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Tuesday, April 29, 2008

Fatigue Series: Introduction

Introducing a new series: The mystery of fatigue and the limits to performance

Here's one of the million dollar questions in sports sciences today: How is it possible for a 10km runner to SPEED UP in the final 400m of his race? And if he had that "reserve capacity" all along, why did he not speed up 800m before the end? Or 2km? The whole way?

As you read that, you're probably thinking "Big deal, what a ridiculous question. It's obvious that you can't speed up, because....um, well, you see, it's the....why was that again?"

And now, physiologically speaking, you are stuck. Because the reality is that there is no single physiological theory that can properly explain why athletes pace themselves the way they do, why fatigue happens and what limits performance. There is no book, no proof, no all-knowing scientist who can tell you the answer to this, the most seemingly basic question in the field! As you read this, there's a good chance you're simply dismissing the question as obvious - "It's experience and training, a conscious decision". And I agree with you, but we still haven't explained the physiology of how this decision was made.

It's become something of a mantra here, but the truth is that if anyone tells you they KNOW the answer, they're lying, or ignorant, or both. Because years of research has failed to answer that question definitively. There are theories, yes, and some do explain fatigue under very specific conditions quite well. But to this day, no one really knows the answer to the simple question posed above.

And before you get your hopes up, we're not going to tell you the answer either! Because we don't know it! But we do know is what it's NOT, and we'll discuss that. And as mentioned, there are theories, some new, some old, which do partly explain performance limits, and we can discuss those. And we can introduce the great unknowns, and hopefully make sense of some of the myths and fallacies that are thrown around concerning fatigue, performance and human exercise limits.

And so with that, we introduce a brand new series here on the Science of Sport. We'll call it Fatigue, pacing strategies and the limits to performance.

It will look at the following:

  • Theories for fatigue - what causes fatigue and limits exercise performance?
  • Pacing strategies - a basic observation with a complex cause
  • Exercise at the "extremes" - exercise in the heat, and at altitude
  • Deceiving yourself - how false information about time and distance influences performance
  • What happens during sprint events? And how is pacing different from endurance events?
  • The anticipatory regulation of exercise: A proposed model for performance using the Perception of Effort
We are ultimately heading for that last installment of the series - a new model for how exercise performance is regulated. That model was actually produced as the concluding section of my (Ross's) PhD thesis, so this series is a personal one for me, and basically a summary of my PhD. I hope it will be as interesting to read as I know it will be rewarding to write. (Incidentally, the model and review is also in review for publication in a scientific journal as you read this, so hopefully in a short while, it'll be out as an academic text as well, for those who are interested.)

The theories - it must be anaerobic lactate production: your muscles are fatigued

There are those who'll try to answer our "simple question" from above. Textbooks will tell you that you slow down because you run out of oxygen, you become anaerobic, lactate forms and "poisons" the muscles, or you get too hot and your brain says "stop!" The books explain how muscle becomes fatigued as a result of these chemicals that build up, caused by a lack of oxygen delivery as you get closer to the VO2max, where you can't use any more oxygen.

And maybe this is true. . .but hang on, that doesn't explain how you SPEED UP in the last 400m. Remember, in a 10km race, you're running quite a lot faster than your "anaerobic threshhold", which is always defined as the speed/intensity above which you start to accumulate lactate. So one thing we do know, is that in a 10km race, with 1km to go, there's a lot of lactate in the system! Similarly, you can be pretty much guaranteed that with 1km to run, the calcium channels are at their most leaky, the phosphate and H+ ions are at their peak, and the body temperature is at its highest.

Now think about it for a moment - if your muscles are becoming weaker and weaker because of chemicals like lactate, or a lack of oxygen, then how is it possible to get FASTER at the end of the race? The end of the race? That's when the lactate levels are the highest! Oxygen levels are the lowest, because for 40 minutes, you've been running yourself into what those textbooks call "oxygen debt," right? Well, if that's true, then the only thing that would happen is that you would get slower and slower and slower.

