Most people are aware that doing some form of exercise is beneficial,
not only for losing unwanted body fat, but also for improving overall
health. However, many are unaware of certain factors that can
significantly increase the fat burning potential while performing
exercise and during recovery (rest). Four of the most important factors
to consider are: time interval from last meal, type of pre-exercise
meal, intensity of aerobic exercise and type of exercise (aerobic versus
resistance training).
Time Interval from Last Meal to Exercise Performance
How
long should someone wait before performing exercise in order to
maximize the amount of fat burned during exercise and while resting?
There are a number of studies that address this very question and have
shown that fat burning is greater when exercise is performed after an
overnight fast or in the morning before having breakfast.
One such
study (1) looked at eleven overweight and untrained men over a 4-month
course of doing aerobic exercise performed after either an overnight
fast or 3-hours after consuming a standard meal. The authors noted that
the amount of fat burned during exercise was significantly higher
following an overnight fast than after 3-hours post-meal. They also
observed that fat burning was even higher during the recovery (resting)
phase in the fasting group. In conclusion, the amount of fat burned
during exercise and while resting was more pronounced when exercise was
performed after an overnight fast as opposed to 3-hours after eating a
meal.
But, what if you cannot exercise first thing in the morning
due to time restraints, and working out later in the afternoon or
evening is more practical - what are your options? The timing of your
last meal is still very important as to the amount of fat burned during
your exercise session. Researches (2) studied the effects of exercise on
fat burning in eight overweight and obese women in two trials of
exercise: one performed 1-hour after a meal and the other performed
3-hours after the consuming the same meal. The amount of fat burned was
greater during exercise and during rest in the 3-hour post-meal group.
Bottom Line:
If your goal is to lose body fat, then the longer you wait after eating
a meal the more fat you will burn not only during exercise, but
afterwards while resting.
Pre-exercise Meal
What you
eat prior to performing exercise is also very important regarding the
amount of fat burned during exercise and afterwards during recovery.
Individuals who consume carbohydrates before exercising, especially
alone, in large amounts or high in glycemic rating, inhibit their
ability to burn body fat during exercise and afterwards at rest. Eight
healthy sedentary women were fed either a high-glycemic or low-glycemic
breakfast 3-hours before walking for 60-minutes(3). Each of the meals
had the same amounts of carbohydrate, protein, fat and total calories,
but differed in glycemic index rating and total fiber: the low-glycemic
index meal was higher in fiber. The researches noted that the amount of
fat burned during exercise was twice as much after the low-glycemic meal
than the high-glycemic meal both consumed 3-hours before exercise. The
amount of fat burned during post-exercise resting was also higher in the
low-glycemic index group.
The glycemic index rating reflects the
speed at which carbohydrates are digested and absorbed into the
bloodstream resulting in elevations in blood sugar and insulin. The
higher the glycemic index rating the more rapid the absorption and
subsequent blood sugar and insulin elevations. Insulin, a hormone
produced by the pancreas gland, regulates sugar and fat utilization.
When elevated, fats release from fat cells is inhibited.
Some
common high-glycemic foods consumed at breakfast are cereals (corn,
rice, wheat), instant oatmeal, white flour baked goods (toast, bagels,
croissants, doughnuts), sweetened jams, and white potatoes (hash
browns).
Bottom Line: If your goal is to burn body fat,
then consume low-glycemic carbohydrates in combination with quality
proteins and fats at least 3-hours prior to performing exercise. Do not
consume sports drinks, sugary fruit juices or high-glycemic
carbohydrates before regular exercise - doing so will inhibit your fat
burning potential.
Intensity of Exercise
Generally,
the amount of fat burned during exercise is inversely proportional to
the intensity level. In other words, the higher the exercise intensity
the less fat is burned (while exercising) with sugar (glucose) becoming
the dominate fuel source. Of course, this is a very simplistic
interpretation - the actual intensity level of exercise is relevant to
your fitness status. The better shape you are in, the more efficiently
your muscles will burn fat during exercise and while at rest.
Aerobic
fitness is determined by an individual's ability (heart and lungs) to
supply the tissues with oxygen during exercise, and is known as VO2max.
The higher someone's VO2max, the greater his or her aerobic fitness. The
goal is to increase your ability to burn fat during exercise while
increasing overall aerobic fitness. Research (4) has shown us that
exercising at 40% VO2max is the optimal for burning fat during exercise
and greater aerobic capacity is achieved when exercising at 60-80%
VO2max. How do you translate VO2max in a more realistic or easy way to
understand and use? Without fancy lab equipment or exercise testing, an
easy way to determine your desired exercise intensity range is to
calculate your maximum heart rate - all you need is your age and a
simple formula (5).
