Grip the bar about shoulder width with your palms facing in. Start with your lats fully stretched in a hanging position. While looking towards the ceiling, pull your body up until your chin is over the bar. Hold yourself over the bar briefly and then lower your body back into the starting position.
Do not use momentum by swinging your legs as this will take away from the effectiveness of the lift. A weight belt and dumbbell should be used if you are able to perform more than 7 reps using your own bodyweight.
Underhand Narrow-Grip Chin-Ups Back Exercise - Start Position
Underhand Narrow-Grip Chin-Ups Back Exercise - Finish Position
Underhand Narrow-Grip Chin-Ups Back Exercise Video