Re: Carbo Collaboration

[Tivers@aol.com]

In a message dated 12/16/99 9:55:24 AM Pacific Standard Time, lb@nismat.org 
writes:

<< 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]:>

Hey, Beth, good to hear from you. If everybody agreed, wouldn't life be 
boring as hell? Everycody'd assume they know everything there is to know from 
the getgo. And we'd all be raving idiots.
 
 <<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". >

And can often be translated to "low or crashing blood sugar".

> 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. >

Just learned something. Thanks, Beth.
 
 <<<<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.>

Correct--slower, less energetic firing.
 
 <>
 
 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.>

Except that elevated glucose/insulin will cause a preferential shift toward 
that energy source over fats and any other slower acting fuels. As Heidi 
suggested, you could intube a flowing source of glucose and nearly eliminate 
the use of fats during exercise.  
 
 
 <<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. >

The key is maintaining elevated blood glucose. Insulin's job is getting it 
"even". A "normal" glucose is about 90, an elevated glucose is above 100 and 
a low glucose, with the ability to cause a case of the staggers, is down 
around 60. And none of this has anything to do with glycogen stores in 
muscles, except that they are being increased as elevated blood glucose is 
pushed into muscle cells with the help of insulin.
 
 <<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
 
  >>

Likewise.

ti


=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=
Ridecamp is a service of Endurance Net, http://www.endurance.net.    
Information, Policy, Disclaimer: http://www.endurance.net/RideCamp   
=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=