From: ekp@mcnc.org (Edward Pavelchek)
Subject: Re: Fitness thoughts
Organization: Good place for a disclaimer
Date: Tue, 1 Sep 1992 18:56:19 GMT

In article <1992Aug31.223257.2937@stortek.com> pae@blackcat.stortek.com (Phil Earnhardt) writes:
>In article <1992Aug31.204409.2463@mcnc.org> ekp@mcnc.org (Edward Pavelchek) writes:
>>In article <1992Aug30.010826.15707@stortek.com> pae@blackcat.stortek.com (Phil Earnhardt) writes:
>>>1. Since the aerobic metabolic paths require the energy released by burning
>>>   carbs at several steps, it certainly seems plausable that the aerobic
>>>   pathways would get shut down when the muscle cell is going at an anerobic
>>>   level of intensity. [...]
>>Could you please expand.  My readings of Lehninger, and the exercise
>>physiologists, are not at all clear on this point.

>It may be about time to drop this discussion into email...

Au contraire.  An earnest discussion of exercise metabolism must be
worth at least 3 average jokes about Adam's legs.

>My understanding is that certain steps in the Krebs cycle can only happen in
>the presence of anerobically burning carbs. Was this incorrect?

I asked you to expand on that. In any event, this requirement is small. 
If resting muscle use is 10% carbs, since ATP production from glucose is 
5% anaerobic and 95% aerobic, this means that in a resting muscle, 
anaerobic metabolism is capable of supporting at least 200x its power
in aerobic metabolism.  In starving people, this fraction appears to be
much lower.

>I'll believe that the aerobic metabolic paths are not totally shut down. The
>question asked in the follow-up was whether or not their output is decreased
>at or above the anerobic threshold. Do you have any information on that?

Of course! Oxygen consumption implies aerobic metabolism.
Obvious first order evidence is that during a  VO2 max test O2
consumption does not drop above the lactate threshold, but continues to
increase.  My previous comments (in response to Bud) were not that
aerobic metabolism shuts down, but that it switches to glucose, rather
than fat.

[about lactate not causing sore muscles]
>This sounds reasonable to me. My main question: was the research done on
>atheletes or non-atheletes?

The one guy put out 400 watts for 2.6 min - depending on his size, this
could be mediocre to pretty damn good, but not world class.

>Ed, are you disagreeing with the overall thesis -- that unfit people getting
>fit should generally stay below the anerobic threshold? In other words, are
>you saying that my thesis is flawed or that my reasoning is incorrect?

No, I've repeated time and time again - it's hard to sustain anaerobic
work, which limits you to too little exercise to really help.  For lots
of the reasons we should be discussing.  On the other hand, some unfit
person who jogs for 2 minutes, then walks until he can jog again, will
probably get as much or more out of 3 miles as someone who just
walks, even though he is above the lactate threshold.  It takes a lot
more willpower, that's all.

I guess I have several questions about your reasoning, though.
-- 
Ed Pavelchek   ekp@mcnc.org
But I make a profit of 3 1/4 cents an egg by selling them for 4 1/4
cents an egg to the people in Malta I buy them from for 7 cents an egg.
Of course, *I* don't make the profit.          Joseph Heller, Catcha 22
Newsgroups: misc.fitness