Ross speaks: Fatigue and the brain

16 Oct 2009 Posted by

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.

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!