PREPARATION
1.Sit astride the bench with a
  dumbbell in front of you.

2.Place your left hand on your
  hip and take the weight in your
  right hand.

3.Raise the weight to your right
  shoulder, then extend it to arms
  length above your head.

EXERCISE
1.Breathe in as you lower the
  dumbbell behind your head. Keep
  your elbow pointing upwards.

2.Breathe out as you straighten
  your arm, pressing the weight
  back up to arms length.

MAINLY FOR: Tricep