Instead, you speed up at the end. Added to this, there's a growing body of evidence that lactate is not the "bad guy" it was once made out to be, maybe it's even the "good guy." We'll look at that as well in the coming weeks.

But this, in a nutshell, is one of the theories for fatigue. It's been called the "Peripheral fatigue model", the "Cardiovascular/anaerobic model", and the "Catastrophe model" (all by Prof Tim Noakes - more on that lower down), but what it is basically saying is the following:
  • Fatigue is the result of failure - something in the physiology fails, causing the athlete to stop or to slow down
  • That failure can be anywhere in the system - it might be failure to supply enough oxygen to the muscles, failure to keep lactate, phosphate or hydrogen ion levels down, a depletion of glycogen, or failure to lose heat, causing the body temperature to rise too high
  • Once this "failure point" is reached, exercise must slow down, or stop altogether. The fatigue is the result of the failure - it's a "catastrophe"
  • The key point is that fatigue is a "limit," and it lies in the muscles or the complete inability of the brain to activate muscle
The other extreme - there's no muscle fatigue, it's all in the brain

On the other end of the spectrum lies the so-called "Central Governor" theory. This theory was developed by Prof Tim Noakes, under whose supervision both Jonathan and I both did our PhDs. In fact, my PhD was titled "Anticipatory regulation of performance" and it examined the very question I asked at the beginning of this post.

Essentially, this theory, which I'll rather called "Anticipatory Regulation" for reasons that will become clear further down, holds that:
  • During exercise, the brain regulates performance to balance all the body's physiological systems
  • Fatigue (or the slowing down in pace) is the result of this regulation, which happens BEFORE any physiological "failure" can occur
  • Therefore, rather than slowing down AS A RESULT of lack of oxygen, high body temperatures, high lactate levels etc., you slow down IN ORDER TO PREVENT THEM.
Notice that key difference - performance and fatigue are regulated to prevent the potentially harmful limits from being reached. These "limits" to exercise are real. If your body temperature is above 41 degrees, you'd stop and be in serious trouble. If you did accumulate too much hydrogen, it would be bad news. But when exercise takes place, they don't happen because the brain is in control, and it regulates the body specifically to protect against that damage. At the same time, it's trying to balance protection with your own desire to perform as well as you can, and that produces a constant balance between two potentially conflicting goals.

In this theory, then, you get what is called a "pacing strategy," which is the output by the muscles, as part of this regulation. Performance is regulated, not determined, by the physiology.

It's all in the timing - when do you slow down?

If you want tangible proof of this, think of the following hypothetical situation:

Let's say you run a 10km race at sea-level, and in cool temperatures. Your time is 40 minutes, giving you a speed of 4min/km.

Now, let's say I transport you instantaneously to the following two places:
  1. Halfway up Mount Everest, an altitude of about 4000 m
  2. The middle of Beijing in the summer time, where it's 35 degrees, and humidity is 60%.
Now, I make you run that same 10km race. What is going to happen? I'm sure that all of you are in agreement that your time of 40 minutes is under threat! You might be lucky to crack 42 minutes in these "extreme" conditions. But here's the million dollar question (another one!):

When do you first slow down?

Do you:
a) Start off at 4 min/km, running the first 5km in 20 minutes, before you suddenly find that you're forced to slow down, because you're suddenly gasping for air at altitude, or because you're incredibly hot and feel close to collapsing?; or...

b) Start off much slower than normal, because you KNOW that if you don't, you'll be in trouble after 5km? Within the first 30 seconds of your run, you have already "decided" to slow down. Perhaps you start off at 4:20 min/km, and manage to hold that pace for a while, then you get slower and slower, until the final kilometer, when you can speed up again?

I'm sure that everyone who has ever run in the heat or at altitude can relate to the fact that the answer is b) - you start slowly. In fact, it takes probably less than 20 seconds for your body to "decide" to run more slowly than usual. Now, you have to ask yourself:

"How do I know to adopt a different pacing strategy in these conditions?"

