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Old 07-12-2008, 09:56 PM   #1
Steven Low
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physiology of energy pathways and implications

Hi guys.

I decided to break my hiatus; however, this will be my last post on the boards as I have decided to permanently move on. Well, my motivation in particular has always been to give back as much as I can to the communities who helped bring me up and influenced me. However, with CF boards in particular I kind of feel obligated most of the time to help out, and the quality of discussion has well degraded in previous months which tends to make me feel obligated to help out more (especially with newbies and influx of terrible “answers”)... and it just becomes a big time sink which I don't need at this point in my life. I will still be around on various other boards and you can contact me through e-mail, but I won't be posting here anymore.

As for this topic, I'm actually going to write about this frankly because I do not believe many of you have a clear understanding on how the energy systems of the body are integrated within the context of muscles and the nervous system. That said, I hope you learn something. All questions/comments to myself can be directed to e-mail.

Part of my motivation was from these two threads. They have terrible posts within them that misunderstand how the body's energy systems work within the context of metcon and the dependency of anaerobic vs. aerobic work. No offense to the posters.. I don't think CFJ has been all exactly that clear in explaining everything.
http://www.board.crossfit.com/showthread.php?t=33640
http://www.board.crossfit.com/showthread.php?t=34007

P.S. All links in the next 3 posts are WFS!

-----------------------------------------------------


What are the energy systems?

All right. So first we have to define what exactly your energy systems are. There are 3 namely (and I will try to keep this all as simple as possible):

1.Creatine phosphate (or phosphocreatine depending on who you're asking,... generally abbreviated by myself here as PCR). This is a short duration energy pathway that gets activated when ATP is needed rapidly.

2.Glycolysis is the second pathway. This is generally referred to as the anaerobic pathway. It's anaerobic because it does not use oxygen. The end result of this pathway is taking one molecule of glucose (or other hexose sugar that the body can metabolize) to 2 pyruvate, 2 NADH and 2 ATP.

3.Oxidative phosphorylation is the final energy pathway. This is generally defined as the aerobic pathway because it utilizes oxygen as a final electron acceptor after moving electrons down a chain of proteins in the mitochondria to produce massive amounts of ATP.

These 3 pathways make up our bodies energy systems. These energy systems are what we are trying to tax especially with the workouts specifically called HIIT (high intensity interval/intermittent training), tabatas as well as our very own metabolic conditioning (metcons).

-----------------------------------------------------


How do these energy systems work

PCR is a high energy compound that can donate a phosphate group to ADP to phosphorylate it back to ATP for more use. PCR is a very short term energy pathway that is used up very quickly when working out. For example, doing a set or two of weightlifting such as deadlifts will exhaust this pathway quickly. When doing higher repetition sets, this pathway is easily exhausted and the body will have to rely on the other pathways for energy.

The glycolytic pathway is also a very short term pathway as well. As you can see from the physiology, it actually produces very little ATP – 2 per turn of it's cycle. This means on the large scale of things that it burns out very quickly especially when put under high intensity. Interestingly enough, it does produce NADH which is used aerobically so it is in a sense tied to oxidative phosphorylation. But we will overlook this.

Oxidative phosphorylation is technically made up of two cycles which are the citric acid cycle (krebs cycle, tricarboxylic acid cycle/TCA cycle, etc.) through which Acetyl-CoA is metabolized (from the pyruvate from glycolysis). This produces CO2, 3 NADH, 1 FADH2, 1 GTP per turn of the cycle. The second part of oxidative phosphorylation occurs in the mitochondria. This is where all of the electron carriers go namely FADH2 and NADH to donate their electrons to a series of ferrous (iron containing) proteins. These proteins pump hydrogen ions across one of the membranes of the mitochondria and then the gradient coupled with an enzyme (ATP synthase) to produce ATP. Approximately 3 ATP are produced for every NADH and 2 for every FADH2.

Oxidative phosphorylation is why we are alive. It has the capability to produce massive amounts of energy from organic compounds.
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Last edited by Steven Low : 07-12-2008 at 09:59 PM.
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Old 07-12-2008, 09:56 PM   #2
Steven Low
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Re: physiology of energy pathways and implications

How do these energy systems work... in tandem?

