Tuesday, 15 April 2014

What slows us down, Part 1

Running Marathons and especially Ultra-Marathon tax out mind and bodies in quite different ways to shorter races, the further you run the less important basic speed is and more important mastering all the other aspects of what effects our running performance.  In a series of posts I'll explore what I've learnt so far about effects our running performance during very long runs and provides some suggestions on what we can do to minimize what slows us down.

What slows us down

In this section I'll quickly enumerate various issues that we have to deal with as the race progress, then in the next section start to look at these in more detail with suggestions on what to do in training and on race day to mitigate how much they'll slow us down.
  1. Conscious and sub-conscious, the role of Central Governor
  2. Homoeostasis
  3. Liver and Muscle glycogen depletion
  4. Fat vs Glycogen/Glucose metabolism
  5. Muscle damage
  6. Injury
  7. Central Nervous System (CNS) Fatigue, and in particular Cramp
  8. Blood imbalances and toxicity
  9. Hormones
  10. Mental Fatigue and Mental State
  11. Heat Stress
  12. Cold Stress
  13. Gastric Stress
  14. Dehydration
  15. Blood pressure
  16. Navigation errors
  17. Terrain
  18. Weather
  19. Night vs Day and the need for sleep.
  20. Pacing + splits
In this Part 1 post, I'll discuss my thoughts on points 1 through to 3, and tackle the others in subsequent posts.  

Disclaimer, I'm not a medical expert so feel free to correct me/add to my own thoughts - it'd be great to spark debate on these topics.  What I write here is is all stuff I've gleaned from books/articles on the web, drawing all this stuff together in the context of marathoning/ultra-marathon hasn't often been done so I think it should make for an interesting discussion - even if it takes a bit of geek to really enjoy this type of pondering! :-)

1. Conscious, sub-conscious and the role of Central Governor

Our brains work at both conscious and sub-conscious levels as we run our races, both sides are entwined together in ways that aren't readily apparent to the conscious thought that we relate to as being the person we are.   Ideas spring up into our conscious thought seemingly randomly, but often it'll be something that one of the sub-conscious activities of our brain need to raise up for us to deal with consciously, be it realising we are thirsty or need the loo through to becoming aware of fatigue or injury.  Understanding that this interplay is at work is crucial to how all our systems mesh together. 

Our sub-conscious brain activities can be quite autonomous and reach down into our central nervous system and down into our gut that itself has a very sophisticated nervous system.  These sub-conscious systems run our body and make sure that our hearts beat, our lungs function, management of  digestion works, heating/cooling of our bodies 

One aspect of this sub-consciousness processing has been labelled in Sport Science as the Central Governor.  The Central Governor is more of emergent behaviour rather than a specific bit of processing or part of brain, it's a likely a collection of different safety mechanisms built into our brains/central nervous system that work to ensure that we will survive whatever endeavour we are pushing our bodies through.

Our conscious thought sits above all these sub-conscious systems and can hint to them that we wish to go faster, but it can only hint, if these systems don't feel it's safe then can be quite unresponsive and reply to us with pain the fatigue.  The is now even speculation that fatigue itself could be an emotion conjured up by our sub-conscious to slow us down.  I believe it's likely that we feel like we've hit "the wall" when running it is likely to be our Central Governor deciding that we don't have a safe reserve of fuel or hydration to push on and passes this message on as fatigue.  This fatigue can be all consuming, where no amount of conscious will can coax us back into swift motion.  This fatigue can also be ephemeral, even small bits of new external or internal information can be enough for the Central Governor to relax it's grip and our pit of fatigue can lift.  

Figuring our what our Central Governor is concerned about can be key to avoid these low points and helping get of them if we find ourselves struggling.  The further and longer your run the more likely you'll hit these low points.  As the Central Governor watches over all our bodies systems, most of the points I raised above are under it's umbrella, all of these elements can individually slow us down, but it's the Central Governor's role to integrate all of this and provide feedback to the brain about overall health status.

