Why can't I run a full marathon at half marathon pace?

Don't confuse "run don't eat" with me. You questioned what "I" quoted/misunderstood. While Noakes must take the blame for his own words, I will take any blame for mistranscriptions, or misinterpretations.I did admit that my short summary might be too short and ambiguous (it would be more clear to those familiar with what Noakes said), and tried to more accurately clarify my interpretation, with a more detailed response.I may still be wrong or incomplete. BTW, I haven't written any research, and I haven't read much more.

areusure? wrote:

Might I suggest you try READING the post before you assert the superiority of your opinion over something you did not understand? Take note I questioned how YOU quoted/understood his thoughts or publications and if you quoted him correctly.

Don't worry though it's not that big of an issue. Writing and reading research are not exactly the same thing and can be confusing! You will figure that out if you publish or have figured it out if you already have.

A lot of misinterpretation of theory is evident here.

Current thinking is that exercise behaviour is regulated through knowledge of the endpoint of exercise (the process is termed telioanticipation). This knowledge is combined with all sorts of feedback on the current status of the physiology (glycogen levels, oxygen saturation, pH, temperature etc) to determine an appropriate muscular workrate that will not result in some kind of catastrophic physiological failure before the end of the event. Workrate itself is basically determined by the muscle mass the brain is willing to recruit. So, you may start a race at what seems like a sensible pace, but some distance into it afferent feedback to the brain says that e.g. muscle glycogen stores are dropping (or you are getting too hot, pH is dropiing etc etc). The brain does a quick calculation and realises that given the rate of use of glycogen and the distance still to cover, then there is no way that the body can maintain the current running speed untill the finish line without damaging itself in some way. In order to prevent this happening, less muscle mass is recruited, thereby reducing the rate of glycogen use, but also reducing the running speed.

Now - obviously when running you do not think to yourself "hmm, glycogens getting a bit low, I'd better slow down". This feedback is proposed to be processed at the subconscious level and you simply experience 'fatigue' in the sense that maintaining your current pace becomes increasing more uncomfortable. A lot of work has looked at the role of the Rating of Perceived Exertion (RPE) in regulating behaviour and what is consistently found is a linear increase throughout exercise culminating in the highest values at the very end. The RPE athletes rate is 'conscious', but this conscious RPE is suggested to be compared to a subconscious 'template' that serves the purpose of preventing self harm. In a race therefore you may start quickly to keep up with rivals, but if this pace is too fast for your physiology to maintain then your (conscious) RPE will quickly increase rapidly above the levels your brain is happy to allow. You therefore experience discomfort untill you slow down to a speed your subconscious brain is happier with (Your brain is 'happier' because it knows that there is no risk of self harm if you maintain current speed to the finishline).

Imagine you are a 30 flat 10k runner. If you were asked to run 1k on the track in exactly 3 minutes I'm sure that if I asked you afterwards to report your RPE it would be low. If I asked your RPE after the first 1K of a 10k race also run in 3 minutes then I would expect it to be a little higher, and if I asked you after you had covered the first 1k of a marathon race in 3 minutes I would expect it to be almost maximal. Why is this? Clearly the actual work you have performed is identical (1k in 3 minutes). The reason is because you have interpreted the feedback from your physiology in the context of what you know is still to come. So if you covered the first 1k of a marathon in 3 minutes your brain is screaming at you to slow down because it knows it cannot maintain this workload for another 41K.

Therefore the simple answer to the original posters question is - because your brain calculates that you cannot complete the marathon at the same speed without risk of some kind of physiological catastrophe, and does everything it can to make any attempts to do so as painful as possible!

My PR in the 800 is 1:56. Why can't I run a 3:52 mile? I'm stuck with a 4:09, damnit!

While i think telioanticipation may slightly influence your RPE according to different race distances, there's no way a thirty minute 10k runner, after running a 3 minute kilometer at the beginning of a marathon, has an 'almost maximal' RPE (presumably 18-19 on the 6-20 Borg scale?). in this situation, your conscious ability to sense pace will let you know this is far too fast, well before changes in energy stores/accumulation of metabolites signals your brain to make you feel fatigued. 'almost maximal' RPE of 17-19, in words, is 'very hard' to 'very very hard.'

AJR you are essentially ignoring some of the previously mentioned potentially important peripheral fatigue mechanisms, which are not the same as the neural sensing of some of these variables, like glycogen status, temperature, pH, etc.

as with most things, and has been mentioned previously in the post, it's probably a combo of central and peripheral fatigue.

AJR's post definitely adds a clearer understanding of the role of our 'intrinsic pacer' in fatigue and race performance.

i think if we all agree not to take slight misinterpretations to mean an entire post is shi*, we'll get a lot closer to our answer in synthesizing the best parts of each person's post.

This was an excellent response.

In Brain Training for Runners, Scott Fitzgerald answers this question something like this: Muscle damage, increase in hydrogen ions in the blood, wide-spread ketosis in the blood, and glycogen depletion send signals to the brain that this sort of activity cannot be sustained. The runner interprets these signals as pain or hitting the wall. In later stages the brain will start to forcibly slow the runner down in order to protect the body.

shoot i meant to say matt fitzgerald. Pretty sure the Great Gatsby guy wasn't that prolific.

CTA wrote:

This was an excellent response.

Best post in like... forever!

AJR wrote:

Mind over matter.

I fixed it, above are your cliff notes.

You're welcome.

AJR wrote:

The brain does a quick calculation and realises that given the rate of use of glycogen and the distance still to cover, then there is no way that the body can maintain the current running speed untill the finish line without damaging itself in some way. In order to prevent this happening, less muscle mass is recruited, thereby reducing the rate of glycogen use, but also reducing the running speed.

