The 'muscle burn' is due to the neural ( nerve ) irritation associated with an altered pH within the worked muscle the altered pH ( acidity ) is due to a multitude of increased metabolic waste products accumulating in the exercised muscle.

When energy is required to perform exercise it is supplied from the breakdown of Adenosine Triphosphate (ATP). The body has a limited store of about 85g of ATP and would use it up very quickly if we did not have ways of resynthesising it. There are three systems that produce energy to resynthesise ATP: ATP-PC, lactic acid and aerobic.
The lactic acid system is capable of releasing energy to resynthesise ATP without the involvement of oxygen and is called anaerobic glycolysis

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This is paraphrased from page 38 of Triathlete's Training Bible by Joe Friel (1st edition)

Build Up of Lactic Acid

To produce energy for movement, fat and carbs are used as fuel. when carb break down lactic acid is formed. As it leaves the muscle and enters the blood hydrogen ions are released the resulting salt is lactate. More intensity, more lactate. At low levels the body can remove it, at higher intensity the body can noot keep up.

When you go from aerobic to anaerobic the bodies production of lactate exceeds its ability to recycle it. It accumulates in the blood interfering with energy production and muscular contraction, causing fatigue.

Because the "lactate" is a salt in your blood stream it may very well cause a burning sensation. This is my opionon, I couldn't find facts to back it up. It just seems to make sense to me, put a bit of salt on a cut and tell me if it burns.

Well I'm off to work this thing will be three pages long by the time I get home.

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Jim

**Note above poster works for a retailer selling bikes and related gear*

If I'm reading Tom's question right (and I don't want to derail it if I'm not, so ignore me if I'm off here), another way of saying it is - what is the life cycle of lactic acid as a function of training intensities? When is it produced, and why, and how does it behave at the various intensities we exercise at? In other words, what's the complete picture of this often maligned chemical?

I agree that we do oversimplify it. Popular opinion is that it's bad (I picture unfrozen cave-man lawyer "Acid bad!"), and we train at high intensities in order to enhance some nebulously understood system of "flushing it out."

The fact that we actually metabolize it makes it much more complex, so I'm very interested to hear what the pros have to say too.

Sleestack!!!!!! Awsome handle baby. God your bringing back memories of Saturday mornings, huge bowls of Fruit Loops to fuel the BB gun fight later and me and 5 or 6 of my friends hoping Manudo doesn't sing a song on ABC.

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customerjon @gmail.com is where information happens.

Thanks Tibbs! Yeah, I have similar memories, only my drug was cocoa puffs.
As a former swimmer, for years my running was very sleestack-like. Now I'm a slightly faster sleestack.

I tend to equate that word not with a "burning" sensation so much as an "enlightened" sense of being. Coincidentally, while out riding, when there is just the right amount of acid in my legs, and the base that is air flowing through my lungs, I feel like I'm floating up the hills.

[reply]Sleestack!!!!!! Awsome handle baby. God your bringing back memories of Saturday mornings, huge bowls of Fruit Loops to fuel the BB gun fight later and me and 5 or 6 of my friends hoping Manudo doesn't sing a song on ABC.[/reply]

Bill Laimbeer was one of the Sleestacks. Just a bit of useless trivia.

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Just Triing
Triathlete since 9:56:39 AM EST Aug 20, 2006.
Be kind English is my 2nd language. My primary language is Dave it's a unique evolution of English.

Pluto is right in that the pain associated with increased lactic acid levels is due to the increase in hydrogen ion and therefore acidity within the muscle. As far as LA being taboo, it is multifactoral and quite complicated. Yes, lactate can be transported to the liver for storage as glycogen to be turned in to glucose for more energy (gluconeogenesis). It can also be shuttled about the muscle fibers and converted in to glucose for immediate energy use. So, to use the analogy of a car's engine, the lactate shuttle works like a turbo charger, it recycles a by-product to get more energy. Think of the pain associated with high intensity levels as one of your gauges. Other things you monitor are HR and respiration. Make any one of these items "redline" and you are going to crap out just like running your motor at too high of an oil pressure or temp. Want to got faster for longer, then build a larger engine with more horsepower (VO2max), then you can run at the same pace without redlining or running near your theshold level. Or, become more efficient by training at or above/below threshold and increasing the enzymes and muscle constituents that help promote the sparing of glucose and aid in encouraging gluconeogenesis.

