries can be used at 100%, but then drop down
to a minimal of a few percent active of the body.
An athlete can physiologically improve their aerobic capacity after several months
of cardiovascular training by the body taking on several adaptations. For one,
cardiovascular adaptations occur by increasing maximal cardiac output, increasing stroke
volume, reducing heart rate at rest and at submaximal exercise and also, increasing the
capillary density, which supports delivery of oxygen and removal of carbon dioxide (Haff
& Triplett). Other adaptations include respiratory, which involves the increase in tidal
volume and reduced breathing frequency with submaximal training, but increased
breathing frequency with maximal intensity. Neural adaptations help with locomotion for
more efficient energy uses and the muscles adapt to increase in aerobic capacity. Muscle
fibers increase in mitochondrial density, which improves the amount of ATP and oxygen
supplied to the muscle. Type I muscle fibers, which are primarily better aerobic training
increase and allows for less effort in aerobic activity. Less impact and energy expended
during the activity allows for more work to be produced by the body, therefore increasing
the aerobic capacity.
REFERENCES
Haff, G. Gregory, Triplett, N. Travis, & National Strength & Conditioning
Association (U.S.). (2016). Essentials of strength training and conditioning (Fourth ed.).
Human Kinetics.
Powers, S., Howley, E. T., & Quindry, J. (2021). Exercise physiology: theory and
application to fitness and performance. McGraw-Hill.
Advanced Exercise Physiology (Powerpoint Slides). Liberty University
WILLIAM LAMBO
