Fatigue and Exercise: Part I A  //  The pacing strategy - why the obvious is crucially important

01 May 2008 Posted by

On Tuesday, we introduced a new series on Fatigue and Performance, which, based on the comments and responses so far, promises to provide much food for thought, interesting discussion and a few strong opinions!

And thinking about the subject (see my thoughts at the bottom of this post), it’s clear that the most difficult part of this whole series is going to be controlling the logical flow of the discussion. It’s such a vast, enormous topic that it’s going to be impossible to put across a vast amount of information without skipping over studies that some might consider relevant. That’s the nature of science – if not, then every review article would have thousands of references! So literally, ten years of academic debate and research studies have to be translated into a (hopefully) understandable and readable summary! The only way to combat this is to stick to the plan we laid out two days ago, and so that means that many of your questions and comments might be quite relevant, and there will be “gaps” in the logic of each individual post, but hopefully, they’ll all be answered eventually.

So with that on the table, knowing where to start is perhaps the most crucial thing of all – the first step on the journey (warning – it’s quite a long post, so I have split it into two parts – the first is published today, the second will be published tomorrow! But you might want to read it in “shifts”!).

And I thought that perhaps I’d return to yesterday’s post and the question I posed about pacing strategies and the mechanism for their existence. Today’s post, then, is all about the pacing strategies, which are simultaneously the most obvious, the most complex, and the most important thing about fatigue and exercise performance.

What do we mean by pacing strategy? And why is it obvious? And important?

Yesterday’s question involved pacing strategies, which anyone who has ever done exercise knows all about. In particular, we spoke about the “endspurt”, which is the characteristically observed “kick” for the finish line in a race. I posed the question that if the athlete has the “reserve” to be able to speed up at the end, then what was keeping them from using that reserve earlier, and potentially running faster? (In hindsight, I probably could have chosen a better illustration of pacing strategy because people tend to dismiss this profound question rather frivolously, but there’s plenty of time for all those questions to be asked!)

Take a look, for example, at the following two graphs. They show the power output during cycling (on the left), and the running speed during a 10km race (on the right):


This pacing strategy is, incidentally, typical of even the elite athlete. To let the cat out of the bag, the graph on the right belongs to a world-record performance – it is the 10km performance is that of Haile Gebrselassie when he ran his 10,000m world record of 26:22.75 in 1998. His final kilometer was run in 2:31.3, compared to high 2:37’s and 2:38’s before that. So even the greatest of the elite follow a similar strategy as a club-level cyclist – faster start, slowing in the middle, with an endspurt to finish. Obviously, the size of the difference is important, and the elite performance shows less variation than the club-level performance. Later in this series, when we discuss pacing strategies, we’ll get to that in greater detail.

A “ridiculous” question with an obvious answer?

But let’s get back to that question – Why the slow down in the middle, with the endspurt at the finish line? And what keeps the athlete from accessing the “reserve” sooner than the final kilomter?

Many say it’s an irrelevant, absurd question, with an obvious answer. They dismiss it out of hand. Some of the typical responses are:

“It’s obvious, because they know that if they ran faster early, they would not finish. It’s training and experience, what a stupid question!”…or;

“It confuses me. To me what they are describing as “anticipatory regulation” is simply wise pacing.” or;

“How can this question even be asked? Any person that has run seriously would not even ask it surely.”

The second and third responses are actual responses to this question, incidentally. These answers reveal two things:

1. Academic exercise science is often quite far removed from “common sense”

Yes, it is actually obvious that people would speed up at the end. I’ll never forget that having freshly graduated with Honours in Exercise Physiology, I was trying to explain to a very successful coach (Olympic champions in his group) the physiology behind performance. Having done my best rendition of the “truth”, he nodded and said “Yes, well, we’ve known that since the 1970’s, haven’t we?” And he took me home, showed me a coaching book with worn pages saying pretty much the same thing…a humbling experience, to be sure!

However, as I thought about it, I realised that firstly, there was very little new under the sun (to quote Ecclesiastes) and so some humility was never a bad idea! But secondly, it was obvious that while people in coaching have always appreciated this endspurt and its meaning, those in the sciences have pursued quite a different course, developing a model that is incomplete and ultimately unable to explain this “obvious” endspurt!

