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Energy required for various activities is provided by ATP (Adenosine Tri Phosphate- energy currency of cell). There are three different energy systems operating during different forms of exercises.
(A) ATP-CP (Creatine Phosphate) system
(B) Anaerobic system
(C) Aerobic system
Body’ metabolic processes (Glycolysis, glycogenesis, glycogenolysis, gluconeogenesis) are carried out continuously. But the rate at which these reactions take place depends upon the body’s demand for energy. When the body is at rest, the rate of glycogenolysis is slow and the energy demands by the body are met through slower aerobic glycolysis.
(A) ATP-CP (Creatine Phosphate) system:
When the physical activity is initiated, increased energy demands can not be fulfilled by slow rate of aerobic glycolysis. The increased energy requirements of contracting muscles are met by the readily available stores of ATP of the active muscles. ATP is broken down to ADP (Adenosine monophosphate) by removal of the terminal phosphate group. One phosphate group provides 7.3 Kcals. The ATP stores of the muscles are limited and can fulfill the energy demands only for the initial 2seconds.
The ADP can not be further utilized for the energy production. After the depletion of muscle ATP stores, CP (Creatine phosphate) donates its phosphate group to ADP and thus carries the continuous supply of ATP for energy to the contracting muscles. However, the energy furnished by CP system lasts for 8- 10 seconds
Examples of the activities deriving energy from this system are weight lifting, football, 100 m sprint.
(B) Anaerobic system:
As the name suggests, this system operates in the anaerobic condition (in absence of oxygen- when the oxygen demand by the body is far greater than its supply). This system becomes active after the depletion of muscle ATP- CP stores and when the physical activity continues beyond 10 seconds. The primary source of glucose for the exercising muscle is its own stored glycogen. Glycogen is broken down to glucose and then each molecule of glucose is converted to lactic acid through anaerobic glycolysis. One molecule of glucose participating in anaerobic glycolysis provides 2 ATP molecules.
The lactic acid produced crosses the muscle cell membrane and is carried to the other body tissues, where its clearance takes place. However, when the rate of lactate production exceeds its rate of clearance, it accumulates in the muscles and causes muscle fatigue which in turn affects the performance of the athlete. Anaerobic system cal fulfill the energy demands for less than 11/2 -2 minutes.
The examples of the activities in which the energy is provided through this system are 400-600meter sprint, swimming of 100-200meter.
(C) Aerobic system:
This system becomes active after 1-2 minutes of physical activity. It provides energy in the presence of oxygen. After the exercise is initiated, liver glycogen can not provide glucose immediately to the exercising muscles. Therefore, these muscles derive energy initially from its stored ATP-CP system followed by anaerobic glycolysis of its own glycogen stores. However, the production of energy through aerobic glycosis is far greater than that of ATP -CP and anaerobic system. Complete oxidation of one molecule of glucose through aerobic glycolysis gives 38 ATPs.
The examples of the activities deriving energy through this system are walking, jogging, cycling, swimming.
However all these energy systems are active together, but depending upon the type, intensity & duration of physical activity, one of the systems is major contributor of ATP while the others synthesize ATP to a lesser extent.
Energy production during Weight training:
It is a high intensity, short duration activity.
Thus, the major contributors of energy are ATP-CP and muscle glycogen. Exhaustion of muscle glycogen and production of lactic acid lead to muscle fatigue.
Energy production during Cardiovascular training:
It is a low to moderate intensity activity for long duration. The goal of this type of activity is to use storage fat as source of energy. Cardiovascular training depends on aerobic system for energy production. In this type of training, minimum amount of muscle and liver glycogen promote fat burning. |
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