Stand up with your torso upright while holding a bar attachment that is attached to a low pulley using a pronated (palms down) and shoulder width grip. Make sure also that you keep the elbows close to the torso. This will be your starting position.
While holding the upper arms stationary, curl the weights while contracting the biceps as you breathe out. Only the forearms should move. Continue the movement until your biceps are fully contracted and the bar is at shoulder level. Hold the contracted position for a second as you squeeze the muscle.
Slowly begin to bring the bar back to starting position as your breathe in.