We’ll work towards explaining all that, but what people don’t realise is that in exercise physiology, the usual explanation for fatigue is completely irreconcilable with this endspurt observation! So the answer, which might be obvious to athletes and coaches actually has no feasible explanation in academia!

So what is that irreconcilable theory?

If you spent time studying exercise physiology, you would be taught that fatigue is caused by metabolite accumulation/depletion, high body temperatures, or some other peripheral change, as we introduced yesterday. This suggests that fatigue (or slowing down – even the definition is contentious) is a result of some change in the muscle. You may have heard, for example, of the theory of leaky calcium channels. In this theory, fatigue happens when muscle becomes “leaky” to calcium, which lowers the contractile capacity of the muscle.

I’ll go into this theory much more in tomorrow’s post, but consider that this theory suggests that you’ll be slowing down progressively during exercise as your calcium channels become more and more leaky.  Why then, would you not simply use muscle fibres that were previously inactive in order to maintain the speed? The “endspurt” which is often dismissed as “wise pacing” shows clearly that those muscle fibres were available. Yet the athlete “chose” not to use the reserve until the very end, rather getting slower or holding the pace. Conscious? Yes, probably part of it is, but what is the physiology behind this? The athlete knows that if they don’t slow down, they’ll become even more fatigued? But the “fatigue” is in the muscle, how do they know this? There has to be a signal, and how do leaky calcium channels fit with the conscious decision?

The point is, from the perspective of some biochemical cause of fatigue, the “obvious” pacing strategy becomes very difficult, even impossible, to reconcile and explain. In that sense, you have to be “priviledged” enough to become “educated” before the obvious question becomes relevant! That’s a problem with academia sometimes – can’t see the wood for the trees, but hopefully understanding this question and its answers reveals some useful information for performance.

But, more importantly, those dismissive answers mentioned above reveal that:

2. We’re still failing to acknowledge the mechanism for this observation.

It may well be a conscious decision to speed up and slow down – “wise pacing” as people say. But apart from the fact that I’m not convinced it’s simply a “decision”, this is also not a mechanism, it’s a description. When people dismiss the question as irrelevant or obvious, and say they know the answer, they never really give it, because the mechanism requires that we explain HOW the athlete knows to slow down?

And it’s not enough to simply palm it off on “training” and “experience”! HOW does training alter pacing? How does experience influence the decision to slow down and speed up? Based on what INFORMATION is the “decision” made – time, distance, memory, pain? If you can honestly say that when you ran your last 10km race, you were consiously comparing it to the one you did in March, I’ll take my hat off to you! So yes, I acknowledge it’s pacing, but have you ever wondered how pacing is achieved? That’s the question here, and I hope that this post so far has demonstrated that a biochemical cause of fatigue is not compatible with pacing.

Speaking of the “decision”, is it conscious, or sub-conscious, and does it matter? In other words, does the athlete literally DECIDE to slow down through a process of rationalization and discussing it with himself: “Mike, time you slowed down now, because if you don’t, you’ll be in trouble at the 8km mark“. But again, HOW does Mike know this? Or does something else cause that slowing down via an independent mechanism the athlete is not aware of?

The key concept – a co-ordinated system with INPUTS and OUTPUTS

All relevant questions, but the one with most merit is this:

What cues, what signals, what experiences, what training, and what physiology are responsible for enabling the athlete to consciously slow down in the middle, and then speeding up at the end of a race and still optimize performance?

Remember, the athlete is still running as “fast as they can” for the distance – Gebrselassie finished his 10km race having gone as fast as he could, just as you probably did in your last 10km race. So you finished, having balanced the requirements to avoid any limit to exercise with the requirement of running as fast as possible. Here, we have to also make mention that some people don’t get it right – they start too fast, or too slow, fail to finish, and we’ll discuss why that happens at some stage. But in general, most people, if left to their own devices and time-targets, will come very close to running an “optimal” race while still avoiding the physiological failures we introduced yesterday!

And here’s the crux – the pacing strategy is the OUTPUT, the work done by the muscles, which are instructed to contract by the brain. But in order to produce this conscious decision to modify the OUTPUT, something (in the brain, you’d think?) must be taking into account a wide range of INPUTS in order to generate that conscious decision.

