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 Like
diet fads, appliance colors, and bell bottoms, the decision to include
mega-loads of cardio or hardly any at all swings through the
bodybuilding culture like the pendulum of a clock. Those in favor of
cardio claim that it allows them to eat more, and after all, eating more
is anabolic. Others insist cardio is the most catabolic thing that can
be done and has to be avoided – simply eat less. Not that I’m going to
solve the issue in one article, but I hope to at least bring to light
some facts that help you decide what format will bring you to the
doorstep of your ultimate condition.
 First,
let’s lock on the target: what is the actual goal in terms of
physiology? The vast majority of “fat” in our body (over 80%) is
collected in one form and stored in body fat cells. To get rid of it –
using it as energy – is a process called lipolysis. I’m going to
briefly explain the mechanism of this process primarily through exercise
(avoiding diet for now), and then the hard part begins: applying those
“truths” to the many different circumstances and body types that we find
in our great sport.
Activity-related hormones epinephrine and norepinephrine speed up
lipolysis greatly. In other words, when we start working out, we start
shuttling out these glycerols and fatty acids (fat) from our body fat
cells. As a matter of fact, research shows that the greatest increase
in fat usage starts immediately upon exercise, hits a peak level within
5 minutes, sharply decreases, by the 15-minute mark starts to plateau,
and within 30 minutes is back almost to a rate matching a control
group. So, what do we do with the common mantra that carbohydrates
(blood sugar) are used exclusively for the first 15-20 minutes of
cardio? In fact, blood sugar is the dominant source of energy used by
the cells of our body during the onset of exercise, but in order to
provide a seamless transition into longer-term energy stores, the liver
(through the action of the hormone glucagon) starts pumping out stored
glycogen and as described, body fat cells start releasing glycerols and
fatty acids. It all sounds good so far, but it gets a little tricky
when the liver runs out of glycogen. When this happens, the liver keeps
trying to contribute to the energy deficit, but it does so by turning
amino acids into glucose. Of course the liver has a reservoir of aminos
available, but still, this is a catabolic event and nothing sends a
bodybuilder shrieking to the blender to pound down another protein shake
like the thought of catabolism. Interestingly, though, even during the
harshest, longest bouts of exercise, only 3 to 6% of energy is consumed
from amino acid use. As long as fat is available, the body spares
protein as if it were the most precious commodity it has. Nice to know
the brain agrees with us on that one. But, as they say, the devil is in
the details. Before we even address things like duration, frequency,
and intensity think about the parameters I just laid out. Even a small
percentage of amino acid use can add up if it’s a repetitive
occurrence. I also mentioned “as long as body fat is available”…what
happens when the supply is reaching a pretty slim margin? This is where
body type comes into play. An ectomorph has to have a healthy fear of
“too much” cardio since they will be at the higher end of the population
in terms of using amino acids for energy. But, those that lose very
slowly need to understand that muscle preservation is their greatest
asset – they need to embrace cardio as a very necessary part of their
contest prep.
Here is
where armchair interpreters of research often start showing that it
takes more than throwing some big words around to master the subject.
The rate of lipolysis is virtually unchanged whether we’re at just 25%
of our VO2 max or 85%. That means that whether you’re walking on a
treadmill or slamming out 12-mile-an-hour sprints, your body is
releasing the same amount of body fat to be used. Before you say,
“Aha!! I knew that slower, longer cardio sessions were the right thing
to do,” you have to differentiate between just releasing fat to be used
and actually using it. If you maintain a slow pace, though the body is
releasing much fat to be used, when it’s not used, it simply
resynthesizes the glycerols/fatty acids to be re-stored as body fat.
So, we’re still stuck with the questions: Due to a slower rate of usage,
should one just perform a longer duration and ultimately use the same
amount of calories as someone doing a shorter but harder session? Which
will use more body fat and which will be less catabolic?
Keep in mind
that the body has a vested interest in using these fatty acids for
energy. Glucose and glycogen aren’t in endless supply and when activity
levels increase, the body needs to turn not only to its larger material
source of energy, but it wants to be efficient at it. As lipolysis is
increased, so is the blood flow to the exercising muscles, and so are
the chemical processes that convert the fatty acids into usable energy.
Here is yet another twist in the road. As intensity increases, these
glycerols are used at a higher rate – a good thing. But, when exercise
intensity reaches a level where blood flow is necessarily shunted more
sharply to the working muscle tissue, blood flow to the available fat
stores is restricted tremendously, decreasing the rate of fat that is
made available to be used as energy.
If we
perform light cardio we release just as much body fat as high-intensity
work, thus we’re not risking losing as much muscle, but then due to a
slower rate of fat usage, we simply re-store the released body fat. We
can do longer sessions of low-intensity cardio, but after 30 minutes,
fat release actually decreases – not increases as conventionally
taught. Trying to keep every variable straight is like trying catch a
greased pig. It’s like the squirrel in the animated movie Ice Age;
as soon as you stick every available finger and toe in the leaking wall
of ice, another confusing point of physiology springs out of a new
crack. No wonder there isn’t a consensus on the subject.
As I
mentioned in the beginning of the article, you would be making a mistake
if you take this article as covering every facet of the subject – think
of this as just an outline and the book isn’t finished. Read on for an
action plan…
The ease of
your body’s ability to burn body fat will affect how much cardio you
do. Being that all of cardio is catabolic, you want to do the least you
have to in order to be shredded. For some that may mean twice a week
and for others that may mean twice a day. Consider two glaring facts:
Your body immediately starts releasing body fat with exercise and
continues for 30 minutes until the law of diminishing returns virtually
eliminates any further benefit. If we are going at too slow of a pace,
the released fat gets re-stored and if we get too high in our intensity,
we shunt blood flow away from fat cells. I believe, therefore, that
there are two types of cardio that we can benefit from and still meet
our goal of sparing as much muscle as possible. The first is
thirty-minute sessions at a good pace – heart rate sustained at 130-150
beats per minute for most people. Remember, even at just 25% of our VO2
max we’re going to be releasing all the body fat that we can, but we
need a pace that will actually use what is released, but not so much
intensity that the body goes into a fight-or-flight mode channeling
blood to the muscle tissue systemically and away from the adipose cells
and organs. I also believe the value of super-high-intensity cardio is
tremendous but you have to weigh the catabolic effects and the fact that
it won’t take long to be counterproductive and decrease the amount of
fat actually being released (due to the changing blood flow patterns).
I would recommend using high-intensity sessions 1 to 3 times per week
for 15 to 20 minutes to create longer-term fat usage through the
increased metabolic effects. Ectomorphs may have plenty by doing just
10-minute high-intensity sessions, but even endomorphs shouldn’t do more
than 2 to 3. The amount of actual leg muscle recovery necessary should
be a limiting factor – you’ll need to recover almost like a leg
workout. The “baseline” 30-minute sessions could be done daily or even
twice a day for those who lose weight slowly or have more lower body
stores to contend with.
That
doesn’t mean that longer, slower cardio is worthless, you just get a
fraction of the fat loss after the first 30 minutes. Breaking up an
hour of cardio into two sessions can net more fat loss if the pace is
high enough and consistent. The great thing about human performance
research, however, is that we’re still very much in a pioneering phase.
Studies conducted with different variables keep adding to our
understanding and more specific information is sure to be discovered.
For now, this is my story and I’m sticking to it.
Dr. Joe
Klemczewski
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