It depends on your goals.Originally posted by Wikked1
Aka: I want to aks more about cardio since I regard your knowledge as DAMN good. Are you saying that in your opinion I am performiong cardio at the worst possible time (first thing in the AM on an empty stomach?)
After an overnight fast, your liver glycogen levels may be nearly depleted. Your muscles may have a lot of glycogen left, but your brain cannot cannot use the muscle glycogen, so there is an increased risk of the body catabolizing muscle to get fuel for the brain. The amount of this risk depends on the type of cardio among other things. Higher intensity or longer duration increases risk because there is a greater demand for glycogen. In additional total fat loss increases with the intensity or duration of the cardio. After an overnight fast, you are likely to have reduced endurance and more fatigue so both intensity and duration may decrease. If your goal is to lose fat while preserving muscle, then doing cardio on an empty stomach or any other time when glycogen levels are low (for example immediately after weightlifting) is probably a bad idea.
If your goal is to get rid of that last little bit of stubborn fat, then the increased fat mobilization related to the low glycogen levels may be beneficial. Many bodybuilders do empty stomach type cardio in conjuction with various supplements that also increase fat mobilization. I recall reading someone (Lyle Mcdonald?) recommending getting rid of the last bit of stubborn body fat by doing AM cardio with some type of supplements. The cardio recommended was going as hard as possible for 5-10 minutes, then doing traditional mod/high intensity cardio for 30-45 minutes. Afterwards it was recommended to not eat carbs in the post workout meal, and instead wait 2 hours later.
I would recommend the first approach. The second is likely to result in lost muscle. It is hard to say just how much muscle would be lost in the second approach. The study at http://www.ncbi.nlm.nih.gov/entrez/q...&dopt=Abstract found that protein may contribute up to 10% of total energy during conditions of glycogen depeletion. Much of this 10% would come from the amino acid pool, but some may come from muscle protein.