OXYGEN DEBT

Oxygen debt means when the demand for oxygen is greater than the supply. It means that when your body works hard you breathe a lot of oxygen but you can not absorb enough oxygen to cope with the level of activity. It is the stage of oxygen debt. As a matter of fact, ATP (or adinosine triphosphate) is the source of energy for muscular contraction . There are three main sources , which provide a continual supply of ATP.

• Creatine phosphate.
• Glycolysis
• Oxidative phosphorylation ( critic acid )

When our muscles remain in resting position, these contain large amount of ATP and creatine phosphate . But, when we start exercise during the first few seconds of muscular contraction, the reserved ATP is used up immediately. During this period , ADP ( or adinosine diphosphate ) levels increase. Creatine phosphate rapidly supplies ATP for the contraction of muscles. The molecule of creatine phosphate contains both energy and phosphate , which are transferred to a molecule of ADP to form ATP and creatine. If the contraction is short , the muscle can drive all its ATP from creatine phosphate. If light exercise is to be done for longer period, other sources of ATP must be available . Glycolysis is the process by which glycogen ( stored from of glucose in muscles ) or glucose from the blood is broken down to  CO₂ and H₂O by oxidative phosphorylation in the citric acid cycle to produce more ATP . The breakdown of ATP , the combination of creatine phosphate with ADP , and glycolysis can occur both aerobically (in the presence of oxygen ) and anaerobically ( in the absence of oxygen ) . Oxidative phosphorylation is an aerobic process . It means it requires the presence of oxygen . If oxygen supplied to muscles gets exhausted ( during heavy muscular activity ) , the pyruvic acid formed in glycolysis is converted to lactic acid . The accumulation of lactic acid in the muscle causes fatigue. At this stage ,m muscle is in oxygen debt . If exercise is continued , then there will be more debt of oxygen . In oxygen debt , lactic acid diffuses out into the blood and is carried to the liver, where it is reoxidised to pyruvic acid. In the liver , pyruvic acid can enter the citric acid cycle and can be broken down to CO₂ and H₂O . It can be said that it is reconverted to glycogen . It has been observed that up to the deficit of 2.3 litres oxygen , the lactic acid is not produced in muscles but , after that , if the amount of lactic acid goes on increasing , the deficit of O₂ will be increased at the same rate .A complete rest helps in removing oxygen debt . During the rest , ATP is again stored in the muscles for activities . Generally , lactic acid is removed approximately in one hour if cooling down is performed properly . It may also take 2 hours or more if cooling down is not done with gentle exercise .