Also, the entire system of energetics (and most systems in the body) works off of feedback similar to your home thermostat. As acid levels change, your body will increase or decrease various organ activity. As acid levelds increase, HR and respiration increase = more blood and O2 to the muscles = good. Go too hard and the systems can't keep up = too much acid = pain = bad thing. Depending on the length of the bout of exercise, you might be able to sustain pace and endure the pain. Otherwise, slow down or crap out. Other body systems can also cause you to slow down such as the central nervous system, thermoregulatory system, ... It's a mess.

Sorry for the incoherent rambling, but I'm in a hurry and did not have time to organize my thoughts.

I read in an article somewhere that the prefered fuel for cardiac muscle is lactic acid (lactate). That goes along with one of the other posts as far as "turbo charging". The heart can take a lot of it while it is the other muscles that wimp out.

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Larry

Don't be afraid to ride too long or too hard. That's what cell phones are for. Rich Strauss

[reply]I read in an article somewhere that the prefered fuel for cardiac muscle is lactic acid (lactate). That goes along with one of the other posts as far as "turbo charging". The heart can take a lot of it while it is the other muscles that wimp out.[/reply]

The "preferred" substrate for cardiac energy production is lactate? Reference please? Because it may be better adapted to use it than other muscles for survivability reasons doesn't mean it is preferred. When substantial lactate is present pH is changed which affects (adversely) the confomation of enzymes making them less efficient.

Lactic acid production is not good for the athlete under any circumstances as it adversely affects performance despite some of these totally theoretically possibilities. This is a crazy thread.

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Frank,
An original Ironman and the Inventor of PowerCranks

It's interesting how you voluntarely show your ignorance in many subjects.

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"Yeah, no one likes a smartass, but we all like stars" - Thom Yorke


smartasscoach.tri-oeiras.com

Hmm.... where to start, well, first off lactic acid is not bad, in fact the acidification elicited as a result of lactic acid production is also not bad, and has been shown to protect muscle during intense contractions. With regard to the pain associated with lactic acidosis, numerous metabolites have been proposed to be responsible for this pain, including hydrogen ion, but none have been conclusively implicated.

We produce lactate at rest and elevated levels of lactate during intense exercise are not an indication of lactate killing our muscles or causing damage, but rather and indication that glycolytic (CHO/glucose) metabolism is increasing to the point that the end product (pyruvate) cannot be further broken down to yield energy in the mitochondria. For a number of biochemical reasons, lactate is produced to allow muscular activity to continue. As I wrote previously, that lactate can be used for energy within the muscle if intensity of activity is reduced. At the same time, it appears as though the lactic acid produced under these conditions maintains the electrochemical balance of the muscle, enabling contractions to occur when they otherwise might not due to inability to depolarize. If the lactate is not used in the muscle it is produced within, it can be exported to the heart or other less active muscles to be used as fuel. A prime example of this is the fact that during extended cycling bouts at low intensity, glycogen from the arms (which is not being used directly for energy) is broken down to lactate, released into the blood and then used to fuel heart or muscle, or transported to the liver. Lastly, lactate that has been exported from the active, or inactive, muscle can be transported to the liver and converted to glucose, to help maintain blood glucose levels.

