Pull-ups are a great exercise for building upper body strength, and they work multiple muscle groups. Here are the muscles that pull-ups work, according to the search results:

• Latissimus Dorsi: This is the largest upper back muscle that runs from the mid-back to under the armpit and shoulder blade.
• Biceps Brachii: These are the muscles in the front of your upper arm.
• Brachialis: This is a muscle in the upper arm that lies underneath the biceps.
• Forearm muscles: These muscles are used to grip the pull-up bar.
• Shoulder stabilizers: These muscles help to stabilize the shoulder joint during the movement.
• Trapezius: This is a large muscle that runs from the back of the neck to the middle of the back.
• Rhomboids: These are muscles in the upper back that connect the shoulder blades to the spine.
• Infraspinatus: This is a muscle in the shoulder blade that helps to rotate the arm.

Its worth noting that the specific muscles worked during pull-ups can vary depending on the type of grip used. For example, chin-ups (which use an underhand grip) tend to work the biceps more than pull-ups (which use an overhand grip). However, both exercises work the same major muscle groups in the upper body.