Humerus

The humerus is the long bone of the upper arm, running from the shoulder joint down to the elbow. It connects to the scapula at the shoulder and to the radius and ulna at the elbow, giving the arm its wide range of motion. Like other long bones, it has a shaft (diaphysis) made of dense cortical bone and wider ends (the proximal humerus and the distal end) with more trabecular bone inside.

Bone adapts to the specific stress it experiences, a principle often called Wolff's Law. Because the humerus is loaded whenever you push, pull, lift, or carry things with your arms, regular upper-body resistance training is often included as part of an overall bone health routine. Studies of athletes like tennis players show that the playing arm's humerus can build noticeably more cortical bone than the non-dominant arm, simply from repeated one-sided loading over years.

That same site-specific quality is also a limitation: exercises that load the humerus don't necessarily do much for the hip or spine, which are the bones most linked to serious fragility fractures. The proximal humerus itself can fracture, especially in a fall onto an outstretched arm or the shoulder, and humerus fractures are tracked clinically as a sign of overall fracture risk, similar to wrist fractures. A DEXA scan typically measures the hip and spine rather than the arm, since those sites better predict overall fracture risk.