This exercise is good for upper body, rear deltoids and shoulders. To perform it you will only need an elastic band.
Wrap an elastic band around something stationary and hold both ends with your arms. Your arms are extended and in front of your chest.
Slowly bring the ends of elastic band behind your back with your arms as straight as possible. Slowly return to starting position.
Exhale as you move your arms behind you back, and inhale as you return them to starting