Circulatory System
The cardiac muscle surrounding the heart hypertophies, resulting in thicker, stronger walls and therefore increases in heart volumes. The more blood pumped around the body per minute, the faster oxygen is delivered to the working muscles.
The number of red blood cells increases, improving the bodies ability to transport oxygen to the muscles for aerobic energy production.
The density of the capillary beds in the muscles and surrounding the heart and lungs increases as more branches develop. This allows more efficient gaseous exchange of oxygen and carbon Dioxide.
The resting heart rate decreases in trained individuals due to the more efficient circulatory system. The accumulation of lactic acid is much lower during high – levels activity, due to the circulatory system providing more Oxygen and removing waste products faster. Arterial walls become more elastic which allows greater tolerance of changes in blood pressure.
Respiratory system and exercise
The respiratory muscles (diaphragm/intercostals) increase strength
This results in larger respiratory volumes, which allows more oxygen to be diffused into the blood flow ( vo2max)
An increase in the number ands diameter of capillaries surrounding the alveoli leads to an increase in the efficiency of gaseous exchange.
Muscle
Increased numbers of mitochondria ( the cells powerhouse) means an increase in the rate of energy production
The muscles, bones and ligaments become stronger cope with the additional stresses and impact put through them.
The amount of myoglobin within the skeletal muscle increases, which allows more oxygen to be stored within the muscle, and transported to the mitochodnria.
Muscles are capable of storing a large amount of glycogen for energy. Enzymes involved in energy production become more concentrated and efficient to aids the speed of metabolism.
ENERGY SYSTEMS USED DURING EXERCISE
The human body uses a variety of energy systems for different purposes and under different conditions. However, we are interested in the types used during exercise under normal healthy conditions and therefore starvation related processes will not be discussed. The primary energy currencies for the human body are adenosine triphosphate (ATP) and to a lesser degree, guanosine triphosphate (GTP). As a result, the efficiency and effectiveness of energy systems will be based on how much ATP or GTP they can produce and the rate at which they can produce it. Also, since GTP is used primarily for protein synthesis and other functions not related to exercise, and its synthesis is similar to that of ATP, this article will deal primarily with the synthesis of ATP.
The primary energy systems used during exercise are, aerobic lipolysis, aerobic glycolysis, anaerobic glycolysis, and stored adenosine triphosphate coupled with creatine phosphate (ATP/CP). It is interesting to note that the systems which produce the higher amounts of ATP are usually the ones that produce it at the slowest rates. As a result, the body is constantly in a state of compromise, and individual energy systems are rarely used in isolation. Instead, the body will often favor one system instead of using it at the exclusion of all the others.
Aerobic Lipolysis
Aerobic lipolysis burns fat in the Krebs cycle. Stored fat is the largest reserve of energy, so even an extremely lean person usually has enough stored fat calories to walk over 100 miles.
Aerobic Lipolysis is the slowest producer of ATP so it is most useful for extremely low energy activities such as slow jogging, walking, breathing, talking, etc.
It is the primary source of energy used to remake ATP from ADP, as well as to recycle spent fuel back into glucose between sets of intense exercise.
Aerobic Glycolysis
Aerobic glycolysis is the second largest producer of usable energy for exercise in the human body, but produces ATP at a noticeably higher rate than aerobic lipolysis. If someone runs out of usable glycogen during an endurance event this is called "hitting the wall", and results in a significant drop in the rate of energy output.
Aerobic glycolysis begins by breaking down glucose into pyruvate to produce some ATP, after which the pyruvate is oxidized in the Krebs cycle to produce even more ATP.
If someone runs out of usable glycogen during an endurance event this is called "hitting the wall", and results in a significant drop in the rate of energy output.
Aerobic glycolysis begins by breaking down glucose into pyruvate to produce some ATP, after which the pyruvate is oxidized in the Krebs cycle to produce even more ATP. The rate of ATP production is limited by the VO2 Max.
Aerobic glycolysis is useful for moderate rates of energy output for moderate time periods such as in running a 2 mile race.
Anaerobic Glycolysis
Anaerobic glycolysis is not limited by oxygen uptake and produces ATP at about 100 times as fast as aerobic glycolysis.
It produces much less ATP per molecule of glucose and is therefore much less energy efficient. It also begins with the breaking down of glucose into pyruvate to produce ATP. When energy is needed at rates that are greater than what can be supplied by aerobic glycolysis and lipolysis, much of the pyruvate undergoes fermentation to produce ATP without the need for oxygen.
One of the end products of anaerobic glycolysis is lactic acid which causes a burning sensation in the muscles, and inhibits further glycolysis. This inhibition of further glycolysis reduces the energy output during the exercise.The lactic acid eventually goes from the muscles into the blood and to the liver where it is converted back to pyruvate and then back into glucose in a process called gluconeogenesis via the Cori Cycle.
Anaerobic glycolysis is usually used in high repetition exercises where the athlete feels the muscles "burning".
Adenosine Triphosphate/Creatine Phosphate (ATP/CP)
Stored ATP reserves are the quickest ways to have ATP available for energy output. However the extremely high rates of energy output is offset by the short supply which lasts only seconds. In many cases, creatine phosphate (CP) will donate a phosphate group to adenosine diphosphate (ADP) to change it back into adenosine triphosphate (ATP).
This increases the amount of ATP available after which the creatine becomes creatinine, which is excreted in the urine. Creatine phosphate is created in the body from amino acids and a phosphate group. However, Creatine that is consumed in either natural form (i.e. beef or salmon) or in supplemental form, gets converted into creatine phosphate when it enters the body, which in turn increases the energy output available via the ATP/CP system. The combination of these energy systems obviously has roots in the survival of our ancestors. However, understanding the energy systems can help us to maximize the benefits that we get from physical exercise. One important point to remember, is that each energy system is rarely used in isolation. Whenever a high output rate energy system (ATP/CP) is being used, the lower output rate energy systems are also being used to assist it.
Finally training plays a large role in the ability of an athlete to compete at a high level as mentioned is vital to provide necessary physiological adaptations. It must be remembered that the training must be in sports specific and the measurements take a determine levels of metabolizes and the performance of the cardiovascular system also be performed in as sport specific nutrion energy drinks, fluid intake , muscular damage accuring in events must also be seen as a vital consideration with athlete . In trying to achieve the best physiological state for the athlete perform under this.
References:
Dr. Brian Mackenzie (2000) Continuous and Interval Training Book
http://www.brianmac.co.uk/enduranc.htm
By: Georgia Theodosiou
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