Aerobic question( alt.sport.weightlifting,misc.fitness.misc,misc.fitness.weights)
Larry DeLuca
In misc.fitness.misc Andrew Stranz <andr...@home.com> wrote:
: It takes over 20 minutes of aerobic activity to start burning fat.
: Otherwise, you are just burning sugars in you system. One theory is
: after you exercize for a long time, and you have "programmed" your body
: to burn fat, it does burns the fat sooner in the workout. Well...in
: laymans terms...
You are burning fat all the time. There are no mechanisms in intermediary
metabolism to inhibit fat-burning - EVER. You have lots of fat (the typical
person has about 100,000 Calories worth!), and so there's no need to inhibit
it.
However, for short bursts of intense activity, fat can't be metabolized
quickly enough to provide all of the energy needed for the activity, so
while fat metabolism increases it's supplemented with higher amounts of
carbohydrate metabolism. For very short bursts of very high intensity
activity the rate of carbohydrate metabolism increases much faster than
that of fat metabolism, and so it appears that the activity is "just burning
carbs." In reality, it's simply that the amount of carbohydrate being
burned at that moment overshadows the amount of fat being burned, which is
still vastly increased over resting levels.
However, these minute-to-minute fluctuations don't seem to make any difference
in long-term weight loss or weight gain. There's a lot of this minute-to-
minute changing of gears (every time you get out of a chair, for example).
The body makes every attempt to spare carbohydrate (and burn fat), both in
the long-term and the short-term, and the net effect is that regardless of
exercise intensity the body burns as much fat as possible.
It's true that as the workout proceeds the ratio shifts in favor of
increased fat burning (but it's really a bit more toward increased
carbohydrate-sparing).
Studies have been conducted comparing weight loss in people who exercise
at different intensities, and it has been repeatedly demonstrated that
as long as the number of calories is kept the same that weight loss is
about the same, regardless of the intensity (and therefore the duration)
of the workout.
larry...
Larry DeLuca
In misc.fitness.misc GymRat <gym...@willinet.net> wrote:
:>It takes over 20 minutes of aerobic activity to start burning fat.
:>Otherwise, you are just burning sugars in you system. One theory is
? Andrew is correct...if you go extremely hard for 10 minutes you will
? only use up your sugar stores. But the 20 minute thing has a lot of
? variables. If you hammer really hard the first 10 minutes you are
? going to use up more triglycerides than you will if you go easy.
? therefore it may take less than that 20 minutes to start burning the
? fat. The sooner you use up the triglycerides the sooner you tap into
? your fat stores. This is what makes fartlek training so effective.
Ummmm..."triglycerides" *are* stored body fat. The name comes from the
fact that they consist of 3 fatty acid chains linked together by a
glycerol backbone (a 3-carbon sugar alcohol). Triglycerides are the
form the body uses for storage of fat.
Further, using up your carbohydrate will not increase fat burning so much
as put a sharp limit on the exercise intensity you're able to maintain.
Marathon runners call the phenomenon "bonking."
larry...
Larry DeLuca
In misc.fitness.misc GymRat <gym...@willinet.net> wrote:
: Again you are right if a person is trying to maintain high intensity
: for a prolonged period. Such as a cyclist time trialing. But would not
: using up gycogen stores leave nothing but fat for fuel at a lower
: intensity afterwards? Hence the effectiveness of interval training?
You need some carbohydrate coming into the system for optimal fat-burning.
If you deplete your glycogen you'll start breaking down muscle tissue
to make the glucose.
This has been discussed at length in the past week or two. Go look in
Deja News and you should be able to find the thread.
larry...
Larry DeLuca
[Bill Phillips - the new kingpin of exercise physiology.]
In misc.fitness.misc Andrew Stranz <andr...@home.com> wrote:
: Larry,
: I agree that you are burning fat all the time, but in the beginning, it
: will be at a much lower level than after approximately 20 minutes
The changing RER (respiratory exchange ratio) - the measure of the ratio of
carbohydrate to fat utilized during activity - does suggest that fat
utilization increases as exercise continues at steady state.
However, it's not an "on/off" thing that occurs at 20 minutes, as it is
commonly misrepresented. Moreover, this is only valid for *STEADY-STATE*
exercise - once you start messing around with intensity at all the process
of readjustment to the new exercise level begins all over again (this
would include adjusting the grade or speed of the treadmill, going up a
"hill" on the stairclimber, etc.).
Moreover, factors besides ratio of fuels burned affects RER. For example,
increasing reliance on anaerobic energy systems will decrease blood pH.
One of the principal means of pH buffering (the bicarbonate system), will
help buffer the pH changes, but will do so by taking up the excess hydrogen
ions (combing them with bicarbonate to form carbonic acid). The
carbonic acid is converted to CO2 + H20, which is removed by the lungs.
The increase in CO2 increases the RER, and it appears that "more"
carbohydrate is being expended when this is not in fact the case.
(Summaried from Wilmore and Costill's _Physiology of Sport and Exercise_,
2nd Edition, and McArdle, Katch, and Katch's _Essentials of Exercise
Physiology_).
: (depending on intensity level). However, your body is designed to SAVE
: AND SPARE fat. As Bill Phillips wrote in the 3rd supplement review
: (documented by some Journal of Medicine ..it's not like I memorize the
: references!) the amount of time humans as a race do not need to "hunt
: and gather" is a mere speck of time in our history. Our body is designed
: to store fat for times of famine, winters, etc.... That's why unless we
: consistently exercise aerobically for prolong periods of time, it burns
: the "active" energy in our system - and NOT our fat stores.
Well, there's a very small grain of truth in this, in that fat is our
primary means of storing excess caloric intake for later use. It's a
much more compact means of storing energy than making glycogen molecules.
However, that very same reason (that fat is easier to store than glycogen)
is precisely the reason that our body *preferentially burns fat all the
time*. We have about 100,000 Calories of stored body fat, whereas we
have only about 1600 Calories of carbohydrate available (including glucose
in body fluids as well as muscle and liver glycogen). If we tried to
preferentially run on glucose we'd be "out of the running" in only a few
hours.
Moreover, RER's at rest indicate that a substantial proportion (nearly 100%)
of our resting metabolic needs are met by fatty acid metabolism, and that
very little carbohydrate metabolism occurs at reast.
Finally, if you look at the metabolic pathways themselves there are
several steps at which increasing levels of fatty acid oxidation can inhibit
glucose metabolism. However, there are no corresponding mechanisms by which
glucose metabolism can inhibit fatty acid metabolism. (See _Harper's
Biochemistry_ for a more detailed discussion).
Bill Phillips is a very charismatic guy, and he's making a lot of money
right now, but it's not because he's a world-class exercise physiologist.
The more people tell me about what he has to say (and the more I see/hear
him on TV) I am utterly amazed that someone with so poor a working knowledge
of basic physiology has catapulted himself to the position he has.
larry...