From: ekp@mcnc.org (Edward Pavelchek)
Subject: Re: Fitness thoughts
Organization: Good place for a disclaimer
Date: Mon, 31 Aug 1992 20:44:09 GMT

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. In other words, I'd bet that the energy from anerobic
>   intensity is going mostly to generate muscle contractions rather than fuel
>   for the aerobic metabolic paths. If something is chasing me, I'm much more
>   worried about getting away first, *then* worrying about removal of waste
>   products from my body.
>
>   I didn't see anything in McArdle either supporting or refuting this
>   model...

Could you please expand.  My readings of Lehninger, and the exercise
physiologists, are not at all clear on this point.  The rate of the
Krebs cycle is controlled primarily by citrate synthase, oxaloacetate,
and acetyl-CoA concentrations.  The Krebs cycle is touted as self
conserving, so that one molecule of oxaloacetate might do an infinite
amount of work.  If the power demand is such that more oxaloacetate is
needed, it is synthesized from pyruvate, the product of anaerobic
glycolysis. Thus if 'something is chasing you', you generate large
amounts  of pyruvate - if only a small % of that is needed to accelerate
the aerobic pathway, it is a token price to pay, since the energy
available from the aerobic pathway exceeds that from anaerobic
glycolysis.  I think it's more likely that oxidation continues.

Astrand discusses the use of short (1/2-3min) bicycle sprints as
measures of the power of the various systems. He summarizes as an
example:

Phosphagen storage - 4000w, for a few seconds
Anaerobic          - 2000w for several seconds, 350 w for 3-6 min
Aerobic            - 1400w


If anaerobic pathways shut down aerobic ones, then you should be able to
sprint as fast in a nitrogen atmosphere. Correct? You really don't need
even that, since you wouldn't be generating any CO2 to get rid of.
Betcha it won't work for a 220.

>3. The accumulation of lactic acid in the muscle cells, without proper
>   warm-down, will hinder recovery, possibly limiting the number of workouts
>   that one can do in a week.  By staying below the anerobic threshold,
>   exercisers will automatically minimize the amount of lactic acid in the
>   muscle cells at the end of their workout.

Although a warm-down does lower blood lactate levels faster than rest, 
the prevailing opinions, based on muscle biopsy, are that muscle
soreness is not based on lactate accumulation.  Lactate does not
accumulate in muscles at endurance levels, but is circulated.
One experiment of dual muscle biopsies and blood levels showed that
muscle lacatate was elevated above blood lactate 
for 7 minutes after exercise (Astrand, p318), but was then
slightly below blood lactate for most of the 40 more minutes to reach
resting levels.  The graph appears to show about a 4 minute time
constant for muscle -> blood lactate.

-- 
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