Remember, it happens so early that nothing is different, except for your sensation that it's either hotter or that the air is thinner - that sensation then, seems to be key. But it can't be that you are already overheating within the first 30 seconds, or even two minutes of your run. You can't already be in oxygen debt at altitude? So how, then, do you "decide" to slow down? Once again, some will dismiss this as obvious, but I'd challenge you to find the answer to this question in a physiology textbook - you can't because it doesn't exist. The book is going to tell you that you slow down because of anaerobiosis, oxygen debt, lactate accumulation. But there's no evidence for it.

A controversial model - but this is not a series aimed at glorifying any model

Now, the Central Governor model is highly controversial, both within the academic world, and among the public who've heard of it, in some form. It's one of the most divisive theories around, because it lies so far to the extreme opposite end of the spectrum compared to the other, "textbook" model(s) for fatigue. The Model has, over the years, been twisted, mis-interpreted, bashed, criticised, hyped, glorified and dismissed in equal measure - for example, it's the subject of a 40-page discussion thread on LetsRun.com, which would take all year to summarize! Part of the problem has been that people read Tim Noakes' work from the late 1990's and 2000, and don't look at the more recent work, and the evidence that has been gathered since.

But perhaps the biggest problem is that the "governor" has been wrongly portrayed (sometimes deliberately by the people who created it, to its detriment, I might add) as a little "black box", that 'magically' controls our physiology and performance. In this concept, the term "Governor" conjures up images of a school headmaster or a little green Martian enforcing control over your exercise, and represents a misunderstanding of the theory.

People have tried to personify the concept, and pinpoint its location in the brain, when in fact it's the concept that counts, and it doesn't need to exist as a specific location. For that reason, we'll steer clear of the term "Governor", and go instead with "Anticipatory Regulation". Also, as knowledge is evolving, the term needs to be more all-encompassing. Hopefully, we can translate some of this evidence in this series...

But let me reassure all the sceptics out there - I'm not going to write this series as a one-dimensional glorification of the Central Governor theory, so don't sharpen your knives (just yet!). For while I studied the regulation of exercise by the brain and am fully behind the concept that exercise is regulated (not limited) in anticipation of a limit, there are physiological and performance findings that the theory cannot explain. It is not, therefore, the single answer we are looking for. It needs critical and thorough analysis, and ultimately, the trick will be to balance the two extremes.

And let me say this now, with the hope of never repeating it: Fatigue is not all in the mind! This misconception, which has unfortunately been propagated by academics and media and the public, is best forgotten at this early stage. Fatigue and the limits to performance are NOT simply mental barriers, and "mind over matter" is a massive oversimplification of the truth! Having said that, mental strength and willpower are key factors, part of the answer, but they never beat physiology. We'll look at the role of willpower, self-belief and mental strength in this series, but I repeat "It's not all in the mind!" The analogy is that "you cannot commit suicide by holding your breath," and the same goes for exercise: physiology wins the day, every day!

The real answer, then, is likely to lie somewhere between these two extremes - a combination of the "Anticipatory Regulation" model and the "Peripheral Fatigue Model".

We'll work towards that answer over the next few weeks. It is an enormously complex and detailed area to tackle, but we'll jazz it up and try to make it entertaining as much as possible! It may take up to a month to get through it all, and we will carry on with our normal news stories and other features between installments.

As usual, comments and feedback are welcome! But bear in mind, we're working towards the answer, so if you feel we've left something out of each post, it might be coming in the future!

Join us again soon!


TriExpert said...

Gents, this is a terrifically promising start. I'm manifesting much Anticipatory Curiosity re: future installments!

Anonymous said...

This comes at a good time. Maybe you are aware of an on-going discussion about the Central Governor himself, over at "letsrun", with a special guest appearance by the creator himself. I'm looking forward to your treatment of fatigue, and the comments. I recall an older discussion (last year?), same subject, same place, where Ross popped in to pose the same questions about speeding up at the end, and what distances suffer most at altitude. Let the series begin...

Anonymous said...

