Contraction of muscles needs phenomenal amounts of energy and therefore, in muscles, one sees a system of energy molecule production which appears nowhere else. Active muscle cells have myoglobin, which is similar to haemoglobin in blood, and this has the capability of absorbing oxygen and storing it as reserve. That is why skeletal muscles that are very active are red in colour like blood. Besides this, the muscle fibres have numerous mitochondria ('power stations') that produce energy molecules or ATP (Adenosine Triphosphates) through aerobic or oxygen-consuming conversion of glucose. Even this often does not produce enough energy to meet the demand, so muscles are gifted by Nature with two other physiological characteristics:

  1. The ability to store glucose in the form of glycogen, which can be broken up as and when energy demand arises, and
  2. The ability to carry out anaerobic (without oxygen) burning of glucose into energy molecules and lactic acid.

Thus we see that Nature has given skeletal muscles some unusual capacity to generate their own energy without depending on the liver and other organs to send the surplus. Skeletal muscles:

  1. have their own oxygen-binding protein (myoglobin)
  2. can carry out both aerobic and anaerobic types of glucose breakup to generate energy
  3. store glycogen (glucose compound)
  4. have a rich network of blood vessels to supply glucose and calcium, which is absolutely vital to the proteins of muscles as they cannot shorten or shrink without these nutrients, as well as remove waste products like carbon dioxide.
Contraction of muscles creates oxygen demand in the entire body, as its own system takes up most of the oxygen from the blood. The body then increases the heart rate and breathing to meet the demand. That is why the breathing is faster and the pulse rate goes up while running or doing strenuous exercises. Even when exercising stops, the breathing and heart rate continue to be high for some time to meet the demand. Exercising is the only natural way to:

  1. improve circulation
  2. make the heart pump more and improve its own muscle tone
  3. increase energy reserves in the body
  4. burn excess fat and sugar deposits or reserve in the body
  5. tone up the muscles in the body to create a feeling of general well-being.