I don't believe this is an adequate explanation of central fatigue. Here's why...

I don't buy that first part. Your brain has no concept of distance. It is up to you, consciously to pick a pace that your body can sustain for a given period of time. If you try to run a marathon at 400m pace you will slow down plainly due to peripheral fatigue. Your moto-neurons will likely be firing at near-maximal frequencies and your muscle membranes will be depolarizing also at near-max freq. the limiting factor will be ATP production rates. Fatigue will occur at the muscular level only.

I also don't buy that your brain is monitoring muscle and liver glycogen levels. I can't fathom of a way that those could accurately be measured.

I do buy that the brain is measuring blood CO2 (via [H+]) and blood O2 and therefore could possibly be measuring what we know as RER... And from that could possibly modulate motoneuron firing frequencies and # of motorunits. (These are of course modulated by other factors as well covered in central fatigue models)

I don't buy that first part. Your brain has no concept of distance. It is up to you, consciously to pick a pace that your body can sustain for a given period of time. If you try to run a marathon at 400m pace you will slow down plainly due to peripheral fatigue. Your moto-neurons will likely be firing at near-maximal frequencies and your muscle membranes will be depolarizing also at near-max freq. the limiting factor will be ATP production rates. Fatigue will occur at the muscular level only.

I also don't buy that your brain is monitoring muscle and liver glycogen levels. I can't fathom of a way that those could accurately be measured.[/quote]

The first part of your question is only an issue if you are not very clever (as an athlete - not an attack on yourself). The point is that nobody with any common sense will even attempt to run a marathon at 400m pace. The brain clearly does have a concept of distance. If I ask you to run 100m as fast as you can then you will automatically run flat out from the beginning. If I ask you to do the same over a marathon then you will start off much more conservatively. If on the other hand I was to ask you to run as fast as you can, the first quetion you would ask is 'how far?' Without this information you have no idea how fast to start.

A lot of studies have experimented by playing with athletes minds. One study (by Baden et al I think) had athletes come into the lab to run on the treamill on a number of occasions. They always ran at something like 70% peak speed achieved during an incremental test (so not that hard). On some occasions they ran for 10 minutes and on others they ran for 20 minutes. During these trials RPE increased fairly linearly throughout (I cant recall what sort of actual values were reported at the end of each). On some occasions though, participants were told that they were running for 10 mins but just prior to what they thought would be the end they were told that actually they had to continue untill 20 minutes. When this happened RPE (and measures of associative thinking) increased dramatically. In the second half of these runs RPE was much higher than on those occasions when they knew in advance that the run would last 20 minutes. I think this is quite clear evidence that knowledge of endpoint is absolutely crucial if you are to know how to pace yourself. You can talk about peripheral physiology, but the brain 'activates' it.

Clearly the peripheral physiology is still important - if you get adaptations as a result of training then there is less physiological strain imposed by any running speed so your brain will allow you to run faster over a given distance because you wont kill yourself attempting to do so.

For the second part o your question - I'm confident that everything is being continually monitired. Tim Noakes actually published a short paper in 2004 relating RPE to glycogen availability. If you exercise to failure at a fixed workload when glycogen depleted then you dont go as far as when glycogen replete. During the glycogen depleted trials the rate of increase in RPE is also faster, and in both conditions exercise terminates on achievement of maximal attainable values. However, if you plot RPE against % exercise time insyead of against absolute time, the the RPE profiles are identical in both conditions. The conclusion was that RPE 'governs' exercise uration based on feedback on glycogen availability (of course this is fixed load versus self paced exercise which is a slightly different debate)

anon wrote:

Although there have been a few mistakes as to why fatigue occurs in this thread, "most of the central questions" surrounding fatigue have in fact been answered. The "running stuff we know" is not just guesswork. Take some time and read the literature available.

So I have no technical background so the literature is often hard for me. Let's say that I have a popular science understanding of fatigue, and I look to articles like this one in the Times:

which starts"One of the great unanswered questions in physiology is why muscles get tired. The experience is universal, common to creatures that have muscles, but the answer has been elusive until now."

Any updates on this research?

I'm just speaking for myself here, but I always get tired at the end of a marathon and it makes me run slow. Slower than I do when I'm not tired. I'm kind of a pussy.

Okay think about it. Say I can bench press 45 pounds 50 times, then I can also bench press 160 pounds 5 times...

You wouldn't raise an eyebrow at this, it makes sense that the muscles can only do so much work at each given work load.

The difference is we don't think of lifting weights in terms of "pace," the way we do running. So much emphasis is put on pace (5 minutes per mile, 6 minutes per mile, etc...) and the simple fact that its only a simplification of stride length and stride frequency, which account for the production of speed. But even more in depth than that is the force in which each leg exerts on the ground in each stride to propel yourself forward.

If you think of each step as a repetition as you do in weight lifting, it becomes easy to understand why you can run faster for shorter distances but cannot maintain the same pace past a certain point. (i.e. a half marathon is somewhere around 18000 reps at however much force you exert on the ground with each step, and a marathon is somewhere around 36000)

I think its a simple factor of how many times the muscle can exert a given amount of force before it exhausts itself.

Pretty sure LT build up is still bad. LT production on the other hand is fine.

Falsebigtime wrote:

AstoriaRunner wrote:

IF an elite were to try to run at LT pace for the full, they would blow up somewhere around an hour as their body would simply not be able to handle the LT buildup..

False, LT buildup is a good thing. Still living in the dark ages i see.

Obviously it is a lack of mental toughness.

notafan wrote:

i can run a 1:50 800, why cant i crack 1:40 in the marathon

Why does everyone on here say H+ ions when there is no such thing? An H+ ion would be a proton. Actually, there are no free protons floating around your bloodstream. They are hydronium ions (H3O+).