Very nice post. I'm looking forward to reading the rest of the series too. My naive (but probably mistaken) understanding was that there are two sets of muscle fibers (fast twitch and slow twitch). The fast twitch muscle fibers are the ones engaged during speed workouts and probably also used towards the end of the race, while the slow twitch ones are the ones which are used during regular aerobic workouts. They have different metabolic pathways - one which uses fat as a source of energy while the other which uses an anaerobic pathway. Your post highlights, that there is a lot more going on than my limited understanding. Great post once again and belated Happy Bday too.

Stan Silvert said...

Hi Ray,

Can you provide a link (or approximate date) where Noakes chimes in on the LetsRun discussion? It's now 41 pages long.

Thanks in advance,


Ian said...

I'm looking forward to the rest of this series. I recently read somewhere that people who are sprinting at the end of races are poor pacers because they shouldn't have that much energy left over for a final push to the finish. It angered me a little because I don't believe that's true. No matter how tired I am after the first 9km of a 10K, I can always find an extra kick to push to the finish, even if it's only the last 100 meters.

I'm interested to see your take.

Anonymous said...

Ummm ... hasn't the "lactate makes you tired" theory been completely debunked?

Ross Tucker and Jonathan Dugas said...

Hi Stan

Tim's post on that thread is near the end - check page 38 or 39, you'll find it there! It's a mammoth series of posts in that thread, I also didn't make all 41 pages!

Then to Ashish, yes, you're quite right, it's now debunked in academic circles especially - I did allude to that in the post. But you're one of the few who knows it - hence the reason to bring it up in this series.

The other day, I picked up RW USA, and a well-known "expert" who writes regularly for them wrote that "Marathon runners must be careful to start the marathon at the right speed, because they must remain below the lactate threshhold". He later wrote about the debilitating effects of lactate on performance. Needless to say, books have been written on this topic, and are still written today.

Similarly, commentators during the Boston Marathon last week spoke with great enthusiasm about the "lactate" that caused heavy muscles in the runners. And if you listen, and look, you'll see reference to it everywhere - magazines especially.

So part of the purpose of this series is to discuss that a little more. It's "old news" to you, but the myth is everywhere!

And finally, to Vanilla, that aspect of pacing is absolutely fascinating - are we supposed to speed up at the end? Let's just say that 90% of all world record holders are "poor pacers" according to that theory! Of course, the size of the sprint is important - you shouldn't be able to jump up five gears at the end!

I think a whole week of this series will be devoted to looking at how the elite pace themselves compared to us regular "mortals". Also, we'll look at how pacing has evolved through the ages, and what factors might account for any differences. So it should be a fun-part of the series!


Alan said...

Excellent topic!

I've been looking for info on the effects of uphills and downhills on pacing strategies in running races and it seems to be pretty much a sport science void.

If you get a chance would love to hear some theories relating to up/down hills.

Thanks for the thought provoking posts!

Stan Silvert said...

Got it. #37. I put the direct link below if anyone else is interested. Noakes' comments make for great reading even without the 36.5 pages that came before it.

Click Here. Noakes' post is second from the bottom.


Anonymous said...

I find this info very interesting. As a competitive mtb and road cyclist I've often noticed that even though my pacing seems to be at the edge of performance, I always find a little extra at the end. Other times, if I get "angry" enough earlier during the race I'm able to raise the pacing level a bit and usually have a better race. The whole key would be to continue to up the edge of performance. That's the holy grail I guess...

Liz said...

Great posts guys, as always.

As a road TT and pursuit racer, pacing is the bane of my life and getting it right is a huge goal, rarely achieved. I look forward to this series.

Have you done looked into recovery? As a rapidly ageing female masters racer (63yo and still working full time in an active job) I am frustrated by my increasingly longer and longer times to recover from training/racing, and would love to hear from your thoughts on the various oft touted methods of recovery....

Anonymous said...

Good stuff, been waiting for you guys to get to the meat :)
Great Blog and an avid fan,

Anonymous said...

just a few questions.

