A cool down exercise is important to bring your heart rate back to a resting heart rate and to help prevent build up of lactic acid in your muscles. This should be done at the end of your practice and should hit all your muscles. This exercise will involve breathing, releases of your chest and working your vertebrae. A cool down exercise should also involves plies and all other basic stretches. It’s important to keep the correct form throughout your cool down stretch. A cool down exercise can also help to prevent some soreness the following day. Since your muscles are warm, you can also increase flexibility during this time.