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Introduction to exercise metabolism

Ironslave

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I alluded to this in the "training frequency" thread, so I thought I'd start this here. A very introductory overview of the metabolic events and adaptations which occur during exercise. The main thing to keep in mind through this is that no system works in isolation . So, with that in mind, let's begin.

Human locomotion, and anything as far as maintaining vital bodily processes is only possible through the use of energy. Most often, this energy comes in the form of ATP. This is the most important equation to consider in exercise bioenergetics:

ATP---> ADP + PI + H+ + energy

The above equation is known as ATP hydrolysis, which produces energy. But, the key thing to keep in mind (which is why I bolded it) is that ATP hydrolysis dissociated a proton (a hydrogen ion). This is important because it lowers the pH, which means that the muscles are now in a state of acidity. For muscles to function properly, enzymes are needed to speed up the rate of reactions by up to trillion folds. It is important to keep in mind that enzymes are proteins, and when in a state of acidity, these enzymes will denature (basically, their structure is disrupted), and the muscle doesn't function. For those who want to get technical, there are other aspects involved, but we won't go into that.

So, now as a result of muscle contraction, we have the dissociation of hydrogen ions. In order to maintain function, the body must buffer these hydrogen ions, to maintain a normal pH (level of acidity). It does so in the following main ways:

1) The coenzymes NAD+ and FAD. These coenzymes are reduced by bonding the hydrogen ions to form NADH and FADH2. NADH and FADH2 then ship the hydrogen and electrons out of the mitochondrial matrix (the inner part of the mitochondria) into the part known as the intermembrane space.

This diagram below is complex, but I circled the parts to focus on. Just pay attention to the point that NADH, and FADH2 in the matrix sends hydrogen ions out into the intermembrane space. These hydrogen ions will eventually go back into the mitochondrial matrix through the ATP synthase motor, which by it's name, forms ATP. Each NADH forms around 2.5 ATP, while each FADH2 forms around 1.5 ATP.

2drdmko 1


2) The bicarbonate buffering system

This works by the following reaction.

H+ + HCO3- ---> H2CO3---> CO2 + H2O

As most are certainly aware, when we exhale, we breathe out CO2. During exercise, obviously we use much more energy than at rest. In turn, we are releasing a lot more hydrogen ions. Therefore, we form much more CO2.

The CO2 formed is a result of bicarbonate buffering of hydrogen ions is the reason we get out of breath during exercise. We don't get out of breath because we need to take more oxygen in, we get out of breath because we need to get CO2 out. CO2 stimulates chemoreceptors in the brain which in turn sends the stimulus to breath.

c) Lactate metabolism.

Typically, the end product of glycolysis is a a 3 carbon sugar known as pyruvate. In turn, pyruvate goes to Acetyl CoA.. which enters the Krebs cycle and goes through all the other steps of metabolism, but we won't worry about that. Originally, it was thought under aerobic conditions, pyruvate was the end product of glycolysis, while under anaerobic (no oxygen) conditions, lactic acid was formed. Relating this to exercise, it was thought that with strenuous exercise, we became short on oxygen, and therefore lactic acid formed which was the cause of the "burning" sensation. This is false. We now know that as mentioned, we breath to get CO2 out, not because we need oxygen in. Hydrogen ions are the cause of the burning sensation.

Lactic acid is formed by the following reaction, catalyzed by the enzyme lactate dehydrogenase

NADH + H+ + Pyruvate --- NAD+ + lactate

From there, lactate has several fates:
1) the main fate is direct oxidation in working muscle
2) it can be shipped to inactive muscles, particularly muscles with slow twitch fibers (because they are abundant in mitochondria).
3) a substrate for energy by something called the Cori Cycle
4) other ways

So, going back to the study by Robergs that Tim posted, the lactate reaction actually prevents fatigue, not causes it. It does so by buffering hydrogen ions, and by providing a substrate for energy

Believe it or not, sitting here right now, we are all producing lactate. But, it gets oxidized before it is spilled over in the blood. So, lactic acid is not produced due to a lack of oxygen.


a good animated video of basic metabolism.

..... this is just a general overview, I could add more and talk about adaptations if requested, though it's not as easy to do on the net.
 
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Eli80Cal

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Very good post IS. Took me back to Physiology with Prof. Brooks.We had a lecture on Creatine once, in the context of this. He brought in adds, etc from magazines, then boiled it all down to ATP> ADP back to ATP with Creatine's phosphate group.

TO ALL OF YOU JUST SKIMMING THE ARTICLE, TAKE THE TIME TO READ IT FULLY, PAUSE, THEN READ IT AGAIN.
 
The_KM

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The fact that a human mind can process and understand this info is mind boggling. Awesome post IS, thanks for taking the time to do this. This is hard info, so I won't comment on it yet because quite frankly i'm lost as are most people.

My question asking process will begin sometime this weekend :ughnoes:

TO ALL OF YOU JUST SKIMMING THE ARTICLE, TAKE THE TIME TO READ IT FULLY, PAUSE, THEN READ IT AGAIN.

haha. It's more like reading over, and over and over until you can visualize the entire process pretty distinctly.

Can't wait until I get into physiology class in college.
 
Eli80Cal

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haha. It's more like reading over, and over and over until you can visualize the entire process pretty distinctly.

Many a sleepless night my friend....

If you understand basic physics, and a high-low pressure gradient, it will make visualizing the process a lot easier. Homeostasis is what drives the body.
 
Ironslave

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Very good post IS. Took me back to Physiology with Prof. Brooks.We had a lecture on Creatine once, in the context of this. He brought in adds, etc from magazines, then boiled it all down to ATP> ADP back to ATP with Creatine's phosphate group.

