Lat Pull downs are a excellent exercise, this is a great exercise for your upper back muscles. A lat pull down is designed to work the Latissimus Dorsi (wings, or v-shape muscle) Muscle though when performed right this exercise also works the rear deltoids (back part of the shoulders), Rhomboids (the muscles that pinch the shoulder blades), Biceps (the guns, or front of the upper arms in anatomical position), forearm muscles (lower arm), and helps with some lower back strength from the lats inserting into the ligaments into the lumbar region.
How to perform this exercise: Grab the bar about double the width of your shoulders (you may vary the grips: (wide, narrow, underarm, ect) for different muscle requirements and stimulus for the lower back). Though beginners stick with the first grip I recommended. Lean your head back and body back slightly so you may pull the bar down towards your upper chest. Focus on keeping your shoulder blades pinched together and pulling down with your lat (upper back muscles), do your best to pull with your back and not so much with your biceps. You only want to pull the bar down until your upper arm touches your back or until the bar is about upper chest, or chin level. Do not pull the bar down by bending your wrist. Your wrist should be straight during the entire movement and never be flexed. Lower the bar back to the starting position straightening your arms while keeping your shoulder blades pinched together and down and avoid from allowing your shoulders to raise upward. Move slowly about a 3-1-3 temp, so take 3 seconds to lower the bar down and pause for 1 second at the bottom position and then extend the bar up for 3 seconds and repeat.
Basic exercise program would to add this to someone exercise program for 3 sets of 8-10 repetitions.
Warning: Never pull the bar behind your neck: risks far outweigh the benefits, not to mention someone became a paraplegic by performing this exercise this way. Avoid at all cost, it doesn’t do much for you different than performing it in front of you.
Again Exercise right = results, better body, healthier you.