This is a classic body builder exercise to build your lower Lats (back muscles).
Muscle group: Back
Sit at a Pull Down machine and place your feet under your knees.
Grasp the bar with a close overhand grip, about 8 inches apart and pull it straight down so it is even with your upper chest.
Hold for a moment and slowly return the bar back to starting position.
Keep your abs drawn in and do not swing your back during this exercise.