HOW: Begin by lying on your back on a bench. Bend your knees and place your feet flat on the bench. Hold one end of a dumbbell straight up over your face keeping your elbows locked out. Let your arms and dumbbell go behind you until you can't extend your arms any further, then bring the dumbbell back up to the starting position.
FEEL: You should feel your lat muscles working.
COMPENSATION: Keep your arms extended throughout the whole exercise.