is time to bring the science of weight loss out of the dark ages
a new understanding of exercise's impact on hormones
and metabolism. The environment in which people choose to live dramatically
affects the processing
and use of energy they consume. Intelligent exercise releases hormones in
the body, and these chemical messengers translate movement into metabolic
action. Hormonal signals are powerful determinants of the fuel our metabolic
engine will use: sugar vs. fat. Therefore, hormones manage much more than
just caloric input and output. An optimal state of hormonal balance enhances
utilization of the body's fat stores; we call this the metabolic effect.
The intelligent manipulation of lifestyle choices, like exercise, is the
chief means of accessing this highly beneficial state of function.
To begin this discussion, let's take a look at how a strictly caloric
model of metabolism holds up in examples of real people. It is useful to use
athletes in this example, since they are widely regarded as extremely functional
and metabolically efficient. Among track athletes, both elite marathoners and
sprinters are extremely lean. Any average person can quickly distinguish the
difference between these two groups of athletes. One is muscular and lean,
while the other is more gaunt and wiry. Of these athletes, sprinters have less
body fat and higher amounts of muscle mass, yet they burn far fewer calories
when training for and engaging in their sport.1-2 Sprinters engage in very
short bursts of all-out effort lasting seconds, while marathoners run for hours
and consume large amounts of caloric energy. If the calorie model is the final
word on fat loss, why is there a discrepancy? Shouldn't marathoners be
the leaner of the athletes?
To understand this glaring contradiction, the discussion must move to hormones
and fuel metabolism. Hormones, as described here, simply refer to all signaling
molecules in the body. In weight loss, these chemical messengers are the ultimate
predictors of the degree and type of energy used. The body is like an engine
that can choose between two fuels. Fat is analogous to diesel fuel; it will
get you far, but it won't provide much performance. Sugar is like high-octane
fuel and delivers exceptional performance but horrible mileage. Hormonal messengers
determine the fuel that dominates. In reality, the body burns both fuels all
the time, but lifestyle choices elicit hormones that determine the amount of
each fuel burned. The body becomes efficient at burning what you feed it, and
it preferentially replenishes used energy by refilling its tanks with the alternative
fuel. In other words, eat sugar at a meal, and you will burn sugar after the
meal, but burn sugar during exercise, and you will burn fat after. With this
understanding, eating and exercise programs can be designed to release the
optimal hormonal situation for the accelerated fat loss we call the metabolic
Excess Post-exercise Oxygen Consumption: The Metabolic Effect of Exercise
Exercise that modulates hormonal effects will burn more calories during activity
and provide greater caloric benefit after exercise.25 This increased energy
use after an intelligent workout is referred to as excess post-exercise oxygen
consumption (EPOC). EPOC is a measure of how much oxygen the body consumes
in the hours and days after a workout. An example of EPOC in the acute sense
can be observed in a climb up a steep flight of stairs. During the climb,
breathing is labored, but respiration becomes most difficult after reaching
the top. The body does this to recover the "debt" of oxygen created
during activity. The EPOC created by climbing a flight of steps is an example
of the much larger metabolic effect created from intelligent movement. Intelligent
exercise drives hormonal machinery towards burning large amounts of energy
during exercise, and creates sustained fat-burning after. The amount of oxygen
consumed is directly correlated to how much energy is burned, but the hormonal
situation determines whether that energy is mostly fat or sugar.
The idea of hormonal influences on calorie-burning is a novel concept to
some and far more complex than simple one-dimensional models of hormonal
For example, we know that exercise of sufficient intensity elevates stress
hormones like adrenaline, nor-adrenaline, and cortisol. As an innate physiological
response to stress, these hormones are generated during a "fight-or-flight"
response. Together, they ensure the switch to high-octane sugar usage, which
supplied the energy to fight for our lives or run like hell. As we run faster
and harder, the body's supply of oxygen drops off. Since sugar is a fuel
that can be burned in the absence of oxygen, highly intense activity depletes
sugar stores. This increase in anaerobic metabolism generates lactic acid,
which is far more than a waste product. Lactic acid is also a buffering aid
and likely signaling molecule.26-28 As lactic acid builds up to extreme levels,
it is correlated with powerful metabolic stimulants like testosterone and human
growth hormone.22-24 The total hormonal environment created acts synergistically
to produce a leaner and more functional physiology.
The effect of these hormonal messengers persists after activity, and that effect,
coupled with empty energy reserves, delivers signals that rebuild, regenerate,
and recycle energy. Since sugar stores are depleted during intense exercise,
fat is used afterwards to repair the body and regenerate sugar reserves. In
this way, the body becomes a fat-burning machine through the hormonal metabolic
effect and the ensuing EPOC. This finely orchestrated hormonal response creates
the perfect scenario for fat-burning and muscle-building and ensures survival
by generating a leaner, faster, and stronger body. It is useful to point out
that humans in natural conditions did low-intensity activity all day everyday.
However, the last activity one should choose when confronted with stress and
high blood sugar is low-intensity exercise. This runs counter to inherited
physiology and biochemical understanding. Our genes and metabolic processes
are still tuned to a fight-or-flight reality. Intelligent hormonal exercise
works along with this ancient machinery.
