Cardio On Empty Stomach

Let's take a look at the reasoning for doing cardio in the morning on an empty stomach. Glycogen is depleted therefore more fat is burned. This is the major benefit people who push this method use to support their position. What they fail to realize is that anyone with weight training experience has or should have more muscle than is needed to sustain a healthy life. All of this extra muscle is detrimental to the survival of a human and first of all the individual body has one purpose in life. 

That purpose is survival. Fat is a much more efficient energy source for survival because it is not energy-costly. It does not require calories to survive because glycogen stores for its depleted that doesn’t mean the body will just go straight to fat stores for its energy. How great that would be, unfortunately, it’s just not that simple in the morning, glycogen is substantially depleted, and so is ATP. 

Heavy productive weight training depletes glycogen & ATP with each contraction. ATP is not only the fuel for muscular contraction, it also plays a large role in protein synthesis & repair. After weight training ATP & glycogen are depleted weight training uses the anaerobic glycolysis mechanism on ATP production & time is needed for the glycolysis mechanism on ATP production. & time is needed for glycogen stores to replenish.

Glycogen replenishment can take up to 3 days to complete. If you deplete more glycogen than is necessary you are putting your body through unnecessary stress, which will inhibit your body's ability to build muscle. Less ATP means less energy for protein synthesis. You want to stimulate as much muscle growth as possible with the smallest amount of glycogen & ATP depletion, which means that you should train as little as possible, while still achieving the desired results.

So how does this matter in this situation? Cardio in the morning on an empty stomach means cardio with little glycogen & thus little ATP, remember that cardiovascular work requires muscle fibers to contract. Just because an activity is aerobic doesn’t mean it does not require muscle fibers to perform the work. The primary source of contraction during aerobic work is the type 1 muscle fibers. They are called upon during aerobic work because they have a long fatigue threshold meaning they can maintain contraction for long periods. Type 1 fibers use oxidative phosphorylation (Kreb’s cycle & electron transport) an aerobic mechanism for energy production.

This is the method of energy production in which the body may also use protein when carbohydrate gluconeogenesis. Carbs are used primarily for this & consequently in aerobic work. This method of energy production produces the bar for the most energy.