It's true that higher intensity cardio workouts burn
more calories per unit of time AND increase metabolism
more after the workout than low intensity workouts.
High intensity cardio, including high intensity interval
training (HIIT), is very effective and time efficient,
(although it's not for beginners or those with certain
health problems).
It's common sense if you think about it - work harder,
burn more calories, right?
Here's where the confusion has come from:
It's well known that low intensity exercise utilizes
primarily fat as fuel and high intensity exercise utilizes
more carbohydrate as fuel.
In the past, this was the basis for the idea that low intensity,
long duration aerobic exercise was superior for fat loss. Some
people were were afraid to exercise too hard because they
thought it would take them out of the "fat burning zone" and
make them them burn only "sugar" and not body fat.
Today, research has proven that this belief in exercising at
a low intensity to stay in the "fat burning zone" was false.
At lower intensities, you burn more calories from fat, but
you burn fewer total calories.
For example, a 1995 study conducted by Grediagin, et al,
published in the Journal of the American Dietetic Association
(95(6):661-5) compared fat loss in two groups over a 12 week period.
One group performed exercise at 80% of VO2 max for a duration
sufficient to burn 300 kcal, the other group performed exercise
at 50% of VO2 max for a duration sufficient to burn 300 calories
(took a lot longer, of course). Hydrostatic body composition
testing revealed that...
***each group lost an identical amount of fat.***
The authors concluded:
"This study suggests that fat loss is a function of energy
expended rather than exercise intensity. Therefore, if fat
loss is the goal and time is limited, persons should exercise
safely at as high an intensity as tolerable to expend as much
energy as possible during their allotted time."
In my opinion, that conclusion pretty much hits the nail on
the head when it comes to answering the questions, "How long and
how hard should your cardio workouts be?"
Another study published by Ballard, et al in the same journal
(51(2):142-6, 1990) showed identical findings. High (80-90%
VO2max) versus low (40-50% VO2max) intensity rates were
compared in two groups with duration carefully controlled
to ensure each group burned the same number of calories.
The high intensity group exercised for only 25 minutes and
the low intensity group for 50 minutes...
***both groups lost the same amount of body fat! ***
Keep in mind BOTH approaches worked, but the high intensity
group got it done in half the time!
Regardless of whether your cardio sessions are 20 minutes,
30 minutes, 45 minutes, or whatever, the higher the intensity
during that time period, the more TOTAL calories you will burn.
The more TOTAL calories you burn, the more fat you burn.
Although many factors are involved in exercise-induced fat
loss, the most important factor is the total number of calories
burned, NOT whether the calories burned are fat or carbohydrate.
It's also important to consider energy expenditure after the
workout, not just the calories burned during the workout.
Higher intensities not only burn more calories per unit of
time, but they also elevate your metabolism more at rest
after the workout is over. This post workout increase in
metabolic rate is known as "excess post exercise oxygen
consumption" or EPOC for short.
It has been proposed, based on the results of several
studies comparing the amount of calories burned at rest
after low intensity versus high intensity exercise, that
HIIT is a superior method of fat loss due to its effect
on post workout metabolic rate.
Clearly, HIIT is the logical protocol of choice if you are
healthy, already fit and you have little time to work out.
However, it's also logical that time permitting,
more frequent and longer duration exercise might cause
even greater overall fat loss if intensity is sufficient,
simply because more total calories can be burned over
the course of a week.
Remember, it's all about the intensity and the calories
burned, not necessarily whether the workout is peformed
with intervals or in a steady state.
For example, if you do 20-25 minutes of very intense
cardio, you might burn about 400 calories. That's a lot
of calories for such a brief workout. But it only adds
up to 1200 total calories in one week if your frequency
is only three days per week.
If you (gradually) built up your frequency to four, five,
then even six days per week, you could double your caloric
expenditure to 2400 calories per week.
If you also increase your duration, your intensity will
decrease so you'll burn fewer calories per minute, but the
calorie expenditure for the entire workout is higher, which
increases your total weekly calorie burn even further.
Duration and intensity are inversely related, so the longer
the workout, the lower the intensity. But that doesnt mean
a 30 or 45 minute workout necessarily has to be "low" in
intensity.
A 30 or 45 minute steady state workout can be "moderate" or
"moderately-high" in intensity. The combination of the highest
intensity you can muster with a 30-45 minute duration can
create an enormous calorie burn. Some of that calorie burn
will occur after the workout as well, because studies have
shown that EPOC is influenced not just by intensity, but
also by duration.
Although infrequent and very brief (15-20 minutes or even less)
HIIT workouts have recently gained great popularity (and
deservedly so), that doesn't mean you should never do steady
state cardio, nor does it mean that certain individuals
aren't better off with longer, less intense cardio.
Respected organizations such as The American College of
Sports Medicine (ACSM) still recommend longer daily and
cumulative weekly exercise duration when the goal is
fat loss.
The ACSM position stand titled, "The recommended quantity
and quality of exercise" states, "A threshold level for total
body mass and fat mass loss generally would require at least
30-45 min of exercise per session for a person of average
fitness. If the primary purpose of the training program is
for weight loss, then regimens of greater frequency and
duration of training and moderate intensity are recommended.
Shorter duration, higher intensity programs may be recommended
for healthy individuals at low risk for cardiovascular disease
and orthopedic injury."
To avoid overtraining, injury or aerobic adaptation, which
become risks with higher intensity, frequency, and duration,
it's important to build up slowly and ALWAYS get your physician's
clearance before attempting high intensity cardio.
naturally, of course, it's not wise to dramtically increase
your training volume or intensity suddenly, but rather to
increase gradually.
If your current goal is to maintain your level of body fat
and stay healthy, I'd recommend starting with at least 20 minutes
of cardio 3 days per week. If your goal is maximum fat loss,
then time permitting, I would recommend higher frequency and
duration, sometimes building up to much as 30-60 minutes
5-7 days per week, if necessary, based on your weekly results.
Once you reach your desired percentage of body fat, then you
can gradually shift back into a "maintenance" program of lesser
frequency, duration and intensity. This is a form of "cardio
periodization," similar in nature to the periodization of
weight training used by elite athletes. Staying on high volume
cardio all year round is counterproductive and may lead to
overtraining, aerobic adaptation and a plateau
in fat loss.
Genetics also play a role in the ideal volume of cardio for
fat loss. If you're one of the few people who are genetically
blessed with the fast metabolism and physical attributes to
burn fat easily, then three days a week for twenty minutes
often provides sufficient stimulus for results. In fact, I
know a few people with hyperactive metabolisms who stay ripped
all year round without doing any cardio at all (I hate those
people, don't you?)
The bottom line is that a single cardio workout prescription,
such as "three days a week for 20 minutes" will not work for
everyone.Exercise programs must be developed on an individual
basis and they are not static. The frequency, duration AND
intensity all need to be adjusted based on your results.
If the intensity is high enough, three twenty-minute cardio
sessions may be sufficient for you, depending on your goals,
your current level of fitness and your actual results, but
longer and/or more frequent cardio sessions are sometimes
a "necessary evil."
For more information on fat burning cardio and fat burning
nutrition, visit
www.burnthefat.com