Please Scroll Down to See Forums Below 
"Free fatty acids are an important source of fuel for many tissues since they can yield relatively large quantities of Quick Facts about: ATP
A nucleotide derived from adenosine that occurs in muscle tissue; the major source of energy for cellular reactionsATP. Typically many cell types can use either glucose or fatty acids for this purpose. However, heart and skeletal muscle prefer fatty acids. On the other hand, brain cannot use fatty acids as a source of fuel, relying instead on glucose."
http://www.absoluteastronomy.com/encyclopedia/f/fa/fatty_acid.htm
So, I think its pretty common knowledge that the body will use glycogen stored in muscle for glucose before it breaks down muscle to make glucose. Thus, as long as you arent burning those glycogen stores and are consuming a small amount of carbohydrate, there is no reason that this prolong exercise will cause muscle loss.
A nucleotide derived from adenosine that occurs in muscle tissue; the major source of energy for cellular reactionsATP. Typically many cell types can use either glucose or fatty acids for this purpose. However, heart and skeletal muscle prefer fatty acids. On the other hand, brain cannot use fatty acids as a source of fuel, relying instead on glucose."
http://www.absoluteastronomy.com/encyclopedia/f/fa/fatty_acid.htm
So, I think its pretty common knowledge that the body will use glycogen stored in muscle for glucose before it breaks down muscle to make glucose. Thus, as long as you arent burning those glycogen stores and are consuming a small amount of carbohydrate, there is no reason that this prolong exercise will cause muscle loss.
