The humerus is the long bone in your upper arm, running from your shoulder to your elbow. You can feel it if you squeeze your upper arm: that solid core underneath your muscles is the humerus. At its top, the humerus connects to your shoulder blade, forming a ball-and-socket joint that lets you rotate your arm in wide circles. At its bottom, it connects to the two bones of your forearm (the radius and ulna) at your elbow joint.

This bone is one of the strongest in your body because it needs to support the weight of everything you lift, throw, or carry. When someone breaks their humerus, usually from a hard fall or sports injury, they may need a cast or sling while it heals, and they might not be able to use that arm for weeks.