TO ALL OF YOU JUST SKIMMING THE ARTICLE, TAKE THE TIME TO READ IT FULLY, PAUSE, THEN READ IT AGAIN.

You are extremely extremely lucky to have had him, most of this comes from work he and colleagues pioneered, he's the man. I emailed him once before a few years ago, and still held on to his reply, lol.

The fact that a human mind can process and understand this info is mind boggling. Awesome post IS, thanks for taking the time to do this. This is hard info, so I won't comment on it yet because quite frankly i'm lost as are most people.

You'll easily get all this within a few months if you wanted to. You're just at the point where you're getting a bunch of pieces from a puzzle, now you just need to get the foundation started and you'll be able to see where the pieces go.
 
The Creator

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I have been tested over this stuff way too many times! Awesome info. It can be a little difficult to understand at first but being able to break it down is very important for understanding this aspect of physiology.
 
Braaq

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Wow great post IS!
KM, depending on what degree you chose you will go into this much more thoroughly. I have taken quite a few classes that go over this exact topic. Biochemistry, Exercise Physiology, then again in Exercise Physiology Measurement and Function, Cell Physiology, and I have covered it again in my Muscle Biology Colloquium. You also cover it briefly in your A & P classes. So if you really like this stuff get yourself into some sort of Physiology program. :tiphat:

But anyways, the thing I love about my degree with that I read this and understand it fully as well as know the info already. This is actually a rather straight forward explanation, it can get much much more in depth if IS wanted to do so.
 
tim290280

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Great summary IS!!!
The CO2 formed is a result of bicarbonate buffering of hydrogen ions is the reason we get out of breath during exercise. We don't get out of breath because we need to take more oxygen in, we get out of breath because we need to get CO2 out. CO2 stimulates chemoreceptors in the brain which in turn sends the stimulus to breath.
Just wanted to add that the free divers figured this out a fair few years ago. They actually breathe out when they dive rather than hold in a breath. So all that brain damage aside they were smart cookies.
 
Ironslave

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Just wanted to add that the free divers figured this out a fair few years ago. They actually breathe out when they dive rather than hold in a breath. So all that brain damage aside they were smart cookies.

Yep, there is also another interesting observation with divers. Often before you see them go under the water, they hyperventilate. Originally, it was thought that the hyperventilation worked by bringing oxygen in, but in actuality it worked by taking the CO2 out. Good addition.
 
Ironslave

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... so, if anybody is interested, I could go into some metabolic adaptations to exercise (mostly endurance)...
 

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Ironslave

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Okay, so let's look further into carbohydrate metabolism.

During exercise, most of the energy utilized comes from muscle glyocogen, the storage form of glucose. Before muscle glycogen goes through the steps of glycolysis, it must first be PHOSPHORYLATED. Phosphorylation is the addition of a phosphate molecule. Enzymes that do this are called KINASES, while enzymes that dephosphorylate (remove a phosphate) are called PHOSPHATASES.

So, muscle glycogen is first phosphorylated by the enzyme.... drum roll....GLYCOGEN PHOSPHORYLASE. (note, for the most part, scientists try and use pretty "common sense" terms when possible. In this instance, the enzyme phosphorylates glycogen).

Phosphorylation of glycogen forms GLUCOSE-1-PHOSPHATE. The important thing to note from the diagram below is the addition of the phosphate group. Note, for "naming" molecules, the name itself is based on it's structure. The molecule formed has the same structure of glucose, except that it has a phosphate group at the #1 carbon. Thus, glucose 1-phosphate.

1zcz76q-1.jpg



From there, glucose-1-phosphate is mutated into glucose 6 phosphate. Notice, the phosphate molecule moves from the #1 carbon, to the number 6 carbon. The enzyme that does this is .......phosphoglucomutase. (sounds difficult to memorize, but it's really not. Just know that this enzyme is "mutating" a glucose molecule that has a phosphate attached.)

2ryros0-1.jpg




When a glucose molecule enters glycolysis, it does NOT go to glucose-1-phosphate, like glycogen does. It goes directly to glucose-6-phosphate. The enzyme that does this is called HEXOKINASE. Again, keeping our naming in mind, break down the components of the name. The name comes from the fact that glucose has 6 carbons (6=hex) and kinase, because it adds a phosphate.

5pj7eh-1.jpg


So, to recap this, let's summarize like this.

Glycogen goes to Glucose 1 phosphate, then to glucose 6 phosphate. This does NOT require ATP.
Glucose goes directly to glucose 6 phosphate. This DOES require ATP.

From there, glycolysis continues.

Here's a diagram.

dmfsbp-1.jpg


... i'll do more later, making all these pics was time consuming.
 
Eli80Cal

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Thanks for the great explanations!! Sure that took an awful lot of time.
 
Ironslave

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Just the messing around with finding the images, using MS paint, uploading, etc.
 
Natzo

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Wow great post IS!
KM, depending on what degree you chose you will go into this much more thoroughly. I have taken quite a few classes that go over this exact topic. Biochemistry, Exercise Physiology, then again in Exercise Physiology Measurement and Function, Cell Physiology, and I have covered it again in my Muscle Biology Colloquium. You also cover it briefly in your A & P classes. So if you really like this stuff get yourself into some sort of Physiology program. :tiphat:

But anyways, the thing I love about my degree with that I read this and understand it fully as well as know the info already. This is actually a rather straight forward explanation, it can get much much more in depth if IS wanted to do so.

whats your degree?
 
The Creator

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Thanks a lot IS! I've been over this stuff a few times in physiology, exercise physiology, nutrition, and a little bit in chemistry but you really can ever learn it enough! Every now and again I will get an intelligent client that actually wants somebody to go in depth about energy production and metabolic systems and it is always good to be able to give a decent explanation.
 
youngmusclejock

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This is all so overwhelming. :ughnoes: I like it though!
 

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