It's not often to hear athlete's talk about mind of matter, that from some where  deep they found the will and energy to carry on.  Personally I believe this shouldn't be a battle of conscious will against the Central Governor.  We shouldn't try to beat it into sub-mission but work with it, listen to what it's telling us even if how it tells us can be a bit indirect, if we fix the problems then it will relax it's grip and we can progress.  

In terms of finding energy from nowhere, this isn't really the case, we have the energy systems within to live for months without food for months before death, all we really are doing when we find these hidden reserves is to metabolize fats and proteins for energy, or empty our liver glycogen stores just a bit further than our Central Governor previously thought safe for us to utilize.  Our bodies are perfectly capable of functioning with low reserves, and if you have trained to use your fat reserves efficiently you can actually move efficiently for many hours.

The better we get at listening to our bodies needs and the sooner we address them the happier our Central Governor will be and the less it'll stand in our way and better we can perform.  The better you get at this the less conscious effort will be required to overcome fatigue and the faster you'll be and the more you'll enjoy your races.

It has been found that the Central Governor includes an ability of it to be predict what will happen to our bodies in the future, so if the day is going to be hot then it can slow us before we generate too much heat of our own.  Central Governor also can be trained so that if your are safely pushed your body before it's far more likely to stay relaxed and allow you to push further and harder.

Conversely if something unexpected happens the Central Governor have rapidly become conservative and hold you back.  If you can avoid sudden and unexpected external changes then Central Governor will itself be able to better predict what will happen next and if it's safe then to stay relaxed and not interfere.

2. Homeostasis

While the Central Governor concept provides a umbrella model of the sub-conscious processes that watch over our body and it's physical output (i.e. our pace), the concept of Homeostasis is a companion concept of collection of physical systems in the body that need to be maintained internal balance with various systems kept with in safe limits for us to remain healthy and fully functional.  The further we push our bodies out of Homeostasis the greater stress, damage and ultimately life threatening risk.

The systems that our bodies attempt to keep in Homeostatis include:

  • Temperature
  • Water
  • pH
  • Blood sugar levels
  • Electrolyte balance
Our nervous and endocrine systems control homeostasis using feedback systems provided by various organs.  I also expect the Central Governor will also be part of the loop as management of these systems are directly effected by the intensity of exercise, so if the Central Governor steps in and slows us down by creating fatigue the pressure pushing us out of homoeostasis can be reduced.

At a conscious level we can also monitor what systems that need to be kept in Homeostatis and react to it or even better plan ahead so that we can alter what we do, wear, or consume to help our bodies remain in Homoeostasis.

3. Glycogen Depletion

Usually when runners think about Glycogen (the form of sugar stored in our muscles and liver) depletion we think of our muscles running our of Glycogen and this causing us to slow. While this is big factor for us to contend with it is far from the mos critical one in terms of the risks of Glycogen depletion as our muscles can turn to metabolising fat for fuel.  The more slow twitch fibres a muscle has the more capable it is of metabolising fat for fuel.

By contrasts the brain can not directly metabolize fat, it relies primarily on blood sugar for it's function.  If our blood sugar drops then our brain will begin to fail, early signs will be poor brain function, but if blood sugar goes lower we loose consciousness, and if lowers still further we will die.  The organ in our body that has the task of maintaining blood sugar is our liver that has stores of glycogen that it steadily releases into our blood stream as required.  If our liver becomes seriously depleted of glycogen it can turn to glycogenesis (converting protein to glucose) and ketosis -- converting fats into ketone bodies our brains can use in place of blood sugar.  However, these systems don't readily take up the slack.

Given the critical nature of blood sugar to our brains and how it's the liver that required to maintain blood sugar the level of glycogen depletion in the liver is crucial organ for the Central Governor to track.  If the Central Governor predicts that we are exhausting our liver glycogen stores then it will fatigue us to dramatically slow us down until the demands are low enough to be taken up by glycogensis and ketosis.  This slowing might mean walking right down to needing to lay down and sleep.