In reality, these pathways are not as distinct as they appear to be. EVERY pathway is working at ONCE all of the time. As you can recall from our nice example in “What is fitness” from CF journal (http://www.crossfit.com/cf-download/CFJ-trial.pdf), we have a scenario where all 3 pathways are working from the getgo as they actually do, BUT the changes that occur only affect where the majority of energy contribution is coming from.

Note: keep that CFJ handy (or at least the picture I am talking about) – I will be referring to it many times within this article.

These pathways however are still distinct. Let me explain in a lot of detail. This is what is tripping up most of you.

1.Each energy pathway contributes the MAJORITY of energy GENERALLY in proper order – PCR then glycolytic and then oxidative phosphorylation. For example, in a 400m run, first PCR contributes the majority of energy (although we have concurrent energy from glycolytic and oxidative), as PCR starts to run out, the glycolytic cycle kicks up a notch to as glycogen stores are used in the muscles to fuel glycolysis for a lot of energy. As this system runs out (~250-300m into the run where you hit that “wall”) the oxidative kicks strongly into gear to donate the rest of the energy to finish the race. All the while as the picture on page 2 in CFJ “What is fitness” indicates ALL pathways are still working; it's just a hybridization of when each produces most of the energy for the workload.

The one “major” exception to this is “cardio” which is an interesting phenomena. If, for example, you are training at 60% VO2max for long periods of time, the body tends to not cut into glycogen stores as much as it normally would and strongly hybridizes it's energy output with oxidative phosphorylation via fat metabolism (metabolism of fat occurs as fatty acids are metabolized partway into glycolysis for glycerol and into CAC/TCA/kreb's cycle for the fatty acid part as Acetyl-CoA). This “steady state” cardio does not really produce any adaptations to it because it is not intense, but it does have the “usefulness” of directly burning fat stores which many people think is good. But this is a discussion for another time.


2.The energy pathways are intensity time dependent AND non-time dependent according to their energy stores. Now, before you get your panties in a bunch let me explain this in depth.

Each energy system has a limited amount of energy except oxidative. For example, your muscles can ONLY hold so many molecules of PCR. The same is true for glycolysis with glycogen storage in the muscles. Since there is a limited supply of energy for each of these pathways, burnout occurs rapidly as we already noted previously in “how they work.”

Now, here is where intensity comes in. The higher the intensity, the higher the need for energy. Therefore, the higher the intensity the faster PCR stores and intramuscular glycogen stores burn out. Thus, the faster there is a significant contribution of oxidative/aerobic pathway to energy for exercise. Physiologically this has huge implications. For example, if you approach a workout such as Fran at 10% intensity, it might take 10 minutes before you deplete PCR and glycogen stores within muscles. Thus, it will become predominately oxidative/aerobic ~9 or so minutes into the workout. If however we approach Fran at say 50% intensity, it may only take 3-4 minutes to burn out the stores, and thus becomes predominately aerobic within 2-3 minutes. However, if approach it at 100% intensity, it may take a minute or a bit less to burn out the two energy pathway's stores. Therefore, we have an example of where a workout becomes oxidative/aerobic extremely quickly.

Don't believe me? Well, screw you. Just kidding. But seriously for example this study (http://www.ingentaconnect.com/conten...00002/art00010) confirms approximately 40/60 ratio of aerobic/anaerobic energy ratio in trained 400m runners and 60/40 ratio for 800m (higher in women most likely due to smaller amount of musculature = less PCR/glycogen stores = more dependence on oxidative/aerobic metabolism for energy). For world class runners one would expect that there is a higher contribution of aerobic energy for these events because it is burned out more quickly at higher intensity. For those of us who are more novices or untrained, expect that the energy contribution is lower because the overall intensity is lower.

Note: This does not take into account relative intensity to one's own fitness level... this also plays a strong factor as well but we will not discuss this as it applies in the same concept as the above paragraph on intensity. For example, if my record in the 400m is say 60s as fast as I can, then if I run it 60s I will have done 100% intensity relative to my fitness. This will burn me out fast aerobic pathway will be reached quicker than say if I had run it in 70s. IF for example, we are comparing my 100% intensity to Michael Johnson's 100% intensity 43.18s he will obviously burn out his energy much sooner than I would on the track even though we are both going at 100% intensity. Therefore, the contribution of both relative and absolute intensity are both factors.

