Q: Professional cyclist Lance armstrong burns around 6000 calories a day when he trains most of the year and has a Body composition of 5%. According to what you said he should have a slow metabolism because he does so much cardio. At 160 pounds he doesnt have much muscle. Is Metabolism only determined by your lean body mass?

A: There are two very big differences between an average person doing cardio to lose weight and Lance Armstrong:

• Lance does not train to lose weight. He eats enough to make up for all the calories he lost during cycling and his weight stays roughly constant. He probably loses some weight during the Tour, but he makes up for it afterwards. Your last question, on the other hand, is talking about doing cardio to lose weight. When undereating to lose weight, excessive cardio will become catabolic (muscle-destroying). Also see http://www.mikesfitness.com/content/burning-calories-muscle-cardio , http://www.mikesfitness.com/content/cardio-does-not-destroy-muscle-when-... , and http://www.mikesfitness.com/content/weight-training-better-than-cardio for similar discussion.
• You should never compare an average person to Lance or to any other elite-level athelete. Lance and other pros did not rise to the top through hard work and dedication alone. They are also incredibly genetically gifted in their area of endeavor. Their bodies are capable of benefitting from much more intense training than an average person and they're capable of performing at much higher level than an average person. This is not a show of disrespect to anyone who trains and aspires to be like the pros, it's just a simple fact. Atheletes like Lance are born with a gift and those without such gift simply cannot match them, no matter how dedicated they are. Because of this fact, you should keep in mind that it's counterproductive to compare your own training and/or progress to that of Lance or other pros.