Busting the 20-Minute Fat-Burning Myth
Back in 1999 when I was studying full-time at university, and
working both a full-time and a part-time job, one of the big challenges
I faced was making the time to exercise.
Despite my best efforts, I often failed to make it to the gym
at all, even for just 20 or 30 minutes. And even if I did manage
to summon the enthusiasm to train, by the time I'd finished changing
and warming up, it was almost time to leave again.
And I hated it. I felt fat, even though (compared to most people
anyway) I still looked in reasonably good shape. I was moody
and found it hard to concentrate on anything for more than a few
minutes at a time. And a good workout
would set me up for the day. Without it, I felt tired and listless.
I felt like an addict in need of my exercise "fix!"
After several weeks of moaning and complaining to anyone
who would listen that it was now "impossible" for me
to do any exercise at all, I decided to do something about it.
My plan was to cut each workout in half. Driving to work in
the morning, I'd stop at the gym and get the first half done.
On the way back home at night, I'd do the second half.
However, a few people I spoke with told me that this idea was
"silly" and "wouldn't
work."
"Your
body doesn't start burning fat until you've been exercising for
at least 20 minutes," they told me. I was warned that I "wouldn't
lose any fat at all" unless I did at least 45 minutes of
continuous aerobic exercise.
It's true that your body relies more on carbohydrate and less
on fat during the early stages of exercise. It's also true
that your body uses more fat and less carbohydrate the longer
you spend exercising.
But this ignores what happens to your metabolism
in the hours after a workout, when the number of fat calories
burned rises significantly.
To lose fat, you need to create a calorie deficit — to consistently
burn more calories than you consume. And it doesn't make
a great deal of difference whether those calories are burned in
one long workout or several shorter ones.
Some evidence for this comes from research carried out at the
University of Pittsburgh School of Medicine
[1]. For the study, a group of overweight women was assigned to
one of two groups. Group one performed a single bout of exercise
lasting 20-40 minutes. Group two did the same amount of exercise,
but it was split into several smaller bouts lasting
just 10 minutes.
And the result?
Twenty weeks later, the women who split their workouts into shorter
bouts had lost 20 pounds, compared to just 14 pounds in the single-bout
group. The reason for the extra weight loss is simply that
women in group two did more exercise (and
thus burned more calories) than women in group one, possibly because
they found it easier to fit shorter workouts into their day.
Research published in the Journal of the American College of
Nutrition shows
similar results [3]. There were no significant differences in weight
loss with three 10-minute bouts of exercise per day compared
with two 15-minute bouts or one 30-minute bout.
Changes in body composition weren't reported in this study, so
we don't know how much of the lost weight came from muscle
and how much came from fat. I'm guessing that the women lost some
muscle, which is fairly common with aerobic-only
exercise programs.
That's why it's always a good idea to
do some kind of resistance training to help preserve lean muscle
when you're losing weight (see How
to Fight Fat and Win II for a highly effective
whole-body resistance-exercise program).
So, what does all of this mean for you?
Fat is stored energy. To lose it, you have to use more energy
(calories) than you get from your diet. And it doesn't really matter
whether you burn those calories in one long workout or several
shorter ones. As these studies and my own experience show,
both approaches work.
About The Author
 Christian Finn holds a master's degree in exercise science, is a certified personal trainer and has been featured on BBC TV and radio, as well as in Men's Health, Men's Fitness, Muscle & Fitness, Fit Pro, Zest and other popular fitness magazines.
If you're stuck
in a rut with your current exercise and diet plan... fed up with
only losing a pound here and there... or still skinny after months
(or even years) of trying to build muscle and gain weight... click here now for instant access to his step-by-step muscle-building and fat-burning workout routines.
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References
1. Jakicic, J.M., Wing, R.R., Butler, B.A., & Robertson,
R.J. (1995). Prescribing exercise in multiple short bouts versus
one continuous bout: effects on adherence, cardiorespiratory fitness,
and weight loss in overweight women. International
Journal of Obesity and Related Metabolic Disorders, 19,
893-901
2. Kanaley, J.A., Weltman, J.Y., Veldhuis, J.D., Rogol, A.D., Hartman,
M.L., & Weltman, A. (1997). Human growth hormone response to
repeated bouts of aerobic exercise. Journal
of Applied Physiology, 83, 1756-1761
3. Schmidt, W.D., Biwer, C.J., & Kalscheuer, L.K. (2001).
Effects of long versus short bout exercise on fitness and weight
loss in overweight females. Journal
of the American College of Nutrition, 20, 494-501
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