Carbo Collaboration

["Beth Glace" <lb@nismat.org>]

Tivers!!
Your back!  How nice to hear from you again.  It sounds like you were 
treated like an Arabian prince - having been a guest in Moroccan 
homes, I have some idea of their idea of hospitality.  Unbelievably 
wonderful hosts.
Well, now lets do a bit of wrastlin' [to preface, I agree with 
ALMOST all you wrote]:

<<Let me add that there is increasing regard for the concept of 
Central Fatigue under circumstances like those outlined above. One of 
the endurance horses I was working with recently "bonked" toward the 
end of a very hard test at 110K. Just. Stopped. We took bloods on all 
the horses post race and this one had the lowest blood glucose of 
all, 57, and thereafter displayed a 41,000 CPK--astronomical! ....
Clearly, he had been burning muscle, and maybe was into malignant 
hyperthermia. Still, his low glucose would have thrown him into 
Central Fatigue.>>>>
I agree that Central Fatigue probably plays a role in the observed
fatigue during very long duration exercise - anectdotally, runners I
coach will often have to take a nap in their car after doing 2-3 hour
trail runs, just unbelievably sleepy.  For those less familiar with
this term, it is defined as " a negative central influence that exists
despite the subject's full motivation".  It is the fatigue observed
that cannot be explained by changes within the muscle itself.  In this
sense, the fatigue one feels at the onset of getting 
 the "flu" can be considered of central origin.  The subject has to
"try harder" to get the same amount of work done.  This is not to say
that nutrition does not play a role  in central fatigue, it does!
Carbo intake during exercise has been shown to decrease the production
of serotonin by the brain in animal models.  Serotonin is a
neurotransmitter that makes us feel sleepy and tired.  So, one
possible effect of carbs during exercise, aside from the well known
benefit of providing substrate, may be to help the athlete remain
mentally sharp and easier to motivate. 

<<<<Central Fatigue is still being studied, but it appears that bothe
muscle temperature and low blood glucose are two key factors. When the
CNS feels threatened by low blood glucose, it shuts down muscle
activity. .  >>>>>>

 I don't think that muscle is "shut down" per se, but it will seem 
harder to continue at the same intensity.

<<I would wrestle with you here. As usual, my best, most honest, most
informed advice is: forget fat! If you're down to fat in a race,
you're into metabolic quicksand. You're also burning muscle along with
the fat.>>

As I've said before, Tiv, Win or Pin!  Must take you on points.  
Forget fat?  As in forget supplementing fat during exercise?  
Absolutely.  Counter-intuitive, unproven, and possible very 
detrimental to performance.  However, we burn fat all the time during 
exercise.  At the anaerobic threshold an athlete is likely using 
50:50 fats to carbs.  Lower 
intensity work relies on fats as a substrate to a large degree, and 
that is good since it spares glycogen.  Providing carbs during 
exercise further spares glycogen.  Of course, I agree that if you 
must rely 100% on lipid while trying to race at moderte intensities, 
the horse has already "bonked" and will be reduced to miserable 
shuffling. 


<<Don't worry about insulin, either. It's your friend. It moves the
glucose into the muscle as glycogen. Just focus on maintaining
elevated levels of blood glucose and all else will follow. >>>

The key is maintaining even blood glucose.  I do suspect that the 
scenario described in earlier posts of bonking during a race with 
long holds, probably was the result of overproduction of insulin.  I 
think Heidi is right to focus on forage while in the hold, and then 
maybe some carbs just as you leave the hold or once out on the trail. 

<<Again, dworry about insulin, worry about keeping an elevated blood
glucose. The insulin is there for a purpose, it's not Public Enemy
Number One.>>

Agreed. 


<<Love you, Beth.>>

Hugs and kisses, Tom.
:)

LB


Beth Glace, MS, CDN
Nicholas Institute of Sports Medicine and Athletic Trauma
Lenox Hill Hospital
New York, NY


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