You mentioned that fatigue is basically caused by two things. Physiological failure or our brain, but how can we tell which one is affecting our performance. How can we tell if our fatigue is being dictated by our brain and how can we tell if its a physiological failure?

If our fatigue is dictated by the brain, how do we overcome it and
if it is physiological failure, how can we train, or what can we do to:
improve our ability to supply enough oxygen to the muscles,
keep lactate, phosphate or hydrogen ion levels down,
keep the glycogen (or something to counteract the depleation thereof,
lose heat.


Anonymous said...

sorry about the double post, i just read the comments page. i'm also naive, but being that "lactate" isn't our enemy, does that make the old LT run useless?

I find that i'm able to speed up at the end because i know theres only 400m left,and if i dig deep enough i can find something there. I want to be completly drained at the end, that way i know i've done my best, so those last 400m, i'm squeezing out the last drop

Anonymous said...

I think we are talking about differents things:
1) the sprint at the end of a long race (differents metabolics pathways, differents fibers).
2)the pace in a given distance.One of the most common mistakes made by a new marathon runner is begin faster than the real pace he can do.
3) the feeling of fatigue in our body (something like feeling tired) and sometimes in our head (a minor amount of neurotransmisors?).

I associate fatigue with the feeling at the km # 40 in a marathon: I want to race faster (at my pace) but my legs say "NO".

Great topic, I'll be waiting for more.

Anonymous said...

Guys - this is great!! It's actually something I came up with regarding myself when I race. I have always thought that if I REALLY wanted to .. I could be going harder, but always felt there was something there regulating (as opposed to restraining) me from NOT going faster - because if I went faster, there would be a chance of blowing to pieces. Often I have been in a race and asking myself "Can you go faster?" and answering "No" to myself ... but then having to participate in a sprint finish ... and oh yes, you CAN go faster ... if you HAVE to!! This is in stark contrast to another athlete I know who seems to be able to over ride this "regulation" and sit on the wrong side of the hurt locker for an entire race. But she doesn't have anywhere to go in the event of a sprint finish though. Interesting stuff, I can't wait to see what else you have to say about anticipatory regulation.

Cristiano said...

Hi Ross, I'll write my degree thesis in Applied Cognitive psychology title "perception of the physical effort on endurance training", so Anticipatory Regulation model is a good news for me. It's possible to have your e_mail address for bibliography indication and support?

thanks a lot

Cristiano from Italy

Ross Tucker and Jonathan Dugas said...

Hi everyone

Thanks for the feedback and interest so far. I must say, reading this response and the other discussions on the internet (courtesy of Ray's link), it's a daunting subject to tackle!

Daunting, because there is so much information to get through, and to present what amounts to literally 1000's of research papers and perhaps 10 years of work is going to cause much confusion! But hopefully, if we stick to the plan and work through it logically, it will make sense!

So bear with me, but there will be times when I can't respond to comments, partly for time reasons and because it would affect the (hopefully) logical flow. So please don't think I'm ignoring comments - they are all being saved and integrated into the future posts in this series! HOpefully, in the series, it'll all be covered in some form!

Looking forward to tackling it!


Anonymous said...


I see you found a link on Page 37. He also chimed in on pages 25 and 30 (or click on 26 and 31) -- look for long "Dear XXXX" letters posted by "thinairunr".

Some doubted the authenticity of the posts, or maybe the poster, and even criticized the English (I didn't see any problems, although I had to look up "torpor" in the dictionary), but I find them credibly authentic. Maybe Ross and Jon will confirm that nothing is out of line.

Ross Tucker and Jonathan Dugas said...

Hi Ray

I am 99.99% sure they Tim Noakes' posts, the language is consistent, and I've heard those arguments many, many times from him personally. So reading that response from him on Page 37, it reads like a collection of his common arguments. And as it goes with people, they tend to focus on certain aspects at certain times, and the focus of Tim's posts is consistent with his current "bugbear" of coaching.

As for the English, Tim's language is exceptional. The only thing he ever does wrong is use "insure" instead of "ensure". He does it in this post as well, which is actually the surest sign it's written by him.

