AM cardio vs. am weightlifting, why so much contradiction

[110%]

ok i always hear this, and i always give out this as advice. when you do cardio first thing in the morning before any meals you will utilize fat as your main source of energy since your glycogen has been depleted from the approx 8 hour fasting during sleep.

then i hear when you lift weights in the morning before any meals your body will break down proteins from your muscles for fuel, since you have no stored glycogen to be used.

i dont get this, why would u burn fat with one supposably, and muscle for the other. is it because the areobic actions with cardio causes the body to use fat and the anaerobic with wieghlifting causes the body to target muscle proteins, does it have something to do with that?

 

[georgie24]

good question bro!!

im usually strung the f*ck out by the time i get outta work, i would like to lift in the a.m hours, but i too hear 2 much conflicting info

 

[Haz]

I used to lift first thing in the morning on an empty stomach. I didn't notice any problems with this. You might be a bit groggy at first, but after a few sets you'll be wide awake. Just make sure you eat something right after and you should be fine.

I don't think our bodies burn one type of fuel during a workout. Its probably a combination of glycogen, fat and a bit of muscle. I doubt that our glycogen is all gone by the time we wake up, cause I've read we have about 24 hours worth.

 

[plornive]

The theory comes from the fact that muscle-loss comes with gluconeogenesis, which can happen as a result of the combination of a lack of muscle glycogen and utilization of type 2 muscle fibers. Resistance training utilizes type 2 muscle fibers (as well as type 1). Type 2 muscle fibers generally do not utilize fat for fuel, so if glycogen stores are empty and blood sugar is low, glucagon is released and amino acids are converted to glucose via gluconeogenesis. These amino acids are likely to come from your muscles. Between sets, there is evidence that fat is utilized for recovery, but this is just a small amount of energy.

Cardio is more likely to use fat for fuel, so muscle loss is not as much of a concern. Cardio utilizes mostly type 1 muscle fibers, which do not store or utilize much glycogen.

Couple the above two paragraphs with the fact that most bodybuilders care about their performance in the gym yet don't really care about "performance" during cardio, I don't think lifting on an empty stomach in the morning is the wisest thing to do unless you have a reason to believe that your glycogen stores are relatively full. They are not likely to be *empty*, but when they are fairly low a high percentage of energy will come from amino acids.

 

[plornive]

This may sound like a contradiction to the above post but I prefer to lift 1.5 hours after a *light* meal (usually just a shake or tuna and a very small amount of carbs). My glycogen stores are still full, yet there is no insulin in my blood or food in my stomach to destroy my performance. If I ate just before bed and only had 6 hours of sleep or something, I might lift in the morning if I so desire. Everybody is different and you may have enough glycogen in the mornings to lift on an empty stomach. It depends on glycogen levels and how each person utilizes glycogen during workouts. It probably also depends on whether one is exercising large muscles or small muscles --- large muscles use more sugar, and thus cause more gluconeogenesis from amino acids.

I prefer to do only cardio in the morning on an empty stomach.

 

[plornive]

One more thing...
Does anyone know if/how/when they body utilizes amino acids from within working muscles for energy? I don't think this is significantly related to this thread, but it could be.