Lactic acid not the cause of muscle fatigue?

doctorSpoc

yes, but the ratcheting up of pain is very effective at limiting how much you can go beyond and for how long from the onset of pain... you are still limited, you can still only go so far beyond when the pain starts.. and what if nature factors in a bit of a buffer incase the organism is hard headed? so you are safe... so nature brings the real pain at 200 but damage doesn't really start 'til 225... but take the drug and you start feeling pain at 220 and can dig deep and get to 240.. denaturing the protiens in your leg muscles, causing permanent nerve damage.... who knows? nature doesn't usually just put limits on things like this just for kicks.... usually there is a really good reason. i mean think about it... a faster organism with greater endurance would likely be a more successful organism, so nature would limit this for nothing.

doctorSpoc

one point... it seems like this is a possible mechanism for the muscles actually getting weak... not necessarilly the mechanism for a feed back loop that causes you to be in pain... that could be a related but completely separate mechanism... e.g. this could be just one many hundreds of signals that causes your brain to sense pain and slow you down.

Urkiola2

Lactic acid (2-hidroxipropanoic acid) is dissociated at a physiological pH to an anion of lactate (C3 H3 O3-) and a proton of Hidrogen (H+). That is, lactic acid is produced in the cytosol and then when in contact with interstitial fluid and of course with blood is dissotiated and converted to lactate. There are several theories about fatigued caused by lactate. However nowadays is been for a few years widely accepted that lactate per se does not cuase muscle fatigue neither acidosis, but the (H+) associated to lactate are the ones who cause acidosis. This can be caused from Lactate production and probably by an excess of ATP hydrolysis as well.

That is about "acidosis". Lactate is an indicator and probably an indirect contributor for that. A differnet thing is musce fatigue. There are many theories about it and still none of them has been fully proven. However Dr. Marks' research opens as Dr. Brooks says an "exciting and provocative"claim.
The study is based in the calcium channels leak in the heart muscle. It is thought that (H+) interferes with exitation-contraction coupling by competing with Ca++ for the binding sites of troponin C an therefore with muscle contraction. However the finding by Dr. Marks was that blocking those calcium channels leakage through a drug would diminish the degree of fatigue, though maybe there is something else different than Ca++ and insetad of (H+) competing with Ca++, maybe both are competing with something else...

Anyways. This finding still has to be proven with humans and with skeletal muscles instead of cardiac muscles.

To me, one thing is for sure. Lactate is a sure indicator that something is not going well within the muscles, whatever you want to name it fatigue or acidosis...but the real thing is that those whose blood lactate leves are lower will be performing better than those whose lactate levels are higher and their time to exhaustion (for whatever the cause could still be investigated) will be earlier.

Cheers.

Urkiola2

Very good point.

TheDarkLord

So, if I am understanding you correctly, when we feel muscle fatigue, there is lactic acid build-up, but that is not what causes the fatigue. Is that right, or am I misunderstanding you?

sogood

But there's no evidence that the pain experienced through these efforts are causing any permanent damage to the muscles. All we know at this point is that micro tears may be induced within the muscle mass and the resulting inflammatory repair process actually promotes hypertrophy, micro-vascularization and positive adaptation of the involved tissue, muscle in this case (just think of all those growth promoting factors being released). So in the end, it's actually leading to an improvement.

PS. Proteins don't denature just because you are working your muscles hard, nor do nerve endings get damaged under these circumstances. Yes, people in the medical field do know about these, no need to guess.

__________________
Morphed Bianchi Camaleonte IV 2006, Ridley Damocles 2006, Garmin, Mac

Urkiola2

Lactate is an "indicator" that something is going "wrong" but not necessarely the cause. It is like when you see smoke coming out of your engine...the smoke is not the cause but it is an indicator that some mechanism is not going good. I know it is a bad example but you may know what I mean.

doctorSpoc

i though this was very good...

"A simple but ill-defined theory
To blame lactic acid for muscular fatigue satisfies the simplistic logic that commands us to find a reason for every problem. And when we've gone as far as blaming something for a particular problem, why not accuse it of being liable for as many problems as possible? This approach offers many advantages. For one, we can avoid having to figure out the cause of each problem. For those who do not want to bother pondering on the process of fatigue, lactic acid is the perfect scapegoat. Nevertheless, reality is more complex than that.
In truth, the concept of a muscular fatigue does not exist; we should rather speak of muscular fatigues. Despite the fact that the outward signs of these fatigues may be the same (they make continued effort impossible) the fatigue felt by a 400m runner is not the same as that felt by a marathoner, which in turn is not the same as that felt by a body builder or a mountain-bike specialist, and so on. It would be naive to think that lactic acid is the only villain responsible for these varied forms of muscular fatigue.
We find that between the brain's neurons (which send out the motor commands) and the muscles' myofilaments (which carry out these commands) there are several links in the information transmission chain that allows for power output. Any of these links can fall short in its task and so block the continuance of muscle contraction and exercise. Thus, these links appear on the long list of possible suspects in the development of the different types of fatigue. This list might, in some cases, include lactic acid. However, it is undoubtedly not the sole or even the main culprit.
Many research studies have shown that lactic acid is, in the end, only marginally responsible for muscular fatigue. As some of these arguments are quite complex, they will not be discussed here; we will only highlight that the most recent reviews on the subject all point to the conclusion that "The disturbance of the balance of the skeletal muscle acid base is not as critical a factor as is sometimes suggested" (FITTS, 1996; JONES et aI., 2003; PERONNET and MORTON, 1994; PERONNET and THIBAULT, 2005, ROGBERGS et aI., 2004; SCHWANE et aI., 1983)."

and thought this was good too..

