From: keg@strathspey.llnl.gov (Keith Grant)
Newsgroups: misc.fitness,rec.running
Subject: Re: Fat Burning Primer
Date: 2 Oct 92 16:23:31 GMT
Followup-To: misc.fitness
Organization: Lawrence Livermore National Laboratory
Originator: keg@strathspey.llnl.gov


In article <1992Sep30.143846.12535@inmet.camb.inmet.com>, mazur@inmet.camb.inmet.com (Beth Mazur) writes:
|> In <1992Sep29.155747.24138@cs.ucla.edu> page@ficus.cs.ucla.edu (Thomas Page) writes:
|> >I'm not sure what you are talking about concerning zip codes.  During the first
|> >10 minutes of exercise, you burn almost exclusively glycogen. 
|> 
|> Please cite a reference for this.  The exercise physiology text I was
|> scanning last night claims that the body is up to 40% aerobic metabolism
|> two minutes after you begin exercise.
|>  
|> Beth Mazur                   "...life is more than a vision.  The sweetest


Based on info in the text:

Powers, Scott K., and Edward T. Howley, 1990: Exercise Physiology - 
Theory and Application to Fitness and Performance, Wm C Brown, Dubuque, IA

The body will reach steady state VO2 (oxygen uptake) within 2-6 minutes of
the start of submaximal exercise.  The time to reach steady-state is slower
in untrained participants relative to trained.  (This is the "aerobic
metabolism" that your physiology book was refering to).

On the other hand, Scott and Howley comment regarding fuel utilization:

"Proteins play only a minor role as a substrate during exercise with fat and
carbohydrate serving as the major sources of energy during activity in the
healthy individual consuming a balanced diet.  In general, carbohydrates are
used as the primary fuel during high intensity exercise.  Further, 
carbohydrates serve as the major substate at the onset of low-to-moderate-
intensity exercise.  However, during prolonged work (i.e. > thirty minutes) 
there is a gradual shift from carbohydrate metabolism toward an increasing 
reliance of fat as a substrate.  Whether fat or carbohydrate is the primary 
substate during work is determined largely by the availability of the fuel 
to the individual muscle cell and those factors that regulate glycolysis, 
the Kribs cycle, and the electron transport chain".  They further cite
the papers:

Gollnick, P., 1985: "Metabolism of substrates: Energy substrate metabolism 
during exercise and as modified by training", Federation Proceedings,
44, pp. 353-56.

Gollnick, P., W. Bayly, and D. Hodgson, 1986: "Exercise intensity, training,
diet, and lactate concentration in muscle and blood", Medicine and Science
in Sports and Exercise, 18, pp. 334-40.

Powers, S., W. Riley, and E. Howley, 1980: "A comparison of fat metabolism
in trained men and women during prolonged aerobic work", Research Quarterly
for Exercise and Sport, 52, pp. 427-31.

I hope this helps to clarify some of the ambiguity about reaching steady-
state metabolism.  It also makes sense to me that if you exercise long
enough to deplete the muscles of their immediate glycogen stores the
metabolic changes will persist after exercise is stopped until the muscles
are replenished.  Thus short rest breaks (e.g. 10 minutes) within a multiple
hour moderate rate workout wouldn't greatly diminish the overall fat-burning 
effect of the entire workout.  Longer runs interspersed with walking would 
also be more effective at fat-burning that shorter high-intensity runs.

  +-------------------------+-----------------------------------------------+
  I                         I                                               I
  I Keith Eric Grant        I The interesting thing about a waltzing bear   I
  I keg@strathspey.llnl.gov I           is not how well it dances!          I
  I                         I                                               I
  +-------------------------+-----------------------------------------------+
  I                                                                         I
  I For certain it is, that any ideas expressed above are of my own humble  I
  I opinion and bear nary a relation to the policies or positions of LLNL   I
  I or of any agency or contractor of the U.S. Government.                  I
  I                                                                         I
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