Collagen is a number of naturally occurring proteins. It can only be found in animals. Collagen is the main protein of connective tissue. In mammals it is the most abundant protein. It makes up to around 25% to 35% of the body protein content.
In muscle tissue it is a major component of endomysium. Collagen constitutes around 1% to 2% of your muscle tissue, and accounts for 6% of the weight of strong, tendinous muscles Gelatin, which is used in food and industry, is derived from collagen.