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Friday, October 16, 2009

Ross speaks: Fatigue and the brain

Anticipatory regulation of exercise

Apologies for the delay in posting after my lecture last week at UIC - the Chicago Marathon came and went, and since then, travels have taken too much time to post properly.

However, what I've done below is post segments of that talk, which was titled "Limits to exercise performance: World records, fatigue and unphysiological performances".  Unfortunately, Jonathan was a little off at an angle, but hopefully the video is clear enough and the sound good enough to make out the argument.  Just in case, the diagram is shown below the video, so you can follow it there (hopefully).  Also, if you're getting this as an email, the YouTube clips might not play, so you may have to click here to go to the site and view the clip there.

The first video, 3:56 long, presents a model which I wrote about in an article published earlier this year in the British Journal of Sports Medicine, called "The anticipatory regulation of performance: the physiological basis for pacing strategies and the development of a perception-based model for exercise performance" (BJSM, 2009 Jun;43(6):392-400)

The model explained:  Complex anticipation and RPE

Obviously, you're watching a part of a presentation slightly out of context, but hopefully it gives you the basic idea.   This is a topic that has been covered a few times on the site - in fact, there's a whole series on Fatigue for those who are interested.

To summarize, your ability to regulate pace (which is something I'll bet you've never even think about) is vastly more complex than you may realize.  Even the most basic decision of how fast to start a 5km versus a 10km race is the result of innumerable calculations, which take into account previous experience, training, motivation, environment (internal and external) and physiological changes during exercise.

It really is a remarkable system, and one which we believe is primarily regulated by the perception of effort.  This is something you probably also haven't thought about much, but the way you perceive exercise is in fact so enormously complex that science is many years away from understanding it.

There is debate in science about whether your perception and the regulation of the pace is done consciously or sub-consciously, and that's where the debate seems "stuck" (or centered) right now.  I suspect that, as with most things, it will turn out to be a combination, for conscious regulation is obvious (you choose to slow down), but so is unconscious regulation - you don't have to think about starting pace, and you also slow down 'involuntarily' during exercise, even though your perception of effort is not necessarily raised (very important point this).

To explain, the physiological inputs before and during exercise result in a conscious perception of effort, which is then interpreted based on the expected duration and the "template RPE", which is a construct representing what would be considered an acceptable rise in RPE.  This interpretation of RPE underscores why exercise intensity changes dynamically during exercise.  It explains how motivation impacts on performance, and it accounts for the effects of changing conditions on performance.  This is why you speed up at the end of a race, even though your body temperature may be close to limiting, whereas you slow down in the middle, when you are not hot.

The idea that your physiology 'controls' pacing is flawed, because it ignores the importance of context - not all physiological inputs are interpreted equally!

Applying the model to the heat

The next video, shown below (2:30 long), shows a simplified model for what would happen during exercise in the heat.

We know that if your body temperature hits 40 degrees (maybe a little higher in highly motivated elite athletes), your ability to exercise is limited - this temperature is associated with nervous system failure, lack of co-ordination, dizziness, and a failure to activate muscle.

Put simply, if you hit an internal temperature of 40 degrees, your race is basically over - you either walk to the finish line, or you fall over in a cool spot and hope to cool off!

But luckily the body is too smart for this - the pacing strategy is adjusted in advance of this failure.  The previous video, on the RPE and the model for regulation, explains how this would happen.  What this second video is showing is that the 'calculation' is made in order to balance the requirements for fastest possible time with physiological 'safety'.

Obviously, stopping at the 36km of a marathon is failure.  So too is death from heatstroke.  But, equally bad is running twenty minutes slower than you could have done, because your brain has been "too conservative".  So the balance is achieved by forecasting the physiological outcome of current behaviour.  Put simply: "If I continue at this pace, storing this heat, will I finish the race before I run into danger?"

On a hot day, when heat storage is higher thanks to reduced heat loss, the answer may well be "NO", in which case the brain reduces muscle activation and thus pace, and the race can be completed in a slower, but feasible time.  The endspurt at the end comes when the body temperature is at its highest, but the risk is now absent, because the brain takes into account the exercise duration remaining, as explained previously.

So that is it in a nutshell - it's not all dreamed out of thin air, mind you!  The BJSM paper I linked to above contains all the references and evidence on which this model was built, so feel free to check that out!

Travel update

Just a quick travel update, seeing as how I'm making my way across the nation meeting all kinds of interesting sports science-related people:  I'm now in the Rocky Mountains, at an altitude of 3,500m, where I am learning new respect for Kenyan and Ethiopian runners who train at this altitude all the time!  I run at least a full minute per kilometer slower than normal, but my lungs feel as though they've completed 10 consecutive 800m races.

I head to Boulder tomorrow, where I will meet with a number of coaches, athletes and experts, and I'll be sure to interview and post interesting comments here.  So join us then!