Interestingly, the scenario above describes the type of exercise sprinters
use in their training. It is important to point out the rise in cortisol many
people fear is only a problem when it is unopposed by growth hormone and testosterone.3-6
Hormones do not work in isolation, and like people, they will behave differently
depending on the social environment in which they find themselves. When cortisol
is "socializing" with testosterone and growth hormone, its muscle
breakdown is blocked, fat storing at the belly is reversed, and the three – cortisol,
testosterone, and growth hormone – synergistically enhance fat-burning.3-6
Attempting to blunt the cortisol response to high-intensity exercise is counterproductive
for burning fat and not necessary in the context of growth hormones.7-10 Long-duration
and low-intensity cardiovascular exercise is more problematic. because it causes
cortisol to rise unopposed by the growth-promoting hormones. This may explain
why standard aerobic prescriptions are not as effective for optimal body composition
and why marathon runners exhibit frail bodies devoid of muscle.14-17,20 The
duration – not the intensity – of exercise is the most salient
issue in regards to cortisol.21
The description above dictates that intelligent exercise must be intense enough
to elicit the hormonal metabolic effect described. There are many tools and
techniques to generate this effect with exercise, but none of them include
long duration or "aerobic zone" training. This new technology
and understanding dictates that the real fat-burning zone exists at higher
intensities. Breaching 85% to 90% of maximum heart rate ensures adequate
intensity and can be managed easily with short duration interval training.
This level of exertion correlates well with the ability to speak during exercise.32
In addition, a weight-training program that uses full body movements, short
rest periods, and forces both mechanical and metabolic muscle failure will
cause a ripple effect lasting long after exercise has ended.18-19
So how long does this metabolic effect last? When the tools and techniques
described are used appropriately, the magnitude and duration of EPOC is substantial.
Two resistance-training studies that combined many of the elements described
above showed a sixteen-hour elevation for women and a forty-eight hour elevation
for men.18-19 Studies on interval training show similar effects.11-13 This
is admittedly hard to swallow when one considers exercisers spend countless
hours doing aerobic workouts, which are largely ineffective for weight loss.14-17
A 2001 study in the American College of Sports Medicine's flagship journal,
Medicine and Science in Sports and Exercise illustrates the point nicely.31
This study compared two groups of women. One group exercised using standard
zone aerobic training while the other group used anaerobic interval exercise.
The anaerobic interval group exercised for two minutes at a highly intense
97% maximum heart rate. They then rested by doing three minutes of low-intensity
activity. The first, more aerobic group performed moderately intense activity
at close to 70% of maximum heart rate. The researchers made sure that each
group burned exactly 300 calories. Despite exercising longer and burning the
same amount of calories, the aerobic group lost less body fat at the end of
the study compared to the interval group. In addition, fitness in the interval
group was substantially greater than in the aerobic group. This study demonstrates
the effect of EPOC and shows that something other than just calories is driving
A similar study published in the same journal in 1996 showed that an anaerobic-trained
interval group burned significantly more fat than their aerobically trained
counterparts.30 Not only did the interval group burn more fat during exercise,
but they exhibited increased fat-burning effects that persisted for 24 hours
after the exercise had stopped. These results clearly show that high-intensity
interval training burns more overall fat and calories during exercise. The
results also demonstrate EPOC leads to a continued fat burn after exercise.
Perhaps the most interesting thing about this study is that the interval group
was able to accomplish all this with an exercise session that was a full 15
minutes shorter than the aerobic group. This shows that intelligent exercise,
moving away from the aerobic paradigm, allows exercisers to have their cake
and eat it too.
Perhaps the most telling study on the effects of high-intensity exercise vs.
aerobic training came in 1994 in the journal Metabolism.29 This study tracked
two groups of people undergoing different modes of exercise. Group 1 did zone
aerobic training for a period of 20 weeks, while Group 2 did 15 weeks of a
high-intensity interval program. The researchers wanted to see how each program
would affect body fatness and metabolism. The results showed that the aerobic
group burned 48% more calories than the interval group (120.4 MJ vs. 57.9MJ)
over the course of the study. However, despite the huge caloric disadvantage,
the interval group enjoyed a ninefold greater loss in subcutaneous fat (fat
under the skin). Most remarkably, resting levels of 3-hydroxyacyl coenzyme
A dehydrogenase (HADH), an enzymatic marker of fat-burning, were significantly
elevated in the interval group. The implications of this study are immense
when you consider the interval group trained five weeks less than the aerobic
group, had shorter workouts, and yet far exceeded the aerobic group in fat-burning
at rest and during exercise. The measurement of fat-burning enzymes in this
study shows for the first time that this new exercise technology can "teach" the
body to be a more efficient fat-burning machine.
The current exercise environment for weight loss is still rooted in the low-intensity,
single-mode, and calorie-burning paradigms. This approach is successful for
some, yet fails the vast majority. New models for exercise are needed to combat
the growing epidemic of obesity and chronic disease. Short-duration, high-intensity
exercise offers a clear departure from current weight loss models. Those who
desire real transformations and are frustrated by cookbook-style exercise prescriptions
need new and improved approaches for overcoming obesity. Training for the metabolic
effect offers health care providers, trainers, and gym managers alike new and
effective exercise techniques to combat obesity and ensure weight loss.
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