ATP powers all the activity of muscles. Muscles move because of the continual and instantaneous breakdown of ATP. The release of energy from ATP is a small thing, but essential to life itself.
Muscle is an excitable tissue that it can be stimulated to produce an action potential. An action potential is an electrical change acrossthe membrane. Muscle contraction requires a great deal of energy. The aerobic energy of a resting muscle comestwo- thirds from fatty acids and one-third from glucoseand occurs because the brain and nerve tissue can only burn glucose to make ATP. The muscles save glucose for the nervous system as often as possible.
When oxygen supplies are inadequate in time of exertion, the use of carbohydrate becomes more important as the intensity of exercise increases. The breakdown of glucose to water and carbon dioxide generates energy. This process is short circuited and lactic acid builds up in the muscle.Lactic acid isan important fuel that is used by the muscles during prolonged exercise. Lactate released from the muscle is converted in the liver to glucose, which is then used as an energy source.
Most of the ATP in cardiac muscle is derived from the aerobic breakdown of fat. During times of exertion as the intensity of exercise increases
the body cannot breakdown fat,fast enough to provide the high levels of energy.
The immediate response of the cardiovascular system during exertion activity and when the levels of oxygen are not enough is to "absorb glucose molecules and used to rebuild their glycogen reserves"(Martini P. 301) in order to increase the output of the heart to meet the demands ofenergy and oxygen.
The cardiac muscle is the greatest beneficiary.With this adaptation, the heart grows stronger. It draws more blood and oxygen through the coronary arteries and increases the amount of blood it pumps with each beat (stroke volume). This potentially adds years …

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