So, reasons lactate is good:

1) enables metabolism to continue when mitochondria cannot handle more lactate

2) protects intensely contracting muscle from electrochemical imbalances that would result in fatigue

3) used for energy during recovery

4) used for energy in heart, less active muscle

5) used to make glucose in the liver and preserve blood glucose

Reasons lactate is bad:

1) causes pain -NO

2) causes muscle damage -NO

3) causes cramping -NO

So, in the words of Unfrozen Caveman Lawyer "Lactate Good". "But I still can't understand your modern fying machines."

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Steve

http://www.PeaksCoachingGroup.com

I always thought that the production of lactic acid was one of the many defense mechanisms in the body, IE, when working your muscles and working them too hard for your body and to keep from injuring yourself the body produces lactic acid to aid in stopping you from injuring itself. And it works, once lactic acid is released it is hard to keep excersizing.

When working out with weights they always say keep going to the burn and feel the burn, thats how you know that youve exhausted your muscles, I usually feel this when working shoulders and doing light weight shoulder workouts and high repetitions with a dumbell, once ive hit the lactic zone I stop because I cant do anymore unless I have a spotter, and then I usually cant lift anything for about an hour afterwards. Light weight and high repetitions is the only way for me to excite the lactic acid flow.

I dont know about all the above posts, that kinda thinking is way above my paygrade

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I have horrible back problems but I have zero problems staying in an aero position for 180k. Why? Because I ride steep and because I train regularly in that position. Simple as that.....Gerard

I take it you can see no bad from the production of lactic acid, in any amount. I would accept that increasing acidosis does increase the extraction of oxygen locally in the short term but, lactic acid is buffered primarily by the bicarbonate system before one ends up with lactate. This is the real problem with lactic acid. For the same number of ATP (which is substantially reduced per glucose when lactate is the end result) there are about 10 times as many CO2 molecule produced. The lungs are not capable of getting rid of this amount when one is exercising at almost any level such that the total pH of the body is lowered and it just shuts down. If it didn't 400 meter racers would race at 100 meter pace. In fact, we would do the IM at 100 m pace. It don't happen and it is because of Lactic acid, not lactate. Lactate is benign (after all, we infuse lactate in IV's - ringers lactate - commonly, even in the very sick but we don't normally infuse lactic acid)

Don't talk about lactate. Talk about lactic acid. That is is the problem.

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Frank,
An original Ironman and the Inventor of PowerCranks

When your credentials match mine I would be happy to discuss the issue of ignorance of topics within the relm of my training. Now, when it comes to math I bow to Francois and aknowledge my ignorance of the esoteric.

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Frank,
An original Ironman and the Inventor of PowerCranks

Lactate production coincides with and retards exercise acidosis. Lactate (which is deprotonated) acts as a base, not an acid, by taking up accumulating Hydrogen ions.

As such, blood lactate levels are a good indicator of exercise intensity and exhaustion. But it's highly improbable that lactate causes fatigue. More likely, it actually retards fatigue.

http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?cmd=Retrieve&db=pubmed&dopt=Abstract&list_uids=15308499

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Josef
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blog

If you're really interested, George Brooks (Cal Berkley) has published more on lactate metabolism than anyone else on the planet.

The following text is a classic.

http://www.amazon.com/...s=books&n=507846

uh oh??!!!

maths are anything BUT esoteric...

HMMMMMM, as I re-read the above posts another thought has come to mind, What is lactate Threshold?????? It seems to me that with all the doctors on this thread that lactate is a fuel source and that may well be when excersizing at the lactate threshold, because at the threshold it is the begining of what is to come, but if you exceed it and proceed down the valley of no return then your body is going to produce a burn that will make you shut down and stop what your doing and not allow you to do what youve been doing for quite a while. I guarantee that if you experience this burn that you will not be able to cycle another inch much less return to your car, ha, but what this burn is was always commonly refered in the weighlifting community as lactic acid burn, perhaps we were wrong and its something else, I dont know, perhaps the "OTHERS" on this thread can expound on this and enlighten me.

.

