Hello again! It’s been a little while since my last post and I need to post for this week or I’ll be docked points from Dr. Myers. I’ve been a little bit behind on things as I’ve been preparing for my upcoming senior seminar, but I did have time to check out at least one cool article I found on different energy systems used while running.
I had a race today and I noticed that every time I do an 8k (5 miles), about three miles in I hit a wall of fatigue. I get dizzy, it’s hard to focus on the guy in front of me, driving my knee up feels next to impossible, and the only thing I care about is eventually getting to the finish line. I know that much of this is probably because I’ve depleted a good portion of my glycogen stores and have worn out my muscles fairly well. But how does this tie in with my nervous system?
According to the article, a good portion of my glycogen stores are found in my liver. If too much of the glycogen is used hypoglycaemia can occur resulting in brain damage. Other bodily harm such as myocardial ischaemia, heat stroke, and severe ATP depletion from my muscles can occur too if my body is allowed to be pushed far enough.
Luckily for me, my muscles have a built in negative feedback to stop me from killing myself out there. My muscles somehow know to send a signal up to the brain for a release of serotonin and inhibition of dopamine secretion, which results in a further lack of ability to move, which results in a slower time, which puts Morris on the backburner in terms of our men’s cross country team. I’m still wondering though, how do my muscles know when to signal my brain to cut back on the neurotransmitters? And how much does mentality (a positive attitude towards the race, or the expectation of a good run) play a role in the regulation of my muscles (do I release more ACh and endorphins by simply having a good attitude, or is the causality the other way around?)? Either way, if you haven’t moved in a while, get out and enjoy this great October weather while it lasts. Or you can check out this pretty funny link of a band I found on youtube.
Interesting.
I began running, and I actually run much shorter distances now that I’m taking anti-dpressant; i just walk the rest — the thrill is gone after about 2 miles. The drug is a combo serotonin and neuroepenephrine uptake inhibitor. So maybe my brain’s response to natural serotonin “whoa” release is amplified?
Hm.
There’s actually quite a bit of information about runner fatigue as it becomes an issue for endurance athletes. I’m in training for my 4th marathon and if you ask any marathoner, the wall is reached around mile 20 when, for most humans, the bodies available glycogen store runs dry; marathons are just over 26 miles. Hitting the wall or “bonking” is both psychologically and physically debilitating, though rarely is it lethal (it only feels that way). Replenishing with carbs and H20 a 1/2 hour before the wall helps. As does mentally preparing yourself for having your psyche revolt against you and the wave of depression that sweeps over.
It’s possible that you hit a small wall at mile two, but, unless your on a weird diet or diabetic, it seems unlikely you’ve exhausted your glycogen stores at this point. What your experiencing might have more to do with simple muscle fatigue than energy shortage.
I guarantee that you did not deplete your glycogen stores after 3 miles! It takes more like 90 minutes of aerobic effort to do that (check the article you linked, which mentions exercise lasting more than 2-3 hours). What you were experiencing is lactate build up; you were running too fast for the distance, kind of like sprinting to finish a marathon.
Good post though; in the event of future point-docking threats, you could always fill us in on how the cross-country team is doing (PZ docks you for not posting? How draconian!)
n
What you were experiencing is lactate build up
There’s no such thing; this is a widely (nearly universally) held myth due to bad science that has only recently been refuted. See http://www.nytimes.com/2006/05/16/health/nutrition/16run.html?ex=1305432000&en=2778e99d7eab85a6&ei=5090
BTW, in case you’re inclined to disbelieve the above article (for no other reason than that you’ve long believed and been told otherwise, because you surely have never scientifically confirmed it yourself), there’s additional reading at
http://www.google.com/search?q=lactic+acid+myth
This long standing scientific error challenges a lot of the epistemologically naive claims that have been made on this blog. None of you believed this myth because you scientifically confirmed it. But neither did you believe it out of faith. Science, and the scientific method, are a community practice, and authority plays an important role. But authority, just like every other empirical source of information, isn’t guaranteed to be correct.
OK, fair enough “truth machine” (can’t we use our real names?), but whatever the mechanism — and if lactate levels aren’t the cause they surely are the symptom — glycogen depletion was not a factor in this runner’s fatigue. Can we agree on that?
n
truth machine- could you give references to papers showing the same thing?Because according to the biochemistry I learned lactic acid is a waste product of the anaerobic burning of glucose.
AntonG: You are right in that lactate is a waste product of anaerobic glycolysis. But we are not anaerobic beings and muscles never really work at anything near a low enough oxygen condition to just produce lactate from glycolysis.
The real situation is more complicated than Noakes got into in his article. Under high intensity exercise there is a lactate efflux from some muscle fibers [fast-twitch with low aerobic potential/mitochondrial content] and a net influx of lactate in the slow-twitch fibers that have a much higher aerobic potential, however the influx in those fibers does not quiite meet the efflux, so you get an increase in lactate in venous blood. Something like 5 lactates are made; 4 are used in the muscles; one ends up in venous circulation where it is a very nice fuel for cardiac muscle and other systems [but not nervous tisues AFAIK].
p.s. George Brooks, the scientist mentioned in the NY Times article would be a good place to start. A number of years ago he wrote a basic exercise physiology text [I taught from it] and he also has a fairly recent massive compendium, massively priced, called Exercise Physiology: Human Bioenergetics and Its Applications.
