A popular fitness tenet is that cardio should be performed first thing in the morning on an empty stomach. The theory behind this belief is as follows: A prolonged absence of food brings about a reduction in circulating blood sugar, causing glycogen (stored carbohydrate) levels to fall. With a diminished availability of glycogen, your body tends to rely more on fat - rather than glucose - to fuel your workout. Under ideal conditions, there is an increased oxidation of fat during exercise - a fact that is supported by research.
When is the Best Time to Perform Cardio Exercise
Is morning really best? Let your biorhythms determine when you should work out. All things considered, it really won't make much of a difference in your results.
By: Brad Schoenfeld
Just Looking At The Amount Of Fat Burned During Exercise Is Shortsighted
The truth is, however, it's not always best to perform cardio as soon as you roll out of bed. Although the prospect of increasing fat oxidation sounds good on the surface, there are several misconceptions that need to be taken into account. For one, the human body is a very dynamic organism and continually adjusts its use of fat for fuel. Substrate utilization is governed by a host of factors (including enzyme levels, substrate availability, internal feedback loops, etc.) and these factors can literally change by the moment. Thus, simply looking at the amount of fat burned during exercise is shortsighted. Fat burning must be considered over the course of an entire day - not on an hour to hour basis - to get a meaningful perspective on its impact on body composition.
What's more, only about half of the fat utilized during aerobic exercise is mobilized from adipose tissue; the balance comes from fat stored intramuscularly (within muscle) . The important point here is that intramuscular fat has no bearing on aesthetic appearance; it's the subcutaneous fat stored in adipose tissue that influences body composition. Consequently, the actual fat-burning effects of the strategy are far less than otherwise thought.
Eating before exercise actually increases caloric expenditure
In addition, studies have shown that eating before exercise actually increases caloric expenditure. This apparently is related to the thermic effect of food (TEF). You see, every time you eat a mixed meal there is a corresponding increase in metabolic rate.
A Pre-Exercise Meal Allows You To Exercise More Intensely
When exercise is performed after the consumption of food, metabolism is heightened by about 20% over fasting levels. Better yet, these effects are maintained for up to three hours post-workout. And since burning more calories means burning more fat, eating before cardio can have thermogenic effects on exercise activity.
Perhaps more significantly, a pre-exercise meal allows you to exercise more intensely. In order to perform at a high level, your body needs a ready source of glycogen; deplete glycogen stores and your performance is bound to suffer.
A popular fitness tenet is that cardio
Compounding matters, not everyone functions well first thing in the morning. If you're more of a night bird, chances are that you'll sleepwalk through a morning workout. The net result is that fewer calories are burned during activity. Again, total caloric expenditure has a direct effect on fat oxidation, so these factors ultimately lead to a lower-quality, less-efficient exercise session.
Exercise When You Are At Your Best
In final analysis, simply increasing the percentage of calories burned from fat doesn't necessarily translate into an improved body composition. There isn't necessarily anything wrong with performing exercise after an overnight fast, but it isn't going to make a significant difference on your body's appearance, either.
The best advice is to exercise when you are at your best; let your biorhythms determine when you should work out. If you are a morning person, go ahead and train early. But if you don't really get going until you've been awake for several hours, by all means train later in the day. All things considered, it really won't make much of a difference in your results.