This creates a situation where intensity is the predominate factor on the “oxidative/aeroboic-ness” of the workout. Thus, for those complaining about the games lacking a longer workout I am basically calling bull**** on you. Any one of the workouts involved at CF games as the people actually competing can tell you were significantly taxing in all energy pathways. Since all of the workouts themselves are heavily aerobic why exactly do we need a long duration workout? Sure not because it's any more “aerobic” than the actual events that went on.

The one thing I skipped is that there is significant stores of glycogen located within the liver. However, they are not quickly mobilized especially during high intensity activity. Only over long durations can they be significantly depleted (such as marathon where you hit the “wall” at 20-22 miles). If you want to read more about oxidative/aerobic refer to these posts:
http://www.board.crossfit.com/showpo...7&postcount=19
http://www.board.crossfit.com/showpo...7&postcount=20

In the above threads I have one last note which is rate of breath. While it is not necessarily the most accurate indicator of how much energy we are using aerobically, as stated in there, heavy breathing and a quick rate of breath do indicate significant turnover of oxygen and CO2 which are critical for aerobic/oxidative energy production. So when you find yourself roasted after that metcon that only took 2-3 minutes, KNOW that you worked yourself aerobically. A lot.
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Old 07-12-2008, 09:57 PM   #3
Steven Low
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Re: physiology of energy pathways and implications

Implications of energy systems on how we train.

Now that we have clarified how these pathways work. How are they distinct? Well, one of the threads I was irked had the thread title “Translating anaerobic capacity to endurance.” The very premise of the statement is wrong. Anaerobic capacity as defined as the glycolytic pathway is distinct from it's oxidative/aerobic counterpart. Thus, increasing glycolytic pathway capacity for example such as running 100m WILL NOT EVER produce an increased aerobic capacity. Ever.

This is a fundamental concept. Even though the pathways themselves overlap in providing energy they are distinct from each other. Each has their own set of adaptations:

A. Anaerobic being on the side of type hypertrophy dominance of type IIb fibers, modification of type IIx fibers towards power by increasing contractile potential & glycolytic ability, increases in glycolysis enzymes, increases in glycogen stores, etc.

B. Aerobic adaptations include increases in oxidative enzymes in TCA/CAC/kreb's cycle, increases in mitochondria, aerobic modification of type IIx fibers to increase mitochondria & work like type I, hypertrophy of type I fibers, etc.

As you can see, there is no “interconversion” of energy pathways. Each one is distinct with its own mechanism and adaptations. Increasing capacity of anaerobic pathway will only help with increases in anaerobic energy only. Never aerobic capacity.

Now, when we look at something like CF which includes HIIT/metcon/tabata we have the scenario where we are obviously hitting all 3. If we are interesting in increasing aerobic capacity such as for running, there are multiple ways we can go about this. For example:

1.Ignore CF completely and do longer runs. This does not necessarily mean LSD (long slow distance) as generally this will not produce good adaptations versus long distance runs where you push yourself. Basically, long runs where you push yourself.

2.We can shorten the rest times between intervals. This will increasing average power thus increasing intensity = more energy needed = burn through PCR/glycogen faster = better adaptations aerobically.

3.We can also push ourselves harder = increase intensity = and so on. This can be done, for example, with scaling down a heavy weight to blast through a workout more quickly. Although heavier weight with a scaled down reps “metcon” can produce similar adaptations as well (see Gant's hybrid programming for more info).

4.We can add on more work... which seems to be the case with CF's metcons now. Unfortunately, with newer people this does not help as because they cannot sustain intensity as long as those monsters with already high work capacity such as those who won the CF games.

Anyway, there's probably some more I'm forgetting, but there's multiple ways to make workouts more aerobic much of which have to do with increasing intensity, length or such modifications. It does not necessarily have to be running.

On the discussion of running though it is a good idea to actually DO your sport or if you are training for something to do it. Don't just rely on energy systems. The body must also adapt to the exercise by becoming more efficient muscularly and movement pattern-wise to perform well. So if you're looking to train for a 5k or 10k and get a good time, you probably will have to run more than CF prescribes. However, if you just want to complete it with a decent time CF will get you there.

