From: pae@blackcat.stortek.com (Phil Earnhardt)
Subject: Re: Fitness thoughts
Organization: StorageTek, Louisville, CO
Date: Sun, 30 Aug 1992 01:08:26 GMT

In article <1992Aug28.211219.11301@hpcvusn.cv.hp.com> harry@cv.hp.com (Harry Phinney) writes:
>mazur@inmet.camb.inmet.com (Beth Mazur) writes:
>: Geez, you mean you haven't heard that people burn more fat exercising at
>: a lower intensity?
>
>I would agree that a person will derive a higher percentage of their
>energy from fat at lower intensities, but I am not convinced that one
>will use less total fat at higher intensities.

This thread started with questions about unfit people getting fit. In that
context, it is indeed *far better* for exercisers to mostly stay well below
the anerobic threshold (i.e. the onset of blood lactase accumulation). There
are several likely reasons why an overfat person on the road to fitness should
stay mostly in the aerobic range:

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...

2. Untrained atheletes have a far lower tolerance for anerobic exercise --
   the blood lactate concentration will kick up at far lower exercise
   intensity than it will for trained atheletes. The discomfort/pain
   associated with accumulating blood lactate could cause exercisers to
   either cut short his current exercise session or perhaps curtail their
   entire exercise program.

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.

4. Even if the rate of fat metabolism is unchanged when one exceeds the
   anerobic threshold, the amount of carbs getting consumed will definitely
   increase. This may lead to cravings for food, etc., soon after
   exercising, and an unfit exerciser may not know that what he really needs
   is complex carbs at that point. 

>: When you start working out so hard that you are gasping,
>: or unable to breath comfortably, you are at the anaerobic threshold.
>
>Even assuming that one equates hard exercise with going beyond the AT,
>there is no reason to believe that the aerobic metabolisms are blocked
>at this higher intensity.  On the contrary, one's maximal oxygen use
>(and thus the maximum output level of the aerobic metabolisms) will
>occur at an exercise intensity beyond AT (i.e.  VO2max).  I don't
>believe that the fat metabolism is blocked at high intensities, but
>rather its power output represents a (much) smaller portion of the total
>power produced.

Harry, have you seen any studies that have looked at VO2max in non-athletes
(specifically, unfit people)?  Does this property hold for them as well?

>[...]  The fat metabolism will reach it's peak output level at a lower
>intensity than the aerobic carbohydrate metabolism, which will in turn peak
>at a lower intensity than the anaerobic mechanism.

What is the relationship of the fat mechanism's peak output and the anerobic
threshold?

>[...]  Many people are likely interested only in those adaptations which
>can be gained at intensities up to the maximum output level of the fat
>metabolism.  For these people there is no reason to put up with the
>additional stress and pain of more intense exercise.

Another "stress and pain" may arise from those people trying to understand
the subtle nuances of human physiology. For unfit people starting an exercise
program, it's unnecessary to read the McArdle text, or even to understand the
wealth of information that Harry and others present in their misc.fitness
postings. All that's needed is something like _The New Fit or Fat_. Read that
book, start your exercise program, then pursue more distinctions about
fitness only if you're really interested.

On the other hand, if you're an athlete, it's a lot more important to have a
rich body of knowledge in the field.

>Harry Phinney   harry@hp-pcd.cv.hp.com

--phil
pae@blackcat.stortek.com
Newsgroups: misc.fitness