" The most convincing argument in this debate is that on the one hand it is possible to observe muscle fatigue while the lactic acid concentration in the muscle remains low and, on the other hand, observe an absence of fatigue when the lactic acid concentration in the muscle is high. For example, at the end of a 100km race, a particularly demanding event, the fatigue level is quite high but the blood lactate concentration is not much higher than in the resting state. Moreover, people who suffer from McArdle's disease are incapable of producing (and thus of accumulating) lactic acid and are very prone to suffering from muscular fatigue. Thus, muscular fatigue can be accompanied by a very low lactic acid level, or even with no lactic acid at all.
On the other hand, if one performs an exhausting isometric effort with the quadriceps (e.g. the 'chair exercise', with the back leaning against the wall), fatigue will tend to reduce strength temporarily. However, this fatigue rapidly fades and goes away almost entirely after a two-minute period of recuperation: after this period, the muscle can once again produce the initial power. When observing the degree of acidity in the muscles, we see that it has increased considerably during the isometric contraction, which might support the hypothesis that asserts lactic acid is responsible for fatigue. However, during the recuperation period, the degree of acidity in the muscles only returns to normal rather slowly. Hence, two minutes after completion of the exercise, the degree of acidity remains very high but since the muscle can once again produce its initial force, the fatigue is obviously gone (see Table 1). For this reason, it is difficult to embrace the idea that the increase in lactic acid in the muscle causes fatigue, since a high degree of acidity without fatigue can be observed."


http://www.coachr.org/lactate.htm


i link to some of the highlight of Brook's work...
http://www.berkeley.edu/news/media/...9_lactate.shtml

TheDarkLord

Thanks docSpoc! The second article gave a clear answer...

Urkiola2

Very good points as well. As for cycling goes, McArdle's disease is not an issue and As I have observed many times in pro cyclists after a stage race, where they feel lots of fatigue afterwards, their Lactate levels are not that high enough at all. However here we are talking about a different level of fatigue and I could be writing 1h about the different mechanisms which could be responsible for "endurance" fatigue. The point for lactate and "fatigue"or whatever we want to name it is that at high intensities, i.e. going up L'alpe D'huez a Pro cyclist on climbing on top is pedaling with lower blood lactate concentration.

Lactate is not an enemy, though as it is not only the MOST important gluconeogenic (the making of new glucose) source during exercise (70-80%) and therefore crucial for blood glucose homeostasis during exercise but also it it could be a "lactohormone" and have some hormonal-like properties/signals which could regulate intermediate metabolism.

doctorSpoc

don't think you are getting me... we are not talking about just working muscles hard, we are talking about working muscles at a completely unatural level that they would not naturally be able to work at because the body puts limits on the level.

pain prevents use from going over a certain level... for whatevery reason... we don't know. remove the pain and we are unfettered and are able to ride at levels not possible otherwise... this is a completely unatural level of performance and not at all normally possible... i'm not saying this WILL cause damage... just saying that it's a definite possibility because why else would the body put such limits?

the only way such an experiment could have been done is to remove the limiters on performance fatigue/pain.. and have someone ride/exercise at this completely unatural performance level.. since this insite on muscle fatigue is not yet known and this research we are talking about here is brand new and not tested on humans (skeletal muscles anyway).. how did they test this in ALL these experiments you are talking about... how did they prevent the experiment subjects from fatiguing or feeling pain? i can't see how it could be done and stay within ethical boundries.. can you point me in the direction of such research.. if it's some holocost stuff done by Dr Mengela... i don't want to see it.

sogood

The pain only tells you that you are working it hard but may not be an absolute indicator of where the limit should and will be. Yes, if you tore the muscle or a tendon, then that's a show stopper and will get a different kind of pain. But these intrinsic muscle pain we experience when working at our limits are a specific response to the level of exertion at that time point, and is perfectly reversible with a bit of recovery. So no, they are not going to cause any permanent damage. As said earlier, stresses of this type will bring about adaptation through the various complex cellular mechanisms.

Biological systems may have some overriding principles that govern their existence, but they are also a lot more complex than what some simple principles would lead you to believe.

__________________
Morphed Bianchi Camaleonte IV 2006, Ridley Damocles 2006, Garmin, Mac

doctorSpoc

in a way you are making my point... what if these addapations are mitigating to the damage and the accompanying pain... your body responds by allowing you to go past the level you were once limited to? i.e. starting the pain at a higher level of performance because the danger at that level no longer exist because of your new found addapations.

what if you don't feel pain after training for a few months at that higher performance level because your body has addapted in such a way that you body no longer needs to stop you at the lower level anymore? i.e. those addapations have made it so that it's no longer dangerous for you to ride at that higher level?

but... what if riding at that higher level for long periods of time without first addapting will result in damage to your muscles, nerves etc?

what if a muscle bathed in substance X for time Y starts to become denatured... what if nerves that are exposed to neurotransmitter Z for time Y is damaged.. exposer to chemical and heat denature proteins... these are both possibilities...

sogood

I'll say it again. Muscle proteins don't denature just through use under these conditions. You might care to find a better term for what you want to express.

You raised a lot of "what if". Well, most of your questions have already been answered by existing scientific knowledge and in actual sports training experiences. It's good to ask questions, but deriving at a conclusion based on hypotheticals without factual knowledge is getting close to religious believes.

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Morphed Bianchi Camaleonte IV 2006, Ridley Damocles 2006, Garmin, Mac