And for the intrepid Bright Lights: Don’t go out so fast, several of those mechanisms that Noakes mentioned is effecting you – very possibly a neural one that is causing feedback from an overtaxed leg and chest muscles. Your fatigue in the race is much closer to the fatigue that shorter distance runners [800, 1500m] encounter when they are making a max effort in their events. One thing that does occur is acidosis – the “lactic” is a fuel, but the “acid” is lowering the pH in your muscles and may be one of the causes of localized pain in muscles along with overstimulation of ventilation, causing excess negative feedback to the part of the brain that are encouraging you to keep going. Remember that when enough of those negative feedback signals occur, you will end up a lot more horizontal, possibly with enough stimulation of several cranial efferents to visceral muscles, causing a forceful evacuation of the contents of the upper GI system. And thereby self-correcting the fatigue situation.
The moral: A wise runner knows his/her proper race pace.
f lactate levels aren’t the cause they surely are the symptom
No, they aren’t — did you read the article?
And how much does mentality (a positive attitude towards the race, or the expectation of a good run) play a role in the regulation of my muscles (do I release more ACh and endorphins by simply having a good attitude, or is the causality the other way around?)?”
Very interesting question. I would think the first thing to do would be to see if the assumption is true. (Question all participants before the race and check with their performance). If true the next question would be to consider what is cause and effect. In other words do you run well because you have a good attitude, or do you have a good attitude because someho you know you are in good shape and can run well?
Sailor – good point, I was thinking the same thing. I’m inclined to think that attitude follows training and when you’re in good shape you feel positive.
Truth Seeker – no I didn’t read the article (had to sleep but will read it today); the main point I was trying to make was that glycogen depletion would not occur after 3 miles. I appreciate that the issue is more complex than simply the build up of lactate, however, it is true that during intense running, blood lactate levels rise (or is that not true either? – I’d better read the article). One of the things that runners often get tested is what level of intensity they can maintain while keeping a peak, but constant lactate level, the so-called “lactate threshold”.
I’ll stay out of the ‘lactate build up’ argument and tell you how much I enjoyed the band instead:
I enjoyed the band a lot. Thanks for posting that link!
Binary Solo!
I got dizzy and had trouble focusing on just reading this post and comments.
This is an interesting subject for amateurs and pros alike, and the accumulation of models hopefully points to a renewed science interest.
Incidentally, the two references truth machine gives are inconsistent regarding the occurrence of lactic acid. Wikipedia synthesizes some information in the later of the two references in another model. (Acidosis as a product of buffer capacity overcome by ATP hydrolysis.)
As the post’s reference article discusses exercise fatigue in the (natural) frame of performance improvement, I miss a total perspective on muscle and nerve growth. The fleeting references to hearth improvements and mitochondria number indicates it may be part of the picture.
It is probably refuted by now, but I remember a hypothesis that muscle and nerve growth occurs primarily due to acidosis. Some evidence was that single sets of weight training to fatigue was enough for roughly 80 % of maximum strength increase possible with repeated sets, and no fatigue meant far smaller gain. (Strength increase have other factors involved of course, especially initially on untrained individuals.)
Are there alternative models out there now?
This is an interesting subject for amateurs and pros alike, and the accumulation of models hopefully points to a renewed science interest.
Incidentally, the two references truth machine gives are inconsistent regarding the occurrence of lactic acid. Wikipedia synthesizes some information in the later of the two references in another model. (Acidosis as a product of buffer capacity overcome by ATP hydrolysis.)
As the post’s reference article discusses exercise fatigue in the (natural) frame of performance improvement, I miss a total perspective on muscle and nerve growth. The fleeting references to hearth improvements and mitochondria number indicates it may be part of the picture.
It is probably refuted by now, but I remember a hypothesis that muscle and nerve growth occurs primarily due to acidosis. Some evidence was that single sets of weight training to fatigue was enough for roughly 80 % of maximum strength increase possible with repeated sets, and no fatigue meant far smaller gain. (Strength increase have other factors involved of course, especially initially on untrained individuals.)
Are there alternative models out there now?
Apparently we don’t hit the wall because our muscles have run out of glycogen, recent biopsies have shown plenty of glycogen (brave people undergoing biopsies on sore muscles). It seems that what is happening is that when glycogen stores are lowered to a particular level your brain gets worried. It gets worried because your brain is an obligate glucose user, it burns no fat. So hitting the wall is your brain saying ‘please stop exercising, the pantry is getting a bit low and you never know when the stores will run out over the long weekend’.
That is why the popularity of glucose gelpaks amongst endurance athletes. Take a gel pack a couple of miles short of 20 (or after about 1h30 of exercise), with a drink to wash it down and the rise in blood glucose pacifies the brain, makes it think things are not so bad. I’ve tried it, and it works. If running with a camelbak drink bladder take a dilute drink, nothing worse than trying to wash down a gelpak with isotonic dextrose… Tried that one too, bleuugh!! My current favourite is dilute pink grapefruit high fruit cordial. Oh and opening and using a gelpak without getting sticky fingers is an art form.
I can probably find the reference to the glycogen biopsy paper if anyone wants, it is late here and after a couple of glasses of a rather nice NZ Sauvignon Blanc and a satisfying meal I am far too mellow at the mo.
And Norm, I concurr with the general analysis. You are going out too fast, save some for a nice withering sprint 300m out (my speciality).
Bright Lights, my only useful advice is to go out a little more slowly at the start, breathe deeply, keep your head up — the usual.
Thanks for the FOTC link.