swole.. this is a quote from
http://www.ast-ss.com/dev/qa_search/full_text.asp?ID=62
This certainly does not mean you shouldn't do cardio in the morning, but never do morning cardio on an empty stomach. This is a guaranteed way to lose lean muscle.
You see, when you wake up in the morning you are entering or you are already in a catabolic state. A serious catabolic state. You're losing muscle. Your priority at this time is to supply your muscles a fast acting nitrogen source to halt the catabolism and ignite anabolism - muscle growth. When you wake up you have just endured a 6, 8, or 10 hour fasting. Your muscle have had no nutrients, no protein over an extended amount of time. The last thing you want to do is enter an intense cardio session under this catabolic condition. Like I said, this is a guaranteed way to lose lean muscle.