The lat pull-down is a machine exercise that works your lats, the latissimus dorsi, or the triangular back muscles that stretch along the ribcage under each arm. If the sides of your ribs feel sore after this exercise, those are your lats. For the seated lat pull-down, sit on the bench and grasp the bar with a wide grip so that your arms reach up in a "V" shape. Don't lock your elbows. Pull the bar down towards your chest until it touches your upper chest. Hold this position for about a second. Keep your chest pushed out and your shoulder blades pushed back and downwards. Slowly release the bar back to starting position. The lat pull-down can be done in various positions and handgrips.