Arm muscles are responsible for the motions of the upper arm. They consist of many different parts, each with its own function. Those parts include biceps brachii, triceps brachii, deltoids, rotator cuff muscles, brachialis, and brachioradialis.
Arm muscles are the muscles in your arms that allow for flexing, extending, rotating, and moving your arms. Your arm muscles are what keep you upright while standing. Arms also have the job of carrying things around by using your forearm muscles to move them.
Arm muscles work in tandem with other muscle groups throughout the body during movement too! Most notably, arm muscles work with the back, chest, and core muscles to perform most tasks.