He's on leave today (we have a series of public/bank holidays this week, so most people took time off), but I'll see him next week and ask, but yes, I believe these are his words.


Ross Tucker and Jonathan Dugas said...

Wow, this has been an absolutely amazing response! I think we thought this series might be too heavy and technical to draw this much interest, but we are so pleased that people are keen to see this.

Regarding the posts on the Let's Run forum, I am confident that they are authentic. All one has to do is read some of Tim's work and you will see the similarities.

Thanks to Ray for directing us there, as it is quite interesting to witness the intersection of the academics and the everyday runner/athlete.

Kind Regards,

knopfler said...

compression tights. placebo or proven results?

Anonymous said...

I will be tuned in for each installment. This is fantastic.

Andy Renfree said...

A fascinating topic for debate and I look forward to your future installments.

I have been aware of the CG model for some time and it does make a lot of sense. However, I am glad that you have emphasised that it is not the single answer to explain exercise performance.

Just a couple of random thoughts in my own mind (that you may well be addressing in forthcoming installments anyway)that relate to the CG model. Please correct me if you think I have misinterpreted anything here:
- The pacing question is an interesting one. There is some relatively old research suggesting that there is a very strong correlation between intramuscular pH and perceived exertion during exercise (the lower the pH then the higher the RPE). If you induce acidosis through administration of ammonium chloride then RPE at any given exercise intensity increases. Likewise, induced alkalosis through administration of sodium bicarbonate reduces RPE at a constant workload, or increases power output at levels of perceived exertion corresponding to workloads above the 'mythical'(?!) LT. This suggests that perhaps the brain is indeed regulating performance in order to prevent some 'catastrophe' (in this case an excessively low intramuscular pH)jeopardising the athletes health. An interesting anecdote relating to this point - I once performed some work with a group of swimmers who had been experimenting with sodium bicarbonate as an ergogenic aid. They found that it could improve their performance, but only after they changed their pacing strategy to include a much faster start in the first part of their races than they would normally use. Presumably becuase they had previously 'learned' how to pace themselves over races of various distances, some of the swimmers actually found changing their pacing strategy much harder than it sounds.

-With regards to the idea of 'anticipatory regulation' causing fatigue prior to any physiological failure occurring. Again, it makes a lot of sense. However, if you do a period of anaerobic training then not only is your sprint performance improved, but you can now produce greater post-exercise blood lactate concentrations and there is a fall in post maximal exercise blood pH. These changes are accompanied by various physiological adaptations to training (eg. increased activity of various enzymes). If fatigue is the result of the brain attempting to stop you before some kind of failure occurs, then why can you now achieve a higher degree of acidosis? Is a level that was previous 'critical' now less so, or has the brain simply learned that you will not kill yourself as a result of such intense exercise? If improved performance is simply a result of some resetting of the central governor, then surely you would expect to see the same improvements in performance regardless of any physiological adaptations?

Sorry for the rambling, but I look forward to further discusison of this topic.

Ross Tucker and Jonathan Dugas said...

Hi Andy

Excellent questions and points. And pH is definitely one of the variables that we'll mention at some stage. I think that the latest post I've just done will do a bit more to explain this aspect.

The way I would present the model (which I'm not going to call the CG model, incidentally, because I don't believe that this explains everything,and besides, it's a misleading name) is that there are inputs and outputs. The output is the pacing strategy, the running speed or power output. The inputs are varied, but pH is one of them. What buffers do is alter the input, and hence the output.

What training does is alter the inputs, but also the interpretation of those inputs by the brain. So a higher body temperature, a lower pH, a reduced pO2, can all be "tolerated" within the body's safe range after training, because you "learn" how to regulate better. So if you ever try to interpret how any intervention (training, heat, altitude, diet, etc) alters performance, you ask how does it affect the inputs, and the interpretation of those inputs? And you get an answer.

More to come! Thanks for the mail!


Quinroxanne said...

Great post and topic, human body is really so amazing. It has lots of surprises.