ATP and Exercise
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Energy, ATP and Exercise

ATP and Energy

For muscles to contract they need energy. And as you probably are aware this comes from what we eat: more importantly the glucose and triglycerides. But the muscles do not straight get their energy from here. The immeadiate source of energy is ATP (Adenosine TrioPhosphate). It has the structure as follows:

diagram of an ATP molecule

As the diagram shows, there are a string of Phosphates coming off the ribose unit. This is where ATP gets its energy from. The last bond contains alot of energy which is released when it is broken down to ADP (adenosine DiPhosphate) which is exactly the same as ATP but with one P removed.

To rebuild energy reserves the body uses energy from respiration to put a P back onto ADP to reform ATP; and thus the molecule is recycled.

Aerobic and Anaerobic

Now we are looking at this in more detail you must know that there are two types of respiration: aerobic and anaerobic, but rather than being two seperate types, they are part of the same pathway.

Anaerobic is the first stage of the reaction, and produces ATP without the need of oxygen and if the reaction continues it will use oxygen to produce even more ATP. However, if there is insufficient oxygen then only anaerobic respiration will take place with lactate as a by-product, which is acidic. The below table summarizes the two systems.

Type of SupplyNear maximum for up to 1 minuteLong term exercise but lower intensity
ATP produced2 per glucose moleculeUp to 36 can be produced per glucose molecule
By productLactateOnly carbon dioxide
Athletic Comparison200m to 400m sprintsFrom 800m to marathons

Muscle Fatigue

When not enough oxygen gets to the muscles, the respiration will become more anaerobic. Continuing this will lead to a build up of lactate which is acidic and causes a pH drop in the blood plasma. This causes muscle fatigue where muscles ache and do not contract correctly, because the pH levels interfere with the functioning of the proteins and enzymes.

All of this built up lactate doesn't stay in the blood indefinitely. It is taken to the liver where it is broken down to glycogen by oxidation. This process in the liver however, requires oxygen. So after exercise we breath heavily to get enough oxygen to break down the excess lactate, this is known as an oxygen debt.

Updated: 15 May 2011