Re: RC: Re: Krebs cycle?

[CMKSAGEHIL@aol.com]

In a message dated 12/17/99 10:01:01 AM Pacific Standard Time, 
fasterhorses@gilanet.com writes:

<< Various "fuels" (carbohydrates & fats... are these the FFAs & VFAs that
 are being talked about?) are processed to create ATP, which is the
 source of energy.  This is called the Krebs cycle.  But the Krebs cycle
 occurs aerobically, and anaerobic work causes the Krebs cycle to be
 "bypassed" and instead lactic acid is formed.  Which can be used
 anaerobically, but not aerobically.  Yes?  No?
 
 Now, *if* this is roughly what is going on, is what Tom is talking about
 a method that bypasses the Krebs cycle, but *doesn't* produce lactic
 acid?  Am I even getting warm here?  >>

1)  FFA's and VFA's are the same thing--free fatty acids or volatile fatty 
acids.  They are not the same as carbohydrates, but yes, both VFA's and 
carbohydrates are utilized in the Krebs cycle to create energy.

2)  Glycogen and glucose can be "used" more immediately directly by the 
muscles in anaerobic work, but a) less net energy is produced this way, and 
b) lactic acid is produced much faster than it can be utilized or gotten rid 
of when this is the primary way of getting energy.  That is one reason why 
anaerobic work can only go on for a short time.  In aerobic work, most of the 
energy comes from the Krebs cycle.  Since very little comes from direct 
glycolysis, what little lactic acid (which is one of the VFA's itself) is 
produced can be burned by the Krebs cycle instead of building up in the 
muscle and causing pain and cramping.  (That's why lactic acid is a factor in 
tying up syndrome in horses that perform anaerobic work, but why it isn't 
generally a factor in endurance horses.)  See Beth's excellent description of 
the Krebs cycle for a scientific description of how glucose goes through the 
Krebs cycle in the aerobic athlete.

3)  You are right on that in anaerobic work, there is some level of energy 
being produced that bypasses the Krebs cycle.  Even in anaerobic work, the 
Krebs cycle is functioning--it's just that the work load increases beyond 
what it will produce, and when that "anaerobic threshhold" is reached, the 
extra demand is met by glycolysis.  So the Krebs cycle isn't exactly being 
"bypassed"--it just doesn't produce fast enough to meet the demand, so 
glycolysis kicks in.  Depending on how far over the anaerobic threshhold you 
are running, you can exhaust the glycogen reserves and the blood glucose very 
quickly with glycolysis, or more slowly if you are only a little "over the 
line."

4)  The more fit the horse, the "higher" his anaerobic threshhold--hence the 
more work he can do (and the faster he can do it) without crossing the line 
into having to use glycolysis instead of being able to sustain his work on 
the energy coming from the Krebs cycle.  No matter how fit he is, though, 
that "line" is there somewhere.  Race horses cross it routinely, going full 
out in short races, and rating how far "over the line" they are in longer 
races so that they still have some "kick" left at the finish.  Endurance 
horses running at the front are flirting with that "line."  Crossing the line 
WILL run you out of gas, so to speak.  Tom's carbs are massaging that line, 
so to speak, to try to get the last little bit without pushing the horse over 
the edge.  However, once again, the higher the line, the better the horse 
will do, even if you "massage" the line with carbs, and in order for the line 
to be high, you have to have a fit horse with maximal utilization of the 
Krebs cycle (not to mention other aspects of fitness).  And as Beth has 
pointed out, the Krebs cycle uses a variety of substrates--including carbs 
and VFA's.

Does that help any?

Heidi


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