What are the bio-chemical changes that occur in a muscle during contraction ?

Explanation

For the contraction of muscle, continuous supply of energy is needed . ATP is the immediate source of energy for muscle contraction . As the ATP content is very low , it is actively replenished, continuously by an energy rich muscle phosphagen .
`ATP to ADP+Pi`
The high energy phosphates of muscles that donate energy phosphate group to ADP are known as phosphagen . In vertebrate muscles creatine phsophate (CP) is the phsophagen, which is an immediate backup source . In invertebrate muscles, It is in the arginine phosphate . This reaction is catalysed by creatine kinase (CK) . Creatine Phosphate is the immediate additional source of energy in the muscle .
Creatine phosphate +ADP `to` Creatine
When creatine phosphate gets exhausted, the next source of reserve energy is utillised, which includes the oxidation of glucose and fatty acids . The energy liberated in this process is transferred to ADP and creatine . Thus ATP and creatine phosphate are formed and which in turn supply energy for muscle contraction .
During rapid activity of a muscle, the respiratory system is unable to supply sufficient oxygen needed by it, which leads to oxygen debt . It is defined as the amount of extra oxygen required by a muscle during recovery from vigorous exercise . Thus the pyruvic acid produced by glycolysis is transformed into lactic acid in the absence of oxygen . Accumulation of lactic acid in the muscle leads to muscle fatigue .
Lactic acid, formed in the anaerobic degradation in the muscle, reaches the liver through blood circulation . In liver, during rest, `80%` of lactic acid is utillised in the resynthesis of glycogen, which is transported back to muscle . This is known as Cori cycle . `20%` of lactic acid is oxidised as `CO_(2)` and `H_(2)O` .