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Date d'inscription : 28/05/2005
 | | The Truth About Fasted Cardio, by Christian Thibaudeau | |
The
Truth About Fasted Cardio,
by Christian Thibaudeau
Is
fasted morning cardio good or bad? First, let's look at the pros:
Pro
#1: Morning cardio could potentially increase the amount of free
fatty acids (FFA) used up as fuel. This is not due to performing
cardio in a glycogen depleted state though, since this isn't happening
here. Unless you go to sleep in an already depleted state, you
won't wake up in such a state.
During
sleep almost 100% of the energy expended comes from fatty acids
because of the extremely low intensity of the activity and because
of the natural hGH burst which occurs 30 minutes or so after you
enter the deep sleep phase (hGH increases fatty acid mobilization).
So
you really aren't depleting your intramuscular glycogen stores
during the night. You might be tapping your hepatic glycogen stores
slightly, but even then that can't account for much since at best
this contains maybe 200-300kcals of stored energy. So it's a fallacy
to believe that when you wake up your muscles are emptied of their
glycogen.
However,
since fat is the primary energy source during your sleeping period,
chances are that upon waking you have a greater amount of free
fatty acids available. Since you don't have to mobilize them (they're
already freed up) they become easier to oxidize for fuel and are
thus more readily used up during morning cardio.
Pro
#2: Fasted morning cardio could also potentially be glycogen-sparing
for the same reason as stated above: the greater availability of
FFAs reduces the reliance of glycogen for fuel during low-intensity
energy systems work.
Pro
#3: Fasted morning cardio could lead to an improved fatty acid
mobilization during exercise and increase insulin sensitivity afterwards.
This might be true of exercise at a low level of intensity (50-75%
of max VO2) since this decreases insulin levels via the stimulation
of adrenergic receptors. A lower insulin level can increase fatty
acid mobilization.
However,
a higher intensity of work (above 75% of max VO2) can actually
have the opposite effect. So in that regard a moderate or even
low intensity of work would seem to be superior in the morning
as far as fat mobilization goes. (Galbo, 1983, Poortmans et Boiseau,
2003)
To
counterbalance the reduction in insulin production during exercise
at a moderate intensity, insulin sensitivity is increased, especially
in the muscle. Since insulin sensitivity is already high in the
fasted state, morning cardio could allow you to significantly increase
glycogen storage and reduce the storage of carbohydrates as body
fat.
So
in that regard, morning cardio in a fasted state could increase
fat loss during a cutting period and allow a bodybuilder in a bulking
phase to significantly increase his carb intake without gaining
more fat.
If
fasted state cardio could potentially increase fat mobilization,
it's also potentially more catabolic to muscle tissue. This is
due to an increase in cortisol production during fasted exercise.
Since cortisol levels are already high in the morning, this could
lead to more muscle wasting than during non-fasted cardio.
In
fact, cortisol levels could increase muscle breakdown and the use
of amino acids as an energy source. This is especially true if
high-intensity energy systems work is performed. If an individual
uses lower intensity (around 60-65% of maximum heart rate), the
need for glucose and cortisol release are both reduced and thus
the situation becomes less catabolic.
I
personally do believe in the efficacy of morning cardio, but not
in a completely fasted state. For optimal results I prefer to ingest
a small amount of amino acids approximately 15-30 minutes before
the cardio session. A mix of 5g of BCAA, 5g of glutamine (yeah,
I know that Dave Barr won't agree with me on this!), and 5g of
essential amino acids would do the trick in preventing any unwanted
muscle breakdown.
However,
I'll also play devil's advocate and say that morning cardio won't
be drastically more effective than post-workout or afternoon cardio
work when it comes to fat loss. Personally, I prefer to split up
my cardio into two shorter sessions (morning and post-workout).
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