If, however, we are looking to bias towards power or strength, we generally want to cut to do the opposite of what we did with aerobic. (1) Increase rest times = better recovery = higher intensity = better power. (2) Cut down the volume to make the most out of a power session without training it metabolically. (3) Push ourselves harder in training, less in rest breaks. For example, HIIT instead of running and jogging we can go to sprint and walking or sprint and standing.

In any case, I wrote this thread a while ago (http://www.board.crossfit.com/showthread.php?t=24418) pretty much on how I disagree with CF as good for elite athletes in power, strength and endurance biased sports. For those looking to get an edge, doing CF is not good as the metcons themselves provide great training through all 3 energy pathways. As argued (correctly I might add) in the thread, the moment we start unbiasing our training towards say 100m by doing significant energy systems work through a metcon, the increases in aerobic adaptations through enzymes, mitochondria, type I fibers, etc will all inevitably bring down our sprinting ability. This is not clearly not wanted.

-----------------------------------------------------


And in conclusion.. or something

Thus, as you might have read recently in this thread (http://www.board.crossfit.com/showthread.php?t=34277) CF is definitely not for everyone especially the athletes in the above paragraph who need their bodies and energy systems geared specifically to their athletic endeavor. Telling that that CF is useful to them (which it is not) is just disrespectful to their training because it will hinder them from achieving what they (hopefully want) athletically.

It is, in this respect, that I write this post. Though CF is a fitness program, I don't think anyone can doubt that most of the program itself is based upon movements done at high intensity across various broad modal domains or whatever. Basically, metcons most of the time. I am not criticizing the program because I know it has helped a lot of people and believe it will continue to do so; however, I would just like you to ask yourself what exactly are you training for? Like Brandon said in the above thread.. do you really need the fitness that CF gives? Find something you enjoy to do. If CF is it then great. If you want to get more involved with Oly or gymnastics go for it. Find out what you want to do and do it; don't just strive for fitness because it's CF. Make this about yourself, not what CF has done for you. Every program is a tool in the toolbox for you to use to attain your goals. If you don't have any do some self introspection and then get on that.


Thanks for listening and goodbye.

Steven Low
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Old 07-13-2008, 05:02 AM   #4
Scott Borre
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Re: physiology of energy pathways and implications

Excellent post Steven. Very informative, I really appreciate it. Sorry to see that you don't want to post here anymore. I feel that some threads have had some excellent discussion as of late.
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Old 07-13-2008, 07:58 AM   #5
Benjamin Walsh
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Re: physiology of energy pathways and implications

Thanks Steven. I've learned a great deal from many of your posts. You will be missed.
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Old 07-13-2008, 08:11 AM   #6
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Re: physiology of energy pathways and implications

Excellent.
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Old 07-13-2008, 09:13 AM   #7
Ari Kestler
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Re: physiology of energy pathways and implications

this might deserve it's own thread, if so I'll start a new one, but my biggest problem is that I have no goals. I don't really know what my goals are.... there are some things I want to work towards cause I think they would be neat to accomplish, but otherwise, I have no goals.

Help?
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Old 07-13-2008, 09:33 AM   #8
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Re: physiology of energy pathways and implications

New thread, Ari.
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Old 07-13-2008, 10:17 AM   #9
Steven Quadros
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Re: physiology of energy pathways and implications

Wonderful read; your ability to distill information is most noteable Steven. I have a feeling that you are not the only one whose time spent on this board will begin to wane.

See you elsewhere, however, as I've already started my P-menu account.
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Old 07-13-2008, 05:45 PM   #10
Phillip Garrison
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Re: physiology of energy pathways and implications

Quote:
Originally Posted by Steven Low View Post
Implications of energy systems on how we train.

Now that we have clarified how these pathways work. How are they distinct? Well, one of the threads I was irked had the thread title “Translating anaerobic capacity to endurance.” The very premise of the statement is wrong. Anaerobic capacity as defined as the glycolytic pathway is distinct from it's oxidative/aerobic counterpart. Thus, increasing glycolytic pathway capacity for example such as running 100m WILL NOT EVER produce an increased aerobic capacity. Ever.

This is a fundamental concept. Even though the pathways themselves overlap in providing energy they are distinct from each other. Each has their own set of adaptations:

A. Anaerobic being on the side of type hypertrophy dominance of type IIb fibers, modification of type IIx fibers towards power by increasing contractile potential & glycolytic ability, increases in glycolysis enzymes, increases in glycogen stores, etc.

