Dr. Laskowski: The lat pull-down is an exercise you can do with a weight machine to work the muscles on the sides of your chest wall and upper back. Done properly, the lat pull-down targets the latissimus dorsi, a muscle on the outer side of the chest wall. A strong back with balanced muscles helps you maintain good posture.
Nicole Campbell: To do a lat pull-down with a weight machine, start by sitting on the weight bench. Place your hands slightly wider than shoulder-width apart on the bar. Slowly pull the bar toward your chest, moving your elbows behind you. Keep your chest high, and pinch your shoulder blades together. Stop when your elbows can go back no farther. The bar won't necessarily reach your chest. Then slowly return to the starting position. You'll feel tension in the muscles in your arms and back.
When you're doing the lat pull-down, don't bring the bar down behind your neck. This can stress your neck and shoulders and lead to injury.
For most people, one set of 12 to 15 repetitions is adequate.
Remember, for best results, bring the bar to the front of your chest while keeping your back straight. Also keep your movements smooth and controlled.