exercise physiology question

hahahaha -- SO EASY TO SAY BUT SO HARD TO DO !!

"However, a small decrease in intensity (e.g. slowing the
pace) earlier in the exercise bout would spare glycogen sufficiently
to avoid depletion."

How many of us have been at the start line of a marathon and taken off
too fast KNOWING we'd pay the price later??


JKal.




wrote:
thanks AHALL

So, i'm exercising at 100 beats/minute heart rate. *I'm an endurance
athlete, well trained. *What am i burning? *Free fat in the bloodstream, fat
stores in my body, or glycogen stores?

And, yes, i've HIT THE WALL. *You can physically sense when the glycogen is
gone and you switch to fat burning. *The balanced chemical reaction, if i
remember correctly, shows that you actually need more oxygen after the
switch - you breathing increases but you're not increasing effort. *ouch,
bad feeling.

JKal.

wrote in message

...

Jeff and Stephanie Kalember writes:

* Jeff Hey all, a question for anyone out there with an exercise
physiology
* Jeff background.

* Jeff My wife has recently embarked on a weight loss/exercise plan at
"Curves"
* Jeff here in our home town. *The gals running the place tell her to
keep her
* Jeff heart rate below 132 beats per minute when exercising or "she'll
be burning
* Jeff muscle instead of fat."

The so called "Fat burning zone" is almost complete nonsense,
and one of the most common exercise myths (spot reduction is
probably the most common myth).

* Jeff From what i know of exercise physiology this is not true. *When
exercising
* Jeff we all burn glycogen stores aerobically (if the heart rate is
below
* Jeff 150-160ish) or anaerobically (if the heart rate is very high) or
fat (if the
* Jeff heart rate is very low - say approximately below 120ish). *There
would never
* Jeff be a situation where a normal person exercising in normal heart
ranges
* Jeff eating a normal diet would burn MUSCLE as a fuel.

Correct.

* Jeff I told her she can get her heart rate up to 140-150-160-170 or
anywhere in
* Jeff between and she'll still be burning up fat stores indirectly - NOT
muscle.

She will be burning them directly too. *The higher the intensity, the
higher amount
of fat burned per minute. *As intensity increases, the percentage of
calories burned
from fat goes down, but the total goes up.

* Jeff The way i learned it is that we all burn up stored glycogen first
and then
* Jeff use food to replace it. *If we are calorie deficient for food
intake then
* Jeff she uses her fat stores to replace the glycogen...

* Jeff am I right or am I wrong ??

Mostly right. *Fat cannot be converted to glucose, but it is all that is
left to burn
once the stored glucose is used up (known at hitting the wall). *Your
stored glucose
will be replaced by food, at a rate of ~5%/hour. *So it takes almost a
full day to
replenish glycogen stores.

The body will definitely burn muscle if it thinks it is not getting enough
calories
(ie a crash diet...). *This is an adaptation to famines. *Muscle demands
energy just
to sit idle, so if the body fears starvation, it will lower metabolic load
by diminishing
muscle. *Protein can be converted to glucose.

--
Andrew Hall
(Now reading Usenet in rec.skiing.nordic...)- Hide quoted text -

- Show quoted text -

Re hitting the wall etc. *The following explains glycogen vs. free
fatty acid utilization and goes in to additional detail of short vs
long events and energy sources.

http://www.nismat.org/physcor/muscle.html
Oxidative Phosphorylation
"The final, and virtually limitless supply of energy, comes from the
process of oxidative phosphorylation. *Maximum energy production rates
from oxidative phosphorylation are not as high as from glycolysis.
Aerobic events like the marathon are run at a considerably slower pace
than a 440 because of this fact. *The substrates for oxidative
metabolism are primarily glucose and fat (free fatty acids, not
cholesterol), although protein can also act as an energy source
through intermediate conversions to glucose, glucose precursors or
free fatty acids. *Because fat can be metabolized aerobically, most
well nourished humans have a near limitless supply of energy for low
intensity exercise. *Limitation of low intensity exercise is rarely
due to substrate depletion, although depletion of muscle glycogen may
also result in fatigue during aerobic events. *The reasons for this
are beyond the scope of this description."

http://www.nismat.org/physcor/energy_supply.html
*Aerobic Metabolism
"The most abundant energy source available to the muscle fiber is fat.
The breakdown of fat to yield ATP is referred to as lipolysis. While
the supply of fatty acids is essentially unlimited, the rate at which
lipolysis occurs is the limiting factor in obtaining ATP. Lipolysis is
responsible for resting muscle activity, but its contribution to the
overall muscle energy supply will decrease as contraction intensity
increases. For example, glycogen depletion occurs when the rate of
lipolysis cannot meet the energy demand of the exercise, and the
reliance on glycolysis expends the available glycogen stores. Once
glycogen depletion occurs, exercise intensity will be reduced
dramatically. However, a small decrease in intensity (e.g. slowing the
pace) earlier in the exercise bout would spare glycogen sufficiently
to avoid depletion. In turn, the importance of facilitating lipolysis
during endurance events cannot be overemphasized. "- Hide quoted text -

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