Anonymous said...

Sorry to say this, but after 3 minutes of video, what I can say is that all I heard was some acoustic noise.

Anonymous said...

How closely do you think the body's ability to regulate pace is related to your body's ability to keep track of time? Reading this article in conjunction with yours made me consider it.


When will there be Science of the Sports t-shirts! I'd buy one in a heartbeat.

Colenso said...

Thanks you once again for a very interesting overview of this topic.

It was not until I moved to the Tropical Far North of Queensland fifteen years ago, in 1994, that I gradually began to discover from personal experience some of what you have described.

Training in the UK, say running 800 m intervals, was psychologically something to which many years of practise had accustomed me from my days as a schoolboy runner. Long habit had taught me exactly what to expect on a typical English summer evening when I was half-way through a series of say six repeats of 800m at, say, 2:24 pace (3 min/k).

Trying to do the same around an 800m loop around the two saltwater ponds in Cairns Centenary Park was to prove a quite different experience. Put simply, I now could not get the same feeling of what I had always assumed was lactate build- up in my legs, as when I had used to train in the UK. This was because, rightly or wrongly, I now perceived that I was overheating long before I believed I was feeling the build-up of lactate in my legs that I had grown to expect when I trained hard.

Staying cool in the Tropics, then, had become my overwhelming training need, physiologically, or so at least it seemed, and certainly psychologically. Further, and I know you are probably sick of me repeating this, but the effects of humidity and solar gain when training hard in the tropics during day-light now became overwhelmingly important in ways that they had never been for me when I used to run even in the height of summer even in the middle of the day somewhere fairly hot, in Southern Spain for example.

Also, I found that being relatively heavy, compared to my eventual racing weight (and of course to most of the better distance runners), when I was undertrained, often starting off with BMI of 25+ at the re-beginning of training seriously, also seemed to have a much larger effect on my sense of comfort when training in the tropics. Of course, I appreciate that this could also have been as much to do with the fact that I was now older, and that my ability to cope physiologically and/or psychologically with the sensation of feeling bloody hot and uncomfortable had diminished.

I am now so affected by the ambient temperature, plus humidity plus solar gain leading to the unpleasant sensation of intense overheating, when training hard in the tropics, that I find it very hard these days to train in the full sunlight of a typical day in the tropical north - I feel that I am about to explode, I feel so hot.

So I now do all my serious training late at night, many hours after the sun has set and the tarmac road surfaces have started to cool.

Increasingly, in fact, I run long distances (fast and slow as is my custom) only when running barefoot on the beach, in the dark, letting the sea water occasionally cool my legs as I run. This all driven by my overwhelming need, as I see it, to try to run hard yet cool.

Colenso said...

PS Shortly after we had moved to the tropics, we got talking with an old chap who told us that he had lived in the tropics for much of his adult life, but was now moving south to cooler climes.

When we asked him why, he said that he could no longer cope with the heat and humidity now that he was that much older.

butterflyblue said...

This is the first I have heard of your site and after some perusing, excellent job! As someone with twenty years in the medical field with an understanding of blood physiology, oxygenation, etc, it is refreshing to see you put your topics into scientific terms with some evidence based research. I am often told by my coach to do certain things when I am training-only when I have scientific reasons does it really click and motivate me to do so. That said, I may need to correct some of his theories... Your website is a tremendous help to this aspiring age grouper triathlete. Sometimes it takes that third person to drive home things you already know to finally connect the dots.

Tom Bernhard said...

I found the Fatigue and the brain - Anticipatory regulation of exercise thread fascinating reading. However, based upon my experience in a half marathon yesterday, I was wondering if there was an additional aspect to the topic not covered. Here is what happened to me. I had a problem with my left glute after 9 miles of the race. This weakness caused me to slow down by 15-20 sec/mile. As a result of this, several runners passed me which was very frustrating. With about a 1/3 of a mile to go, one more runner passed me and I decided he was not going to beat me. I struggled to stay with him and with about 150m to go he had about an 8-10m lead on me. At that point, I went into a dead sprint, blew by him and ended up beating him by 4 secs (or at least 3.1 sec with the round-up). Now obviously, my glute did not miraculously heal itself to allow me to do this. I think what may have happened is that by going anaerobic I utilized the fast twitch muscle fibers and neurons and these fibers were less damaged than the slow twitch fibers of the glute. Therefore, I could sprint without a problem.

Now one of the main points in the Fatigue and the Brain piece is that runners are able to speed up at the end of the race because the brain (governor) knows the race is almost over and allows the body to go all out without fear of damage, i.e., psychology over physiology. I think that is a very valid point. However, I’m wondering how big a factor, if any, the fact that the runner is going from an aerobic pace to an anaerobic pace may be. Perhaps that physiology plays an important role as well.