Is it true..?

~Actually, One of the best ways to burn fat while you keep your muscle mass is to eat fewer calories and more protein. (Meat, poultry, fish, eggs, cheese, yogart... are all good foods to eat.)

try this:

http://www.tomvenuto.com/

http://www.fitnesslynn.com/

http://www.muscleandfitness.com/

You lose muscle mass when you reduce calories and do not strength train to give your body a reason to keep it. When you drop your calories it signals the body to burn off muscle first. The body assumes it's going to starve. This is why you drop calories slowly. You don't go and drop 1000 calories off the bat. This is also why calorie reduction plus strength training and cardio works the best.

You lose muscle when you over train. The muscles atrophe and get smaller.

You will lose muscle if your nutrition levels are not correct to support the muscle.

You will lose muscle with improper rest which is also part of over training.

Cardio should also be cycled.

think its if you keep your heart rate between 65 to 75% of max will burn fat and if you go over 75% you will increase your cardio capacity but will not burn the optimum amount of fat

http://www.twrc.rowing.org.uk/coach/heartrate.htm

There are different levels of exertion that will condition your body in different ways.

I don't believe there is any zone that causes you to LOSE muscle mass... but there is only 1 zone in which your body burns fat directly for the energy to continue your workout.

http://www.prevention.com/article/0,5778,s1-2-92-7...