Friday, July 26, 2013

Eat Early, Eat Often, But Don't Eat A Lot

All endurance athletes are aware of, and to some degree fear, the dreaded bonk. This bonk is often attributed to your body not being able to access our stores of fuel in our body and turn them into energy. Our muscle contract by continually utilizing ATP which requires glucose(ahhhhh... the Kreb's cycle). The body likes doing the minimal amount of work possible so it prefers to use the readily available glucose in our blood streams which we get from carbohydrates(gels, sports drinks etc). The thought is that when our body's run out of carbohydrates(glucose), it has to slow itself down in order to turn fat cells into energy. Great for weight loss, not so good for race performance.

As Amber has mentioned before, the bonk can also occur because of the central-governer, which is your brain slowing you down to prevent tissue damage. It anticipates disaster and slows you down to avoid it! There have been several studies that show that peripheral fatigue(i.e. your muscles) occurs due to decreased stimulus from the central nervous system and this can be overridden with volitional activity. The governer has also been famously discovered to cause bonks by anticipating a carbohydrate depletion(before it even occurs) and thus proactively slows you down. It would be like your car turning itself off before it ran out of fuel!  This is different than the mental bonk which isn't your body shutting down all at once but rather slowly turning off. There have been studies looking at dopamine release in our brains and there has been correlations made with those feelings of lethargy and loss of motivation(like I get during ultras) and an increased level of serotonin to dopamine.

Okay so peripheral fatigue is caused by our bodies' inability to store enough glucose to convert to energy to fuel us. Central fatigue can be a protective mechanism to avoid tissue damage or it can be a shift in our neurotransmitters in our brain that causes a slow decline in motivation and energy.

What to do? First, let's train the brain. A study looking at central fatigue, and the central governer in particular, found that cyclists time trial performance would decline as the intervals were performed(as expected right? we get tired and slow down), however, the very last interval were actually one of the fastest! Now these intervals weren't at 90% effort where they were holding back a little for the last one(at least they weren't supposed to), but rather 100% effort. So why did this occur? And this did consistently occur. No matter how many intervals. You guessed it. The central governer was slowing them down and when the mind was able to override it by saying "look I'm almost there, I can do this" the cyclists were able to speed up. Just by doing interval training and speed work you can train your brain into increasing its exercise tolerance before it shuts you down!

Okay so you're not limited by the governah, so is it your brain's neurotransmitter ratio shifting or glucose/glycogen depletion? Well they may not actually be separate entities. Actual glucose depletion and anticipated glucose depletion can both be remedied by ingesting carbs. In fact, all you need to do to trick the brain into thinking it has enough carbs is to swish it around in your mouth and then spit it out(see the article here). You don't need all that much carbs to keep going but a nearly constant stream of the energy will not only help you stay fueled but will also help keep your dopamine levels at a level to avoid the lethergy of a mental bonk. Interestingly, glucose ingestion during exercise has also been implicated in the cytokine production. IL-6 is a classic inflammatory cytokine produced by muscle contraction and ingesting glucose during exercise can inhibit its release allowing for a decrease in the inflammatory response.

So train your brain and ingest carbs. Ease enough and most marathoners do this with speed work during their training and with gels, bars potatoes etc during the race. And yet, without fail a portion of the racers will bonk. Why? Once you've ruled out dehydration, the likely culprit is probably the fueling method. I would make the argument that consuming a gel every 6 miles(about 40 minutes) all at once is not the best strategy. Rather, try taking that same gel and savoring it over 3-4 miles starting from the start of the race, every quarter mile or so taking a small nip. This will keep your brain thinking it has plenty of carbs, your body's fuel source staying steady and helps break down the distance to more manageable goals. Plus you're far less likely to get GI issues(your GI system isn't a high priority for your circulation system(see parasympathetic vs sympathetic nervous system) during races so reducing the demands on it by smaller doses of glucose may be helpful). (Sorry for the parenthetical explanation within another parenthetical explanation-poor form I know). (I further apologize for use of parenthetical explanations to apologize for my poor use of parenthetical explanations). (Ad infinitum...)


So next time you're running a marathon(or better still try this in a long run first), try to eat your gel as early and slowly as possible. You most likely won't have blood sugar spikes, GI issues and hopefully no bonks:) Try it tomorrow at Bear Brook Trail Marathon. I will be.

Up Next: Besides a likely ill-advised last minute decision by Danny to do the Bear Brook marathon, only a few more weeks until Amber starts up her second half of the tri season with Timberman 70.3!

1 comment:

  1. Good luck at Bear Brook. I'm heading up the transition area at Timberman 70.3 so I'll see you guys there.