B. Aerobic adaptations include increases in oxidative enzymes in TCA/CAC/kreb's cycle, increases in mitochondria, aerobic modification of type IIx fibers to increase mitochondria & work like type I, hypertrophy of type I fibers, etc.

As you can see, there is no “interconversion” of energy pathways. Each one is distinct with its own mechanism and adaptations. Increasing capacity of anaerobic pathway will only help with increases in anaerobic energy only. Never aerobic capacity.

Now, when we look at something like CF which includes HIIT/metcon/tabata we have the scenario where we are obviously hitting all 3. If we are interesting in increasing aerobic capacity such as for running, there are multiple ways we can go about this. For example:

1.Ignore CF completely and do longer runs. This does not necessarily mean LSD (long slow distance) as generally this will not produce good adaptations versus long distance runs where you push yourself. Basically, long runs where you push yourself.

2.We can shorten the rest times between intervals. This will increasing average power thus increasing intensity = more energy needed = burn through PCR/glycogen faster = better adaptations aerobically.

3.We can also push ourselves harder = increase intensity = and so on. This can be done, for example, with scaling down a heavy weight to blast through a workout more quickly. Although heavier weight with a scaled down reps “metcon” can produce similar adaptations as well (see Gant's hybrid programming for more info).

4.We can add on more work... which seems to be the case with CF's metcons now. Unfortunately, with newer people this does not help as because they cannot sustain intensity as long as those monsters with already high work capacity such as those who won the CF games.

Anyway, there's probably some more I'm forgetting, but there's multiple ways to make workouts more aerobic much of which have to do with increasing intensity, length or such modifications. It does not necessarily have to be running.

On the discussion of running though it is a good idea to actually DO your sport or if you are training for something to do it. Don't just rely on energy systems. The body must also adapt to the exercise by becoming more efficient muscularly and movement pattern-wise to perform well. So if you're looking to train for a 5k or 10k and get a good time, you probably will have to run more than CF prescribes. However, if you just want to complete it with a decent time CF will get you there.

If, however, we are looking to bias towards power or strength, we generally want to cut to do the opposite of what we did with aerobic. (1) Increase rest times = better recovery = higher intensity = better power. (2) Cut down the volume to make the most out of a power session without training it metabolically. (3) Push ourselves harder in training, less in rest breaks. For example, HIIT instead of running and jogging we can go to sprint and walking or sprint and standing.

In any case, I wrote this thread a while ago (http://www.board.crossfit.com/showthread.php?t=24418) pretty much on how I disagree with CF as good for elite athletes in power, strength and endurance biased sports. For those looking to get an edge, doing CF is not good as the metcons themselves provide great training through all 3 energy pathways. As argued (correctly I might add) in the thread, the moment we start unbiasing our training towards say 100m by doing significant energy systems work through a metcon, the increases in aerobic adaptations through enzymes, mitochondria, type I fibers, etc will all inevitably bring down our sprinting ability. This is not clearly not wanted.

-----------------------------------------------------


And in conclusion.. or something

Thus, as you might have read recently in this thread (http://www.board.crossfit.com/showthread.php?t=34277) CF is definitely not for everyone especially the athletes in the above paragraph who need their bodies and energy systems geared specifically to their athletic endeavor. Telling that that CF is useful to them (which it is not) is just disrespectful to their training because it will hinder them from achieving what they (hopefully want) athletically.

It is, in this respect, that I write this post. Though CF is a fitness program, I don't think anyone can doubt that most of the program itself is based upon movements done at high intensity across various broad modal domains or whatever. Basically, metcons most of the time. I am not criticizing the program because I know it has helped a lot of people and believe it will continue to do so; however, I would just like you to ask yourself what exactly are you training for? Like Brandon said in the above thread.. do you really need the fitness that CF gives? Find something you enjoy to do. If CF is it then great. If you want to get more involved with Oly or gymnastics go for it. Find out what you want to do and do it; don't just strive for fitness because it's CF. Make this about yourself, not what CF has done for you. Every program is a tool in the toolbox for you to use to attain your goals. If you don't have any do some self introspection and then get on that.


Thanks for listening and goodbye.

Steven Low
Good post Steven, very thorough summation of the energy pathways.
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