So, far from being dismissed as an obvious conscious decision, understanding the pacing strategy is going to give us insights into two key physiological features:

  1. Inputs which will consist of changes in the periphery that ultimately have to be defended or regulated. One can quite easily appreciate how changing these inputs might alter performance. Therefore, if training and preparation can alter performance through these inputs, then understanding them is incredibly useful. In this series, the most interesting input to look at is HEAT, but we’ll also spend some time on ALTITUDE, DIET/ENERGY, and also DECEPTION, when athletes are “tricked” into running or cycling further or shorter than they expect.
  2. Outputs, which are going to comprise the muscles, which must of course be stimulated by the brain – remember the sequence is that muscle contracts only when stimulated to do so. So when the athlete slows down, there are only two possible causes: Either the muscle is fatigued and cannot do its job any longer (the peripherial model), or less muscle is being activated. The analogy here is that if you and five men are carrying a Grand Piano, it gets heavier either because each of your six-man team gets weaker, or one or more of your team leaves, leaving the rest of you to do the work. You’d slow down in response.
  3. The set of inputs and outputs must be interpreted, co-ordinated and responded to. I’m sure it’s not difficult to appreciate that this job must be done by the brain, and not some “little green Martian” as some have sarcastically joked in previous discussions!

Now, if this sounds suspiciously like a homeostatic loop for all of you with some biology training, you’d be 100% correct! For those who don’t know, “homeostasis” is just a fancy term for the system which maintains the internal “balance” of the body – signals in, outputs out, all designed to regulate the system.

Also, if you want to call this the Central Governor, that’s fine. As I wrote on Tuesday, I’m going to steer clear of this term, because it is too easily misconstrued as a centre or a “black-box” with a specific location in the brain. It’s not that at all – if you look at the ten paragraphs above, we’ve already introduced at least four aspects of it, which would involve perhaps four areas of the brain that could contribute, and so to pin-point one location is a futile task. So I’ll go with “Anticipatory Regulation” for this series, and hopefully, this post has portrayed this anticipatory regulation as more than a simple conscious pacing strategy. That pacing strategy is in fact merely the output component of a very complex, very interesting physiological system.

Wrap-up of Part I A – more to follow tomorrow…

That’s it for the first part of Part I. As I said, I’m mindful that these are “epic” articles, which might be testing your own “fatigue” just to read them! I do apologize, but hopefully you are able to break the article up and squeeze some time out to get through it. I’d rather be “longer” and more detailed than make the mistake of cutting out valuable information, so do bear with me! The one consolation for you is that because they take so long, I’ll only post once every two or three days, so there’s time to grind through it!

Join us tomorrow for the conclusion and an example of what we’ve discussed today, taken from exercise in the heat!


P.S. The paragraph below is just some musings after reading some rather heated responses to this kind of discussion – thought I’d issue a call for “open debate”! It’s not crucial to read!

Last word: Debating the issues moving forward

Last night, I read through a discussion forum on LetsRun.com, where the topic of the “Central Governor” was being discussed. It was quite clear from this forum that the fatigue issue will attract its fair share of opinion, argument and debate. And that’s fantastic – it is, after all, the reason for our existence! However, what I would like to request is that any debate be done with an open mind, regardless of which side you’re coming from.

The discussion on LetsRun reveals a characteristic trait of people – they approach debates with their minds already made up, and little can convince them to even listen to any other possibilities – we’re all that way, to some extent. Our goal with this (or any other) series is not to change minds or win people over, but rather to encourage the recognition that if your perception is ever shown to be incomplete or incorrect, then by listening to others, you may improve your own understanding enough to move nearer to the “right” answer (whatever that may be!). The problem for many people is that the debate tends to rapidly degenerate into a situation where the facts are no longer discussed, and instead, abuse is hurled back and forth – let’s hope that this series doesn’t provide the platform to create this situation, as it did on the forum mentioned above!

So with the hope that it doesn’t, and as I said in a response to a comment in the previous post, bear with us having to attempt to summarize literally thousands of articles and ten years worth of debate into a month-long series! Also, we’re not here to indoctrinate, but to gradually work through a very complex topic, which, as I said, could literally be written as a dozen PhD theses (and has been!)

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