Most people don't consider stretching to be a part of working out or just flat out ignore stretching. Stretching has been proven to not only increase muscle elasticity but prevent injury before a rigorous workout.
The reason being is that muscles stretch and contract and for this very reason before a workout the muscles are stiff and need to be stretched out so they are primed and ready to perform. Check out these videos on some great stretches to perform both before and after a workout!!