Using All That Oxygen.

Last month, I introduced the topic of oxygen delivery. This month, I’ll talk about how this oxygen is used once it gets to the muscle.

How We Use Oxygen
Once oxygen is delivered to the muscles, the muscles need to make use of the delivered oxygen. Oxygen moves from one place to another by the process of diffusion – this is the downhill movement from a place of high concentration (blood) to a place of low concentration (muscle in this case).

Remember oxygen is carried by hemoglobin in the red cells. When blood enters the capillaries surrounding the low oxygen environment of muscle, oxygen leaves the hemoglobin, passes into the liquid part of the blood, pass through the capillary vessel wall, through the liquid surrounding the cells, then through the muscle cell wall, then into the muscle interior to a hemoglobin-like molecule called myoglobin.

From myoglobin, the oxygen moves to the real engine of the cell called the mitochondria where the energy is actually produced.

“Making Energy”
I use quotes because we don’t make energy. Our energy comes from the sun. What we do is transfer energy from the food we eat to be made available for biologic work. The body is pretty smart. Unlike a car that has one fuel and one way to use that fuel (I’ll ignore the newer hybrid cars), the body has options for fuel and different ways to use that fuel.

In the body, energy is located in a molecule called ATP (adenosine triphosphate). Adenosine is a molecule with three phosphates attached.

Most people think the phosphates are the energy. But the energy is in the ‘glue’ that holds these phosphates to each other and to the adenosine. We get energy when we split a phosphate off the ATP (three phosphates) releasing the energy leaving an ADP (diphosphate – two phosphates).

If needed, we can get energy from the ADP by splitting off a second phosphate, liberating the energy leaving a monophosphate (AMP).
I read one time that if you could put all the body’s ATP in one place, you might fill up a glass somewhere between the size of shot glass and a small juice glass (depending on who’s doing the calculation). So when ATP is used, we better replenish ATP fast because we can run out of the stuff real quickly.

So, when a phosphate is split off an ATP, there is all this energy around for work. Too bad that, the body isn’t a perfect machine. Only about 40% of the energy released is used by the cell, the rest is released as heat.

Ever wonder where your body temperature comes from? From the basal breakdown of ATP and the 60% of available energy released as heat. It doesn’t take much to see that during exercise more energy is needed (breakdown of ATP) and more heat is produced so you body temperature rises.

Anaerobic Energy
The methods of energy production fall under one of two headings: aerobic and anaerobic. “Anaerobic” means in the absence (an-) of oxygen (aerobic).

ATP-PC System
This is a quick, but limited way to get energy. The body constantly exchanges phosphates between molecules. Remember, ATP is a molecule (not the only molecule) where energy is stored between phosphate molecules. Phosphate, and the subsequent energy, also is stored when connected to creatine (the same creatine you’ve been hearing about as a supplement).

When the energy in an ATP molecule is used, a phosphocreatine (PC) molecule transfers its energy and its phosphate to the ADP. What’s left now is an ATP and a creatine. Soon after this transfer, energy and a phosphate must be put back on that creatine so that PC can feed the next ADP.

Energy is always in a state of flux. If things get really tight for energy, the body can use two ADP’s, transfer energy and a phosphate to one of the ADPs. What left is an ATP and an AMP (which may end up as ammonia). As you should see, the body is constantly transferring energy and phosphates around. The body is never in a state where these transfers cease.

The Lactic Acid System
There is a second anaerobic way to get energy. The starting point here is sugar…blood glucose or the storage form of glucose called glycogen. The chemistry of this is difficult for most people. So, I will try to make matters simple.

Glucose is a molecule that contains six carbons. This metabolic process breaks glucose into two 3-carbon molecules. When all the twisting and bending of these 3-carbon molecules is said and done, two new ATP molecules are assembled. At the end of this is a waste product called lactic acid.

Don’t worry about the chemistry of this process. Just accept it on faith. To experience what lactic acid production feels like, run up 2-3 flights of stairs and take stock of your quads.

You can’t make energy as fast through the lactic acid system as you can through the ATP-PC system (lower rate of production), but it can make energy for a longer period of time (greater capacity for energy). The problem with metabolic processes is a waste product that can upset the chemistry (the pH) of the muscle, in this case lactic acid. So the body better have a way to make energy that doesn’t potential damage the tissue with low pH.

Once lactic acid is produced, the body must work to get rid of it – and this is recovery which I always say is the key to success in ball games like soccer.

Next month – aerobic energy production.

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