logic/science behind AM cardio...

**UpstateTank** · 12-01-2006, 04:48 PM

Had a quick question regarding why its best to do cardio first thing in the morning on an empty stomach. I constantly have read on this board that its the best thing to do (and I myself do it as well--low impact

)...Im not questioning that its the best just wondering what makes it so good. My idea is moring cardio on an empty stomach is the best because when you wake up your glycogen stores are depleted therefore your body goes straight to fat to burn for energy?

Continuing w/ this I've heard/read from other people that it takes 20minutes for your body to start burning calories when doing cardio...is this simply a myth or is it factual if ones glycogen stores were "full" thats how long it would take to deplete them hence rendering morning cardio "the best time" to do cardio?

My last question is why wouldnt it be ideal for a person to do cardio after a workout. A persons glycogen stores are depleted following a workout (someone correct me if im wrong in any of my statements please) which would make it an ideal time? but then i take into consideration your muscles are in a catabolic state following a workout therefore placing further strain on them via cardio (even low impact) could result in further muscular depletion?

Sorry for the long post guys

but thank you for the help! just trying to get my thoughts straight on this

**UpstateTank** · 12-02-2006, 02:42 PM

**MuscleScience** · 12-02-2006, 05:47 PM

Doing cardio in the morning is good because it brings your metabolic rate up faster than if you didnt do it. Most people's metabolism peaks sometime in the afternoon. Cardio in the morning is a great way to speed up to get to the peak metabolic rate. You also have to remember that glycogen is stored in the liver in great amounts relative to its size. In the morning your muscles are not depleted of glycogen they are probably at there highest amounts. The digestive tract is very active when your at rest. Makes since because you only have a finite amount of blood circulating at once. And the working muscle will get priority over the digestive tract. Cardio on an empty stomach is not the most effiencient way to burn fat. Most people on this board will argue otherwise but they dont have two degrees in physiology along with training olympic caliber athletes as i do. You will still burn fat but its not as efficient as if you had a light meal with lots of complex carbohydrates that dont spike insulin rapidly.
When you do aerobic exercise it takes time for your body to ramp up and start buring fat efficiently. The process of burning fat and using it as energy is called beta-oxidation. Relatively speaking it a much slower energy pathway than the Phospo-creatine and glycolytic energy systems. There is no magic time frame for fat buring however at about 14-20 minutes into steady state (same intensity) exercise. The body starts to adapt to the exercise and begins to catch up with its Oxygen demand. Remember that no fat can be burned without oxygen. So if your muscles are in an anareobic state then all they are burning is glygogen and producing lactic acid. As the body adapts to the exercise and the Oxygen debt is paid back then you start buring more fat calories per calorie than you were in the first ten minutes. Notice that I said a higher amount of fat is being burned per calorie. You will already be burning fat its just the ratio of calories from fat vs calories sugars.
For your last question why does cardio after exercise burn more calories. Its multiple factors that help you. The very basics of it is your body goes into a state called afterburn. After resistance exercise your bodies metabolism is ramped up. two things are occuring. One, your body is trying to restore glycogen stores to the muscles and liver as fast as possible. And second, your muscles are starting to produce proteins to fix the microtrama to the muscle fibers. Both of these processes require vast amounts of energy and nutrients. Remember how i said that you body produces lactic acid durning anareobic exercise. That lactic acid is shuttled to the liver where its converted back to glycogen. This process is a multi step process and requires lots of energy to convert the lactic acid back to a usable process. Unlike conventional wisdom lactic acid does not stay in the muscles for days on end, thats not what causes soreness. No that the muscles are in a state of repair, they require energy and nutrients. this causes lots of blood to be shunted to the working muscles. The reason that this cause and increase in metabolic rate after cardio is that the muscles need to replenish glycogen stores and need to repair trama. You will not lose muscle mass unless you do a couple of things. One is if you dont intake enought calories, pretty simple. The second is if you dont get enough sleep and enough rest between exercise bouts to the muscle. If you do these two things then your muscles will be fine.

The last thing to remember is that your body at anyone time during exercise is using all three energy systems at once. The intensity and duration of exercise determines which energy system is being predominately used.

**goose** · 12-02-2006, 05:50 PM

The truth is, anytime will get results. It doesn't matter what time of day you do your cardio workout, you will be burning calories every time. BUT, the real question is, which of those times is the most effective? And the answer is .... first thing in the morning.Doing cardio first thing in the morning, on an empty stomach, before you eat anything, is by far, the most effective. Whether you run, jog, walk, swim, jump rope, ride a bike, etc., doing it first thing in the morning is the best time to do it for maximum fat loss. Why? Its simple. When you do your cardio workout, you are burning calories. Lets say you wake up, eat breakfast, eat lunch later in the day, and then a few hours after lunch, you do your cardio. All you will be doing during that cardio is burning the calories and carbs of the food you just ate. When you do cardio first thing in the morning, you haven't eaten anything for the last 8 or so hours because you were sleeping. So, when your body sees that there are no carbs to burn, it goes directly to stored bodyfat. And stored bodyfat is the fat that is on your body, which is the fat that you want to lose!
Understand how it works? When you do your cardio sometime during the day other then first thing in the morning, you spend most of that time burning off carbs that you already ate that day. When you do it first thing in the morning, there are no carbs to burn, so all your body can burn is body fat!
It`s a real bitch if you dont own your own cardio treadmill at home,I never like the idea of going to the gym on a emty gut.I`m more harcore as I run on the streets as I live on the beach.Good luck...