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I have horrible back problems but I have zero problems staying in an aero position for 180k. Why? Because I ride steep and because I train regularly in that position. Simple as that.....Gerard

[reply]Lactate production coincides with and retards exercise acidosis. Lactate (which is deprotonated) acts as a base, not an acid, by taking up accumulating Hydrogen ions.

As such, blood lactate levels are a good indicator of exercise intensity and exhaustion. But it's highly improbable that lactate causes fatigue. More likely, it actually retards fatigue.

http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?cmd=Retrieve&db=pubmed&dopt=Abstract&list_uids=15308499[/reply]

From the abstract: It is only when the exercise intensity increases beyond steady state that there is a need for greater reliance on ATP regeneration from glycolysis and the phosphagen system. The ATP that is supplied from these nonmitochondrial sources and is eventually used to fuel muscle contraction increases proton release and causes the acidosis of intense exercise. Lactate production increases under these cellular conditions to prevent pyruvate accumulation and supply the NAD(+) needed for phase 2 of glycolysis. Thus increased lactate production coincides with cellular acidosis and remains a good indirect marker for cell metabolic conditions that induce metabolic acidosis. If muscle did not produce lactate, acidosis and muscle fatigue would occur more quickly and exercise performance would be severely impaired.

This restates what I said before. If lactate was not produced when lactic acid was produced that would mean there was no buffering system and exercise intensity would certainly be affected. However, lactate itself does not improve anaerobic exercise ability as infusing lactate would have no effect on this. The real problem, however, is when lactic acid is produced and it is buffered by the bicarbonate system (resulting in lactate) for each molecule of lactate produced one CO2 is produced. The problem for the athlete is not the production of Lactic acid or lactate or anything else but the amount of CO2 produced when lactic acid is buffered, which overwhelms the bodies elimination mechanism (lungs) resulting in acidosis. If the CO2 production is under the elimination X amount then the body compensates for the lactate production fine because the excess CO2 can be eliminated and pH will remain "normal" for a long period of time. The higher it is above X amount the faster the excess acid accumulates and the faster the body fails.

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Frank,
An original Ironman and the Inventor of PowerCranks

[reply]uh oh??!!!

maths are anything BUT esoteric...[/reply]

beauty, as esoteric, is in the eyes of the beholder.

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Frank,
An original Ironman and the Inventor of PowerCranks

allright, this may have already been answered, but if not, here's what's going on. Lactic acid is a byproduct of anaerobic respiration. as fuel (glucose) enters glycolysis (the first step the six carbon glucose goes through in it's catabolism), it forms pyruvate. This pyruvate has two options. in aerobic respiration, the pyruvate will enter the TCA cycle giving you about 36 ATP molecules that will be used for energy. in which case there is not enough oxygen in your bloodstream to be able to enter aerobic respiration, your metabolism will enter into anaerobic respiration. basically, the TCA cycle gets backed up b/c the body does not have enough oxygen to process all of the products in the TCA cycle. instead, the pyruvate goes into anaerobic respiration, forming lactic acid. in this transformation, a byproduct is formed (NAD). this byproduct is required regardless to allow glycolysis (which is a minor energy producing process) to continue. by allowing glycolysis to continue, more energy is being produced (even though it is in relatively low proportions to aerobic respiration.) on your other point, lactic acid DOES NOT cause muscle soreness. it does make your muscles formed, because the NAD is formed from NADH, so when the NADH is transformed, it loses a hydrogen, thereby raising the acidity of your blood. however, if anybody believes that lactic acid causes muscle soreness, they failed exercise physiology ;)

Are we talking about your quack credentials?

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"Yeah, no one likes a smartass, but we all like stars" - Thom Yorke


smartasscoach.tri-oeiras.com

no, it doesn't restate what you're saying. You said above that lactic acid production negatively affects performance.

They're saying, it doesn't.

It's not the lactic acid that's the problem. It's the hydrogen ion.

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Josef
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blog