Maximum Heart Rate (HRmax) = 205.8 - (0.685 x age)
- Example Age = 45
- 205.8 - (0.685 x 45)
- 205.8 - 30.83 = 175
- HRmax = 175 beats per minute
Now that you know
how to calculate your maximum heart rate, all you have to do is take a
percentage of that number based on your desired intensity level for
maximizing your fat burning potential: 40% VO2max is equivalent to 63%
of maximum heart rate (6). To improve aerobic capacity and fitness,
increasing to and 60% VO2max is equivalent to 75% maximum heart rate,
and 80% VO2max is equivalent to 88% maximum heart rate. Using the
maximum heart rate example above, you can easily determine your optimum
fat burning and aerobic fitness heart rate zone.
- 175 maximum heart rate x 63% = 110 beats per minute
- 175 maximum heart rate x 75% = 131 beats per minute
- 175 maximum heart rate x 88% = 154 beats per minute
In
the above example, the optimum heart rate during exercise for fat
burning is 110 beats per minute, and to increase aerobic fitness the
heart rate range is 131-154 beats per minutes. However, since burning
fat is best achieved at lower intensities and improved aerobic fitness
is accomplished when exercising at higher intensities - how does one
manage to accomplish both?
One solution is interval aerobic
training. This type of aerobic exercise incorporates both low-intensity
and high-intensity in one workout session. An example of this type of
exercise: warm up for a few minutes at a low intensity then increase
your intensity to 63% of your maximum heart rate or in the above
example, 110 beats per minute. Exercise at this intensity for 5-minutes
then increase your intensity to 75%-88% of your maximum heart rate for
1-minute (131-154 beats per minute in the above example). Next, slow
your intensity returning to your 63% maximum heart rate for another
5-minute session, repeat this 5 to 1, 5 to 1 minute interval until your
desired time of exercise is finished. At the end of the session, cool
down for a few minutes at a lower intensity before stopping.
Bottom Line: If
your goal is to burn fat, implement an interval aerobic training
program. Exercise at 63% of your maximum heart rate with periodic
increases in intensity to between 75 to 88% of your maximum heart rate.
Of course, only exercise if you are a physically able and have been
cleared to do so by your doctor.
Type of Exercise (aerobic versus resistance training)
Both
aerobic and resistance training (weight-lifting) are important forms of
exercise that develop different systems and require various forms of
fuels to sustain. As explained above, aerobic exercise performed at
lower intensities burns more fat during the exercise, but when the
intensity in increased more sugar is utilized. Resistance training is a
high-intensity form of exercise and consequently requires the
utilization of sugar rather than fat while performing the exercise, but
during post-exercise recovery the amount of fat burned increases. So the
question becomes how should one incorporate these types of exercises?
Is
doing aerobic exercise combined with resistance training
(weightlifting) performed in the same session (concurrent training)
better than doing them separately on alternating days? Studies show,
that doing resistance training alone is superior to aerobic exercise in
burning fat calories within two hours post-exercise. This is known as
excess post-exercise oxygen consumption (EPOC) and represents the amount
of oxygen utilized by the body to return to pre-exercise status -
during this time period, body fat is broken down to supply the energy
needed.
Researchers (7) also compared two exercise sessions:
aerobic immediately (within 5-minutes) followed by resistance training
and then resistance training immediately (within 5-minutes) followed by
aerobic exercise. They concluded that doing aerobic immediately followed
by resistance training was comparable to doing resistance training
alone regarding EPOC. In other words, performing resistance training
alone (separate session) and doing aerobic immediately followed by
resistance were comparably effective in burning body fat, with a slight
edge to resistance training alone. Regarding overall performance as
measured by the physiological intended effects of aerobic exercise and
resistance exercise, performing each type of exercise alone is superior
than combining them into the same session. In other words, maximum
results are achieved from resistance training when performed separately
and on alternating days, and the same is true of aerobic exercise.
Resistance
training routines should be designed based on individual ability,
medical and fitness status, and should be adjusted and/or changed every 6
to 8 weeks reflecting progress. Incremental adjustments to exercise
type, sequence, frequency, intensity and duration are critical in
preventing muscle adaptation and "burnout," and allows for continued
overall improvement.
Bottom Line: Overall, the only real
advantage of doing concurrent exercise is time-efficiency. Otherwise,
doing aerobic and resistance training separately and on alternating days
is superior when considering fat burning (EPOC) potential and maximum
exercise performance. Periodic adjustments based on individual progress
are important to avoid muscle adaptation and to allow for continued
metabolic and fitness improvement.