Another organ that is reliant upon blood sugar is our digestive system.  When blood sugar is low it's ability to digest food and water is impaired.  This may be a factor is why gastric stress can plague us during the second halves of ultra-marathons.

Given the reliance of our brains and gut function in blood sugar levels and their reliance upon the liver to maintaining it, avoiding liver glycogen depletion is likely more important to avoid than muscle glycogen depletion.  When we eat during an ultra-marathon consider foods that replenish the liver efficiently and maintaining blood sugar rather the viewing food as fuel as fuel for our muscles. 

Glucose gets absorbed via the small intestine into the blood stream, while Fructose (fruit sugar) and Lactose (milk sugar) get shunted directly to the liver.  We can't absorb as much Fructose and Lactose as Glucose so it doesn't make sense to just rely upon these pathways, instead the most productive route is likely to consume something like a 2:1:1 mix of Glucose, Fructose and Lactose.   

Glucose can be consumed in the form of complex carbohydrates rather than straight Glucose, the digestive system breaks down the complex carbohydrates down into Glucose which is then absorbed into the blood stream.  Carbohydrates takes longer to digest than Glucose so provide a steadier release into our blood streams so generally is likely to be preferable for longer races.

The Central Governor also watches what we eat and uses this into own predictions.  It has been found in study that even washing your mouth with sugary drink and then spitting it out can fool the Central Governor into thinking that glucose is safely on it's way and that it can release it's grip on our pace and we can feel a boost of energy.  This isn't something you'd want to do during the first part of long race, but near the end where gastric stress can be limiting what you can consume it can be a useful trick to coaxing your body over the line. 


In Part 2 I'll work through more items on my shopping list of what slows us down, I'll try to get to this over the next week.

1 comment:

  1. I strongly agree that in marathons and ultras many different physiological systems are under stress, so performing well is not merely a matter of power and aerobic capacity. I also agree that the central governor concept is very useful. As you say, it is almost certainly not located at a single site within the brain though I believe that a network of brain systems that interact to produce a small number of quite specific signals. Dopamine transmitted from midbrain to deep grey matter, especially the ventral striatum, is one of the key signals. Depletion of dopamine results in profound lethargy. Increase in dopamine promotes a feeling of energy and drive.

    I agree that we are more likely to perform well when we work with the governor rather than fighting it. So what strategies allow us to do this? Using stimulants such as amphetamine to promote dopamine release can work dramatically, but not only is this cheating it is also dangerous because we might fool the governor into allowing too much effort. The roar of a supporting crowd is also likely to promote dopamine release. That can be a big factor in city marathons, and perhaps to a lesser extent in ultras. But in an ultra, the need is to find one’s own form of internal imagery or dialogue that achieves a similar effect.

    But the governor is more than just a controller of the dopamine ‘thermostat’

    I agree that conserving liver glycogen and ensuring the supply of glucose to the brain is a key issue, but think you underplay the need to sustain glycolysis in muscle. Because fat is metabolised more slowly a runner would have to be extremely well fat-adapted in order to sustain a running pace on fat alone. But more importantly, fat metabolism leads to energy production via the Krebs cycle, but unlike glucose metabolism, fat metabolism cannot restock the pool of Krebs cycle metabolites. This pool gets depleted due to the production of glutamine – an amino acid produced in muscle by an offshoot of the Krebs cycle. Glutamine is transported for the muscle to other organs, most importantly to the gut where it plays a key role in keeping the gut functioning well. So I think even an ultra-runner relies on at least a small amount of glucose metabolism. The key question is what this tells us about nutrition during an ultra. Clearly a supply of carbs is required but the stomach rejects simple sugars after a few hours. In part this might be a matter of the consistency of the food, but probably even more important the body craves other things –amino acids including glutamine but probably other things as well. I look forward to you returning to these issues in topics 8 and 13.